WO2022110085A1

WO2022110085A1 - Flip-chip package having improved thermal performance

Info

Publication number: WO2022110085A1
Application number: PCT/CN2020/132538
Authority: WO
Inventors: Okamoto Keishi; Ningjun ZHU; Hitoshi Sakamoto; Chengpeng Yang
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2020-11-28
Filing date: 2020-11-28
Publication date: 2022-06-02
Anticipated expiration: 2023-05-28
Also published as: CN116601748A; CN116601748B

Abstract

A flip-chip package (200) comprises: at least one chip (202) configured to connect with a substrate (201); a molded member (209) formed on the substrate (201) to wrap a side portion of the at least one chip (202) and lay a top surface of each chip (202) bare, wherein an upper surface of the molded member (209) has a first area continuous with the top surface of each chip (202), a second area to which an adhesive (210) is applied and a wall-like structure (209a) placed to surround the top surface of each chip (202), and the first and second areas are separated by the wall-like structure (209a); a heat spreader (206) placed above the top surface of each chip (202) and glued to the molded member (209) by the adhesive (210) filled in the second area; and a thermal interface material (205) filled in a spatial region formed by the first area, the top surface of each chip (202), at least a part of a bottom surface of the heat spreader (206), and a first side of the wall-like structure (209a).

Description

FLIP-CHIP PACKAGE HAVING IMPROVED THERMAL PERFORMANCE

TECHNICAL FIELD

The present disclosure relates to a flip-chip package having improved thermal performance, an apparatus equipped with circuitry to which a structure of the flip-chip package is applied, and a method for assembling the flip-chip package.

BACKGROUND

Recent advancement of semiconductor packages in processing performance derives needs for higher thermal performance sufficient for ensuring stable operation. In this regard, a flip-chip package is advantageous in thermal performance since its structural feature that a chip connects with a substrate via bumps under the chip, enables to locate a heat spreader on a top surface of the chip.

For enhancement of cooling performance, a thermal interface material (TIM) such as thermal grease is applied to the top surface of the chip and sandwiched between the chip and at least a part of the heat spreader. From the viewpoint of reducing thermal resistance in the TIM to improve the thermal performance of the package, it is preferable to make a thickness of the TIM smaller.

U.S. Patent No. 8,368,194 proposes a flip-chip package having a heat spreader that comprises a flat lid and a side wall extending downward from an end of the flat lid. In this proposed package, a distance between the flat lid and a substrate on which a chip is disposed, is defined by a height of the side wall in the heat spreader made from solid metal. In this case, a thickness of the TIM is defined by a distance between a bottom surface of the flat lid and a top surface of the chip on the substrate, so that a thickness of the TIM is also defined by the height of the side wall. Accordingly, it is difficult to finely control the thickness of the TIM during an assembling procedure of the proposed package. This means that it may be difficult in some cases for the proposed package to implement a small thickness of the TIM for the higher thermal performance sufficient for ensuring stable operation.

In addition, differences in coefficients of thermal expansion among the heat spreader, the substrate and the chip cause enlargement of a gap (hereafter, "TIM gap" ) between the chip and the flat lid during a reflow process when assembling the proposed package. The enlargement of the TIM gap facilitates delamination of the TIM from the heat spreader. The delamination of the TIM degrades the thermal performance and increases junction temperature in operation, thereby decreasing reliability. As mentioned above, the proposed package has to-be-solved issues for implementing the higher thermal performance sufficient for ensuring stable operation.

Desmond Y.R. Chong et al., "Development of a New Improved High Performance Flip Chip BGA Package" , Electronic Components and Technology Conference, 2004, pp. 1174-1180 proposes a flip-chip package having a structural feature for reducing enlargement of the TIM gap during the reflow process. This proposed package has a molded member formed on the substrate and glued by an adhesive applied to an upper surface of the molded member. The molded member may act a support member to physically maintain a gap between the heat spreader and the substrate, thereby reducing enlargement of the TIM gap during the reflow process.

However, the proposed package lacks a structure for controlling a thickness of the TIM and/or a size of the TIM gap, so that it is difficult to finely control the TIM gap to implement the small thickness of the TIM for the higher thermal performance sufficient for ensuring stable operation. In addition, the TIM of the proposed package is in contact with the adhesive applied to an upper surface of the molded member, and at least a part of the TIM may flow into the adhesive and/or at least a part of the adhesive may flow into the TIM during the reflow process.

If the TIM flows into the adhesive during the reflow process, voids would be generated in the TIM to cause increase of thermal resistance in the TIM. Also, if the adhesive flows into the TIM during the reflow process, an effective volume of the TIM would decrease to cause increase of thermal resistance in the TIM. Increase of the thermal resistance in the TIM causes decrease of the thermal performance. As mentioned above, the proposed package has to-be-solved issues for implementing the higher thermal performance sufficient for ensuring stable operation.

SUMMARY

Embodiments provide a flip-chip package, an apparatus equipped with circuitry to which a structure of the package is applied, and a method for assembling the package.

For example, the circuitry to which the package is applied may be processing circuitry such as a central processing unit (CPU) , a field-programmable gate array (FPGA) , an application specific integrated circuit (ASIC) , a graphics processing unit (GPU) or the like. Also, the circuitry to which the package is applied may be communication circuitry such as a high frequency circuit used in a wired communication interface, a wireless communication interface, an optical communication interface, a network switch or the like. In addition, the circuitry to which the package is applied may be power control circuitry such as a power control unit used in a vehicle, an energy management system or the like.

The apparatus may be a mobile device such as a mobile phone, a smart phone, a tablet computer, a wearable computer or the like. Also, the apparatus may be a computer such as a personal computer, a workstation, a server, an artificial intelligence (AI) cluster, a cloud computing system, an Internet of Things (IoT) device or the like. In addition, the apparatus may be a camera such as a digital still camera, a digital video camera, a security/surveillance camera, a network camera, a video camcorder, an automotive/transport camera, a medical camera, a machine vision or the like. Also, the apparatus may be a component including the above-mentioned circuit such as a module or an electronic unit in a computer or a computing system.

Hereafter, modifiers such as "top" , "bottom" , "upper" , "lower" , "upward" and "downward" may be used but these merely indicate relative positional relationship in a target element thereof and do not point in any particular direction relative to the ground. For example, a top surface of a chip may represent a front side surface of the chip that faces a heat spreader in a flip-chip package, and a bottom surface of the chip may represent a reverse side surface of the chip that faces a substrate in the package.

A first aspect of the embodiments provides the flip-chip package. In a first possible implementation form of the first aspect, the package comprises:

at least one chip configured to connect with a substrate;

a molded member formed on the substrate to wrap a side portion of the at least one chip and lay a top surface of each chip bare, wherein an upper surface of the molded member has a first area continuous with the top surface of each chip, a second area to which an adhesive is applied and a wall-like structure placed to surround the top surface of each chip, and the first and second areas are separated by the wall-like structure;

a heat spreader placed above the top surface of the at least one chip and glued to the molded member by the adhesive applied to the second area; and

a thermal interface material filled in a spatial region formed by the first area, the top surface of each chip, at least a part of a bottom surface of the heat spreader, and a first side of the wall-like structure.

Optionally, the heat spreader may be made from Cu, Ag-diamond or Co-Mo. The heat spreader using lower coefficient of thermal expansion (CTE) materials may reduce stress on the thermal interface material during the reflow process.

According to the first possible implementation form of the first aspect, the thermal interface material is formed in the spatial region surrounded by the top surface of each chip, the bottom surface of the heat spreader, the first area of the molded member, and a side of the wall-like structure in the molded member. Thus, a thickness of the thermal interface material is defined by a height of the wall-like structure in the molded member. The height of the wall-like structure composed of a mold compound may be easily controlled in a molding process, so that it can be realized to adjust the thickness of the thermal interface material to a desired small thickness for implementing improved thermal performance.

Additionally, in the first possible implementation form of the first aspect, the first and second areas of the molded member are spatially separated by the wall-like structure, thereby avoiding mixture of the thermal interface material applied to the first area and the adhesive applied to the second area during the reflow process. This enables to avoid formation of voids in the thermal interface material and outflow of the thermal interface material into the adhesive, thereby improving the thermal performance. Moreover, the molded member may act as a support member to maintain a distance between the bottom of the heat spreader and the substrate, thereby reducing a risk of delamination of the thermal interface material from the heat spreader during the reflow process. For reasons mentioned above, the package according to the first possible implementation form of the first aspect may achieve improved thermal performance that can ensure adequate reliability in operation.

A second possible implementation form of the first aspect provides: the package according to the first possible implementation form of the first aspect, wherein the package further comprises:

a stiffener having a structure like a square frame, wherein the stiffener is formed on the substrate to surround outer sides of the molded member, and the molded member is formed to fill an inside region of the stiffener.

According to the second possible implementation form of the first aspect, the stiffener may enhance strength of the package, thereby increasing resistance to external impact on the package.

A third possible implementation form of the first aspect provides: the package according to the first possible implementation form of the first aspect, wherein

the heat spreader has a lid portion placed above the at least one chip and a side portion extending downward from an end of the lid portion, wherein the side portion is placed outside the molded member, and an end of the side portion is glued to the substrate by an adhesive.

According to the third possible implementation form of the first aspect, the side portion of the heat spreader may enhance strength of the package, thereby increasing resistance to external impact on the package. Also, a structure of the heat spreader having the side portion may secure a large area for dissipating heat to enhance cooling efficiency, thereby improving the thermal performance thereof.

Optionally, in the package according to any one of the first to third possible implementation forms of the first aspect, the second area comprises an adhesive pool for filling the adhesive, wherein a second side of the wall-like structure forms at least a part of a side of the adhesive pool.

Optionally, in the package according to any one of the first to fifth possible implementation forms of the first aspect, a height of the wall-like structure may be around 200μm or less, and also a width thereof may be 3.0mm or less.

Optionally, in the package according to any one of the first to third possible implementation forms of the first aspect, the thermal interface material may be composed of an organic-based material such as Silicone or the like, a metal such as InSn, InAg or the like, a Ag sintered material including nano-Ag, or a carbon nanotube (CNT) based material.

A second aspect of the embodiments provides the apparatus. In a first possible implementation form of the second aspect, the apparatus comprises circuitry composed of a flip-chip package which comprises:

at least one chip configured to connect with a substrate;

Optionally, the heat spreader may be made from Cu, Ag-diamond or Co-Mo. The heat spreader using lower CTE materials may reduce stress on the thermal interface material during the reflow process.

According to the first possible implementation form of the second aspect, the thermal interface material is formed in the spatial region surrounded by the top surface of each chip, the bottom surface of the heat spreader, the first area of the molded member, and a side of the wall-like structure in the molded member. Thus, a thickness of the thermal interface material is defined by a height of the wall-like structure in the molded member. The height of the wall-like structure composed of a mold compound may be easily controlled in a molding process, so that it can be realized to adjust the thickness of the thermal interface material to a desired small thickness for implementing improved thermal performance.

Additionally, in the first possible implementation form of the second aspect, the first and second areas of the molded member are spatially separated by the wall-like structure, thereby avoiding mixture of the thermal interface material applied to the first area and the adhesive applied to the second area during the reflow process. This enables to avoid formation of voids in the thermal interface material and outflow of the thermal interface material into the adhesive, thereby improving the thermal performance. Moreover, the molded member may act as a support member to maintain a distance between the bottom of the heat spreader and the substrate, thereby reducing a risk of delamination of the thermal interface material from the heat spreader during the reflow process. For reasons mentioned above, the package according to the first possible implementation form of the second aspect may achieve improved thermal performance that can ensure adequate reliability in operation, so that stable operation of the apparatus can be realized even in high load environments.

A second possible implementation form of the second aspect provides: the apparatus according to the first possible implementation form of the second aspect, wherein the package further comprises:

According to the second possible implementation form of the second aspect, the stiffener may enhance strength of the package, thereby increasing resistance to external impact on the apparatus.

A third possible implementation form of the second aspect provides: the apparatus according to the first possible implementation form of the second aspect, wherein

According to the third possible implementation form of the second aspect, the side portion of the heat spreader may enhance strength of the package, thereby increasing resistance to external impact on the apparatus. Also, a structure of the heat spreader having the side portion may secure a large area for dissipating heat to enhance cooling efficiency, thereby improving the thermal performance thereof. This may contribute stable operation of the apparatus in high load environments.

Optionally, in the apparatus according to any one of the first to third possible implementation forms of the second aspect, the second area comprises an adhesive pool for filling the adhesive, wherein a second side of the wall-like structure forms at least a part of a side of the adhesive pool.

Optionally, in the apparatus according to any one of the first to third possible implementation forms of the second aspect, a height of the wall-like structure may be around 200μm or less, and also a width thereof may be around 3.0mm or less.

Optionally, in the apparatus according to any one of the first to third possible implementation forms of the second aspect, the thermal interface material may be composed of an organic-based material such as Silicone or the like, a metal such as InSn, InAg or the like, a Ag sintered material including nano-Ag, or a CNT based material.

A third aspect of the embodiments provides the method for assembling a flip-chip package which comprises at least one chip, a substrate, a molded member, a thermal interface material and a heat spreader. In a first possible implementation form of the third aspect, the method comprises:

connecting the at least one chip with the substrate;

filling a mold compound around the at least one chip on the substrate so as to wrap a side portion of the at least one chip and lay a top surface of each chip bare, and molding the molded member with a structure that an upper surface of the molded member has a first area continuous with the top surface of each chip, a second area to which an adhesive is to-be-applied and a wall-like structure placed to surround the top surface of each chip, and the first and second areas are separated by the wall-like structure;

applying the adhesive to the second area of the molded member;

forming the thermal interface material on the first area and the top surface of each chip;

attaching the heat spreader to the thermal interface material and the molded member by the adhesive; and

performing a reflow process of the package.

According to the first possible implementation form of the third aspect, the thermal interface material is formed in the spatial region surrounded by the top surface of each chip, the bottom surface of the heat spreader, the first area of the molded member, and a side of the wall-like structure in the molded member. Thus, a thickness of the thermal interface material is defined by a height of the wall-like structure in the molded member. The height of the wall-like structure composed of the mold compound may be easily controlled in a step of the molding, so that it can be realized to adjust the thickness of the thermal interface material to a desired small thickness for implementing improved thermal performance.

Additionally, in the first possible implementation form of the third aspect, the first and second areas of the molded member are spatially separated by the wall-like structure, thereby avoiding mixture of the thermal interface material applied to the first area and the adhesive applied to the second area during the reflow process. This enables to avoid formation of voids in the thermal interface material and outflow of the thermal interface material into the adhesive, thereby improving the thermal performance. Moreover, the molded member may act as a support member to maintain a distance between the bottom of the heat spreader and the substrate, thereby reducing a risk of delamination of the thermal interface material from the heat spreader during the reflow process. For reasons mentioned above, the package according to the first possible implementation form of the first aspect may achieve improved thermal performance that can ensure adequate reliability in operation.

A second possible implementation form of the third aspect provides: the method according to the first possible implementation form of the third aspect, wherein

before the filling the mold compound, the method further comprises forming a stiffener on the substrate, wherein the stiffener has a structure like a square frame surrounding an entire area on which the at least one chip is disposed, and the molded member is formed to fill an inside region of the stiffener.

According to the second possible implementation form of the third aspect, the stiffener may enhance strength of the package, thereby increasing resistance to external impact on the package.

A third possible implementation form of the third aspect provides: the method according to the first possible implementation form of the third aspect, wherein

the heat spreader has a lid portion placed above the at least one chip and a side portion extending downward from an end of the lid portion, wherein the side portion is placed outside the molded member, and

in the attaching the heat spreader, an end of the side portion is glued to the substrate by an adhesive.

According to the third possible implementation form of the third aspect, the side portion of the heat spreader may enhance strength of the package, thereby increasing resistance to external impact on the package. Also, a structure of the heat spreader having the side portion may secure a large area for dissipating heat to enhance cooling efficiency, thereby improving the thermal performance thereof.

Optionally, in the method according to any one of the first to third possible implementation forms of the third aspect, the molding may be implemented using a transfer-type molding method or a compression-type molding method.

Optionally, in the method according to any one of the first to third possible implementation forms of the third aspect, a height of the wall-like structure may be controlled to be around 200μm or less, and also a width thereof may be around 3.0mm or less.

Optionally, in the method according to any one of the first to third possible implementation forms of the third aspect, the thermal interface material may be composed of an organic-based material such as Silicone or the like, a metal such as InSn, InAg or the like, a Ag sintered material including nano-Ag, or a CNT based material.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic block diagram for describing exemplary configuration of an apparatus according to an embodiment of the present disclosure,

FIG. 2 is a schematic cross-sectional view of a flip-chip package according to the embodiment of the present disclosure,

FIG. 3 is a partially enlarged view of the flip-chip package in FIG. 2, according to the embodiment of the present disclosure,

FIG. 4 is a schematic top view of the flip-chip package in FIG. 2, according to the embodiment of the present disclosure,

FIGs. 5A to 5E are schematic diagrams for describing an assembly process of the flip-chip package in FIG. 2, according to the embodiment of the present disclosure,

FIG. 6 shows simulation results of gap changes during the assembly process of the flip-chip package in FIG. 2, according to the embodiment of the present disclosure,

FIG. 7 shows a first exemplary variation of the flip-chip package according to the embodiment of the present disclosure,

FIGs. 8A and 8B show package structures in a second exemplary variation of the flip-chip package according to the embodiment of the present disclosure,

FIGs. 9A and 9B show package structures in a third exemplary variation of the flip-chip package according to the embodiment of the present disclosure,

FIGs. 10A and 10B show package structures in a fourth exemplary variation of the flip-chip package according to the embodiment of the present disclosure,

FIGs. 11A to 11F are schematic top view of the flip-chip package for describing some possible shapes of the molded member therein according to the embodiment of the present disclosure,

FIGs. 12A and 12B show possible variations of the flip-chip package according to the embodiment of the present disclosure, and

FIGs. 13A and 13B show examples of conventional flip-chip packages.

DESCRIPTION OF EMBODIMENTS

The following describes technical solutions of the embodiments, referring to the accompanying drawings. It will be understood that the embodiments described below are not all but just some of embodiments relating to the present disclosure. It is to be noted that all other embodiments which may be derived by a person skilled in the art based on the embodiments described below without creative efforts shall fall within the protection scope of the present disclosure.

(Conventional flip-chip packages) Prior to description of the embodiment of the present disclosure, let us introduce conventional flip-chip packages and issues thereof with reference to FIGs. 13A and 13B. FIGs. 13A and 13B show examples of conventional flip-chip packages.

FIG. 13A schematically shows a cross-sectional view of a first conventional flip-chip package. As shown in FIG. 13A, the first conventional flip-chip package comprises a substrate, a chip, an underfill, a thermal interface material (TIM) , and a heat spreader.

The chip is connected with the substrate via bumps under the chip, and a bottom region of the chip is filled by the underfill. The heat spreader has a flat lid and a side wall extending downward from an end of the flat lid. The flat lid of the heat spreader is arranged such that a bottom surface of the flat lid is parallel to a top surface of the chip. The side wall of the heat spreader is placed to surround the chip and glued by an adhesive applied to an end of the side wall to the substrate.

The TIM is sandwiched between at least a part of the bottom surface of the flat lid in the heat spreader and the top surface of the chip. Hereafter, a gap to which the TIM is applied between the heat spreader and the chip may be referred to a TIM gap. From the viewpoint of reducing thermal resistance between the chip and the heat spreader, it is preferable to make a thickness of the TIM smaller.

In the first conventional flip-chip package, the TIM gap is defined by a height of the side wall in the heat spreader, thereby making fine adjustment of the height thereof to implement the small TIM gap (e.g. around 200μm or less) difficult. This means that it is difficult to implement a small thickness of the TIM in the first conventional flip-chip package. Also, differences in coefficients of thermal expansion among the heat spreader, the substrate and the chip cause enlargement of the TIM gap during reflow processing in an assembly process of the flip-chip package, thereby facilitating delamination of the TIM from the heat spreader. The delamination of the TIM degrades thermal performance and increases junction temperature in operation, thereby reducing reliability of the flip-chip package.

In order to reduce enlargement of the TIM gap during the reflow processing, proposed is a second conventional flip-chip package having a molded member (MOLD) around the chip as shown in FIG. 13B. The molded member is formed on the substrate and glued by an adhesive applied to an upper surface of the molded member. In the second conventional flip-chip package, the molded member may act a support member to physically maintain a gap between the heat spreader and the substrate, thereby reducing enlargement of the TIM gap during the reflow processing.

However, the second conventional flip-chip package lacks a member that physically defines a thickness of the TIM or a size of the TIM gap, thus it is difficult to control the TIM gap to implement the small thickness (e.g. around 200μm or less) of the TIM. This issue remains even if the heat spreader of the first conventional flip-chip package may be applied to the second conventional flip-chip package.

Additionally, in the second conventional flip-chip package, the TIM is in contact with the adhesive on the molded member, so that a portion of the TIM may flow into the adhesive and/or a portion of the adhesive may flow into the TIM during the reflow process. If the portion of the TIM flows into the adhesive during the reflow process, voids would be formed in the TIM to increase thermal resistance of the TIM. If the portion of the adhesive flows into the TIM during the reflow process, an effective volume of the TIM would decrease to increase thermal resistance of the TIM. Increasing the thermal resistance of the TIM causes decrease of thermal performance in operation.

In view of the foregoing, an embodiment of the present disclosure described below provides solutions against the issues of conventional flip-chip packages like the above-mentioned first and second conventional flip-chip packages. The embodiment of the present disclosure relates to a flip-chip package, an apparatus equipped with circuitry to which a structure of the package is applied, and a method for assembling the package.

(Exemplary configuration of the apparatus) Following describes exemplary configuration of an apparatus according to an embodiment of the present disclosure.

FIG. 1 is a schematic block diagram for describing exemplary configuration of an apparatus according to an embodiment of the present disclosure.

An apparatus 10 in FIG. 1 is an example of the apparatus according to the embodiment of the present disclosure. For example, the apparatus 10 may be a mobile device such as a mobile phone, a smart phone, a tablet computer, a wearable computer or the like. Also, the apparatus 10 may be a computer such as a personal computer, a workstation, a server, an AI cluster, a cloud computing system, an IoT device or the like. In addition, the apparatus 10 may be a camera such as a digital still camera, a digital video camera, a security/surveillance camera, a network camera, a video camcorder, an automotive/transport camera, a medical camera, a machine vision or the like.

As shown in FIG. 1, the apparatus 10 comprises processing circuitry 11 and communication circuitry 12. For example, the processing circuitry 11 may comprise at least one processor such as a CPU, a FPGA, an ASIC, a GPU or the like. The communication circuitry 12 may comprise at least one high frequency circuit used in a wired communication interface, a wireless communication interface, an optical communication interface, a network switch or the like. Optionally, the apparatus 10 may further comprise power control circuitry used in a vehicle, an energy management system or the like.

Each of the processing circuitry 11, the communication circuitry 12 and the power control circuitry is an example of the circuitry to which a flip-chip package according to the embodiment of the present disclosure may be applied. The configuration of the apparatus 10 described here is an example, and a scope to which the embodiment of the present disclosure is applicable is not limited thereto.

(Structure of the flip-chip package) Following describes a structure of the flip-chip package according to the embodiment of the present disclosure.

FIG. 2 is a schematic cross-sectional view of the flip-chip package according to the embodiment of the present disclosure. A flip-chip package 200 of FIG. 2 is an example of the flip-chip package according to the embodiment of the present disclosure.

As shown in FIG. 2, the package 200 comprises a substrate 201, a semiconductor chip (die) 202, bumps 203, an underfill 204, a thermal interface material (TIM) 205, a heat spreader 206, a stiffener 207, and a molded member 209. The molded member 209 is composed of a mold compound. The TIM 205 may be composed of an organic-based material such as Silicone or the like, a metal such as InSn, InAg or the like, a Ag sintered material including nano-Ag, or a CNT based material.

The stiffener 207 is glued to the substrate 201 by an adhesive 208. The heat spreader 206 is glued to the molded member 209 by an adhesive 210. In this example, the adhesive 210 is also filled in a region formed by a side of the heat spreader 206 and the molded member 209, thereby enhancing adhesion of them.

The chip 202 is configured to connect with the substrate 201 via the bumps 203 which are sandwiched between an upper surface of the substrate 201 and a bottom surface of the chip 202. The molded member 209 is formed on the substrate 201 to wrap a side portion of the chip 202 and lay a top surface of the chip 202 bare.

An upper surface of the molded member 209 has a first area continuous with the top surface of the chip 202, a second area to which the adhesive 210 is applied, and a wall-like structure 209a.

The wall-like structure 209a is a convex portion with a width W and a height H shown in FIG. 3. FIG. 3 is a partially enlarged view of the flip-chip package in FIG. 2, according to the embodiment of the present disclosure. For example, the width W may be around 3.0mm or less, and the height H may be set to around 200μm or less. These configurations are merely examples, so the width W and the height H may be set to values other than the above-mentioned values.

Also, the wall-like structure 209a is placed to surround the top surface of the chip 202 as shown in FIG. 4. FIG. 4 is a schematic top view of the flip-chip package in FIG. 2, according to the embodiment of the present disclosure. In FIG. 4, the heat spreader 206 is omitted for simplicity, and a II-II cutting line corresponds to the cross-sectional view of FIG. 2. As shown in FIG. 4, the TIM 205 is filled in an inside region surrounded by the wall-like structure 209a, and the adhesive 210 is applied to an area (the second area) outside the wall-like structure 209a. In this example, the second area acts as an adhesive pool for filling the adhesive 210.

In FIG. 2, the first area on the upper surface of the molded member 209 is a flat portion close to the chip 202 and extends toward an edge of the chip 202 from an inside wall of the wall-like structure 209a. The second area of the molded member 209 extends outward from an outside wall of the wall-like structure 209a. Here, modifiers "inside" and "outside" represent one side closer to a center of the chip 202 and another side closer to an edge of the package 200, respectively.

The heat spreader 206 is placed above the top surface of the chip 202 and glued to the molded member 209 by the adhesive 210 applied to the second area. The heat spreader 206 may be made from a low CTE material such as Cu, Ag-diamond or Co-Mo. Using the low CTE material to the heat spreader 206 may reduce stress on the TIM 205 during a reflow process in an assembly procedure of the package 200.

As shown in FIG. 2, the heat spreader 206 is supported by the wall-like structure 209a, and the first and second areas on the upper surface of the molded member 209 are spatially separated by the wall-like structure 209a. This configuration enables to avoid mixture of the TIM 205 applied to the first area and the adhesive 210 applied to the second area during the reflow process, thereby avoiding formation of voids in the TIM 205 and outflow of the TIM 205 into the adhesive 210.

The TIM 205 is filled in a spatial region formed by the top surface of the chip 202, the bottom surface of the heat spreader 206, the first area of the molded member 209, and the inside wall of the wall-like structure 209a. Thus, the thickness of the TIM 205 is defined by the height H of the wall-like structure 209a as shown in FIG. 3.

The stiffener 207 has a structure like a square frame and is formed on the substrate 201 to surround outer sides of the molded member 209, as shown in FIG. 4. Also, the molded member 209 is formed to fill an inside region of the stiffener 207. The stiffener 207 may enhance strength of the package 200, thereby increasing resistance to external impact on the package 200.

As mentioned above, in the package 200, the TIM 205 is formed in the spatial region surrounded by the top surface of the chip 202, at least a part of the bottom surface of the heat spreader 206, the first area of the molded member 209, and a side of the wall-like structure 209a. Accordingly, a thickness of the TIM 205 is defined by the height H of the wall-like structure 209a that may be easily controlled in a molding process. This means that it can be realized to finely adjust the thickness of the TIM 205 to a desired small thickness (e.g. around 200μm or less) for implementing improved thermal performance.

In addition, the first and second areas of the molded member 209 are spatially separated by the wall-like structure 209a, thereby avoiding mixture of the TIM 205 and the adhesive 210 during the reflow process. This enables to avoid formation of voids in the TIM 205 and outflow of the TIM 205 into the adhesive 210, thereby improving the thermal performance. Moreover, the molded member 209 may act as a support member to maintain a distance between the heat spreader 206 and the substrate 201, thereby reducing a risk of delamination of the TIM 205 from the heat spreader 206 during the reflow process.

For the above-mentioned reasons, the package 200 may achieve improved thermal performance that can ensure adequate reliability in operation.

(Assembly process of the package) Following describes a method for assembling the flip-chip package according to the embodiment of the present disclosure.

FIGs. 5A to 5E are schematic diagrams for describing an assembly process of the package 200 of FIG. 2.

As shown in FIG. 5A, the chip 202 is placed on the substrate 201 to sandwich the bumps 203 between the bottom surface of the chip 202 and the substrate 201. Also, the stiffener 207 is placed on the substrate 201 to sandwich the adhesive 208 between a bottom surface of the stiffener 207 and the substrate 201.

Next, as shown in FIG. 5B, the underfill 204 is filled in a region under the chip 202 to cover the bumps 204, where the underfill 204 may cover a portion of side walls of the chip 202. The underfill 204 is cured after dispensing it.

Next, as shown in FIG. 5C, the mold compound is filled around the chip 202 on the substrate 201 so as to wrap a side portion of the chip 202 and lay the top surface of the chip 202 bare. Also, molding is performed to form the molded member 209 that the upper surface of the molded member 209 has the first area b1, the second area b2 and the wall-like structure 209a. For example, the molding may be implemented using a transfer-type molding method or a compression-type molding method.

The first area b1 is an area continuous with the top surface of the chip 202, and the second area b2 is an area to which the adhesive 210 is to-be-applied. The wall-like structure 209a is a portion of the molded member 209 that is placed to surround the top surface of the chip 202. The first area b1 and the second area b2 are separated by the wall-like structure 209a. In this example, the second area b2 forms an adhesive pool for filling the adhesive 210.

Next, as shown in FIG. 5D, the adhesive 210 is applied to the second area of the molded member 209. Also, the TIM 205 is filled in a region surrounded by the first area b1, the wall-like structure 209a and the top surface of the chip 202. The TIM 209 and the adhesive 210 are cured after dispensing them.

Next, as shown in FIG. 5E, the heat spreader 206 is placed on exposed portions (top ends) of the wall-like structure 209a to seal the TIM 205 and to sandwich the adhesive 210 between the heat spreader 206 and the wall-like structure 209. After attachment of the heat spreader 206, the reflow process for connecting the chip 202 to the substrate 201 is performed.

During the reflow process, the package 200 is heated up to around 250 degrees Celsius. However, since the first area b1 applied to the adhesive 210 and the second area b2 applied to the TIM 205 are spatially separated by the wall-like structure 209a, mixture of the TIM 205 and the adhesive 210 is avoided during the reflow process. This enables to avoid formation of voids in the TIM 205 and outflow of the TIM 205 into the adhesive 210, thereby improving the thermal performance.

In addition, the molded member 209 may act as a support member to maintain a distance between the heat spreader 206 and the substrate 201, thereby reducing a risk of delamination of the TIM 205 from the heat spreader 206 during the reflow process.

(Gap changes during the assembly process) Following describes changes of the TIM gap during the reflow process.

FIG. 6 shows simulation results of gap changes during the assembly process of the flip-chip package in FIG. 2, according to the embodiment of the present disclosure. In graphs of FIG. 6, vertical and horizontal axes thereof indicate the TIM gap and time, respectively. Additionally, another axe indicating temperature of the package 200 is shown in FIG. 6. In FIG. 6, solid rectangular dots represent data corresponding to the package 200 (embodiment) , and blank circles represent data corresponding to the conventional package shown in FIG. 13A.

At time t ₁, the temperature is set to be around 150 degrees Celsius that is temperature for curing the adhesive. In this example, the packages are cooled down to around 30 degrees Celsius toward time t ₆, and the temperature gradually increases up to around 250 degrees Celsius toward time t ₁₅ for the assembly reflow. In a case of the conventional package, the TIM gap sharply increases up to about 185μm during the reflow process. On the other hand, in a case of the package 200, the TIM gap gradually increases but the TIM gap thereof is kept below 110μm that is obviously shorter than the conventional package. This means that the package 200 enables to reduce a risk of delamination of the TIM 205 from the heat spreader 206 during the reflow process.

(First exemplary variation of the flip-chip package) Following describes a first exemplary variation of the flip-chip package according to the embodiment of the present disclosure.

FIG. 7 shows the first exemplary variation of the flip-chip package according to the embodiment of the present disclosure. A flip-chip package 300 shown in FIG. 7 is an example of the flip-chip package according to the first exemplary variation.

As shown in FIG. 7, the package 300 comprises a substrate 301, a semiconductor chip (die) 302, bumps 303, an underfill 304, a TIM 305, a heat spreader 306, a stiffener 307, and a molded member 309. The stiffener 307 is glued to the substrate 301 by an adhesive 308. The heat spreader 306 is glued to the molded member 309 by an adhesive 310.

The package 300 differs from the package 200 described above in structures of the heat spreader 306 and the molded member 309. Specifically, the heat spreader 306 extends to an outer edge of the package 300 to be wider than the heat spreader 206 of the package 200, and the molded member 309 also extends to under the extended portion of the heat spreader 306, as shown in FIG. 7. The adhesive 310 is further applied to the extended portion of the molded member 309, and sandwiched between the heat spreader 306 and the wall-like structure 309.

According to the first variation, since a volume of the heat spreader 306 is enlarged, cooling performance by the heat spreader 306 may be enhanced. Also, since an adhesion area between the heat spreader 306 and the wall-like structure 309 is extended, the first variation enables to effectively reduce a risk of delamination of the TIM 205 from the heat spreader 206 during the reflow process.

(Second exemplary variation of the flip-chip package) Following describes second exemplary variation of the flip-chip package according to the embodiment of the present disclosure.

FIG. 8A shows a package structure in the second exemplary variation of the flip-chip package according to the embodiment of the present disclosure. FIG. 8B shows another package structure in the second exemplary variation of the flip-chip package according to the embodiment of the present disclosure. A flip-chip package 400 shown in FIG. 8A or FIG. 8B is an example of the flip-chip package according to the second exemplary variation.

The package 400 comprises a substrate 401, a semiconductor chip (die) 402, bumps 403, an underfill 404, a TIM 405, a heat spreader 406, and a molded member 409. The heat spreader 406 is glued to the molded member 409 by an adhesive 410. The package 400 of FIG. 8A differs from the package 200 described above in omitting a member corresponding to the stiffener 207.

In the package 400 of FIG. 8A, an area to which the adhesive 410 is applied, has a structure like a flat tray on which the adhesive 410 is added. On the other hand, in the package 400 of FIG. 8B, an area to which the adhesive 410 is applied, has a structure like a pool in which the adhesive 410 is filled.

(Third exemplary variation of the flip-chip package) Following describes third exemplary variation of the flip-chip package according to the embodiment of the present disclosure.

FIG. 9A shows a package structure in the third exemplary variation of the flip-chip package according to the embodiment of the present disclosure. FIG. 9B shows another package structure in the third exemplary variation of the flip-chip package according to the embodiment of the present disclosure. A flip-chip package 500 shown in FIG. 9A or FIG. 9B is an example of the flip-chip package according to the third exemplary variation.

The package 500 comprises a substrate 501, a semiconductor chip (die) 502, bumps 503, an underfill 504, a TIM 505, a heat spreader 506, a stiffener 507, and a molded member 509. The stiffener 507 is glued to the substrate 501 by an adhesive 508. The heat spreader 506 is glued to the molded member 509 by an adhesive 510.

The package 500 differs from the package 200 described above in structures of the heat spreader 506 and the stiffener 507. Specifically, the heat spreader 506 extends to an outer edge of the package 500 to be wider than the heat spreader 206 of the package 200, and the stiffener 507 is buried in the molded-structure 509, as shown in FIGs. 9A and 9B. Also, the molded member 509 covers an upper surface of the stiffener 507, and the adhesive 510 is further applied to a portion of the molded member 509 that covers the stiffener 507.

In the package 500 of FIG. 9A, an area to which the adhesive 510 is applied, has a structure like a flat tray on which the adhesive 510 is added. On the other hand, in the package 500 of FIG. 9B, an area to which the adhesive 510 is applied, has a structure like a pool in which the adhesive 510 is filled.

(Fourth exemplary variation of the flip-chip package) Following describes sixth and seventh exemplary variations of the flip-chip package according to the embodiment of the present disclosure.

FIG. 10A shows a package structure in the fourth exemplary variation of the flip-chip package according to the embodiment of the present disclosure. FIG. 10B shows another package structure in the fourth exemplary variation of the flip-chip package according to the embodiment of the present disclosure. A flip-chip package 600 shown in FIG. 9A or FIG. 9B is an example of the flip-chip package according to the fourth exemplary variation.

The package 600 comprises a substrate 601, a semiconductor chip (die) 602, bumps 603, an underfill 604, a TIM 605, a heat spreader 606, and a molded member 609. The heat spreader 606 is glued to the molded member 609 by an adhesive 610 and also glued to the substrate 601 by an adhesive 608.

The package 600 differs from the package 200 described above in omitting a member corresponding to the stiffener 207 and in a structures of the heat spreader 606. Specifically, the heat spreader 606 is formed by a flat lid and a side wall extending downward from an end of the flat lid, where the flat lid extends to an outer edge of the package 600 to be wider than the heat spreader 206 of the package 200, as shown in FIGs. 10A and 10B.

In the package 600 of FIG. 10A, an area to which the adhesive 610 is applied, has a structure like a flat tray on which the adhesive 610 is added. On the other hand, in the package 600 of FIG. 10B, an area to which the adhesive 610 is applied, has a structure like a pool in which the adhesive 610 is filled.

The variations mentioned above are merely a part of the variations of the embodiment, and other variations of the embodiment can be implemented based on the embodiment described above and the variations thereof. Also, such variations may be included in a scope of the embodiment of the present disclosure.

(Other possible shapes of the molded member) Following describes some possible shapes of the molded member in the flip-chip package according to the embodiment of the present disclosure.

FIGs. 11A to 11F are schematic top view of the flip-chip package for describing some possible shapes of the molded member therein according to the embodiment of the present disclosure. In FIGs. 11A to 11F, the heat spreader is omitted for simplicity.

Each of FIGs. 11A and 11B shows a structure of the molded member (MOLD) such that the TIM is formed to have a rectangular portion and four arms protruding from four corners of the rectangular portion toward four corners of the package. In a case of FIG. 11A, an area to which the adhesive is applied, has a structure like a flat tray on which the adhesive is added. On the other hand, in a case of FIG. 11B, an area to which an adhesive is applied, has a structure like a pool in which the adhesive is filled.

FIG. 11C shows a structure of the molded member such that the TIM is formed to have a rectangular portion and four arms protruding from four corners of the rectangular portion toward four corners of the package. The structure of FIG. 11C differs from that of FIG. 11B in configuration of an area to which the adhesive is applied. In the case of FIG. 11B, there exists four separate adhesive pools as the region to which the adhesive is applied. On the other hand, the structure of FIG. 11C has one enlarged adhesive pool to which the adhesive is applied, where the enlarged adhesive pool is arranged to surround an area of the TIM.

An example of FIG. 11D is a modification of the structure in FIG. 11C so that the area of the TIM has a star-like shape. Likewise, an example of FIG. 11E is a modification of the structure in FIG. 11C so that the area of the TIM has a circular shape. Also, an example of FIG. 11F is a modification of the structure in FIG. 11C so that the area of the TIM has a rectangular shape rotated 45 degrees.

The exemplary shapes of the molded members mentioned above are merely a part of possible shapes of the molded member according to the embodiment, and other shapes thereof can be implemented based on the examples described above. Also, such possible shapes of the molded member may be included in a scope of the embodiment of the present disclosure.

(Multiple-chips configurations of the flip-chip package) Following describes multiple-chips configurations of the flip-chip package according to the embodiment of the present disclosure. These multiple-chips configurations respectively correspond to possible variations of the flip-chip package according to the embodiment of the present disclosure.

FIG. 12A shows a possible variation of the flip-chip package according to the embodiment of the present disclosure. FIG. 12B shows another possible variation of the flip-chip package according to the embodiment of the present disclosure. A flip-chip package 700 shown in FIG. 12A or FIG. 12B is an example of the flip-chip package according to the possible variation of the embodiment.

The package 700 comprises a substrate 701, semiconductor chips (dies) 702a and 702b,

bumps

703a and 703b, underfills 704a and 704b,

TIMs

705a and 705b, a heat spreader 706, a stiffener 707, and a molded member 709. The stiffener 707 is glued to the substrate 701 by an adhesive 708. The heat spreader 706 is glued to the molded member 709 by an adhesive 710.

The package 700 of FIG. 12A differs from the package 200 described above mainly in a structure that has a plurality of chips (the

chips

702a and 702b) . Although the number of the chips in the package 700 is two, techniques according to the embodiment of the present disclosure may be applied to a package with three or more chips based on the similar manner to the package 700 of FIG. 12A.

Optionally, the molded member 709 may have an additional adhesive pool to that an adhesive 710a is applied between adjacent chips, as shown in FIG. 12B. Addition of the adhesive 710a enhances adhesion between the heat spreader 706 and the molded member 709, thereby reducing a risk of delamination of the

TIMs

705a and 705b from the heat spreader 706 during the reflow process.

The above-mentioned multiple-chips configuration may be applied to the variations shown in FIGs. 7, 8A to 8B, 9A to 9B and 10A to 10B. Also, the possible shapes of the molded member shown in FIGs. 11A to 11F may be applied to the multiple-chips configuration. Even in cases of the multiple-chips configuration, the package of the embodiment may achieve improved thermal performance that can ensure adequate reliability in operation.

The foregoing disclosure merely discloses exemplary embodiments, and is not intended to limit the protection scope of the present invention. It will be appreciated by those skilled in the art that the foregoing embodiments and all or some of other embodiments and modifications which may be derived based on the scope of claims of the present invention will of course fall within the scope of the present invention.

Claims

A flip-chip package comprising:

at least one chip configured to connect with a substrate;

a molded member formed on the substrate to wrap a side portion of the at least one chip and lay a top surface of each chip bare, wherein an upper surface of the molded member has a first area continuous with the top surface of each chip, a second area to which an adhesive is applied and a wall-like structure placed to surround the top surface of each chip, and the first and second areas are separated by the wall-like structure;

a heat spreader placed above the top surface of the at least one chip and glued to the molded member by the adhesive filled in the second area; and

a thermal interface material filled in a spatial region formed by the first area, the top surface of each chip, at least a part of a bottom surface of the heat spreader, and a first side of the wall-like structure.
The flip-chip package according to claim 1, further comprising:

a stiffener having a structure like a square frame, wherein the stiffener is formed on the substrate to surround outer sides of the molded member, wherein the molded member is formed to fill an inside region of the stiffener.
The flip-chip package according to claim 1, wherein

the heat spreader has a lid portion placed above the at least one chip and a side portion extending downward from an end of the lid portion, wherein the side portion is placed outside the molded member, and an end of the side portion is glued to the substrate by an adhesive.
The flip-chip package according to any one of claims 1 to 3, wherein

the second area comprises an adhesive pool for filling the adhesive, wherein a second side of the wall-like structure forms at least a part of a side of the adhesive pool.
An apparatus comprising: circuitry to which a flip-chip package is applied, wherein the package comprising:

at least one chip configured to connect with a substrate;

a molded member formed on the substrate to wrap a side portion of the at least one chip and lay a top surface of each chip bare, wherein an upper surface of the molded member has a first area continuous with the top surface of each chip, a second area to which an adhesive is applied and a wall-like structure placed to surround the top surface of each chip, and the first and second areas are separated by the wall-like structure;

a heat spreader placed above the top surface of the at least one chip and glued to the molded member by the adhesive filled in the second area; and

a thermal interface material filled in a spatial region formed by the first area, the top surface of each chip, at least a part of a bottom surface of the heat spreader, and a first side of the wall-like structure.
The apparatus according to claim 5, further comprising:

a stiffener having a structure like a square frame, wherein the stiffener is formed on the substrate to surround outer sides of the molded member, and the molded member is formed to fill an inside region of the stiffener.
The apparatus according to claim 5, wherein

the heat spreader has a lid portion placed above the at least one chip and a side portion extending downward from an end of the lid portion, wherein the side portion is placed outside the molded member, and an end of the side portion is glued to the substrate by an adhesive.
The apparatus according to any one of claims 5 to 7, wherein

the second area comprises an adhesive pool for filling the adhesive, wherein a second side of the wall-like structure forms at least a part of a side of the adhesive pool.
A method for assembling a flip-chip package which comprises at least one chip, a substrate, a molded member, a thermal interface material and a heat spreader, the method comprising:

connecting the at least one chip with the substrate;

filling a mold compound around the at least one chip on the substrate so as to wrap a side portion of the at least one chip and lay a top surface of each chip bare, and molding the molded member with a structure that an upper surface of the molded member has a first area continuous with the top surface of each chip, a second area to which an adhesive is to-be-applied and a wall-like structure placed to surround the top surface of each chip, and the first and second areas are separated by the wall-like structure;

applying the adhesive to the second area of the molded member;

forming the thermal interface material on the first area and the top surface of each chip;

attaching the heat spreader to the thermal interface material and the molded member by the adhesive; and

performing a reflow procedure of the flip-chip package.
The method according to claim 9, wherein

before the filling the mold compound, the method further comprises: forming a stiffener on the substrate, wherein the stiffener has a structure like a square frame surrounding an entire area on which the at least one chip is disposed, and the molded member is formed to fill an inside region of the stiffener.
The method according to claim 9, wherein

the heat spreader has a lid portion placed above the at least one chip and a side portion extending downward from an end of the lid portion, wherein the side portion is placed outside the molded member, and in the attaching the heat spreader, an end of the side portion is glued to the substrate by an adhesive.