HK1078990B - Method of forming a semiconductor package and leadframe therefor - Google Patents

Description

Method of forming a semiconductor package and forming a lead frame thereon

Technical Field

The present invention relates generally to packages and, more particularly, to methods of forming semiconductor packages and leadframes.

Background

In the past, in manufacturing semiconductor packages, semiconductor packages and lead frames have been manufactured using various methods. One lead frame fabrication method is to make a lead frame with a dam-bar extending laterally between and connected to each lead of the lead frame. The lead extends through the dam bar and is adhered to the primary panel area of the leadframe strip. When the lead frame is molded into a package, the dam bars tend to prevent the molding compound from reaching the leads of the package. The dam must be positioned far enough away from the package to allow room for cutting the dam without damaging the package. The large gap between the encapsulant and dam bar allows the molding material to leak out and fill the gap. The material also adheres to the sides of the leads. Such molding materials are often referred to as stacks (flash or flash).

Other methods produce lead frames that do not contain dam bars. The molding equipment or mold used to make the semiconductor package contains channels or recesses for the placement of the leads. During the molding operation, the molding material moves through the channels and forms a stack that adheres the sides of the leads.

After the molding operation is complete, the stack of plates resulting from these processes must be eliminated from the leads. In some cases, the stacks are along the entire lead length and can be up to 0.15 mm thick. The stack removal process includes removing the stack using a high pressure water jet or a force or chemical jet. The pressure is typically about two hundred fifty to four hundred twenty five kilograms per square centimeter (250-²) The range of (1).

As semiconductor packages and the size of leads used in the packages continue to decrease, the more sophisticated the leads and packages become and the more susceptible they become to damage. The smaller lead and package size makes it more difficult to prevent the molding material from leaking out of the mold cavity, which makes it more difficult to prevent the molding material from sticking to the leads. In some cases the stack is longer than the finished lead length and may be thicker than the lead width. This makes the removal of the stack very difficult. In addition, the smaller lead and package sizes make it more difficult to remove the stack without damaging the leads and package.

In addition, it is desirable for a lead frame to contain small leads, which reduces the amount of molding material that leaks out of the mold cavity and along the leads, and reduces the amount of molding material or the stack to which the leads are adhered, as well as minimizing lead damage during stack removal.

Disclosure of Invention

To solve the problems of the prior art, an aspect of the present invention provides a method of forming a semiconductor package, including: providing a lead frame having a main panel, a cavity, and a plurality of leads extending from the main panel into the cavity, the main panel being no greater than a first distance from an outer edge of the cavity, and at least a first lead of the plurality of leads extending from the cavity to the main panel no greater than the first distance, a proximal end of the first lead being attached to the main panel at an intersection between the first lead and the main panel, wherein the main panel is connected to the proximal end of the first lead and does not extend through the proximal end of the first lead to the cavity; sealing the cavity region of the lead frame to form a package body; forming a first portion of the main panel to a portion of the first lead, including forming a portion of the first lead that extends more than a first distance from the package body; and cutting a second portion of the main panel away from the first leads and leaving the first leads extending from the package body.

Another aspect of the present invention provides a lead frame for a semiconductor package, including: a main panel comprising a plurality of zones, wherein, from an outer edge of one of the plurality of zones, an edge of the main panel facing the zone is located no farther than a first distance; and a plurality of leads extending from the main panel into the one of the plurality of cavities, the plurality of leads extending from an outer edge of the one of the plurality of cavities toward the main panel no greater than the first distance.

Yet another aspect of the present invention provides a method of forming a lead frame for a semiconductor package, comprising: forming a leadframe strip including a main panel and a plurality of cavity regions, including forming the main panel from an outer edge of one of the plurality of cavity regions, the main panel being positioned facing the edge of the cavity region no greater than a first distance; and forming a plurality of leads extending from the main panel into one of the plurality of cavity regions, including forming the plurality of leads with a length extending from the one of the plurality of cavity regions to the main panel that is no greater than the first distance, wherein the first distance is selected to minimize sealing material that leaks out of the mold cavity and sticks to the leads during the sealing process.

Drawings

FIG. 1 shows an enlarged plan view of a portion of one embodiment of a lead frame according to the present invention;

FIG. 2 shows an enlarged plan view of one example of a portion of the lead frame of FIG. 1 in accordance with the present invention;

fig. 3 shows a plan view of a portion of the lead frame of fig. 2 at a stage in the manufacture of a semiconductor package in accordance with the present invention;

fig. 4 shows an isometric view of a portion of the lead frame of fig. 3 at a subsequent stage in the manufacture of a semiconductor package in accordance with the invention;

fig. 5 shows an enlarged plan view of a portion of another embodiment of a lead frame according to the present invention;

fig. 6 is an enlarged plan view of the lead frame portion of fig. 5 at a subsequent stage in the manufacture of a semiconductor package in accordance with the present invention;

fig. 7 is an enlarged plan view of a portion of another embodiment of the lead frame of fig. 5 at a stage in the manufacture of an alternative semiconductor package in accordance with the present invention;

for simplicity and clarity of illustration, elements in the figures are not necessarily to scale, and the same reference numbers in different figures denote the same elements. In addition, details and elements of the described and well-known steps have been omitted for simplicity of the description.

Detailed Description

Fig. 1 shows an enlarged plan view of an embodiment portion of a leadframe strip or frame 10. The lead frame 10 is typically fabricated as a strip containing a plurality of package sites 12 where semiconductor packages are formed. The lead frame 10 includes a main panel portion or main panel 11 that typically supports other components of the lead frame 10 during manufacture. As is well known in the art, the main panel 11 is typically an elongated sheet of metal, such as copper or an alloy 42. In most embodiments, the panel 11 is less than 0.6 mm thick, preferably about 0.25 mm thick.

Fig. 2 illustrates a further enlarged plan view of the lead frame 10 of fig. 1 showing one embodiment of a portion of one package site 15 of the plurality of package sites 12 shown in fig. 1 in accordance with the present invention. The explanation refers to fig. 1 and 2. The locations 15, typically each location 12, include a cavity region 16 that tends to be encapsulated during the formation of a semiconductor package on the leadframe 10. The outer edges of the cavity region 16 are generally indicated by dashed boxes. The faceplate 11 surrounds the cavity region 16 and extends a distance 32 from the outer edge of the cavity region 16. In some embodiments, the panel 11 may have a different distance from one side of the cavity region 16 than the other side thereof. The distance 32 is described in more detail next. Site 15, and thus site 12 and leadframe 10, includes a plurality of leads, including leads 17, 18, 19 and 20, extending from panel 11 into cavity region 16. Leads 17, 18, 19 and 20 may hereinafter be referred to as a plurality of leads or leads 17-20. Leads 17-19 are shown to have a width 22 and lead 20 has a width 23 that is greater than width 22. For clarity of description and illustration, four leads are shown, however, one skilled in the art will recognize that various numbers of leads may extend into the cavity region 16, each of which may have the same or different widths. Distal ends 29 of leads 17-19 are in lumen region 16. A distal end of lead 20 is also in cavity region 16 and contains a die attach region or flag 21 in cavity region 16, which is formed for attaching a semiconductor die thereto. Leads 17-20 extend a distance 32 outward of cavity region 16, wherein a proximal end of each lead 17-20 is adhered to faceplate 11. The portion of the leads 17-20 outside the portion 16 refers to the outer portion of the leads 17-20. The distal ends 29 of the leads 17-19 contain a bonding area that will typically be used to attach a bonding wire to the semiconductor die with the flag 21 attached. The bonding pads may also be used to attach the chip directly or flip-chip to the leads 17-19. Such labels, bonding regions, and methods of adhesion are well known to those skilled in the art.

Fig. 3 shows a plan view of the site 15 explained in the description of fig. 2 after several steps in the manufacture of one semiconductor package 30 using the lead frame 10. A semiconductor die (not shown) is typically attached to flag 21 and wire bonded to leads 17-20 as is well known in the art. Thereafter, the leadframe 10 is placed in a mold (mold) and the cavity region 16 is sealed. During the encapsulation process, the mold closes over the lead frame 10. A mold cavity in the mold typically corresponds in shape and location to cavity region 16. The mold clamps the portions of leads 17-20 outside of cavity region 16 and the portion of panel 11 surrounding cavity region 16. During the sealing step, the portion of the face plate 11 outside of the cavity region 16 and the portions outside of the leads 17-20 between the face plate 11 and the cavity region 16 block the sealing material and restrict its leakage out of the mold cavity. Thus, it is important that the distance 32 be very small to prevent the encapsulant from leaking out and adhering to the leads 17-20. During the sealing process, distance 32 is selected to minimize and preferably prevent sealing compound from leaking out of the mold cavity and adhering to leads 17-20. To accomplish this, distance 32 is typically no greater than about fifty (50) microns, and preferably no greater than about ten (10) microns from the outer edge of cavity region 16. Some of the sealing material may leak from the mold cavity into the void formed by distance 32. This is done to minimize the distance 32 to minimize the amount of stack plate that accumulates in the open hole formed by the distance 32.

Following the sealing and subsequent curing operation, a package 38 is left to seal the cavity region 16 and surround the distal ends of the leads 17-20. Typically, body 38 has a length 37 and a width 36 that is less than length 37. In other embodiments, length 37 and width 36 may be approximately equal.

After the molding operation, the leads 17-20 are trimmed and formed to the desired length and width from the material of the panel 11. Thereafter, the leads 17-20 are formed into a sheet and the package 30 is then cut from the panel 11. As will be further seen below, these operations may be performed in a variety of orders.

In a preferred embodiment, the leads 17-20 are first trimmed and formed using a first portion of the panel 11 material for forming an extra length, or portion of the leads 17-20 that extends to the proximal ends of the leads 17-20. In the preferred embodiment, the trimming lead 17-19 has a width approximately equal to the width 22 of the distal portion of the lead 17-19 and the trimming lead 20 has a width approximately equal to the width 23 of the distal portion of the lead 20 as shown in fig. 2. Various trimming and forming tools well known in the art may be used to trim and form the leads 17-20 from the panel 11. An example of a suitable trim and form is the Diehard Engineering model MPS C286, manufactured by Diehard Engineering inc. In this embodiment, the leads 17-20 are formed to have a width of no greater than about 0.5 millimeters and a length of between about 1.0-2.5 millimeters. In addition, formation 38 is between about 1 and 5(1-5) millimeters wide and between about 1 and 5(1-5) millimeters long. The trimming operation leaves a hole 34 through the panel 11 to expose the leads 17-20.

Fig. 4 shows an isometric view of location 15 of fig. 3 at a subsequent stage in the manufacture of one of the semiconductor packages 30. After the trimming and forming operations, all of the packages 30 are cut from panel 11 except for the distal ends of leads 20. The adhesive panel 11 assists in handling and placing the package 30 during other operations. It should be noted that a small amount of sealing material may leak out of the mold cavity to the distance 32 and adhere to the outside of the body 38 as a stack 35. However, the small size of the distance 32 limits the width of the stack 35 to be less than the distance 32. In this way, stack 35 does not affect the ability of package 30 to adhere to other substrates. After this partial cutting operation, the leads 17-20 are coated by electroplating or various other well-known coating operations. By forming the leads 17-20 prior to plating, the edges and ends of all leads, except the proximal end of the lead 20, are coated in this operation. The package 30 is then cut from the panel 11 by cutting the connections between the leads 20 and the panel 11. It can be seen that forming the face plate 11 no further than the distance 32 from the cavity region 16 eliminates the need for a dam bar and minimizes the number of stacks of adhesive leads 17-20. Thus, there are no dam bars between the face plate 11 and the cavity region 16. Due to the small length of distance 32, no stack removal step is required after forming and cutting package 30. The elimination of the stack removal step eliminates damage caused by these operations, thus improving manufacturing yield and reducing cost.

In other embodiments, after the leads 17-20 are formed, the proximal ends of the other leads of the leads 17-20, or all of the leads 17-20, may remain adhered to the panel 11. For example, a proximal end of leads 17 and 19 may remain adhered to lead 18 and cut 20. Leads 17-20 may then be coated and the adhered leads may then be cut to form package 30.

In yet another embodiment, the package 30 may be coated before the leads 17-20 are trimmed and formed from the panel 11, and then the leads 17-20 may be formed from the panel 11 and the package 30 cut. Thus, it can be seen that a portion of the leads 17-20, such as a portion of the outer portion of the leads 17-20, can be formed by cutting a first portion of the main panel away from the plurality of leads and leaving a second portion of the main panel as a portion of the plurality of leads extending from the package body 38 greater than the distance 32.

In an additional embodiment, all of the leads 17-20 may be trimmed and formed from the panel 11 and then cut from the panel 11 to form the package 30. The leads 17-20 are then coated by various known methods, such as barrel plating.

Fig. 5 shows an enlarged plan view of a portion of an embodiment of a packaging location 40, the location 40 being an alternative embodiment of the location 15 explained in the description of fig. 2-4. The site 14 is one of a plurality of sites formed on the main panel 11 of the lead frame 10. Location 14 includes a cavity region 54 that functions similarly to portion 16. Location 40 also contains a plurality of leads, including leads 41, 42, 43, 44, 45, 46, 47, and 18, extending from panel 11 to cavity area 54. Leads 41-48 are similar and function similar to leads 17-20. The portions of leads 41-48 in cavity region 54 form an interior portion of each respective lead. The outer portion of each lead is outside of the cavity region 54. The distal end 49 of each lead 41-48 is in portion 54. The sign 51 is adhered to the panel 11 by a joint 52 extending from the sign 51 through a cavity region 54 to the panel 11.

Fig. 6 shows a plan view of the site 40 explained in the description of fig. 5 after several steps of manufacturing a semiconductor package 60 using the lead frame 10. After sealing the location 40, the package 60 is manufactured by selectively forming a desired set of external leads for the package 60. Typically, a die (not shown) is adhered to the flag 51 and electrically connected to the desired number of leads 41-48. In the example shown in fig. 6, the die is electrically connected to leads 42, 43, 46, and 47. The leadframe 10 is then placed into a mold and the cavity area 54 is sealed, as explained in the description of the package 30. During the sealing process, the face plate 11 and distance 32 minimize the amount of sealing material that leaks out of the mold cavity, as described above.

After the sealing operation, the trim leads 41-48 are selected and formed to the desired length and width from the material of the panel 11. Since only four leads contain outer portions, the leads 42, 43, 46 and 47 are formed from the material of the panel 11, and the material of the panel 11 is trimmed from the locations of the outer portions of the leads 41, 44, 45 and 48. In the trimming operation, the leads 41, 44, 45, and 48 are even trimmed approximately using the body 58. Thereafter, the leads 42, 43, 46, and 47 are plated, and then the package 60 is cut from the panel 11 in a manner similar to the method of forming the package 30.

Fig. 7 shows an enlarged plan view of a package 61 of an alternative embodiment of a package 60. After sealing the location 40, the package 61 is manufactured by selectively forming a desired set of three leads for the package 61. After the sealing operation, the trim leads 41-48 are selected and formed to the desired length and width from the material of the panel 11. Since package 61 contains only three leads, leads 43, 46 and 47 are formed from the material of panel 11, and the material of panel 11 is trimmed from the locations of the outer portions of leads 41, 42, 44, 45 and 48. Thereafter, the leads 43, 46 and 47 are plated, and then the package 61 is cut from the panel 11 in a manner similar to the method of forming the package 30.

As can be seen from the description of fig. 5-7, a package site may contain any number of internal lead portions to the interior of a cavity region, such as cavity regions 16 and 54. Typically, the maximum number of internal lead portions is determined by the size of the package, the lead width, and the spacing. However, a desired number of outer leads may be selectively formed from the inner lead portions. It can thus be seen that the number of outer lead portions can be chosen to be smaller than the number of inner lead portions. The selective number of external leads formed after encapsulation allows one package location, and thus one leadframe configuration, to be used for several different package configurations, thereby reducing manufacturing costs.

In view of all of the above, it should be apparent that a new method of forming a semiconductor package and leadframe is disclosed. Extending the leadframe panel near the cavity region of the leadframe allows the panel to be used to minimize leakage of encapsulant material during the encapsulation operation, thereby minimizing stacking on the package and on the leads. Trimming and forming the leads from the panel material after the sealing operation also facilitates the use of the panel to block the sealing material. Lowering the stack from the leads minimizes stack removal, thereby increasing assembly yield and reducing cost.

Claims (10)

1. A method of forming a semiconductor package, comprising:

providing a leadframe having a main panel, a cavity, and a plurality of leads extending from the main panel into the cavity, the main panel being no greater than a first distance from an outer edge of the cavity, and at least a first lead of the plurality of leads extending from the outer edge of the cavity to the main panel no greater than the first distance, a proximal end of the first lead being attached to the main panel at an intersection between the first lead and the main panel, wherein the first distance is selected to minimize encapsulant material leaking from the mold cavity and adhering to the lead during the encapsulation process, wherein the main panel is connected to the proximal end of the first lead and does not extend through the proximal end of the first lead to the cavity;

sealing the cavity region of the lead frame to form a package body;

forming a first portion of the main panel to a portion of the first lead, including forming a portion of the first lead that extends more than a first distance from the package body; and

the second portion of the main panel is cut away from the first leads and the first leads are left extending from the package body.

2. The method of claim 1, wherein the step of cutting the second portion of the main panel away from the first lead comprises leaving a third portion of the main panel attached to an end of at least one lead of the plurality of leads.

3. The method of claim 1, wherein forming the first portion of the main panel to a portion of the first lead of the plurality of leads comprises trimming the first portion of the main panel to form the portion of the first lead to the plurality of leads.

4. The method of claim 1, wherein forming the first portion of the main panel to a portion of the first lead of the plurality of leads comprises forming the portion of the first lead extending no more than 0.5 millimeters from the package body.

5. The method of claim 1, further comprising coating the plurality of leads and the main panel prior to the step of forming the first portion of the main panel to a portion of the first leads.

6. The method of claim 1, wherein the step of providing a leadframe having a main panel, a cavity, and a plurality of leads extending from the main panel into the cavity comprises forming the leadframe without dam bars between the main panel and the cavity.

7. A lead frame for a semiconductor package, comprising:

a main panel comprising a plurality of cavity sections, wherein, from an outer edge of one of the plurality of cavity sections, an edge of the main panel facing the cavity section is located no farther than a first distance, wherein the first distance is selected to minimize sealant material that leaks out of the mold cavity and adheres to the leads during the sealing process; and

a plurality of leads extending from the main panel into the one of the plurality of cavities, the plurality of leads extending from an outer edge of the one of the plurality of cavities toward the main panel no greater than the first distance.

8. The leadframe of claim 7, further comprising the leadframe without dam bars between the main panel and the cavity region.

9. A method of forming a leadframe for a semiconductor package, comprising:

forming a leadframe strip including a main panel and a plurality of cavity regions, including forming the main panel from an outer edge of one of the plurality of cavity regions, the main panel being positioned facing the edge of the cavity region no greater than a first distance; and

forming a plurality of leads extending from the main panel into one of the plurality of cavity regions includes forming a plurality of leads having a length extending from an outer edge of the one of the plurality of cavity regions toward the main panel that is no greater than the first distance, wherein the first distance is selected to minimize encapsulant material leaking out of the mold cavity and adhering to the leads during the encapsulation process.

10. The method of claim 9, wherein the step of forming the main panel comprises forming a first distance of no more than 0.5 millimeters.