JP2002204043A - Wiring board and method of manufacturing the same - Google Patents

Abstract

(57) [Summary] [Problem] To bury a wiring layer in an insulating sheet,
There is little variation in the wiring width of the wiring layer of the high-density pattern,
Further, a highly reliable wiring board free from occurrence of a short circuit between adjacent wiring layers can be obtained. A metal foil (14) formed on one surface of a transfer sheet (13) is subjected to an etching process to form a wiring layer (16) having a substantially trapezoidal cross section with a base angle of 0 to 45 ° and a minimum wiring interval of 30 µm or less. After the transfer sheet 13 is pressed against the surface of the soft insulating sheet 11, the transfer sheet 13 is peeled off and the wiring layer 16 is embedded and formed on the surface of the insulating sheet 11, and then the wiring formed on the surface of the insulating sheet 11 is formed. Until the bottom angle of the layer 16 becomes 45 to 85 °, only the surface of the insulating sheet 11 and the wiring layer 16 or only the surface of the wiring layer is selectively removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wiring board used for, for example, a package for accommodating a semiconductor element and a method of manufacturing the same, and more particularly to a wiring board having a high-density wiring layer formed on an insulating sheet surface and a method of manufacturing the same. Things.

[0002]

2. Description of the Related Art Wiring boards used for multi-layer wiring boards and packages for housing semiconductor elements, etc., will become more and more dense in the future along with the high performance of various electronic devices, and the wiring width and wiring pitch will be reduced to 20 μm or less. Is required, and via holes are also interstitial via holes (IVH)
And the mounting method of the IC chip also changes from the wire bonding to the flip chip, so that the flatness of the substrate itself needs to be reduced.

[0003] As such a wiring board, for example, a wiring board formed on the surface or inside of an insulating substrate containing an organic resin such as a thermosetting resin is known. In such an organic wiring substrate, for example, a wiring pattern is formed by etching and removing unnecessary portions of a metal foil adhered to the surface of an insulating substrate.

[0004]

However, the insulating substrate may be deteriorated by a chemical such as etching,
Since the wiring layer formed using the metal foil is only placed on the surface of the insulating substrate, poor adhesion between the wiring layer and the insulating substrate occurs, so that a gap is easily generated at the interface between the two, and as a result, wiring failure is caused. There was a problem that it could not be used at all. In addition, in order to form a multi-layered structure, it is necessary to sequentially form layers to form an IVH.

Furthermore, the flatness of the surface of the insulating substrate is low due to the wiring layer formed with a predetermined thickness inside or on the surface of the insulating substrate, and the flatness required for flip chip mounting is not satisfied.

Accordingly, the present inventors controlled the etching conditions and the like for the metal foil adhered to the surface of the transfer sheet to form a wiring layer made of a metal foil having a trapezoidal cross section.
By pressing this against the insulating sheet surface in a soft state, a wiring layer having an inverted trapezoidal cross section can be buried in the surface of the insulating sheet, thereby preventing a decrease in flatness due to the thickness of the wiring layer, This has the effect that it is not necessary to bring the insulating sheet into contact with the chemical.

In this method, since the etching is performed from the matte surface of the copper foil, a footprint of the copper foil, which is a serious problem in the ordinary subtractive method, does not occur, so that a fine wiring can be formed by a simple method. there were.

However, as shown in FIG. 5A, a wiring layer 22 composed of a high-density pattern having a minimum wiring interval w smaller than 40 μm is formed on the metal foil adhered to the surface of the transfer sheet 21. At this time, when the wiring layer 22 having a trapezoidal cross section is formed by etching,
As shown in FIG. 5A, the adjacent wiring layer 22 and the skirt overlap or are very close to each other, resulting in a large variation in the line width of the wiring layer 22 as shown in FIG. In some cases, there is a problem that a short circuit occurs between adjacent wiring layers.

Therefore, according to the present invention, the wiring layer is embedded in the insulating sheet, the variation in the wiring width of the wiring layer of the high-density pattern is small, and the high reliability without the short circuit between the adjacent wiring layers is obtained. It is an object of the present invention to provide a wiring board and a method of manufacturing the same.

[0010]

A wiring board according to the present invention is a wiring board in which a wiring layer made of metal foil is buried and formed on the surface of an insulating substrate. 30 μm or less, wherein the wiring layer has a substantially inverted trapezoidal shape, and the base angle of the substantially inverted trapezoidal shape is 45 to 85 °.

According to the method of manufacturing a wiring board of the present invention, a) etching a metal foil formed on one surface of a transfer sheet to form a substantially trapezoidal cross section having a base angle of 0 ° to 40 °; Forming a wiring layer having a pattern having a minimum wiring interval of 30 μm or less; and b) pressing the transfer sheet against a surface of a soft insulating sheet, peeling the transfer sheet, and connecting the wiring layer to the insulating sheet. C) removing the surface of the insulating sheet and the wiring layer until the bottom angle of the wiring layer formed on the surface of the insulating sheet becomes 45 ° to 85 °, or forming the wiring layer on the surface of the insulating sheet. Removing only the surface of the wiring layer until the bottom angle of the wiring layer becomes 45 ° to 85 °, and d) the steps a) to The wiring layer manufactured through c) is provided. It is characterized in that it comprises the steps of stacking a plurality insulating sheet that, the.

That is, according to the present invention, a wiring layer composed of a substantially trapezoidal high-density circuit pattern having a base angle of 0 ° to 40 ° is formed on the surface of a transfer sheet, and this is formed on the surface of a soft insulating sheet. After the transfer, the inverted trapezoidal wiring layer is removed until the bottom angle of the wiring layer becomes 45 ° to 85 °, so that the wiring layer can be buried in the insulating sheet without hindrance. And a wiring board having a highly reliable circuit pattern free from short-circuiting between adjacent wiring layers can be obtained.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a wiring board according to the present invention will be described with reference to the drawings.

FIG. 1 is a schematic sectional view of a wiring board according to the present invention, and FIG. 2 is an enlarged sectional view of a main part of a wiring layer forming portion.

As shown in FIG. 1, the wiring board of the present invention comprises:
A wiring layer 2 is adhered and formed on the surface or inside of an insulating substrate 1 formed by laminating a plurality of insulating layers 1a to 1c, and a through hole is formed to electrically connect the wiring layers 2 of different layers. Via-hole conductor 3 formed by filling conductor paste
Are formed.

In such a wiring board, a high-density circuit pattern in which the minimum wiring interval of the wiring layer 2 is 30 μm or less, particularly 25 μm or less, and further 20 μm or less is formed. As shown in the schematic cross-sectional view of the wiring layer 2 formed in such a high density, the wiring layer 2 has a cross section orthogonal to the wiring direction of the wiring layer, as shown in FIG. Has an inverted trapezoidal shape larger than the lower surface width w1. When the cross section of such a wiring layer 2 has an inverted trapezoidal shape, the insulating layers 1 a to 1
As a result, the flatness of the wiring board can be improved.

It is important that the bottom angle α of the wiring layer 2 in the inverted trapezoidal shape is 45 ° to 85 °, particularly 45 ° to 80 °. If the base angle α ° is larger than 85 °, the thickness of the wiring layer 2 becomes extremely thin as is apparent from a manufacturing method described later. If the angle is smaller than 45 °, insulation failure occurs between the adjacent wiring layers 2 and the line width of the wiring layers 2 varies greatly.

The side surface 2a and the lower surface 2b of the wiring layer 2 embedded in the insulating layers 1a to 1c are preferably roughened to have a surface roughness (Ra) of 200 nm or more, particularly 400 nm or more. Thus, the wiring layer 2 and the insulating layers 1a to 1c are anchored with the insulating layers 1a to 1c.
Can be firmly bonded. Further, the insulating layer 1a
1c, the upper surface 2c in contact with the other insulating layers 1a to 1c is roughened to 200 nm or more, particularly 400 nm or more in the same manner as described above. And the adhesiveness with the film.

The insulating substrate 1 constituting the wiring substrate A is made of, for example, a composite material containing at least one selected from inorganic fillers, inorganic fibers, and organic fibers together with an organic resin. The inorganic filler, the inorganic fiber, and the organic fiber are preferably uniformly dispersed in the organic resin at a ratio of 20 to 80% by volume.

The organic resins constituting such a composite material include PPE (polyphenylene ether resin), BT
It is made of a resin such as a resin (bismaleide triazine), an epoxy resin, a polyimide resin, a fluororesin, a phenol resin, and a polyaminobismaleimide, and it is particularly preferable that the raw material is a liquid thermosetting resin at room temperature.

On the other hand, as the inorganic filler, SiO 2
₂ , Al ₂ O ₃ , ZrO ₂ , TiO ₂ , AlN, SiC, B
_{aTiO 3, SrTiO 3, MgTiO 3} , zeolite,
Known materials such as CaTiO ₃ and aluminum borate can be used. In addition, the shape can be any shape such as a spherical shape and a needle shape.

Further, as the inorganic or organic fiber, there are glass fiber, aramid fiber, cellulose fiber and the like, and any property such as woven fabric and non-woven fabric may be used. In any case, it is desirable to include at least one or more insulating layers containing fibers in order to increase the strength of the wiring board A and obtain a highly reliable board.

It is preferable that the low-resistance metal material forming the wiring layer 2 includes at least one selected from copper, aluminum, gold and silver. A high-resistance metal such as Ni-Cr may be used as necessary for the circuit. Further, the metal powder to be filled in the via-hole conductor 3 is desirably made of at least one low-resistance metal among copper, aluminum, silver, and gold.

Next, a method of manufacturing a wiring board according to the present invention will be described with reference to the process chart of FIG.

First, an insulating sheet is prepared (FIG. 3).
(A)). Taking the case of producing an insulating sheet composed of an organic resin and an inorganic filler as an example, a composition obtained by adding a liquid organic resin to an inorganic filler is sufficiently mixed by means of a kneader (kneader) or three rolls. . Thereafter, the mixture is formed into a sheet by a rolling method, an extrusion method, an injection method, or a doctor blade method, and the insulating sheet 11 is manufactured. At this time, handling can be facilitated by semi-curing the insulating sheet 11.

The insulating slurry is preferably prepared by adding the above-mentioned composite material of the organic resin and the inorganic filler constituting the insulating sheet 11 to toluene, butyl acetate, methyl ethyl ketone, methanol, methyl cellosolve acetate, isopropyl alcohol, methyl isobutyl. It is composed of a fluid having a predetermined viscosity by adding a solvent such as ketone and dimethylformamide. From such a viewpoint, the viscosity of the slurry is
Although it depends on the forming method, 100 to 3000 poise is appropriate.

In the case of semi-curing, when the organic resin is a thermoplastic resin, the mixture thereof is cooled under heating, and in the case of a thermosetting resin, the temperature is slightly lower than a temperature sufficient for complete solidification. It may be heated to. When a woven or nonwoven fabric is used, a varnish-like resin is impregnated into fibers such as a woven or nonwoven fabric and dried to produce a semi-cured prepreg.

Next, a desired through-hole is formed in the insulating sheet 11 produced as described above by a punching method or laser processing, and a conductive paste is filled to form a via-hole conductor 12 (FIG. 3 ( b)). Copper, aluminum, silver,
It is desirable that the paste be made of at least one low-resistance metal among gold, and a paste can be obtained by adding an organic solvent and a binder.

Next, in forming a wiring layer on the semi-cured insulating sheet 11, first, a wiring layer is formed on the surface of the transfer sheet. FIG. 4 shows a process of forming this wiring layer.
First, as shown in FIG. 4 (a), a metal made of at least one or two or more alloys selected from copper, gold, silver, aluminum, etc. is applied to the surface of a transfer sheet 13 made of a resin film via an adhesive A foil 14 is prepared. At this time, copper or an alloy containing copper is most desirable.

Next, as shown in FIG. 4B, a resist layer 15 having a desired high-density circuit pattern is provided by printing or the like. Then, as shown in FIG. 4C, a wiring layer 16 having a trapezoidal cross section is formed in the portion where the resist layer 15 is formed, as shown in FIG. At this time, the angle formed by the trapezoidal base 16a and the lateral side 16b is such that when the interval between the wiring layers 16 is very narrow, the base angles β are 0 to 45 due to the trapezoidal skirts approaching or overlapping each other. °. In order to form such a trapezoidal wiring layer,
The etching rate is preferably set to 2 to 50 μm / min.

Thereafter, the resist layer 15 is removed (FIG. 4).
(D)). After the wiring layer 16 is formed, the wiring layer 1 is formed.
6 has a surface roughness Ra of 200 n
m or more, formic acid or NaClO ₂ , Na
It is desirable to perform a surface treatment with a mixed solution of OH and Na ₃ PO ₄ or the like. This surface roughness can be controlled by the roughening speed, and is 1 μm /
Can be satisfactorily roughened at a roughening rate of at least minutes.

Next, the wiring layer 1 manufactured as shown in FIG.
The transfer sheet 13 provided with 6 is positioned and laminated on the insulating sheet 11 on which the via-hole conductor 12 is formed in FIG. 3, and is applied at a pressure of about 10 to 500 kg / cm ² (FIG. 3C). Then, by peeling off the transfer sheet 13 together with the adhesive layer (not shown), a one-layer wiring board in which the wiring layer 16 having an inverted trapezoidal cross section is buried in the surface of the insulating sheet 11 can be manufactured (FIG. 3
(D)).

According to the above manufacturing method, the insulating sheet 11
By making the cross-sectional shape of the wiring layer 16 to be transferred onto the surface of the wiring sheet 16 into the predetermined trapezoidal shape, the wiring layer 16 is
When pressed against the surface, the insulating sheet 1 around the wiring layer 16
As a result, the pressure is pressed against the insulating sheet 11 over the substantially inverted trapezoidal side surface and lower surface of the wiring layer 16, and the wiring insulating sheet is compared with a case where the cross section of the wiring layer 16 is rectangular. 11 can be greatly improved.

However, when the minimum wiring width is 30 μm or less, the variation in the line width of each wiring layer 16 due to the high-density circuit pattern is large in the state as shown in FIG. Is more likely to occur.

According to the present invention, in order to maintain the insulation between the adjacent wiring layers 16, the bottom angle of the wiring layer 16 in the substantially inverted trapezoidal cross section is from 0 to 40 ° to 45 to 85 °,
In particular, by processing so that it becomes 45-80 degrees,
Variation in the line width of the wiring layer 16 and occurrence of a short circuit between adjacent wiring layers can be prevented.

That is, if the base angle α at this time is smaller than 45 °, variations in line width and the reliability of insulation between adjacent wiring layers decrease, and if it is larger than 85 °, it is necessary to increase the removal amount. For this reason, the thickness of the wiring layer becomes extremely thin.

Since the bottom angle is formed by a curved side surface in the cross section of the wiring layer 16, it is possible to gradually increase the bottom angle by removing at least the bottom angle in parallel from the surface of the wiring layer 16. The base angle can be adjusted to an arbitrary value by adjusting the depth of the removal.

This removal can be performed by a) planar polishing, b) sand blast, c) etching or the like. In the methods a) and b), the bottom angle of the wiring layer 16 can be increased by simultaneously removing the surface of the wiring layer 16 and the surface of the insulating sheet 11 as shown in FIG. In the case of a chemical method such as c) etching, by adjusting the etching conditions, only the wiring layer 16 can be selectively removed by etching as shown in FIG. Can also increase the base angle.

In particular, in the method c), since the thickness of the insulating sheet does not change, it does not affect the design of the size of the wiring board. In addition, when the insulating sheet is made of a composite of glass cloth and resin, such as a prepreg, it is preferable because characteristics such as strength of the insulating sheet are not affected.

The single-layer wiring board thus manufactured was thereafter subjected to a heat treatment under the condition that the thermosetting resin in the insulating sheet 11 was completely cured, so that a wiring layer was formed on both surfaces or one surface. A wiring substrate can be manufactured.

Further, this wiring board is used as a core board,
An insulating layer made of a photosensitive resin by a well-known build-up method and wirings and via-hole conductors formed by a thin film forming method such as plating can be sequentially laminated on the surface to produce a high-density wiring board.

Further, a plurality of wiring boards manufactured in the same manner as in FIGS. 3 and 4 are aligned, laminated and pressed, and then heat-cured collectively to manufacture a multilayer wiring board.

[0043]

[Example] BT resin, PPE (polyphenylene ether) or polyimide thermosetting resin has an average particle size of 5 μm
Of SiO ₂ , BaTiO ₃ , and MgTiO ₃ of 50% by volume, and butyl acetate, toluene, ME
K (methyl ethyl ketone) and the like are added, and a catalyst for accelerating the curing of the organic resin is further added. The mixture is mixed for 1 hour by a stirrer in which a stirring blade revolves and rotates, and then the slurry is subjected to a doctor blade method to form a 200 μm-thick insulating sheet. (Samples 1 to 20 in Table 1).

As another insulating sheet, a glass cloth, a glass nonwoven cloth, and an aramid nonwoven cloth were impregnated with BT resin and polyimide at 50% by volume and dried to prepare a semi-cured prepreg for forming a 200 μm-thick insulating sheet (Table 1). 1
Samples 21 to 24).

These insulating sheets were cut into 150 mm square, and via holes having a diameter of 100 μm were formed using a CO ₂ laser. A copper paste containing copper-silver alloy powder as a main component was embedded in the via hole by screen printing.

On the other hand, polyethylene terephthalate (PE)
Applying an adhesive to the transfer sheet surface of T)
Was adhered. Then, a photosensitive resist is applied to the surface of the copper foil using the insulating slurry as a resist, and after exposing through a glass mask to form a pattern, this is immersed in a ferric chloride solution to remove a non-pattern portion. Etching was performed at an etching rate of 3 μm / min. After the resist was peeled off, the upper surface and side surfaces of the wiring layer were treated with 10% formic acid to roughen the surface roughness Ra to 0.4 μm or less. In addition, in the manufactured wiring layer, the wiring has a bottom width of 30 μm,
Minimum wiring interval (wiring pitch) between wirings is 20 μm
Is a fine circuit pattern.

Then, the transfer sheet on which the wiring layer is formed and the insulating sheet are aligned, and 30 kg /
After applying a pressure of 30 cm ² for 30 seconds, only the transfer sheet and the adhesive layer were peeled off, and the wiring layer was transferred to the surface of the insulating sheet.
Most of the transferred wiring layer was buried in the surface of the insulating sheet, and the surface of the wiring layer and the surface of the insulating layer were almost flush. At this time, five electron micrographs were taken of the wiring layer on the wiring board, the base angles of the inverted trapezoidal shapes were measured, and the average value was taken as the base angle before removal.
It was shown to. Further, the surface of the insulating sheet and the wiring layer is polished by buffing the wiring layer and the insulating sheet with a buffing machine, or only the wiring layer is selectively polished by half-etching at a rate of 2 μm / min. The polishing amount was changed.

Thereafter, heat treatment was carried out at 200 to 240 ° C. for 1 hour to completely cure, thereby producing a wiring board. The base angle of the wiring layer of each wiring board was determined based on a scanning electron micrograph in the same manner as described above, and is shown in Table 1 as the base angle β after removal.

The obtained wiring board has a length of 0.5 m.
m maximum wiring width Wmax and minimum wiring width W
min is measured, and the difference between the wiring widths (Wmax−Wmi) is measured.
n) is shown in Table 1.

[0050]

[Table 1]

As is clear from Table 1, the difference in wiring width between wiring layers can be reduced to 3 μm or less by polishing and removing the surface and setting the base angle α ° (= β °) to 45 ° to 85 °. Thus, a highly reliable wiring board was obtained.

Further, five insulating sheets to which the wiring layers were transferred before the above-mentioned curing were laminated, and heated at 200 ° C. for one hour to produce a multilayer wiring board. The surface smoothness of this multilayer wiring board was measured with a three-dimensional measuring device. As a result, the waviness of the board surface was of a level that allowed flip-chip mounting of 10 μm or less.

[0053]

As described above, according to the present invention, even if the wiring pattern is a high-density pattern having a minimum wiring interval of 20 μm or less, the wiring layer can be formed without impairing the embedding property of the wiring layer in the insulating sheet. It is possible to obtain a wiring board having a highly reliable circuit pattern with a small variation in wiring width and no occurrence of short circuit between adjacent wiring layers.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a wiring board of the present invention.

FIG. 2 is an enlarged sectional view of a main part of a wiring layer forming portion in FIG.

FIG. 3 is a process chart for explaining a method for manufacturing a wiring board of the present invention.

FIG. 4 is a view for explaining a method of manufacturing a transfer sheet having a wiring layer according to the present invention.

FIG. 5A is a schematic cross-sectional view for explaining the structure of a wiring layer on a transfer sheet in a conventional method, and FIG. 5B is a plan view showing the shape of the wiring layer when the structure is transferred to an insulating sheet. .

[Explanation of symbols]

 1a to 1c Insulating layer 1 Insulating substrate 2 Wiring layer 3 Via hole conductor 11 Insulating sheet 12 Via hole conductor 13 Transfer sheet 14 Metal foil 15 Resist layer 16 Wiring layer

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) H05K 3/46 H01L 23/12 NF term (reference) 5E338 AA03 AA16 CC01 CD05 EE23 5E343 AA02 AA12 AA18 BB02 BB24 BB67 CC62 DD56 EE43 EE52 ER12 ER18 ER51 ER52 FF08 GG08 5E346 AA15 AA32 AA43 BB20 CC02 CC08 CC32 CC34 CC38 CC39 CC55 DD02 DD11 EE04 FF01 FF18 GG02 GG14 GG15 GG22 GG23 GG27 GG28 HH26

Claims (4)

[Claims] 1. A wiring board in which a wiring layer made of a metal foil is buried and formed on a surface of an insulating substrate, wherein a minimum wiring interval in a pattern of the wiring layer is 30 μm or less, and the wiring layer is substantially A wiring substrate having an inverted trapezoidal shape, wherein the base angle of the substantially inverted trapezoidal shape is 45 ° to 85 °. A) a metal layer formed on one surface of the transfer sheet is subjected to an etching treatment to form a wiring layer having a substantially trapezoidal cross section having a base angle of 0 ° to 40 ° and a minimum wiring interval of 30 μm or less. B) pressing the transfer sheet against the surface of the soft insulating sheet, peeling the transfer sheet, and burying the wiring layer on the surface of the insulating sheet; c) forming the insulating sheet The bottom angle of the wiring layer formed on the surface is 4
Removing the surface of the insulating sheet and the wiring layer until the angle reaches 5 ° to 85 °. 3. A wiring layer having a substantially trapezoidal cross section having a bottom angle of 0 ° to 40 ° and a minimum wiring interval of 30 μm or less by etching a metal foil formed on one surface of a transfer sheet. B) pressing the transfer sheet against the surface of the soft insulating sheet, peeling the transfer sheet, and burying the wiring layer on the surface of the insulating sheet; c) forming the insulating sheet The bottom angle of the wiring layer formed on the surface is 4
Removing only the surface of the wiring layer until the angle reaches 5 ° to 85 °. 4. The method according to claim 2, further comprising the step of: d) laminating a plurality of insulating sheets having the wiring layers produced through the steps a) to c). The method for manufacturing the wiring board according to the above.