JP2001068802A - Insulation sheet for wiring board and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a wiring board which can transfer excellently a fine wiring circuit layer composed of a metal foil on an insulation sheet, reduces thermal expansion difference from a semiconductor element, and is excellent in resistance to moisture. SOLUTION: In an insulation sheet in an uncured state or a semi-cured state (B stage), 30-70 vol.% of spherical silica whose average particle diameter is at most 10 μm is contained to thermosetting resin whose melt viscosity at 60-150 deg.C is 103-107 poise. The insulation sheet for a wiring board wherein the coefficient of thermal expansion (20 deg.C) is at most 250 ppm/ deg.C and the void content is 5-20% after perfect thermosetting is used. By transferring a wiring circuit layer constituted of a metal foil previously formed on a transfer sheet surface on the surface of the insulation sheet, a wiring board is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulating sheet for a wiring board for manufacturing a wiring board, and a method of manufacturing a wiring board using the same, which is suitable for a package for housing semiconductor elements or a multilayer wiring board. is there.

[0002]

2. Description of the Related Art In recent years, electronic devices have been reduced in size.
In recent years, with the development of portable information terminals and the spread of so-called mobile computing in which a computer is carried and operated, there is a tendency that a smaller, thinner, and higher-definition multilayer wiring board is required.

[0003] Further, electronic devices that require high-speed operation, such as communication devices, have been widely used. The requirement for high-speed operation includes various requirements such as accurate switching of high-frequency signals. In order to cope with such electronic devices, a multilayer printed wiring board suitable for high-speed operation is required.

In order to perform high-speed operation, it is necessary to reduce the length of wiring and shorten the time required for transmitting an electric signal. In order to reduce the length of the wiring, there is a tendency for a small, thin, and high-definition multilayer wiring substrate in which the width of the wiring is reduced and the gap between the wirings is reduced.

In order to respond to such a demand for high-density wiring, a process similar to the manufacturing process of the ceramic multilayer wiring board,
That is, a multilayer printed wiring board in which a plurality of insulating sheets on which via-hole conductors and wiring circuit layers are formed is proposed in Japanese Patent Application Laid-Open No. Hei 10-27959.

In this method, specifically, after a via hole is formed in an insulating sheet, a metal powder is filled in the insulating sheet to form a via hole conductor, and then a transfer sheet having a wiring circuit layer made of a metal foil formed on a surface thereof is used. The wiring circuit layer is transferred to form a wiring circuit layer to form a single-layer wiring sheet, and a plurality of wiring sheets created in the same manner are laminated and integrated to form a multilayer.

Recently, there has been a demand for a printed circuit board on which a semiconductor element is mounted on the surface, a wiring board in which the semiconductor element is embedded inside the printed circuit board, and the like.

[0008]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Laid-Open No. 10-2 is disclosed.
In the transfer method proposed by JP-A-7959, the insulating sheet can be manufactured by a dry process that is not immersed in a chemical such as an etching solution or a plating solution. Since the layers are buried in the surface of the insulating sheet, the flatness is excellent, and there is an advantage that good mounting is possible when flip-chip mounting the semiconductor element.

However, for the insulating sheet to be used, a) when the wiring circuit layer made of dense metal foil on the surface of the transfer sheet is transferred to the insulating sheet, the wiring may be cut even in a fine circuit. Good transfer without
b) The thermal expansion coefficient of the insulating sheet finally cured is as close as possible to the thermal expansion of the semiconductor element, and c) The wiring board on which the semiconductor element and the like are mounted has excellent moisture resistance. Is required.

However, in the conventional insulating sheet, in order to enhance the transferability, it is desirable to increase the amount of resin in the insulating sheet to increase the adhesiveness. However, there has been a problem that a difference in thermal expansion between the insulating sheet and the insulating sheet becomes large. At present, sufficient investigation has not been made on an insulating sheet that can satisfy all of the above characteristics.

Accordingly, the present invention is to solve the above-mentioned conventional problems, and it is possible to satisfactorily transfer a fine wiring circuit layer made of a metal foil to the surface of an insulating sheet and to reduce a difference in thermal expansion from a semiconductor element. Provided is an insulating sheet capable of manufacturing a wiring board having excellent moisture resistance, and a method of manufacturing a wiring board for manufacturing a highly reliable wiring board with a high yield using such an insulating sheet. With the goal.

[0012]

Means for Solving the Problems As a result of repeated studies on the above objects, the present inventors have found that a thermosetting resin having a melt viscosity at 60 to 150 ° C. of 10 ³ to 10 ⁷ poise has an average Spherical silica having a particle size of 10 μm or less
An insulating sheet in an uncured or semi-cured state (B stage) containing a volume percentage of 25% and having a coefficient of thermal expansion (20 ° C.) of 25 ppm / ° C. or less after complete thermal curing.
It has been found that the above object can be achieved by a wiring board insulating sheet having an open porosity of 5 to 20%.

A method of manufacturing a wiring board includes forming a via hole in a predetermined portion of the insulating sheet, filling the via hole with a conductive composition containing metal powder to form a via hole conductor. And a transfer step of transferring a wiring circuit layer made of a metal foil previously formed on the transfer sheet surface to the insulating sheet surface on which the via-hole conductor is formed, and an insulating sheet on which the via-hole conductor and the wiring circuit layer are formed. And a thermosetting step of heating to cure the thermosetting resin.

In order to manufacture a multi-layered wiring board, a via hole is formed at a predetermined position on the insulating sheet.
A via-hole conductor forming step of forming a via-hole conductor by filling the conductive composition containing a metal powder in the via-hole, and forming the via-hole conductor by forming a wiring circuit layer made of a metal foil formed in advance on a transfer sheet surface. A transfer step of transferring to the surface of the insulating sheet, a laminating step of laminating and pressing a plurality of insulating sheets produced through the via hole conductor forming step and the transferring step, and heating the laminate to cure the thermosetting resin. And a step of causing

[0015]

According to the insulating sheet for a wiring board of the present invention, it is particularly preferably used for forming a wiring circuit layer made of a metal foil by a transfer method, wherein the insulating sheet is made of a thermosetting resin and an inorganic filler. And a thermosetting resin having a predetermined melt viscosity as a thermosetting resin, and having an average particle size of 1 as an inorganic filler.
By using a spherical silica of 0 μm or less, when the metal foil is transferred, the fluidity of the thermosetting resin and the spherical silica increases, so that when the metal foil is pressed against the surface of the insulating sheet, the metal foil is insulated. The wiring circuit layer made of metal foil from the transfer sheet to the insulating sheet as a result of increasing the adhesiveness of the thermosetting resin embedded in the sheet and the reduced viscosity of the thermosetting resin and increasing the adhesiveness with the metal foil. Transferability can be improved. Moreover, the amount of the spherical silica is 30
By setting the content to 70% by volume, the balance between the adhesion of the resin to the metal foil and the action of reducing the thermal expansion coefficient of the spherical silica can be maintained.

Furthermore, by reducing the open porosity of the insulating sheet, it is possible to suppress the generation of voids after complete curing, and to prevent a decrease in moisture resistance due to the voids. In particular, it is most desirable to use a thermosetting polyphenylene ether resin from the viewpoint of improving moisture resistance.

Further, according to the method of manufacturing a wiring board of the present invention, after forming a via-hole conductor on the above-mentioned insulating sheet, a wiring circuit layer made of metal foil is transferred onto the surface of the via-hole conductor. When forming the wiring circuit layer, the occurrence of transfer failure of the wiring circuit layer is prevented, and the wiring circuit layer can be easily buried on the surface of the insulating sheet without deformation of the via hole conductor. Since the electrical connection with the via-hole conductor is excellent, it is possible to produce a wiring board and a multilayer wiring board which are excellent in flattening of the wiring board and highly reliable in both single layer and multilayer.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION (Insulating Sheet) The insulating sheet for a wiring board of the present invention comprises a thermosetting resin and an inorganic filler as constituents, and the thermosetting resin and the inorganic filler in the insulating sheet are , Thermosetting resin 70-30
%, And an inorganic filler composed of silica (SiO ₂ ) is contained at a ratio of 30 to 70% by volume.

The reason why the proportion of the thermosetting resin and the inorganic filler is limited to the above range is that when the content of the thermosetting resin is less than 30% by volume and the content of the inorganic filler is more than 70% by volume, the thermal expansion of the insulating sheet is reduced. Although the coefficient is small, the transferability of the metal foil is extremely reduced due to the small amount of resin,
When the thermosetting resin is more than 70% by volume and the inorganic filler is less than 30% by volume, the thermal expansion coefficient after curing of the insulating sheet becomes larger than 25 ppm / ° C.,
This is because mounting defects are likely to occur when mounting or incorporating the semiconductor element. Preferably, the thermosetting resin is 40 to 60% by volume and the inorganic filler is 60 to 40% by volume.

The thermosetting resin used is 60
Melt viscosity at ~ 150 ° C is 10 ³ to 10 ⁷ poise,
In particular, it is important that the pressure is 10 ⁴ to 10 ⁶ poise. This has a large influence on the resin content of the flowability and adhesion during metal foil transfer, when the melt viscosity is greater than 10 ⁷ poise, the resin does not flow, can not transfer the copper foil, 10
^If it is smaller than ³ poises, the resin will flow too much and the metal foil will be displaced.

As the thermosetting resin, for example, PP
E (polyphenylene ether), BT resin (bismaleimide triazine), epoxy resin, polyimide resin,
Fluororesins, phenolic resins, and the like, and further contain a curing agent for those resins. Of these, thermosetting polyphenylene ethers have characteristics of low dielectric constant, low dielectric loss, low water absorption, and high Tg. It is the most desirable material because it is suitable for high frequency.

It is important to use spherical silica having an average particle size of 10 μm or less as an inorganic filler in the insulating sheet. This is excellent in that silica has a lower specific gravity and a smaller coefficient of thermal expansion than Al ₂ O ₃ or the like. It is important that the particles have a spherical shape. This is because, compared to the crushed powder, the spherical particles are more excellent in the fluidity of the particles, so the silica particles become finely packed by rearrangement due to the fluidity of the inorganic filler at the time of transferring the metal foil, The resin oozes out between the resin and the metal foil, whereby the adhesion of the metal foil to the insulating sheet can be enhanced.

On the other hand, if the average particle size is larger than 10 μm, when forming a via hole, the particles are shed or the via shape is distorted, and the flatness is reduced. Especially 7μ
m or less.

Further, when the insulating sheet is formed of a composite material of a thermosetting resin and an inorganic filler, the mechanical strength as well as the thermal stability of the insulating sheet can be increased.
Further, since the interface between the glass and the resin, in which migration easily progresses, is isolated as compared with a normal glass-epoxy substrate or the like, the insulation reliability is excellent.

According to the present invention, it is important that the open porosity of the insulating sheet is 5 to 20%, particularly 7 to 15%.
When the open porosity is limited to the above range, when the open porosity is lower than 5%, when the metal foil or the wiring circuit layer made of the metal foil is adhered or transferred to the surface of the insulating sheet, the metal foil and the insulating sheet are not bonded. Even if air is trapped in between, the trapped air cannot be released out of the system through the open pores, and remains as a void between the metal foil and the insulating sheet. As the nature decreases,
This is because transfer failure, adhesion failure, and the like are likely to occur.

On the other hand, when the open porosity exceeds 20%, a large number of voids are present on the surface of the insulating sheet after heat curing, and as a result, moisture in the atmosphere is easily trapped by the presence of the voids. This degrades the moisture resistance of the cured substrate. Further, the green strength of the insulating sheet is reduced. The average open pore diameter of the insulating sheet was 10 μm.
m or less, especially 8 μm or less, is desirable in order to increase the processing accuracy when forming the via-hole conductor and to prevent deformation of the wiring circuit layer.

The insulating sheet of the present invention is prepared by slurrying a mixture obtained by mixing a predetermined thermosetting resin and spherical silica at a predetermined ratio with toluene or the like as a solvent, and then using this slurry to form a doctor blade method or a calendar. It can be manufactured by molding into a sheet by a roll method or the like.

The insulating sheet of the present invention is preferably in an uncured state or a semi-cured state (B stage). When cured, the adhesive strength of the insulating sheet decreases, and not only the adhesion to the metal foil, but also the adhesiveness between the insulating sheets decreases, and delamination occurs during multilayering. Further, this insulating sheet has a bonding strength of 60 to 150 ° C., a pressure of 2 kgf / cm ² , a surface having a surface roughness Ra of 0.5 to 1 μm pressed against the insulating sheet, and a copper foil having an adhesive strength of 0 to 1.0 mm. . 1kgf
/ Cm or more, particularly preferably 0.3 kgf / cm or more. Since the adhesive strength between the transfer sheet and the copper foil is usually about 0.1 kgf / cm, only the transfer sheet can be peeled off when the transfer sheet is peeled off after heating and pressing the metal foil of the transfer sheet on the insulating sheet. Transferability is obtained.

(Method of Manufacturing Multilayer Wiring Board) Next, a method of manufacturing a wiring board, particularly a multilayer wiring board using the above-mentioned insulating sheet will be described with reference to FIG. First, a desired via hole 2 is formed on the insulating sheet 1 by punching, laser or the like in an uncured state (B stage state) (a), and the via hole 2 is filled with a conductive paste to form a via hole conductor 3. (B).

The conductor paste is made of copper, aluminum, gold,
It is composed of a metal powder mainly composed of at least one or two or more alloys selected from the group consisting of silver, a solvent, a thermosetting resin and a curing agent. The solvent is α-terpineol, 2-
Octanol or a thermosetting resin liquid at room temperature is used. As the thermosetting resin and the curing agent, a resin having the same composition that does not hinder the curing of the insulating sheet or a resin that cures at the same temperature is selected. This is used to maintain the shape retention of the conductive compositions after curing.

Next, a metal foil is adhered to the surface of the transfer sheet 4 and then a wiring circuit layer 5 is formed by a process such as etching (FIG. 3C). As the transfer sheet 4, a sheet having mechanical properties and dimensional stability that can withstand processes such as etching when forming the wiring circuit layer 5 is used, and a polyethylene-based sheet is preferably used. Further, as an adhesive for bonding the metal foil, an acrylate ester which is resistant to acid and alkali is preferably used.

Thereafter, the transfer sheet 4 on which the wiring circuit layer 5 is formed is positioned and laminated on the insulating sheet 1 on which the via hole conductor 3 is formed, and the B-staged insulating sheet is heated to 70 to 200 ° C. While applying a pressure that allows the wiring circuit layer 5 to be embedded in the surface of the insulating sheet 1, the transfer sheet 4 is then peeled off, so that the wiring circuit layer 5 is transferred to the surface of the insulating sheet 4 to form a single-layer wiring sheet. a
(D). The pressure for embedding the wiring circuit layer 5 is 10 kg / cm ² or more, especially 20 to 70 kg.
/ Cm ² is desirable.

In the transfer step, the wiring circuit layer 5 formed on the insulating sheet 1 having the predetermined open pores is formed on the surface of the insulating sheet 1 due to the shrinkage or compressibility of the insulating sheet 1 in the thickness direction. Flattening can be performed so that the surface of the wiring circuit layer 5 is flush with the surface. The via-hole conductor 3 is compressed in the thickness direction by burying the wiring circuit layer 5, so that the filling property is improved and the resistance can be reduced.

Thereafter, the insulating sheets b and c having the wiring circuit layer transferred to only one side and both sides by the same process as described above.
Are prepared, and they are aligned and laminated, and then heated to a temperature at which the thermosetting resin in the insulating sheet 1 is completely cured, whereby a multilayer wiring board can be produced (e).

According to the present invention, a wiring circuit layer and a through-hole conductor are generally formed on the front and back surfaces of an insulating plate made of a composite material of a fibrous body such as glass and a thermosetting resin, which is called a prepreg. Producing a core substrate, laminating a plurality of wiring sheets having via hole conductors and wiring circuit layers formed on the front and back surfaces of the core substrate, and then thermosetting as described above to produce a multilayer wiring substrate. Can be.

[0036]

EXAMPLES As the insulating sheet, various thermosetting polyphenylene ethers (PPE) having a melt viscosity of 10 ² to 10 ⁸ poise at 60 to 150 ° C. were used.
Using spherical fused silica powder or crushed silica powder as shown in Table 1, weighed in the ratio of Table 1, toluene was added as a solvent to form a slurry by a stirrer, and this was formed into a sheet having a thickness of 120 μm by a doctor blade method. It was molded and dried at 60 ° C. for 1 hour to produce a semi-cured insulating sheet.

The open porosity of the produced insulating sheet was measured by the Archimedes method. In addition, the seat
After heating at 0 ° C. for 1 hour to completely cure the PPE,
The coefficient of thermal expansion at 0 ° C. was measured.

Next, a through-hole having a diameter of 0.1 mm was formed at a predetermined position by punching using each of the insulating sheets shown in Table 1.
A via-hole conductor was formed by filling a metal paste obtained by mixing 100 parts by weight of copper powder coated with silver on the surface of μm, 0.2 parts by weight of cellulose, and 10 parts by weight of 2-octanol,
It was dried by heating at 50 ° C. for 60 minutes.

Thereafter, a copper foil having a thickness of 12 μm was bonded
Fine wiring circuit layers for the front and back sides having a line width of 100 μm or less were formed on the copper foil of the transfer sheets by a photoresist method. Then, the transfer sheet is positioned and superimposed on the front side and the back side of the insulating substrate on which the via-hole conductor is formed, and a pressure of 5 kg / cm ² is applied to at least the position where the through-hole conductor is formed, and both ends of the through-hole conductor are applied. The wiring circuit layer was buried in the insulating layer from the side to prepare a core wiring sheet. At this time, the minimum diameter of the wiring circuit layer provided at the end of the through-hole conductor was 0.2 mm.

Similarly, four wiring sheets having a wiring circuit layer formed on only one surface of the insulating sheet having via-hole conductors formed thereon were prepared, and two wiring sheets were positioned on the upper and lower surfaces of the core wiring sheet. After stacking together, temperature 2
The composition was cured at 00 ° C. and a pressure of 20 kg / cm ² to prepare a multilayer wiring board having six wiring circuit layers.

The transferability of the wiring circuit layer made of a metal foil was evaluated, and when the wiring circuit layer made of a copper foil was satisfactorily transferred without disconnection of the wiring at the time of transfer, it was evaluated as ○. Noted.

The flatness of the obtained multilayer wiring board was measured, and the moisture resistance was evaluated. Evaluation,
The flatness is 30 mm for the wiring circuit layer on the front and back surfaces of the substrate
The flatness in □ was measured and the average was calculated. The moisture resistance was measured by measuring the water absorption rate, and the results are shown in Table 1 below.

Further, the produced multilayer wiring board was heated at 121 ° C.
A pressure cooker test (PCT) under a humidity of 100% and a pressure of 2 atm was performed.
Table 1 shows the percentage of non-defective products among the 0 samples.

[0044]

[Table 1]

As is clear from the results shown in Table 1, in the sample No. 20 in which the open porosity of the insulating sheet is smaller than 5%, irregularities due to voids are observed between the metal foil and the insulating sheet, and the flatness is low. Was something. In addition, the yield after the PCT test was low and the reliability was low. Samples Nos. 1, 2, and 3 having an open porosity of more than 20% had poor moisture resistance and a low yield after the PCT test.

Further, in Sample No. 11 in which the melt viscosity of the resin was greater than 10 ⁷ poise, the viscosity was too high and transfer failure of the copper foil occurred. In Sample No. 15 having a melt viscosity of less than 10 ³ poise, transfer failure occurred due to deformation during transfer. In Samples Nos. 17 and 18 in which the amount of spherical silica was less than 30% by volume, the fluidity of the resin was large, the metal foil was displaced during transfer, and the coefficient of thermal expansion was 25 pp.
m / ° C. or more and more than 70% by volume
In No. 8, transfer failure of the copper foil occurred due to a small amount of resin.

In Samples Nos. 1, 2, and 3 in which the average particle size of the spherical silica was larger than 10 μm, the flatness, the moisture resistance, and the via shape were poor, and the yield rate after the PCT test was low.

Further, it was found that the transferability of Sample No. 21 using crushed silica was lower than that of Sample No. 9 containing the same amount of spherical silica.

In contrast to these comparative examples, all of the samples of the present invention had a flatness of 10 μm or less, an adhesive strength of copper foil of 0.4 kgf / cm or more, good transferability, and a coefficient of thermal expansion. Also showed good characteristics of 25 ppm / ° C. or less, and was also excellent in moisture resistance.

[0050]

As described above in detail, according to the present invention, a fine wiring circuit layer made of a metal foil can be satisfactorily transferred to the surface of an insulating sheet, the difference in thermal expansion from a semiconductor element can be reduced, and A wiring board with excellent moisture resistance can be manufactured.

[Brief description of the drawings]

FIG. 1 is a process diagram illustrating an example of a method for manufacturing a multilayer wiring board according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulation sheet 2 Via hole 3 Via hole conductor 4 Transfer sheet 5 Wiring circuit layer

Claims (5)

[Claims] 1. A melt viscosity at 60 to 150 ° C. of 10 ³
Relative ^{to 107} poise thermosetting resin, an average particle size of 1
Uncured or semi-cured state containing spherical silica of 0 μm or less at a ratio of 30 to 70% by volume (B stage)
An insulating sheet having a thermal expansion coefficient (20 ° C.) of 25 ppm / ° C. or less after complete thermal curing and an open porosity of 5-2.
An insulating sheet for a wiring board, which is 0%. 2. The insulating sheet for a wiring board according to claim 1, wherein said thermosetting resin mainly comprises thermosetting polyphenylene ether. 3. A melt viscosity at 60 to 150 ° C. of 10 ³
Relative ^{to 107} poise thermosetting resin, an average particle size of 1
Uncured or semi-cured state containing spherical silica of 0 μm or less at a ratio of 30 to 70% by volume (B stage)
An insulating sheet having a thermal expansion coefficient (20 ° C.) of 25 ppm / ° C. or less after complete thermal curing and an open porosity of 5-2.
A via hole conductor forming step of forming a via hole at a predetermined position of a wiring board insulating sheet at 0%, filling the via hole with a conductive composition containing a metal powder to form a via hole conductor, and forming a via hole conductor on the transfer sheet surface. A transfer step of transferring a wiring circuit layer made of a metal foil formed in advance onto the surface of the insulating sheet on which the via-hole conductor is formed; and heating the insulating sheet on which the via-hole conductor and the wiring circuit layer are formed to form the thermosetting resin. A method for manufacturing a wiring board, comprising: a thermosetting step of curing a resin. 4. A melt viscosity at 60 to 150 ° C. of 10 ³
Relative ^{to 107} poise thermosetting resin, an average particle size of 1
Uncured or semi-cured state containing spherical silica of 0 μm or less at a ratio of 30 to 70% by volume (B stage)
Forming a via hole in a predetermined portion of the insulating sheet, filling the conductive composition containing a metal powder in the via hole to form a via hole conductor forming a via hole conductor,
A transfer step of transferring a wiring circuit layer made of a metal foil previously formed on the transfer sheet surface to the surface of the insulating sheet on which the via-hole conductor is formed; and a plurality of insulating sheets produced through the via-hole conductor forming step and the transfer step. And a step of heating the laminate to cure the thermosetting resin. 5. The method for manufacturing a wiring board according to claim 3, wherein said thermosetting resin mainly comprises thermosetting polyphenylene ether.