JP3522165B2 - Wiring board and manufacturing method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wiring board suitable for, for example, a multilayer wiring board and a package for accommodating semiconductor elements, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Recently, electronic devices have been downsized,
In recent years, due to 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 for a smaller, thinner, and higher-definition multilayer wiring board. As represented by communication equipment,
In electronic devices that are required to operate at high speed, it is necessary to shorten the length of wiring and shorten the time required for electric signal propagation. In order to reduce the length of the wiring, there is a tendency that the width of the wiring is narrowed, and a small-sized, thin and high-definition multilayer wiring board is required.

Further, as the amount of information processed by a semiconductor element increases, the number of terminals for inputting / outputting information (signal) increases dramatically. Therefore, the number of pads (I / O pads) formed on the silicon chip is increasing, and it is necessary to form a large number of pads on the lower surface of the silicon chip. This increases the density of I / O pads on the silicon chip,
After the distance between the pads became less than 200 μm,
It is predicted that the necessary wiring will not be drawn.

In order to meet such demands for high-density wiring, a manufacturing method called a build-up method is used in manufacturing a multilayer printed wiring board. This build-up method is classified into two types of (1) base + build-up method and (2) full-layer build-up method in the JPCA standard.

(1) In the base + build-up manufacturing method, an insulating layer is laminated on the surface of a base substrate, a via process is performed by a photoresist method or the like, and a wiring circuit layer and a via hole conductor are formed by a plating method. This is a method of forming a multilayer by repeating this and is suitable for forming fine wiring.

(2) A method for manufacturing a full-layer build-up is, for example, as disclosed in Japanese Patent No. 2587593, a via hole is formed in a predetermined insulating sheet with a laser or the like, and the via hole is filled with a conductive paste containing metal powder. By doing so, via-hole conductors are formed, the wiring circuit layers are electrically connected, and the wiring layers thus produced are repeatedly formed to form a multilayer structure.

[0007]

However, in recent years, the problem has become clear with the spread of the build-up method.
The first problem is that the material properties of the resin forming the insulating layer are inferior. (1) In the base + build-up method, a photosensitive epoxy resin or the like is often used as an insulating layer, but the epoxy resin originally has a low glass transition point and is made photosensitive, so that the water absorption rate increases and the high temperature and high humidity There is a problem that reliability is deteriorated such that the insulation property is deteriorated when left as it is.

The second problem is that the formation of via-hole conductors is generally carried out by forming a through hole in a microdrill and plating it with copper, but the hole diameter in such a microdrill is at most 0. If it is about 2 mm, a through hole smaller than that cannot be formed, and the installation density of via-hole conductors cannot be increased.

A third problem is that high stress and heat are generated on the substrate during microdrilling. Therefore, when a through hole is formed in an insulating substrate containing a woven or non-woven fabric made of glass fiber, the through hole after the processing is processed. On the inner wall of the hole, the glass fiber called the work-affected layer and the resin were separated, and a gap was formed. Therefore, when copper is plated in the through holes, the active plating solution enters this gap, and in the reliability test after the substrate is completed, the metal diffuses through this gap and CAF (cond
There is a problem that insulation failure occurs due to a phenomenon called uctive Anodic Filament). As a result, it has been impossible to increase the via hole density by narrowing the distance between the through holes by the conventional method.

Further, in forming the through holes, it has been attempted to process the through holes by laser light instead of the microdrills and plate the inside with copper, or to fill a conductive paste to make an electrical connection. There is.

However, even when laser light is used, a work-affected layer is formed due to heat, and when plating is performed, the plating solution penetrates into the gaps as in the case of the microdrill, and the insulation reliability is reduced. Further, when the conductive paste was filled, the plating solution did not penetrate, but the conductive metal powder penetrated into the gaps along the work-affected layer, and satisfactory insulation reliability was not obtained.

On the other hand, (2) a method of forming a conical column with a conductive paste, which is one of all-layer build-up methods, and penetrating an insulating layer (JP-A-8-78799), narrows the via pitch, When the vias are densely packed, there is a problem that it is difficult to penetrate the conical column and the insulation reliability between the via-hole conductors is deteriorated, so that high density formation is not possible.

When an aramid non-woven fabric-epoxy resin type insulating substrate is used, the insulating substrate is entirely made of resin, so via processing with a laser is easy. However, since the aramid resin itself has high hygroscopicity, epoxy resin is used. However, there is a problem that the moisture absorption progresses and the insulation reliability between the via-hole conductors decreases.

Therefore, the present invention provides a wiring board which enhances insulation reliability between adjacent via-hole conductors and enables high-density formation of via-hole conductors, and a manufacturing method for easily manufacturing the wiring board. To do.

[0015]

According to the present invention, a through hole is formed in an insulating substrate formed by impregnating a thermosetting resin in a woven or non-woven fabric made of glass fiber, and the through hole is formed in the through hole. A wiring board comprising a via-hole conductor filled with a conductive paste containing metal powder, wherein a lump larger than the average diameter of the glass fiber is formed at the end of the glass fiber exposed on the wall surface of the via-hole conductor. The interface portion between the glass fiber and the thermosetting resin on the via hole conductor wall surface is sealed by the lump portion, thereby sealing the gap generated at the interface portion between the glass fiber and the resin. Therefore, it is possible to prevent the paste from diffusing into the gap, and as a result, it is possible to improve the insulation reliability between the via-hole conductors.

In particular, it is desirable that the lumps at the ends of the glass fibers are fused to each other, and the minimum diameter of the lumps is 1.2 times or more the average diameter of the glass fibers. However, it is desirable to effectively seal the interface portion.

Further, according to the method for manufacturing a wiring board of the present invention, (a) a prepreg made by impregnating a woven cloth or a non-woven cloth made of glass fibers with a thermosetting resin is provided with a through hole using a laser beam. Forming and melting the tip of the glass fiber exposed on the inner wall surface of the through hole to form a lump larger than the average diameter of the glass fiber, and (b) a metal powder in the through hole. A step of forming a via-hole conductor by filling a conductive paste containing
(C) By applying pressure while heating the prepreg having the via-hole conductor formed therein, the thermosetting resin in the prepreg is caused to flow, and the glass fiber and the thermosetting resin on the wall surface of the via-hole conductor are separated. It is characterized by comprising a step of sealing an interface portion with a lump of the glass fiber end portion, and a step of curing the thermosetting resin in the prepreg after the steps (d) and (c). Is.

The diameter of the lump is preferably 1.2 times or more the average diameter of the glass fiber. Further, the laser beam is irradiated with an energy of 2 to 20 mj per shot to form a through hole, so that the lump portion can be effectively formed. In addition, the heating and pressurizing treatment is 80 to
It is desirable to carry out under conditions of 150 ° C. and 10 to 50 kg / cm ² .

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION A wiring board 1 of the present invention has, as a basic structure, an insulating board in which a woven cloth or a nonwoven cloth 2 made of glass fibers is impregnated with a thermosetting resin 3 as shown in FIG. 4 has a through hole 5 formed therein, and has a via hole conductor 6 filled with a conductive paste containing a metal powder inside the through hole 5. The via-hole conductor 6 electrically connects the wiring circuit layers 7 formed on the front surface and the back surface of the insulating substrate 4 to each other.

According to such a wiring board structure, as shown in the enlarged cross-sectional view of the via hole conductor 6 forming portion in FIG. 2, the glass fiber 8 in the insulating substrate 4 is inevitably exposed to the inside of the via hole conductor 6. However, according to the present invention, the end portion of the glass fiber 8 exposed on the wall surface of the via-hole conductor 6 is formed by the lump portion 9 larger than the diameter (average) of the glass fiber, and the wall surface of the via-hole conductor 6 is formed. It is important that the interface portion 11 between the glass fiber 8 and the thermosetting resin 10 is sealed by the lump 9.

The poor insulation between the via-hole conductors 6 is caused by the intrusion or diffusion of the paste component of the via-hole conductors 6 at the contact interface between the glass fiber 8 and the resin 10 as described above. By sealing the interface portion 11 between the glass fiber 8 and the thermosetting resin 10 on the wall surface of the conductor 6 with the lump portion 9, it is possible to prevent the paste from entering from the interface portion 11 as a starting point.

Further, as shown in FIG. 2, the mass portion 9 has
The interface portion is that the lumps 9 at the ends of several glass fibers are fused together to form a lump having a large diameter, rather than independently existing at the end of one glass fiber. It is desirable to improve the sealing property of 11. In particular, the effect is recognized when the minimum diameter of the lump portion 9 is 1.2 times the diameter of the glass fiber, and a more sufficient effect is exhibited when the minimum diameter is 1.4 times or more.

Examples of the thermosetting resin that constitutes the insulating substrate 4 in the wiring board of the present invention include thermosetting PPE (polyphenylene ether), BT resin (bismaleimide triazine), epoxy resin, polyimide resin, polyamide bismaleimide and the like. Resin is preferred. Further, an inorganic filler powder such as SiO ₂ or Al ₂ O ₃ may be added to the thermosetting resin to improve the characteristics.

The woven or non-woven fabric made of glass fiber preferably has a fiber diameter of about 5 to 20 μm, and the glass fiber is compounded in the insulating substrate at a ratio of 30 to 60% by volume. Is appropriate.

To form the via-hole conductor having such a structure, as shown in the manufacturing process diagram of FIG. 3, first, an uncured prepreg 13 containing the glass fiber 12 is prepared (a). Then, a through hole 14 is formed in the prepreg 13 with a laser, and the tip end of the glass fiber 12 exposed on the inner wall surface of the through hole 14 is melted to form a lump portion 15 larger than the average diameter of the glass fiber 12. (B).

Further, the prepreg is required to form the through holes in an uncured state, and the resin is softened by the heating and pressurizing treatment described later to seal the interface between the glass fiber and the thermosetting resin. Can be increased.

At this time, the lump portion 15 is preferably 1.2 times, particularly 1.4 times or more of the average diameter of the glass fiber 12, and the lump portion 15 is made up of several glass fibers. It is desirable that the end masses are fused to each other.

The size of the lump 15 can be changed by the energy of the laser and is preferably 2 to 20 mj per shot, particularly 5 to 10 mj. If this is smaller than 2 mj, the formation of the lump is insufficient,
If it exceeds 20 mj, the thermosetting resin may be burnt.

At this time, the lump portion 15 formed by the laser beam projects into the through hole 14, and the through hole 1
A gap 17 still exists at the interface between the glass fiber 12 and the thermosetting resin 16 on the four wall surfaces.

Next, a conductive paste is filled in the formed through holes 14 to form via-hole conductors 18 (c).
This conductive paste is prepared by kneading at least one metal selected from the group consisting of copper, aluminum, gold and silver, or a metal powder mainly containing an alloy of two or more, a solvent, a thermosetting resin and a curing agent. It The solvent used is α-terpineol, 2-octanol, or a thermosetting resin that is liquid at room temperature. 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, the prepreg 13 on which the via-hole conductor 18 manufactured through (c) is formed is subjected to a heat and pressure treatment. This heat and pressure treatment is 10 to 50 kg / c
The temperature at which the thermosetting resin in the prepreg 13 softens but does not cure while applying a pressure of m ² , specifically 80 to
Treated at 150 ° C. By such heat and pressure treatment,
As shown in FIG. 3C, as a result of the thermosetting resin 16 on the wall surface of the via-hole conductor 18 being extruded toward the via-hole conductor 18, the lump portion 15 seals the interface between the glass fiber 12 and the thermosetting resin 16. Ready to go.

The heating and pressurizing process at this time may be performed independently, but may be performed at the same time when the wiring circuit layer is formed on at least one end of the via-hole conductor 18.

In that case, the surface of the prepreg and /
Alternatively, a metal foil 19 such as a copper foil is attached to the entire back surface (d),
After performing the heating and pressing treatment under the above conditions, the wiring circuit layer 20 is formed on the surface copper foil by the photoresist method (e).

As another method, a metal foil is adhered to the surface of the resin film in advance and a circuit pattern is formed by a photoresist method or the like, and then the wiring circuit layer is laminated on the surface of the prepreg under the above conditions. After applying heat and pressure, the wiring circuit layer can be formed by peeling only the resin film.

Finally, by heating to a temperature sufficient to completely cure the thermosetting resin in the prepreg, wiring circuit layers are formed on the front surface and the back surface, and these wiring circuit layers are formed by the via-hole conductors. A connected basic wiring board can be produced.

The above-mentioned thermosetting process can be simplified by continuously performing the heating and pressurizing process.

Further, before forming the via-hole conductor,
If the prepreg after the through holes are formed is heated and pressed under the above conditions, the glass fiber
As a result that the lump portion 15 can seal the interface portion between the thermosetting resin 16 and the thermosetting resin 2, the glass fiber 12 and the thermosetting resin 1
It is possible to prevent the paste component from entering the interface portion with 6.

In order to manufacture a multilayer wiring board, a plurality of prepregs, which have been manufactured through the above steps (a) to (e) and which have not been completely cured, are laminated and pressure-bonded and then completely heat cured to form a multilayer wiring. A substrate can be obtained.

As described above, according to the wiring board of the present invention, a lump portion having a diameter larger than the fiber diameter is formed at the end of the glass fiber exposed on the inner wall of the via hole conductor, and the lump portion forms the wall surface of the via hole conductor. Since the interface between the glass fiber and the thermosetting resin is sealed, the occurrence of migration can be suppressed.

As a result, even when the via-hole conductors are formed close to each other, insulation failure does not occur between the via-hole conductors, the insulation reliability can be improved, and high-density formation of via-hole conductors can be dealt with. Moreover, the fusion of the lumps of a plurality of glass fibers further reduces the occurrence of CAF and further reduces migration.

In the method for manufacturing a wiring board, the uncured prepreg is laser-processed, and then heated and pressed to promote the fluidity of the thermosetting resin, thereby forming the glass fiber by the lump. The sealing property at the interface with the thermosetting resin can be improved.

Further, according to the manufacturing method of the present invention, since the via-hole conductor is formed not by plating but by filling with a conductive paste, the amount of harmful drug such as cyan or formalin contained in the plating solution is reduced. It can be reduced, and there is an environmental advantage.

[0043]

[Examples] Examples 1 to 4 and Comparative Example 1 Thermosetting polyphenylene ether (PP
5) A glass woven cloth with an average fiber diameter of 10 μm
Via diameter 10 with CO ₂ laser on prepreg containing 8% by volume
A through hole having a diameter of 0 μm and a via pitch of 250 μm was processed with the laser output shown in Table 1, and then 100 parts by weight of copper powder coated with silver on the surface having an average particle diameter of 4 μm, 0.2 parts by weight of cellulose, 2- A metal paste mixed with 10 parts by weight of octanol was filled to form a via-hole conductor, which was heated at 50 ° C. for 60 minutes and dried.

On the other hand, P with a 12 μm thick copper foil bonded
A wiring circuit layer was formed on a copper foil of a resin film made of ET by a photoresist method. Then, the resin film is aligned and laminated on the prepreg,
The printed circuit layer was transferred by heating and pressing under the conditions shown in Table 1 and peeling off the resin film.

Then, three layers of this prepreg were laminated, and a transparent fluororesin-based release film was attached to the surface of the outermost insulating layer, and then 20 kgf / c using a vacuum press machine.
The thermosetting resin was completely cured by heating at 200 ° C. for 1 hour while applying a pressure of m ² .

Examples 5 and 6 In the same prepreg as in Examples 1 to 4, through holes having a via diameter of 100 μm and a via pitch of 250 μm were formed by using a CO ₂ laser in the same manner, and then the through holes were used in Examples 1 to 4. One was filled with the same conductive paste. Then 12
A copper foil having a thickness of μm is heated and pressed at 120 ° C. and 30 kg / cm ² for 1 minute, adhered to the entire surface of the substrate, and a pressure of 20 kgf / cm ² is applied using a vacuum press machine at 200 ° C.
The substrate was heated for a period of time to completely cure it. Next, a wiring circuit layer was formed on the surface copper foil by a photoresist method.

Then, a prepreg having a via-hole conductor produced in the same manner as described above is aligned and laminated on the surface of the above wiring board, and the temperature is 120 ° C. and 35 kg / cm ^2.
The substrate was completely cured by heating at 200 ° C. for 1 hour while applying a pressure of 20 kgf / cm ² .

Comparative Example 2 As the core substrate, the same prepreg as in Example 1 was prepared. Then, apply 12 μm thick copper foil to the front and back surfaces.
The mixture was heated and pressed at 0 ° C. and 20 kg / cm ² , adhered to the entire surface of the substrate, and heated at 200 ° C. for 1 hour while applying a pressure of 20 kgf / cm ² using a vacuum press device to completely cure the substrate. Via hole 200μ with micro drill on the obtained substrate
m, a via pitch of 350 μm was processed, and the inner wall of the through hole was plated with copper to form a via hole conductor. Next, a wiring circuit layer was formed on the copper foil on the surface by a photoresist method to manufacture a wiring board.

Comparative Example 3 As the core substrate, the same prepreg as in Example 1 was prepared. Then, apply 12 μm thick copper foil to the front and back surfaces.
It was heated and pressed at 0 ° C. and 30 kg / cm ² , adhered to the entire surface of the substrate, and heated at 200 ° C. for 1 hour while applying a pressure of 20 kgf / cm ² using a vacuum press device to completely cure the substrate. After that, a through hole having a via diameter of 100 μm and a via pitch of 250 μm was processed with a CO ₂ laser, and then the same conductive paste as in Example 1 was filled in the through hole. Next, a wiring circuit layer was formed on the surface copper foil by a photoresist method.

Comparative Example 4 A prepreg obtained by impregnating an aramid nonwoven fabric with an epoxy resin was processed with a CO ₂ laser to form through holes having a via diameter of 100 μm and a via pitch of 250 μm, and then the same conductive paste as in Example 1 was placed in the through holes. Filled. Then 12μ
A copper foil with a thickness of m is heated and pressed at 120 ° C. and 30 kg / cm ² to adhere it to the entire surface of the substrate, and then 20 k using a vacuum press machine.
The substrate was completely cured by heating at 170 ° C. for 1 hour while applying a pressure of gf / cm ² . Next, a wiring circuit layer was formed on the surface copper foil by a photoresist method. After that, a prepreg having a via-hole conductor produced in the same manner as described above is aligned and laminated on the surface of the wiring board, and a pressure of 40 kgf / cm ² is applied to the prepreg.
The substrate was completely cured by heating at 0 ° C. for 1 hour.

(Evaluation) The obtained via-hole conductors or via-hole conductors of each wiring board were cut and the cross-sectional shape was observed, and the presence or absence of sealing by lumps and the end of the exposed fibrous body on the inner wall of the via-hole conductors were checked. The diameter of the lump was measured, and the ratio to the average diameter of the fiber is shown in Table 1.

Further, 20 wiring boards were prepared for each of the examples and comparative examples, and tested under the following conditions a and b. (A) 120 ° C., 2.1 atmospheric pressure, 100% humidity Hold in atmosphere for 300 hours.

(B) A temperature of 130 ° C., a humidity of 85%, a voltage of 5.5 V is applied to the via-hole conductor or the via-hole conductor, and 3
Hold for 00 hours.

Table 1 shows the number of wiring boards having insulation failure between adjacent via-hole conductors after the test.

[0055]

[Table 1]

As shown in Table 1, when a through hole was formed by a microdrill by a conventional method as in Comparative Example 2, as shown in FIG. 4, no lump was formed at the end of the glass fiber 21. As a result, glass fiber 21
Penetration of the plating solution was confirmed through the gap 23 at the interface between the resin 22 and the resin 22.

In Comparative Example 3, the formation of the lump 25 at the end of the glass fiber 24 was recognized as shown in FIG. 5, but the interface between the glass fiber 24 and the resin 26 was not sealed, and As a result, the gap 27 between the glass fiber 24 and the resin 26
Copper powder invaded into and caused insulation failure.

Further, in Comparative Example 4, as shown in FIG. 6, no lump was formed at the end of the glass fiber 28, and as a result, a gap 30 at the interface between the glass fiber 28 and the resin 29 was formed. Moisture penetrates through and oxidizes the via-hole conductor, resulting in poor insulation.

Further, under the heating and pressurizing condition, the pressure is weak in Comparative Example 1, so that the interface between the glass fiber 24 and the resin 26 is not sealed as shown in FIG. 5, and as a result, the copper powder is left in the gap. Had entered and caused insulation failure.

In contrast to these comparative examples, in the wiring boards manufactured according to the present invention, a lump was formed in each case, and the interface between the glass fiber and the resin was sealed by the lump, which resulted in migration. It showed excellent connection reliability with no generation of water or intrusion of water.

[0061]

As described in detail above, according to the present invention,
Generation of migration between adjacent via-hole conductors can be suppressed, insulation reliability between the conductors can be improved, and via-hole conductors can be formed with high density on the wiring board.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a basic structure of a wiring board of the present invention.

FIG. 2 is an enlarged cross-sectional view of a via-hole conductor in the wiring board of the present invention.

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

FIG. 4 is an enlarged cross-sectional view for explaining an example of a conventional via-hole conductor.

FIG. 5 is an enlarged cross-sectional view for explaining another example of the conventional via-hole conductor.

FIG. 6 is an enlarged cross-sectional view for explaining still another example of the conventional via-hole conductor.

[Explanation of symbols]

1 wiring board 2 woven cloth 3 Thermosetting resin 4 insulating substrate 5 through holes 6 Via hole conductor 7 Wiring circuit layer 8 glass fiber 9 chunks

Claims (7)

(57) [Claims] 1. A through hole is formed in an insulating substrate obtained by impregnating a woven cloth or a non-woven cloth made of glass fiber with a thermosetting resin, and a conductive paste containing a metal powder is provided in the through hole. In a wiring board having a filled via-hole conductor, the end of the glass fiber exposed on the via-hole conductor wall surface is formed by a lump larger than the glass fiber diameter, and the glass fiber on the via-hole conductor wall surface. A wiring board, wherein an interface portion with the thermosetting resin is sealed by the lump. 2. The wiring board according to claim 1, wherein the lumps of the plurality of glass fibers are fused to each other. 3. The wiring board according to claim 1, wherein the minimum diameter of the lump is 1.2 times or more the average diameter of the glass fiber. 4. (a) A prepreg obtained by impregnating a woven or non-woven fabric made of glass fiber with a thermosetting resin is used to form a through hole by using laser light, and is exposed on the inner wall surface of the through hole. A step of melting the tip of the glass fiber to form a lump having a diameter larger than the average diameter of the glass fiber; and (b) filling the inside of the through hole with a conductive paste containing a metal powder to form a via-hole conductor. And (c) subjecting the prepreg on which the via-hole conductor is formed to heat and pressure treatment to flow the thermosetting resin in the prepreg so that the glass fiber and the thermosetting resin on the via-hole conductor wall surface are formed. A step of sealing an interface portion with a resin with a lump portion of the glass fiber end portion, (d)
(C) A step of curing the thermosetting resin in the prepreg after the step, and a method for manufacturing a wiring board. 5. The method of manufacturing a wiring board according to claim 4, wherein the minimum diameter of the lump is 1.2 times or more the average diameter of the glass fiber. 6. The laser light is applied to 2 to 2 per shot.
The method for manufacturing a wiring board according to claim 4, wherein the through hole is formed by irradiating with an energy of 0 mj. 7. The heat and pressure treatment is performed at 80 to 150 ° C. for 1 hour.
The method for manufacturing a wiring board according to claim 4, wherein the method is performed under a condition of 0 to 50 kg / cm ² .