JPH08172269A - Manufacture of printed-wiring board - Google Patents

Abstract

PURPOSE: To obtain a printed-wiring board which enhances the through insertion property of a bump and which enhances the connection reliability of a conductor wiring part to a metal foil by a method wherein a glass cloth for a prepreg is constituted by laminating fibers of small count through impregnation of a synthetic resin. CONSTITUTION: An electrolytic copper foil is used as a support base body 1, a thermosetting epoxy resin-bases silver paste is printed by using a metal mask so as to be dried, its printing operation to the same position is repeated, conductor bumps 5 are formed. Then, a glass cloth wherein the thread count is reduced as compared with that in normal cases and whose density (number/25mm) is longitudinally 8±2 and transversely 8±2 to longitudinally 44±2 and transversely 33±2 is impregnated with an epoxy resin so as to be dried, and a prepreg 2 is formed. The support base body 1, the prepreg 2, an elastic sheet 3 and an electrolytic copper foil 4 are stacked and pressurized, and bumps as a group are passed and inserted in the thickness direction of the prepreg, and a through conductor wiring part is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a highly reliable printed wiring board which enables wiring at high density and mounting by connecting wiring layers with a through conductor wiring portion.

[0002]

2. Description of the Related Art Conventionally, in a double-sided printed wiring board or a multilayer printed wiring board, electrical connection between wiring layers such as conductive patterns has been performed as follows. For example, in the case of a double-sided printed wiring board, perforating processing is performed at a predetermined position on the double-sided copper clad board, chemical plating is applied to the entire surface including the inner wall surface of the hole, and metal layer on the inner wall surface of the hole is electroplated. The thickness of the wiring layer is increased to improve reliability and electrical connection between wiring layers is performed. Further, in the case of a multilayer printed wiring board, after patterning the copper foil attached to both surfaces of the inner layer copper-clad substrate, the copper foil is laminated on the patterning surface via a prepreg and integrated by heating and pressing. As with the double-sided printed wiring board, after making electrical connection between the wiring layers by drilling and chemical / electroplating treatment, the surface copper foil is patterned to obtain a 4-layer multilayer printed wiring board. There is. In the case of a multilayer printed wiring board having more than four wiring layers, it can be manufactured by a method of increasing the number of inner layer copper-clad boards to be inserted in the middle.

In the method of manufacturing a printed wiring board, as a method for electrically connecting wiring layers without using a plating process, a double-sided copper-clad substrate is punched at a predetermined position and a conductive paste is printed in the holes. There is also a method in which the resin component of the conductive paste poured into the hole is cured to electrically connect the wiring layers.

[0004]

As described above, in the method of manufacturing a printed wiring board which utilizes the plating method for electrical connection between wiring layers, a substrate boring process for the electrical connection between wiring layers and a hole inner wall surface are used. It requires a plating process including
There is a drawback that the manufacturing process is redundant and the process management is complicated.

On the other hand, in the case of pouring a conductive paste into the holes for electrical connection between the wiring layers by printing or the like,
As in the case of the plating method, a substrate boring step is required. Moreover, it is difficult to pour the conductive paste uniformly into the bored holes, and there is a problem in reliability of electrical connection. In any case, the need for the board boring step is reflected in the cost and yield of the printed wiring board,
It has a drawback that it cannot meet the demand for cost reduction.

In any case of the electrical connection by the plating process or the flow of the conductive paste, holes for electrical connection between wiring layers are provided on the front and back surfaces of the printed wiring board. Since wiring cannot be formed / arranged in the area of the hole and electronic parts cannot be mounted, there is a problem that improvement in wiring density is restricted and improvement in component mounting density is also hindered. In other words, the printed wiring board obtained by the conventional manufacturing method cannot fully meet the demand for compact circuit devices by high-density wiring and high-density mounting, and further miniaturization of electronic devices. There has been a demand for a practical method of manufacturing a printed wiring board including a surface.

In order to meet the demand, the inventors have pressed the bump group provided on the supporting base against a synthetic resin sheet (for example, prepreg), and inserted the bump group in the thickness direction of the synthetic resin sheet. We proposed a method of forming a through-type conductor wiring part and connecting it to the metal foil placed on the upper surface of the synthetic resin sheet, but the synthetic resin sheet was lifted to the upper part of the bump when pressure was applied. There was a problem in reliability of electrical connection between wiring layers because the through-type conductor wiring portion could not be formed and the connection area with the metal foil to be connected on the bump was reduced.

The present invention has been made in order to eliminate the above-mentioned drawbacks in the case of forming a through-type conductor wiring portion in a prepreg. An object of the present invention is to provide a method for manufacturing a printed wiring board having improved yield and improved connection reliability with a metal foil.

[0009]

DISCLOSURE OF THE INVENTION As a result of intensive studies aimed at achieving the above object, the present invention has found that the above object can be achieved by using a fiber having a small number of fibers as a glass cloth for a prepreg. The present invention has been completed.

That is, according to the present invention, a step of laminating and placing a main surface of a prepreg in which a glass cloth is impregnated with a synthetic resin is brought into contact with a main surface of a supporting substrate having a group of conductor bumps formed at predetermined positions, and the main surface is laminated. A step of forming a through-type conductor wiring portion by pressing the laminate to insert the conductor bump groups in the thickness direction of the prepreg, and a step of arranging a metal foil on the upper surface of the prepreg and integrally molding. The method of manufacturing a printed wiring board is characterized in that the glass cloth of the prepreg is made of a fiber having a small number of fibers.

The present invention will be described in detail below.

Examples of the supporting substrate used in the present invention, that is, the supporting substrate on which the conductor bump group is formed, include a conductive sheet or foil or a synthetic resin sheet having a good peeling property. The sheet may be a sheet or a patterned sheet, and the shape thereof is not particularly limited. Further, the conductor bump group may be formed not only on one main surface of the support base but also on both main surfaces.

In the present invention, the conductor bump group on the supporting substrate is formed using a conductive composition or a conductive metal. This conductive composition is a mixture of a synthetic resin serving as a binder and conductive powder. As the synthetic resin serving as a binder, a thermosetting resin, a thermoplastic resin, or a mixed resin thereof can be used. For example, urea resin,
Melamine resin, phenol resin, resorcinol resin,
Examples thereof include epoxy resin, polyurethane resin, vinyl acetate resin, polyvinyl alcohol resin, acrylic resin, vinyl urethane resin, silicone resin, α-olefin maleic anhydride resin, polyamide resin, and polyimide resin. The conductive powder used here is gold powder,
Examples thereof include silver powder, copper powder, solder powder, nickel powder, carbon powder, and powder having a conductor layer on the surface. These can be used alone or in combination of two or more.

As described above, the conductive composition contains a synthetic resin and a conductive powder as main components, but it is a solvent for adjusting viscosity as long as it does not deviate from the object of the present invention, and if necessary. , A coupling agent, and other additives can be added. Examples of the solvent used here include dioxane, benzene, hexane, toluene, solvent naphtha, industrial gasoline, cellosolve acetate, ethyl cellosolve, butyl cellosolve acetate, butyl carbitol acetate, dimethylformamide, dimethylacetamide, and N-methylpyrrolidone. These can be used alone or in combination of two or more. A bump group is formed on a supporting substrate using the conductive composition thus obtained.

A method of forming a bump group using a conductive composition may be a printing method using a metal mask, but is not particularly limited. Generally, the height of the bump group is preferably about 100 to 400 μm, and bumps with a high aspect ratio can be formed by using a relatively thick metal mask, and the desired bump height can be obtained by printing twice or more. You can Further, the height of the bump group may be such that a height capable of penetrating one layer of prepreg and a height capable of penetrating a plurality of layers of prepreg are appropriately mixed.

On the other hand, as a method of forming a bump group with a conductive metal, (a) a fine metal block having a certain shape or size is sprinkled on the surface of a supporting substrate provided with an adhesive layer in advance,
When selectively fixing (at this time, a mask may be arranged), and (b) a copper foil or the like is used as a supporting substrate,
Printing and patterning plating resist, copper, tin,
Selectively form minute metal column groups by plating gold, silver, solder, etc. (c) Apply solder resist to the support substrate, pattern it, and immerse it in a solder bath For example, forming a group of metal columns. Here, the minute metal blocks or minute metal columns formed as bumps may have a multilayer structure or a multilayer shell structure in which different metals are combined. For example, the surface having a copper core may be coated with gold or silver to impart oxidation resistance, or the surface having a copper core may be coated with solder to have solder jointability. When the bump group is formed of a conductive composition, it is advantageous in terms of cost reduction because the steps and the like can be further simplified as compared with the case of using a method such as a plating method.

The prepreg as referred to in the present invention means a sheet in which glass cloth is impregnated with synthetic resin or raw rubber, and the conductor bump group is inserted to form a through-type conductor wiring portion, and its thickness It is preferably about 50 to 800 μm. Specific examples of the impregnated synthetic resin or raw rubber include thermoplastic resins such as polycarbonate resin, polysulfone resin, thermoplastic polyimide resin, tetrafluoropolyethylene resin, hexafluoropolypropylene resin, and polyetheretherketone resin. Next, thermosetting resins that are kept in a pre-cured state, for example, those in the B stage state such as epoxy resin, bismaleimide triazine resin, polyimide resin, phenol resin, polyester resin, melamine resin, or raw rubber , For example, butadiene rubber, butyl rubber, natural rubber, neoprene rubber,
Examples include silicone rubber. These synthetic resins or raw rubbers may be synthetic resins or raw rubbers alone, but may also contain inorganic or organic insulating fillers.

As the glass cloth in the prepreg used in the present invention, a glass cloth made of fibers having a small number of fibers is used. The density (pieces / 25mm) of this glass cloth is vertical
8 ± 2 horizontal 8 ± 2 to vertical 44 ± 2 horizontal 33 ± 2 is desirable. If the density is out of this range, the bump penetration is poor,
Further, the connection reliability is lowered and the reinforcing effect by the glass cloth cannot be exhibited, which is not preferable.

The prepreg main surface is placed in contact with the main surface of the supporting substrate on which the above-mentioned conductor bump group is formed so as to be laminated, and the laminate is heated as it is or is heated and pressed. At that time, as a base (abutting plate) on which the prepreg is placed, a metal plate or a heat-resistant resin plate with little size or deformation, for example, a stainless plate, a brass plate, a polyimide resin plate (sheet), a polytetrafluoroethylene resin plate ( Sheet) is used. When the pressure is applied to the laminated body, if the resin content of the prepreg is softened by being heated, the stack of bumps can be satisfactorily inserted.

A printed wiring board can be manufactured by laminating a prepreg on which a through-hole type conductor wiring portion is formed by penetrating a group of bumps and integrally molding the metal foil. The molding conditions at that time can be appropriately selected depending on the type and composition of the conductive composition of the conductor bump and the prepreg.

[0021]

According to the method for manufacturing a printed wiring board of the present invention, the conductor bump groups are respectively inserted in the thickness direction of the prepreg to form the through-type conductor wiring portion. It will not be possible to form a through-type conductor wiring part because it will be lifted to the top of the conductor bump, and the connection area between the bump top and the conductive metal foil of the laminated body will not decrease, ensuring reliable electrical connection between wiring layers. Connection is obtained. That is, the bump penetration property is improved, and the connection reliability between the through-type conductor wiring portion and the conductive metal foil of the laminate is also improved.

[0022]

EXAMPLES Examples of the present invention will be specifically described with reference to the drawings, but the present invention is not limited to these examples.

Example 1 An electro-deposited copper foil having a thickness of 35 μm as shown in FIG.
As a result, the thermosetting epoxy resin silver paste is printed using a metal mask (stainless steel, plate thickness 0.2 mm, hole diameter 0.4 mm), dried, and then printed at the same position using the same mask four times. , A conductor bump 5 with a height of about 200 μm
Was formed. Next, as a prepreg, the thickness of the glass cloth with the density (lines / 25 mm) reduced to 22 ± 2 in length and 16 ± 2 in width is impregnated with epoxy resin and dried 1
00 μm of prepreg 2 was used. The laminated body of the support base 1 and the prepreg 2 on which the conductor bumps 5 are formed is laminated with the elastic sheet 3 of the insertion assisting material and the electrolytic copper foil 4 having a thickness of 35 μm as a back sheet (abutting plate), which is pressed. The bump groups are inserted in the thickness direction of the prepreg to form a through-type conductor wiring portion. Then, the elastic sheet 3 of the penetration assisting material is removed, and the electric field copper foil 4 is left.
A double-sided printed wiring board was manufactured by integrally molding under heat and pressure at 50 ° C. and 50 kg / cm ² for 90 minutes.

Example 2 As shown in FIG. 1, a 35 μm thick electrolytic copper foil was used as a supporting substrate 1.
As a result, the thermosetting epoxy resin silver paste is printed using a metal mask (stainless steel, plate thickness 0.2 mm, hole diameter 0.4 mm), dried, and then printed at the same position using the same mask four times. , A conductor bump 5 with a height of about 200 μm
Was formed. Next, as a prepreg, the thickness of the glass cloth, the number of which was driven in is reduced from the usual (density / 25 mm) to 15 ± 2 in length and 11 ± 2 in width, is impregnated with epoxy resin and dried. 1
00 μm of prepreg 2 was used. The laminated body of the support base 1 and the prepreg 2 on which the conductor bumps 5 are formed is laminated with the elastic sheet 3 of the insertion assisting material and the electrolytic copper foil 4 having a thickness of 35 μm as a back sheet (abutting plate), which is pressed. The bump groups are inserted in the thickness direction of the prepreg to form a through-type conductor wiring portion. Then, the elastic sheet 3 of the penetration assisting material is removed, and the electric field copper foil 4 is left.
A double-sided printed wiring board was manufactured by integrally molding under heat and pressure at 50 ° C. and 50 kg / cm ² for 90 minutes.

Comparative Example Using a 35 μm-thick electrolytic copper foil as a supporting substrate, a thermosetting epoxy resin-based silver paste was used as a metal mask (made of stainless steel,
Printing was performed using a plate thickness of 0.2 mm and a hole diameter of 0.4 mm), and after drying, printing was performed at the same position using the same mask four times to form bumps with a height of about 200 μm. Next, on a normal density (pieces / 25mm) glass cloth with a length of 44 ± 2 and a width of 33 ± 2,
A double-sided printed wiring board is manufactured by using a 100 μm-thick prepreg and an elastic sheet formed by impregnating with an epoxy resin and drying, and a 35 μm-thick electrolytic copper foil as a back sheet (patch plate) in the same manner as in Example 1. did.

The printed wiring boards manufactured in Examples and Comparative Examples were tested for bump penetration rate and through hole reliability. The results are shown in Table 1. The present invention showed excellent characteristics, and the effects of the present invention could be confirmed.

[0027]

[Table 1] * 1: Regarding the through-type conductor wiring part, we conducted a continuity test from the front and back sides of each conductor wiring part using a tester. * 2: Make a through-hole substrate with 1872 holes and conduct immersion for 1 second in 260 ° C oil for 12 seconds and then for 20 seconds in 20 ° C oil for 1 cycle, and measure the conduction resistance for each cycle. Then, the number of cycles until the through hole was broken was tested.

[0028]

As is apparent from the above description and Table 1, according to the method of manufacturing a printed wiring board of the present invention, the penetration of bumps is improved and the conductive wiring portion of the through type and the conductivity of the laminated body are improved. It is possible to manufacture a printed wiring board that improves reliability with a conductive metal foil, has a good yield, and contributes to cost reduction.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view separately explaining a layer structure of a printed wiring board of the present invention.

[Explanation of symbols]

 1 Support Base 2 Prepreg 3 Elastic Sheet 4 Electrolytic Copper Foil 5 Conductor Bump

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location // H05K 1/03 630 F 7511-4E

Claims (2)

[Claims] 1. A step of stacking a main body of a supporting substrate having conductor bump groups formed at predetermined positions on a main surface of a prepreg in which a glass cloth is impregnated with a synthetic resin is placed in contact with each other, and the laminate is added. And a step of forming a through-type conductor wiring portion by inserting the conductor bump group in the thickness direction of the prepreg, and a step of integrally forming a metal foil on the upper surface of the prepreg. A method of manufacturing a printed wiring board, characterized in that the glass cloth of the prepreg is made of a fiber having a small number of fibers. 2. The glass cloth has a density (pieces / 25 mm) length 8 ±.
2. The method for producing a printed wiring board according to claim 1, wherein a prepreg having a width of 8 ± 2 to a height of 44 ± 2 and a width of 33 ± 2 is used.