JP3774932B2 - Method for manufacturing printed wiring board - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a printed wiring board used for various electronic devices.
[0002]
[Prior art]
2. Description of the Related Art In recent years, printed wiring boards that are widely used in various electronic devices and the like have been required to have high reliability along with higher wiring density as electronic devices have become smaller and more multifunctional. In particular, the demand for improved productivity and cost reduction of printed wiring boards has been remarkable in recent years. By filling the through-holes with silver paste as a conductive material from copper through-hole printed wiring boards for interlayer connection by electrolytic copper plating A so-called silver through-hole printed wiring board that performs interlayer connection has attracted attention.
[0003]
A conventional silver through-hole printed wiring board will be described below with reference to the drawings. FIGS. 3A to 3C are cross-sectional views showing a conventional method for producing a silver through-hole printed wiring board, and FIGS. 4A to 4C show problems of the conventional silver through-hole printed wiring board. It is sectional drawing. 3 (a) to 3 (c) and 4 (a) to 4 (c), 21 is a printed wiring board, 22 is a base material, 23 is a conductor circuit, 24 is a through hole, 25 is a land pattern for double-sided conduction, 26 is a solder resist, 27 is a silver paste, 28 is a conduction hole, 29 is a silver land, 31 is an insulating film, 32 is a poor adhesion of the silver land 29, 33 is a peeling of the insulating film 31, and 34 is a small diameter defect of the silver land 29 , 35 are poor protrusions of the silver land 29.
[0004]
First, copper foil is laminated on both surfaces of the base material 22 and a through-hole 24 is provided by drilling on a substrate cut to a predetermined size (not shown), and then etched as shown in FIG. The land pattern 25 and the conductor circuit 23 are formed by resist printing and copper foil etching, and the printed wiring board 21 on which the solder resist 26 is formed as a protection of the conductor circuit 23 is obtained. Next, as shown in FIG. 3B, the silver paste 27 mainly composed of silver powder, epoxy resin and curing agent is filled and printed on the land pattern 25 and the through holes 24, and the silver paste 27 is heated and cured in a hot air oven. Then, the conduction hole 28 and the silver land 29 are formed. Thereafter, as shown in FIG. 3C, an exposed conductive hole 28 on the land pattern 25 and an insulating film 31 for preventing silver migration on the silver land 29 are formed.
[0005]
[Problems to be solved by the invention]
However, the silver through-hole printed wiring board according to the above-described conventional manufacturing method is easily influenced by the conditions at the time of filling and printing of the silver paste 27 as a factor that determines the connection reliability of the conduction hole 28, and is generally a copper through-hole printed wiring board. There was a tendency for the reliability to become lower. That is, the small diameter defect 34 of the silver land 29 as shown in FIG. 4A due to insufficient filling of the silver paste 27 and the protrusion of the silver land 29 where the silver paste oozes out from the land pattern 25 as shown in FIG. 4B. The insulation film 31 is thinned due to the defect 35 and the bulge of the silver land 29 as shown in FIG. 4C, and the adhesion of the silver land 29 is poor due to the peeling 33 of the insulation film 31 and the impact load when the thin film portion is processed. 32 may occur and the conduction resistance may increase.
[0006]
In addition, when an oxide film is formed on the land pattern 25 and the insulating films 31 on both sides flow into the conduction holes 28 and the conduction holes 28 are completely filled and sealed from both sides, the component mounting is performed. There is a possibility that the gas remaining in the conduction hole 28 suddenly expands when heated at the soldering temperature, and stress is applied to the silver land 29 to weaken the adhesion between the silver land 29 and the land pattern 25. It was.
[0007]
Therefore, as a solution to the above problems, conventionally, the viscosity adjustment of the silver paste 27, the examination of the filling / printing conditions, the surface treatment conditions of the land pattern 25, and the mold shape at the time of outer shape processing have been carried out. I couldn't. Moreover, although the method of enlarging the shape of the conduction hole 28 or the land pattern 25 has been taken, it cannot be said that it is a preferable method in dealing with a high-density silver through-hole printed wiring board.
[0008]
SUMMARY OF THE INVENTION The present invention solves the above-described conventional problems, and has an object to provide a printed wiring board that improves the reliability of through holes, significantly improves the productivity and yield of manufacturing processes, and improves the reliability of electronic devices. And
[0009]
[Means for Solving the Problems]
In order to achieve this object, the present invention includes a step of providing a through hole in a substrate having copper foil on both sides, a step of forming a conductor circuit and a land pattern on both sides, a silver on the land pattern and in the through hole. A step of filling and printing the paste, a step of curing the silver paste and forming a conductive hole in the land land and the silver land and the through hole, and insulating on the conductive hole and the silver land on the land pattern Forming a film, wherein the land pattern has a plurality of defect portions around the through hole and a plurality of defect portions in the land pattern, and the silver land fills the defect portion with the silver paste. The printed wiring board is manufactured by using the method for manufacturing a printed wiring board, which is formed into a shape having a smooth surface. It is possible to obtain a printed wiring board having improved adhesion between the de pattern and silver land and silver lands and the insulating film.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
According to the first aspect of the present invention, there are provided a step of providing a through hole in a substrate having copper foil on both sides, a step of forming a conductor circuit and a land pattern on both sides, the land pattern and the through hole. Filling and printing a silver paste; curing the silver paste; forming a silver land and a through hole in the through hole on the land pattern; and on the silver land on the conductive hole and the land pattern. A step of forming an insulating film, wherein the land pattern has a plurality of defect portions around the through hole and a plurality of defect portions in the land pattern, and the silver land is formed on the defect portion of the silver paste. It is a printed wiring board manufacturing method characterized in that it is formed into a shape having a smooth surface by filling, and this manufacturing method eliminates defects on the land pattern. Adhesion structure between land pattern and conductive material by filling and printing with conductive material, expanding the contact area between copper foil cross section and conductive material, and directly adhering conductive material and base material at the defective part And enhances the reliability of the conduction hole.
[0011]
In addition, the conductive material on the land pattern is flattened by filling and printing the conductive material in the defective part on the land pattern, which ensures a uniform film thickness when printing the insulation film. It has the effect | action that an insulating film with a high can be formed.
[0012]
(Embodiment 1)
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0013]
FIG. 1 is a plan view showing the shape of a land pattern of a silver through-hole printed wiring board according to an embodiment of the present invention, and FIGS. 2 (a) to 2 (c) are printed wiring boards according to Embodiment 1 of the present invention. It is sectional drawing which shows this manufacturing method.
[0014]
1 and 2 (a) to 2 (c), 1 is a printed wiring board, 2 is a substrate, 3 is a solder resist, 4 is a through hole, 5 is a land pattern, and 6a and 6b are defects on the land pattern 5. 7 is a conductor circuit, 8 is a silver paste, 9 is a conduction hole, 10 is a silver land, and 11 is an insulating film.
[0015]
Using the screen plate or mask film on which the land pattern shape and the printed circuit pattern as shown in FIG. 1 are drawn, an etching resist is formed and etched on the copper foil by a known screen printing method or a photographic development method. Get 5. The land pattern 5 is composed of a plurality of defect portions 6a around the through-hole 4 and a plurality of defect portions 6b having a predetermined size on the land pattern 5, and the defect portions 6a and 6b are configured such that the surface of the substrate 2 is exposed. It is.
[0016]
Hereinafter, the printed wiring board manufacturing method of the present invention will be described in detail with reference to FIGS. First, as shown in FIG. 2 (a), copper foil is laminated on both surfaces of the base material 2 and a through hole 4 is formed by drilling on a substrate cut to a predetermined size (not shown). The land pattern 5 and the conductor circuit 7 having the defect portions 6 a and 6 b as shown in FIG. 1 are formed, and the printed wiring board 1 on which the solder resist 3 is formed as protection of the conductor circuit 7 is obtained. At this time, the land pattern 5 has a defect portion 6a in the vicinity of the through-hole 4 and a defect portion 6b in the land pattern 5, the side surfaces in the defect portions 6a and 6b are the copper foil cross sections of the land pattern 5, and the bottom surface is The base material 2 is exposed.
[0017]
Next, as shown in FIG. 2B, the silver paste 8 mainly composed of silver powder, epoxy resin and curing agent is filled and printed on the land pattern 5 and the through holes 4, and the silver paste 8 is heated and cured in a hot air oven. Then, the conduction hole 9 and the silver land 10 are formed. At this time, the silver land 10 has a structure filled and hardened on the defective portions 6a and 6b in the through hole 4 and the land pattern 5, and the silver paste 8 has a side surface and a copper foil cross section in the defective portions 6a and 6b. The lower surface has a structure in which the connection is in close contact and the lower surface is in direct contact with the base material 2, and the silver land 10 becomes a smooth shape by filling the defect portions 6 a and 6 b with the silver paste 8.
[0018]
When filling and printing the silver paste 8 in the through-holes 4, the filling amount of the silver paste 8 is increased by adjusting printing conditions, viscosity adjustment, etc., and the small diameter defect of the silver land is eliminated, and the size and shape of the defect portions 6 a and 6 b Further, by setting the number in advance, the excess silver paste 8 is filled in the defective portions 6a and 6b, so that the protrusion of the silver land can be prevented.
[0019]
Thereafter, as shown in FIG. 2C, an insulating film 11 is formed on the exposed silver land 10 on the land pattern 5 in order to prevent silver migration and protect the conduction hole 9. As described above, since the silver land 10 on the land pattern 5 is formed in a shape having a smooth surface, the insulating film 11 formed on the silver land 10 is also formed in a structure having a smooth and constant thickness. be able to.
[0020]
When various tests and environmental reliability of the silver through-hole printed wiring board manufactured by the above-described method according to the present invention were confirmed, the adhesion of the silver land 10 and the resistance value and the resistance change rate of the conduction hole at 500 hours in the humidity were It was confirmed that it was improved by 10% or more compared with the prior art. This is because when the through-hole 4 has a hole diameter of 0.6 mm and the land pattern 5 has a diameter of 1.0 mm, the contact area of the silver paste 8 and the land pattern 5 on the copper foil cross-section of the plurality of defect portions 6a and 6b Due to the presence, it is 2.0 to 5.0 times that of the prior art, and the adhesion between the resin component constituting the substrate 2 immediately below the defect portions 6a and 6b and the epoxy resin in the component of the silver paste 8 is strong. Therefore, it is estimated that the reliability of the silver land 10 and the conduction hole 9 is improved.
[0021]
Moreover, since the small-diameter defect of the silver land 10 and the protruding defect of the silver land 10 at the time of filling and printing of the silver paste 8 can be reduced and the insulating film 11 having a certain thickness can be formed, the insulating film 11 after the outer shape processing. By preventing the occurrence of peeling and impact loads on the conductive holes 9 and eliminating the occurrence of abnormal resistance values, it is possible to produce a high-quality silver through-hole printed wiring board with a high yield.
[0022]
【The invention's effect】
As described above, the present invention increases the contact area of a conductive material such as silver paste by forming a defect portion in a land pattern during pattern formation of a printed wiring board, thereby increasing the adhesion strength with the land pattern. It is possible to improve the reliability of the hole, eliminate the small diameter defect of the silver land and the protrusion defect of the silver land, and provide a high-quality printed wiring board with a high yield.
[Brief description of the drawings]
FIG. 1 is a plan view showing the shape of a land pattern of a silver through-hole printed wiring board in one embodiment of the present invention. FIG. 2 (a) to (c) of the printed wiring board in one embodiment of the present invention. 3 is a cross-sectional view illustrating a manufacturing method of a conventional silver through-hole printed wiring board. FIG. 4 is a cross-sectional view illustrating a problem of a conventional silver through-hole printed wiring board. [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Printed wiring board 2 Base material 3 Solder resist 4 Through-hole 5 Land pattern 6 Defect part 7 on a land pattern Conductor circuit 8 Silver paste 9 Conductive hole 10 Silver land 11 Insulation film

Claims (1)

A step of providing through holes in a substrate having copper foil on both sides, a step of forming conductor circuits and land patterns on both sides, a step of filling and printing silver paste on the land patterns and in the through holes, and the silver Curing the paste and forming a conductive hole in the land and the silver land on the land pattern, and forming an insulating film on the conductive hole and the silver land on the land pattern,
The land pattern has a plurality of defect portions around the through hole and a plurality of defect portions in the land pattern,
The method for producing a printed wiring board, wherein the silver land is formed into a shape having a smooth surface by filling the defective portion with the silver paste.

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