JP3663044B2 - Method for manufacturing printed wiring board - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for manufacturing a printed wiring board.
[0002]
[Prior art]
In recent years, there has been a demand for finer, narrower pitch, surface treatment, etc., in the pattern of a printed wiring board in order to cope with miniaturization and narrower pitch of electronic components to be mounted. In order to meet these requirements, processing techniques such as printed wiring board etching techniques and lamination techniques have been improved, and finer and narrower pitches are being promoted. Even if the processing technique is improved, the component mounting pads, the through holes and the via holes must be provided at different positions. Alternatively, attempts have been made to fill through holes, via holes, and the like with solder using a solder leveler that immerses the printed wiring board in a solder bath, and to use these through holes, via holes, etc. as component mounting pads. Alternatively, attempts have been made to use a component mounting pad by filling a through hole, a via hole, or the like with a resin and providing a conductor layer thereon.
[0003]
[Problems to be solved by the invention]
However, in the method of filling the through holes and / or via holes with solder using a solder leveler that immerses the printed wiring board in the solder bath, an air pocket (17 in FIG. 2) can be formed inside these through holes and / or via holes. There are problems such as large irregularities, and the positions of through holes and / or via holes to be filled cannot be selected selectively.
[0004]
[Means for Solving the Problems]
In the present invention, a metal paste containing two or more metal components composed of a combination of an organic acid metal salt / organic acid metal salt or an organic acid metal salt / metal powder is applied to a through hole and / or a via hole and heated. By making the metal paste applied by the metal alloy into a metal alloy, there is no air accumulation inside the through hole and / or via hole, the surface unevenness is small and uniform, and the position of the filling through hole and / or via hole can be selected selectively. The present invention provides a method for manufacturing a printed wiring board that solves the above problems.
[0005]
Hereafter, the manufacturing method of the printed wiring board concerning this invention is explained in full detail. The method for producing a printed wiring board according to the present invention generally applies a metallized paste to a through hole and / or a via hole formed on a printed wiring board by a known method such as screen printing, a dispenser method, etc. A reaction of alloying is caused by heating the metallized paste, and the alloyed metal alloy is filled, solidified, fixed, etc. in the through holes and / or via holes and / or on the surface lands.
[0006]
More specifically, the printed wiring board manufacturing method according to the present invention is, for example, a printed wiring board manufactured by a method known per se as shown in FIG. 1 [insulating layer 1 such as glass epoxy resin, conductor such as copper foil, etc. A layer 2, a via hole 5 having a land 6 having a land width w, a pitch d via hole 5, a solder resist 3, a through hole, and the like. ] Is screen printed at a desired position (via hole 5, land 6, conductor layer 2, through hole) using a screen mask (metal mask, mesh mask, etc.) having two or more kinds of metal components. The coating amount of the metallized paste by screen printing is the thickness of the metal mask, the mesh of the mesh mask, the thickness of the emulsion of the mesh mask, the opening area of the mask, etc. The screen gap of the screen printing, the pressure of the squeegee, It can be determined to be substantially constant by controlling the speed, tension of the screen mask, and the like. A preferable coating amount is a thickness of 10 to 500 μm on the land and the conductor layer. Before screen printing the metallized paste, the printed wiring board is pretreated (surface polishing of the conductor layer, degreasing and pickling, soft etching of the surface of the conductor layer, etc.) to It is preferable to remove the metal oxide film.
[0007]
The metallized paste applied by a screen printing method, a dispenser method, or the like is subjected to a heat reaction process to become a metal alloy 4 and fills only the inside of the applied via hole 5, and only the surface of the applied land and conductor layer is applied. Cover. It is obvious that the inside of the through hole is filled if it is applied to the through hole. Further, as the heating method, the entire printed wiring board may be heated, or local heating may be performed by infrared rays, laser, high frequency, or the like.
[0008]
After the heat reaction treatment, the solvent, flux, residue, etc. are washed by a method known per se corresponding to the components.
[0009]
Additional metallization paste, 2 kinds or more print-coating in those containing a metal component is intended pasty heatable reaction of a metal alloy and Do Ri, organic acid metal salt / organic acid metal salts, organic It is a metallized paste comprising a combination of an acid metal salt / metal powder. A metallized paste composed of a combination of an organic acid metal salt / metal powder is preferable. Examples of the organic acid metal salt include lead carboxylate, tin carboxylate, copper carboxylate, and the like. Examples of the metal powder include lead powder, tin powder, indium powder, antimony powder, silver powder, copper powder, zinc powder, bismuth powder, nickel powder, phosphorous powder, gallium powder, and gold powder. Most preferably, in order to use a through hole and / or a via hole as a component mounting pad, the metal alloy obtained by alloying the metallized paste by a heat reaction has a melting point higher than the melting point of the solder used for component mounting. This is a metallized paste. In addition, the metal powder that is not completely alloyed with metal powder or the like but partially alloyed may be included.
[0010]
As metal alloy, Sn-Pb, Sn-Sb , Sn-Ag, those mainly containing an alloy of Sn-Zn, etc. can be exemplified. Preferably, Sn—Pb is the main component because of cost and the temperature of the heating reaction. In addition, when the metal alloy powder is printed in the form of a paste that can be printed and applied, and then re-melted by heat treatment, air can be trapped inside the through hole and / or via hole (as shown in 17 in FIG. 2). It is not preferable to use a paste made of a metal alloy powder because the air reservoir may be ruptured by reheating at the time of component mounting.
[0011]
The printed wiring board manufactured in this manner is filled with the metal alloy 4 without enclosing air pockets in the through holes and / or via holes, and the land and conductor layers are evenly wet with little unevenness. The through hole and / or via hole can be used as a component mounting pad because it is fixed in place with a high density, high reliability, and selection of the desired application position for applying the metallized paste by the printing method This can be done without performing a mask process.
[0012]
【Example】
Examples of the method for producing a printed wiring board according to the present invention will be described below. In addition, the manufacturing method of the printed wiring board based on this invention is not restricted to a following example.
[0013]
(Example 1) Using a conventional printed board manufacturing method, a printed board having a three-layer structure and through holes and via holes as shown in FIG. 1 was manufactured. [Circuit pattern is formed on a double-sided copper-clad epoxy board (FR-4) by a photoresist method, prepreg and copper foil are laminated, a hole for a via hole is formed by drilling a through hole and a countersink of a drill, copper Plating was performed to form through holes and via holes 5, and solder resist 3 was formed to produce a printed circuit board. The via hole pitch d of the printed circuit board was 0.8 mm, and the land width w was 0.1 mm.
[0014]
Degreasing treatment and sulfuric acid / hydrogen peroxide soft etching were performed as pretreatment of the printed circuit board to degrease the surface of the copper foil and remove the oxide film. Subsequently, using a metal mask (thickness 0.2 mm, opening is 0.2 mm wider than the pad size at the desired position) having an opening at a desired application position on the printed circuit board, a component mounting pad, via hole 5 and via hole land 6 and the like were printed and coated with a metallized paste (product name: SP-101, manufactured by Super Solder Technologies Co., Ltd.) by urethane squeegee movement.
[0015]
Subsequently, the entire printed board was heated through a nitrogen atmosphere electric furnace (peak temperature: about 220 ° C., peak temperature passing time: about 2 minutes) to cause the metallized paste to react by heating. By the heating reaction, the metallized paste was alloyed to become a Sn—Pb-based metal alloy 4 which was filled, solidified, and fixed to a component mounting pad, via hole 5, via hole land 6, and the like.
[0016]
Subsequently, in order to clean and remove the residue of the metallized paste after the heating reaction, a residue cleaning process is performed by an alternative Freon AK-225 (manufactured by Asahi Glass Co., Ltd.) to fill, solidify, and fix the metal alloy. Was made.
[0017]
The printed wiring board manufactured in this way is filled and solidified with the metal alloy 4 in the via hole 5, the metal alloy 4 is fixed to the land 6, and the metal alloy does not bridge even at a narrow pitch d. There is no air accumulation inside (by observation of a plurality of cross-sections), there is little unevenness on the surface, it is uniform, and it is suitable for using the via hole 5 and the pad as a component mounting pad.
[0018]
(Example 2) A printed wiring board in which a through hole was filled with a metal alloy and solidified in the same manner as in Example 1 was produced. The center of the through hole of the printed wiring board manufactured in this way was cut with a cutter. The cut surface was reinforced with a metal alloy, and the through hole was divided into two without peeling off the copper foil. The half-halved through hole can be used as a component mounting pad, and the printed wiring board for surface mount components uses the half-divided through hole as an external lead for surface mount components. It can also be.
[0019]
(Comparative Example 1) A printed wiring board was manufactured in substantially the same manner as in Example 1 except that a Sn-Pb eutectic solder paste was used instead of the metallized paste. Since the printed wiring board made of eutectic solder thus produced has a large amount of air pockets in the via holes, there is a problem in that the air pockets burst when components are mounted.
[0020]
【The invention's effect】
In the method for manufacturing a printed wiring board according to the present invention, there is no component mounting such that the metal alloy by heating reaction has no air accumulation in the through holes and / or via holes, and the surface unevenness is small and uniformly filled, solidified, fixed, etc. It is possible to provide a highly reliable printed wiring board that forms a convenient pad surface.
[0021]
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment in which a metal alloy is filled in a via hole of a printed wiring board according to the method for manufacturing a printed wiring board according to the present invention. FIG. 2 is a cross-sectional view illustrating an embodiment according to the prior art.
[0022]
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1,11 Insulation layer 2,12 Conductor layer 3,13 Solder resist 4,14 Metal alloy 5,15 Via hole 6 Land d Pitch w Land width 17 Air pool

Claims (1)

A metal paste containing two or more kinds of metal components composed of a combination of organic acid metal salt / organic acid metal salt or organic acid metal salt / metal powder was applied to the through holes and / or via holes and applied by heating. A method for producing a printed wiring board, wherein the metal paste is a metal alloy.

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