JPH0669649A - Manufacture of printed wiring board - Google Patents

Abstract

PURPOSE:To make the thickness of solder uniform so as to prevent the occurrence of tilting or insufficient continuity of surface-mounted parts by selectively removing the solder so that the solder can be left at necessary parts only. CONSTITUTION:A photoresist 3 is formed on the upper surface of a plated layer except pads 1 for mounting electronic parts, parts of the surrounding areas of through holes 5, and wiring layer forming areas 2 and, at the same time, a thick copper layer is stuck to the part of the plated layer exposed through the resist layer 3. Then, after forming a solder layer on the surface of the copper, the resist 3 is removed and the plated layer is etched off except the pads 1, the internal surfaces and parts of the surrounding areas of the holes 5, and the parts 2 and an outer wiring layer is formed. Then a dry film is vacuum-laminated on the wiring board and a resist 6 is formed on the pads 1 and in the surrounding areas of the holes 5. When the resist 6 is removed thereafter, the solder remains on the pads 1 and internal surfaces and surrounding areas of the holes 5 and a printed wiring board on which the copper of wiring pattern is exposed is obtained.

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 multilayer printed wiring board in which pads and component lands are soldered so that electronically mounted components can be easily mounted on a final printed wiring board.

[0002]

2. Description of the Related Art Conventionally, a printed wiring board having a solder resist formed on its final finish must be coated with solder in order to improve solder wettability when components are mounted on pads and component lands. (Hereinafter, referred to as solder coat treatment) is usual, and there are the following two methods as a method of manufacturing a printed wiring board to which the solder coat treatment is applied. The following is a brief description of the description using a multilayer printed wiring board as an example. A plurality of inner layer circuit boards each having an electric wiring layer formed of a copper foil, together with an outer layer copper foil, are prepregs (glass Non-woven fabric is impregnated with epoxy resin and is semi-cured) and laminated, and a through hole is drilled to connect the electrical wiring layers of the inner circuit board and the outer circuit board, and the inner wall surface of this through hole is Electroless copper plating and electrolytic copper plating are applied to cover with copper for electrical conduction, and plated layers are formed on the surface of the laminate and the inner wall surface of the through hole, respectively.

Next, a photoresist is formed in a pattern on the surface of the plating layer except for a part around the through hole, a pad and a wiring layer forming portion, which is a portion exposed from the photoresist layer, that is, an outer layer wiring pattern. Copper sulfate is plated on the outer wiring layer to form a wiring pattern, and copper is electrolytically plated on the surface of the copper. (This solder becomes an etching resist for the next etching.) Then, the plating resist is peeled off, and the inner wall surface of the through hole and a part of the periphery and a portion other than the wiring layer forming portion are removed by etching. An outer wiring layer is formed.

Next, the solder used as the etching resist is dissolved and removed, and the wiring layer of the outer layer plate with the exposed copper is completed. The thermosetting solder resist is applied to the substrate by the curtain coating method, and the component land and the like are masked. The exposure film is placed, exposed and developed to form a solder resist. The wiring board with the solder resist is
In order to improve the solder wettability when mounting a component on a component land, it is necessary to apply solder to the wiring board in advance and perform a solder coat treatment. The solder coat treatment is 23
Dip the wiring board in a molten solder bath at 0 to 240 ° C for 3 to 5 seconds, pull up the wiring board in the vertical direction, blow off excess solder with hot air, and add solder only to the component land and through hole. It is a method for obtaining a treated multilayer printed wiring board.

As for the solder coat treatment, there are the following methods in addition to the above method. In the following, the explanation will be given by taking a multilayer printed wiring board as an example.The steps up to etching are performed in the same steps as the conventional steps described above. Print on the part that leaves the area with Peeloo coat ink, dissolve and remove the solder of the wiring pattern, for example, except for the pads and lands, peel off the peel coat ink, heat the exposed solder and once melt it to form a homogeneous alloy. To do. This is what is called fusing. In the wiring pattern, if there is a narrow space between the wiring patterns during the fusing, the melted solder may cause a gap defect, and the parts will not be mounted. Need to be removed. By the way, the solder plating is properly tin-lead alloy plating, and once melted, the eutectic solder structure is completed and the solder wettability is improved. Then, the printed wiring board is manufactured by performing solder resist printing on the wiring board after the fusing.

[0006]

The method of immersing a wiring board in the molten solder bath will be described in more detail.
The wiring board is immersed in a molten solder bath at 0 to 240 ° C for 3 to 5 seconds, the solder application surface of the wiring board is parallel to the vertical direction and the wiring board is pulled up, and hot air is blown at a certain height from the liquid surface of the solder. Hot air is blown from the means to the solder application surface to make the solder layer uniform, but at a constant speed (about 230 mm / S).
constant pressure (4.
Hot air of 8 kg / cm ² ) is blown to remove excess solder applied and to make the solder layer uniform. In recent years, in the solder coating process for printed wiring boards,
It is required to form a solder layer having a uniform thickness on the surface of a predetermined portion of the printed wiring board for reasons such as stabilization of sitting of the IC chip on the printed board and prevention of contact failure.

However, in the conventional solder coating method,
While the printed wiring board is always pulled up at a constant speed, hot air with a constant pressure is blown over the entire area from the top to the bottom of the solder application surface. Due to its own weight, the deposited solder always flows from the upper part to the lower part of the solder application surface and accumulates in the lower part, and the solder solidifies with time. As a result, the thickness of the solder layer becomes thinner in the upper part and thicker in the lower part, and there is a problem in that the thickness of the solder layer as a whole becomes unacceptable and uneven.

Further, in a method of forming a resist with a peel coat ink or the like on a portion where the solder is left and fusing the partially left solder, when peeling the resist such as the peel coat ink before the fusing, Ink gets stuck in component holes and through holes for mounting components, and it is necessary to remove ink that has been manually clogged.
However, there is a problem that workability is extremely low. There is also a method of laminating a dry film as a resist for peeling the solder, but wrinkles are more likely to occur during lamination, resulting in resist failure, and the solder that should be left when peeling the solder is peeled off. There was a problem.

[0009]

That is, according to the present invention, a copper clad laminate is etched by using solder as an etching resist to form an outer wiring layer, and the solder used as the resist is peeled off to obtain a wiring pattern. In the method for producing a multilayer printed wiring board, a dry film is vacuum laminated on a wiring board after the formation of the wiring layer after the etching step by a vacuum laminating machine, and the dry film is formed into a pattern so that the dry film remains at a desired portion. A method for manufacturing a printed wiring board, which comprises forming a resist and then partially leaving the solder by using the dry film as a resist when the solder is peeled off.

[0010]

According to such a manufacturing method, solder is formed by electrolytic plating, etching is performed by using the solder plating as an etching resist, and after forming an outer wiring layer, a dry film is vacuum laminated by a vacuum laminator machine to form a resist. Since the resist is formed, the resist can be formed with high accuracy, and thus the solder can be surely left. Then, by heating the printed wiring board to melt the solder and homogenize the solder, the thickness of the solder such as pads for mounting the electrical mounting components (for example, IC package) of the printed wiring board is uniform. It is possible to stabilize the sitting of the IC chip on the printed circuit board.
The contact failure can be prevented.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 to 3 are manufacturing process diagrams of a printed wiring board of the present invention. 1 is a plan view of a printed wiring board when an outer layer pattern is formed by a dry film in an embodiment of the present invention, and FIG. 2 is a plan view of a printed wiring board after etching,
FIG. 3 is a plan view of a printed wiring board in which a dry film is vacuum laminated to form a resist. The present invention relates to an inner layer circuit board having an electric wiring layer formed of a copper foil, an inner layer circuit board and an outer layer circuit board, which have been laminated by heating and pressurizing the inner layer circuit board with an outer layer copper foil through a prepreg. To form a plated layer on the surface of the laminated body and on the inner wall surface of the through hole by performing electroless plating and electrolytic cylinder plating to cover the inner wall surface of this through hole To do.

Next, as shown in FIG. 1, a photoresist (3) is formed on the upper surface of the plating except for the electronic component mounting pad (1), a part around the through hole, and a wiring layer forming portion (2).
Is formed in a pattern, and copper is thickly applied to a portion exposed from the photoresist layer by copper sulfate plating in a portion to be a wiring pattern of an outer layer circuit. Then, solder is formed on the copper surface by electrolytic plating at 1 A / dm ² for 25 minutes to form a 20 μ solder layer, and the photoresist (3) is peeled off to remove the electronic component mounting pad and through hole. Except for the wall surface and a part of the periphery and the portion where the wiring layer is formed, the outer wiring layer is formed by etching as shown in FIG. At this time, the solder having a thickness of 20 μm is a solder thick film necessary for obtaining an effective solder thick film when the fusing is performed later. Further, when mounting an electronic mounting component on the surface, a method is usually used in which cream solder is placed on a pad, leads of an IC package or the like are placed on the pad, and the cream solder is once melted to be soldered. However, in the case of this embodiment, since the thickness of the solder is thick and uniform, cream solder is not used, and the solder previously thickly coated on the printed wiring board can be once melted and mounted.

Printed wiring board (4) after etching
Overlaid with a dry film, a negative film from which the portion of the solder to be left is removed is overlaid, and a vacuum laminator machine is used to bring the printed wiring board and dry film into close contact with each other at a temperature of 85 ° C. Laminate with a platen (silicone lever) for 60 seconds.
Next, it is exposed with a light amount of 60 mJ and developed to form a resist (6) around the pad (1) and the through hole (5) for surface-mounting the electronic component as shown in FIG.
At this time, if the dry film is not adhered, the accuracy of the resist will deteriorate and the resist will not remain on the pad reliably, so that the solder necessary for solder peeling will be removed or the resist will remain on the conductor near the pad. As a result, the solder remains, which may cause a short circuit during fusing. Since the accuracy of the resist is also important from the above, it is possible to reliably set the pad and the resist by adhering the dry film in a vacuum state, and it is possible to improve the accuracy of the resist. Also, the problem of wrinkles during lamination can be solved by using a vacuum laminator machine.

As described above, since the dry film is superposed on the printed wiring board by using the vacuum laminator machine, the resist can be accurately formed even if the width of the pad for surface mounting the printed electronic mounting component is narrow. Therefore, the solder can be surely left.

In the printed wiring board on which the resist is formed, the solder in other portions including the wiring layer forming portion (2) is dissolved and removed. Then, when the resist (6) is peeled off with a sodium hydroxide solution or a potassium hydroxide solution like peeling of a dry film used for normal patterning, a pad for surface-mounting electronic mounting components and Solder remains on the inner wall surface of the through hole (5) and its periphery, and a printed wiring board in which copper is exposed in the wiring pattern is obtained. When the resist is peeled off by the above method, the resist does not remain in the through hole (5).

However, the above-mentioned solder is used as a resist for etching during the formation of the outer layer wiring pattern, and the surface is roughened during etching. Therefore, the solder is once melted to flatten the surface. In addition, by melting the solder, short circuit between pads due to overfilled solder fillet is prevented, rust on the side wall of the pad is prevented, and a eutectic solder structure of tin and lead is used for solder wetting. Improve sex.

For the above reasons, the printed wiring board has two
The solder is once melted by heating for 5 seconds at a temperature of 40 ° C., and fusing is performed. Then, a solder resist is applied to the outer layer surface excluding the periphery of the pad (1) and the through hole (5) for surface mounting the electronic mounting component.

[0018]

As described above, according to the present invention, the conventional method of dipping the printed wiring board in the solder bath in which the solder is once peeled and then melted again and pulled up in the vertical direction is adopted. Instead, the solder formed by electrolytic plating is selectively peeled off to leave only the necessary portion, and the solder is fused so that the thickness of the solder becomes uniform, and when the surface mount component such as an IC package is mounted, It does not cause scratches and does not cause poor continuity. Furthermore, in order to leave only the necessary part of the solder, the dry film is laminated by the vacuum laminator machine to form the resist, so the solder can be left with good accuracy, and when the resist is peeled off, Since the resist is peeled off in the same manner as the dry film peeling, the resist does not remain in the through holes, so that it is not necessary to manually remove the resist as in the conventional case, and the workability is improved.

[Brief description of drawings]

FIG. 1 is a plan view of a printed wiring board in the manufacturing process of the present invention.

FIG. 2 is a plan view of the printed wiring board in the manufacturing process of the present invention.

FIG. 3 is a plan view of the printed wiring board in the manufacturing process of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Pad 2 ... Wiring layer formation site 3 ... Photoresist 4 ... Printed wiring board after etching 5 ... Through hole 6 ... Resist

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshihiro Momota 1-5-1, Taito, Taito-ku, Tokyo Toppan Printing Co., Ltd. (72) Hiroshi Shibato 1-5-1, Taito, Taito-ku, Tokyo Toppan Imprint Co., Ltd.

Claims (1)

[Claims] 1. A method for producing a multilayer printed wiring board, wherein a copper clad laminate is etched with solder as an etching resist to form an outer wiring layer, and the solder used as the resist is peeled off to obtain a wiring pattern. A dry film is vacuum-laminated on the wiring board after the formation of the wiring layer after the etching step by a vacuum laminating machine, a resist is formed in a pattern so that the dry film remains at a desired portion, and then the solder is peeled off. A method for manufacturing a printed wiring board, characterized in that the dry film is used as a resist to partially leave solder.