JP3130707B2 - Printed circuit board and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed circuit board and a method for manufacturing the same, and more particularly, to a printed circuit board in which solder connection portions on the surface of a substrate including through holes are coated with electroless solder plating and a method for manufacturing the same.

[0002]

2. Description of the Related Art When soldering electronic component terminals to a printed circuit board, the solder is supplied to the soldered parts of the printed circuit board by various methods. Alternatively, a method of performing solder plating by electroless plating is known.

[0003] Among them, the electroless solder plating method is a method of electroplating or a solder coating method (a solder coating method of dipping a substrate in a molten solder bath, pulling it up, and blowing off excess solder to form a solder alloy film on the substrate). Some methods have been conventionally proposed as an excellent method capable of forming a more uniform film than a method such as a coat, a solder leveler, etc.).

(1) One of them is a manufacturing method in which electroless solder plating is combined with a solder coating method. The printed circuit board surface after the formation of the wiring circuit is brought into contact with molten solder (solder coating method) to form a solder alloy film on the surface of the copper conductor circuit on the board, and the copper conductor circuit is removed except for the land in the through hole and its opening. In this method, a solder resist is formed on the entire surface of the substrate including the upper portion, electroless solder plating is performed using the solder resist as a mask, and electroless solder plating is selectively performed on the inner wall of the through hole.

(2) As a method similar to the above (1), copper plating is performed on the inside of the through hole and on the surface of the copper conductor circuit on the substrate, and then electroless solder plating is performed on them, and then the copper plating is performed on the substrate. The molten solder is brought into contact with the surface of the copper conductor circuit plated with electrolytic solder (solder coating method) to form a thick solder layer on the copper conductor circuit.

(3) In this manufacturing method, after copper plating is performed on a copper conductor circuit surface in a through hole and on a substrate, electroless solder plating is performed thereon, and copper is removed except for lands in the through hole and its opening. In this method, a solder resist is formed on the entire surface of the substrate including the conductor circuit, and the solder resist is used as a mask to perform electric solder plating, and the electric solder plating is selectively formed on the inner wall of the through hole and the land.

As related to these techniques, for example, Japanese Patent Application Laid-Open Nos. Sho 52-76833 and
-85368 and JP-A-64-82692.

[0008]

However, in the example of the above (1), the process is very complicated due to the combination of the contact of molten solder (solder coating) and the electroless solder plating, and the molten solder is applied to the substrate surface. Even if a solder layer is formed by contacting the copper conductor circuit, the solder may easily penetrate into the through-holes due to height variations, etc. Yes, not practical. In addition, since a solder layer is formed on the copper conductor circuit on the board surface covered with solder resist,
Due to the curing heat at the time of forming the resist and the heating of the flow solder at the time of mounting the components, the underlying solder layer is dissolved, the resist is peeled off, and the insulating properties are significantly deteriorated. Furthermore, since the electroless solder plating in the through-holes is a replacement type from the time of its establishment, a thick copper plating film must be formed as a base treatment from the beginning in consideration of this in advance, so that high-density circuit creation Not suitable for In this type of conventional technology, the processing accuracy of the circuit pattern is 100 to 120 μm at most in terms of the wiring width, and it is impossible to further reduce the line width.

Also, the example of the above (2) has a step of forming a solder layer by bringing molten solder into contact with the copper conductor circuit on the substrate surface as in the case of (1). There is a problem of clogging of holes due to molten solder, and there is a problem of making a high-density circuit by increasing the thickness of a base copper plating film in consideration of electroless solder plating in through holes.

In the case of (3), both copper plating and solder plating are a combination of electroplating and electroless plating, and the process becomes very complicated. Also in this example, prior to electroless plating, the underlying copper plating was subjected to electrolytic copper plating following electroless copper plating to increase the film thickness. There is a problem in creating a density circuit. Further, since the electroless solder plating layer is formed on the copper conductor circuit on the surface of the substrate covered with the solder resist, the curing heat during the formation of the resist and the component mounting are the same as in the above (1). There is a problem in that the underlying solder layer dissolves due to the heating of the flow solder at that time, the resist is peeled off, and the insulating characteristics are significantly deteriorated.

Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, and to make the most of the feature that electroless solder plating is superior in forming a uniform film, to realize a high-density wiring pattern. It is an object of the present invention to provide an improved printed circuit board capable of forming a printed circuit board and a method for manufacturing the same.

[0012]

The object of the present invention is to provide a through-hole whose inner surface is electrolessly solder-plated on copper plating, a copper-plated layer on the copper foil around the opening, and one of the copper-plated layers.
And replace the surface layer with electroless solder plating
A land having a coated electroless solder plating layer, a circuit portion in which copper foil on the substrate surface is patterned by selective etching, and a solder in which the surface of the substrate outside the solder connection region including on the copper foil circuit portion is tightly covered. This is achieved by a printed circuit board having a resist. It is desirable that the thickness of the electroless solder plating be 0.5 μm to 10 μm.
Since the circuit portion on the substrate covered with the solder resist is formed of a thin copper foil pattern, a high-definition wiring pattern can be formed by selective etching. The solder resist is preferably made of an epoxy resist in consideration of heat resistance and adhesion. Since the solder resist directly covers the copper foil circuit portion, the problem of resist peeling does not occur even when heating at the time of forming the resist or at the time of solder connection. As described above, the problem of resist peeling has arisen because a solder layer has conventionally been interposed on a circuit.

The object of the present invention is to form a through-hole in a double-sided copper-clad substrate and a catalyst applying step, and then selectively etch the copper foil on the substrate surface using a predetermined resist mask to form an opening in the through-hole. A step of forming a land on the periphery of the part and a wiring circuit pattern in the other region, and a step of forming a land and a wiring circuit pattern on the substrate surface,
A step of forming a solder resist pattern by tightly covering at least the wiring circuit pattern except for a region requiring solder plating, and a post-process in the through hole and on the land using the solder resist pattern as a mask.
Electroless copper plating thick film and a step of selectively forming, by performing an electroless solder plating on the electroless copper plating film, the electroless copper exceeding the thickness corresponding to the solder plating film thickness of in formation Leave part of the plating film in front of its surface
The present invention is also achieved by a method for manufacturing a printed circuit board having a step of performing displacement plating with the solder plating film.

Further, a step of forming a solder resist pattern on the surface of the substrate having a through hole whose inner surface is plated with copper and a wiring pattern plated with copper on the surface of the copper foil, excluding a region requiring solder plating. And, using the solder resist pattern as a mask, a step of selectively forming an electroless copper plating film having a thickness corresponding to the solder plating film thickness, and then performing electroless solder plating on the electroless copper plating film. And substituting the selectively formed electroless copper plating film with a solder plating film.

[0015]

[Effect] Unlike electroplating, electroless solder plating is deposited on an independent circuit with a uniform thickness, so that surface treatment with less surface irregularities can be obtained for component mounting. In addition, since the electroless solder plating proceeds while replacing the underlying copper, the amount of the underlying copper dissolved during the solder plating is previously deposited by the electroless copper plating during the electroless solder plating. Furthermore, in the electroless solder plating and the electroless copper plating, the unnecessary portion of the plating on the substrate is masked with a solder resist, but the solder resist used for this is not electrolytically eroded by both of these processing solutions. ,
Use solder resist with high chemical resistance. The epoxy resist satisfies these conditions.

[0016]

An embodiment of the present invention will be described below with reference to the drawings. Embodiment 1 FIG. 1 is a cross-sectional view of a main part of a printed circuit board showing a manufacturing process according to an embodiment of the present invention. Hereinafter, steps in a case where the present invention is applied to a general method of manufacturing a printed circuit board by a subtractive method will be described.

First, as shown in FIG. 1 (a), a copper-clad laminate (specifically, a copper foil bonded to an insulating plate) or a copper-clad laminate with an inner layer preliminarily formed by laminating an inner circuit is used as a substrate. The through hole 2 is provided at a predetermined position in the substrate by a known perforation means such as a drill or a laser beam.

Next, as shown in FIG. 1 (b), the entire surface of the substrate including the inner wall of the through hole 2 is subjected to a catalyst treatment and a chemical copper plating treatment by a commonly used process, and then a necessary minimum amount of a wiring conductor is obtained. A copper plating 3 having a minimum thickness is deposited by electrolytic plating or thick electroless copper plating.

Next, as shown in FIG. 1C, in order to form a necessary circuit, a portion to be a circuit is masked by a tenting method using a dry film or the like, and unnecessary copper other than the circuit is etched in an etching step. Is dissolved and removed.

Next, as shown in FIG. 1 (d), only a part (for example, an inner wall of the through hole and a land) necessary at the time of component mounting is exposed, and a high chemical resistance containing an epoxy thermosetting resin as a component. The solder resist 4 is formed by a screen printing method. Note that the solder resist 4 can be formed by a so-called lithography technique using a photographic technique, and it is more preferable to manufacture a high-density printed circuit board.

Next, as shown in FIG. 1 (e), a commercially available thick electroless copper plating solution comprising an alkali, copper sulfate, a chelating agent or the like is required for the exposed copper portion. The copper plating 5 having a thickness to be deposited is deposited. The required thickness of copper plating is a thickness corresponding to the thickness of the solder plating formed in the subsequent electroless solder plating step.

Thereafter, as shown in FIG. 1 (f), using a commercially available electroless solder plating solution, for example, trade name “Solderposit XP-8955” manufactured by Shipley Far East Co., Ltd. The solder plating 6 is deposited until the thickness becomes equal to the thickness of the solder plating 6, and the copper plating 5 is replaced with the solder plating 6.

In this method, when the copper plating 3 is deposited on the entire surface in the step of FIG. 1B and simultaneously the thickness of the electroless solder plating 5 is also deposited, as shown in the step of FIG. As described above, double copper plating is not required, but when forming a circuit in the step of FIG. 1C, the thickness of the copper to be dissolved increases, which increases the cost and makes it difficult to form a high-density circuit. . If necessary, hot oil reflow or fusing is performed as a process for melting the solder, and the solder is completed. Thus, a high-density printed board having a wiring width of 70 μm was obtained.

<Embodiment 2> In this embodiment, a structure and a manufacturing method of a printed circuit board suitable for forming a wiring pattern having a higher density than that of Embodiment 1 will be described with reference to the process chart 2 shown below. is there. First, as shown in FIG. 2A, a copper-clad laminate or a copper-clad laminate with an inner layer in which an inner layer circuit is previously formed is prepared as a substrate 1, and a through hole 2 is provided at a predetermined position in the substrate. Is provided by a known perforation means such as a drill and a laser beam.

Next, as shown in FIG. 2B, a circuit is formed by applying a palladium-based catalyst to the entire surface including the inner wall of the through-hole and then forming a necessary circuit by a tenting method using a dry film. The portion is masked, and unnecessary copper foil other than the circuit is dissolved and removed in an etching process to form a circuit pattern.

Next, as shown in FIG. 2C, a high chemical resistance solder resist 4 mainly composed of an epoxy resin and having a shape exposing only a portion required for copper plating and a portion required for component mounting. Is formed by a screen printing method. At this time, as described in the first embodiment, the formation of the solder resist pattern can be performed by lithography.

Next, as shown in FIG. 2D, using a solder resist 4 as a mask, a commercially available thick plate made of an alkali, copper sulfate, a chelating agent, or the like is applied to an exposed portion of the copper plating that is required. Using an electroless copper plating solution, a copper plating 5 having a thickness obtained by adding the thickness of the solder plating deposited in the next step to the copper plating finally having a thickness required as a circuit conductor is deposited.

Finally, as shown in FIG. 2E, a commercially available electroless solder plating solution, for example, trade name "Solderposit XP-8955" manufactured by Shipley Far East Co., Ltd., was used again using the solder resist 4 as a mask. To deposit solder plating 6 having a required thickness. With this method,
It is not necessary to deposit copper plating twice (copper plating 3 and 5) as in Example 1, and the copper dissolution thickness (copper) when forming a circuit as shown in the step of FIG. (A foil), it is possible to obtain a low-cost, high-density printed circuit board. Finally, if necessary, hot oil reflow or fusing is performed as a process for melting the solder to complete the process. Thus, the wiring width of 60 μm
m was obtained.

As described above, the features of this example are as follows.
(1) The manufacturing process is shorter than that of Example 1 shown in FIG. 1 ((Electroless copper plating process (copper plating 3) in FIG. 1B is omitted), (2) Solder resist 4 covers The wiring circuit on the substrate is made of copper foil that was first adhered to the substrate without copper plating, and the etching process was completed in a short time because the target to be etched when forming the circuit was copper foil. A circuit pattern can be formed with high accuracy.

[0030]

As described above, the intended object can be achieved by the present invention. That is, it is possible to form a high-density wiring pattern by making the most of the feature that the electroless solder plating is excellent in forming a uniform film. In the prior art, the line width of the circuit pattern is 100 μm to 120 μm.
m was changed to 60 μm to 70 μm in the present invention.
Was made possible.

[Brief description of the drawings]

FIG. 1 is an essential part cross sectional view showing a manufacturing step of a printed circuit board according to one embodiment of the present invention;

FIG. 2 is an essential part cross sectional view showing a printed circuit board manufacturing process according to another embodiment;

[Explanation of symbols]

1 ... copper-clad laminate, 2 ... through-hole, 3 ... copper plating, 4 ... solder resist, 5 ... electroless copper plating,
6 ... Electroless solder plating.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akihito Kawakami 216 Totsuka-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Within the Information and Communication Business Department, Hitachi, Ltd. (72) Inventor Tohru Suzuki 3-chome, Sanbancho, Chiyoda-ku, Tokyo (72) Inventor Joji Tsuchiya Examiner, Takafumi Nakagawa, 3-8 Sanbancho, Chiyoda-ku, Tokyo (56) Inventor Takashi Nakagawa (56) References JP-A-4-239796 ( JP, A) JP-A-3-4595 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H05K 3/24 H05K 3/28 H05K 3/34 H05K 3/42

Claims (4)

(57) [Claims] 1. A a through hole inner surface is electrolessly solder plating on the copper plating, the surface layer leaving a portion of the copper plating layer Contact <br/> spare the copper plating layer on the copper foil of the opening peripheral edge Electroless solder plating layer where the part is replaced by electroless solder plating
Having a land having a pattern, a circuit portion in which a copper foil on the substrate surface is patterned by selective etching, and a solder resist which closely covers the surface of the substrate outside the solder connection region including on the copper foil circuit portion. substrate. 2. The thickness of the electroless solder plating layer is 0.5.
2. The printed circuit board according to claim 1, wherein the thickness of the printed circuit board is 10 to 10 [mu] m. 3. The printed circuit board according to claim 1, wherein said solder resist is composed of an epoxy-based resist. 4. A step of forming a through-hole in a double-sided copper-clad substrate and a step of applying a catalyst, and then selectively etching a copper foil on the surface of the substrate using a predetermined resist mask to form a through-hole around the opening. Land, a step of forming a wiring circuit pattern in other areas, and tightly covering at least the wiring circuit pattern on the surface of the substrate on which the lands and the wiring circuit pattern are formed, except for an area requiring solder plating. Forming a solder resist pattern, and using the solder resist pattern as a mask , forming a thick electroless copper plating film in the through hole and on the land, the thickness of which exceeds a thickness corresponding to a solder plating film thickness to be formed in a later step. selectively forming, by performing an electroless solder plating on the electroless copper plating film, leaving a part of the electroless copper plating film Process and PCB fabrication method comprising a replacing plating surface layer portion in the solder plating film.