JPS59149091A - Both-side printed circuit board and method of producing same - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a through-hole structure of a so-called copper-clad laminate in which metal foil is laminated to an insulating substrate. The present invention relates to a finely formed double-sided printed wiring board and a manufacturing method thereof.

(Conventional configuration and its problems) In recent years, there has been a growing trend toward smaller, lighter, and thinner consumer devices. Many of the parts that make up these devices have been developed in line with the above trends, and it can be said that they have made significant contributions to various devices. In particular, resistors and capacitors were made into chips, spurring further miniaturization. On the other hand, although improvements have been made to miniaturize printed wiring boards in line with these trends, full satisfaction has not yet been achieved.

In general, double-sided printed wiring boards are made by using a drill or the like to drill through holes in an insulating board with metal foil (copper foil) pasted on both sides of the board. After attaching the conductor, electrolytic plating is applied to ensure the reliability of the inner wall conductor. After applying the required amount of plating film to the inner wall,
Etching resist is provided on the entire surface of the copper foil. At this time, in order to prevent the conductor plated on the inner wall of the hole from being etched, it is necessary to fill the hole with synthetic resin or to protect the plating film on the inner wall of the hole by a method called tenting with a film such as a dry film. Next, either an elachinbre cyst is printed on the desired E-turn using a screen printing method, or a photographic film of the desired Q-turn is brought into close contact with a substrate laminated with a photosensitive resist in advance, and then exposed and developed. The unnecessary parts are removed using the etching method. However, according to this method, it is difficult to obtain the aforementioned fine patterns, for example, a line width of around 100 microns. By electrolytic plating, a plating film is formed on the inner wall of the hole, and at the same time, the copper foil on both sides is plated to the same thickness as the inner wall of the hole.

Moreover, in this case, the peripheral effect (creepage effect) of electrolytic plating
Due to this, there is a phenomenon in which the plating film is thinner at the center of the substrate and becomes thicker as it approaches the periphery. Therefore, when etching, the etching rate is the same for all parts, so the center reaches the underlying insulating substrate faster, but
A phenomenon occurs in which copper foil still remains in areas where the surrounding plating film is thick. However, if you leave the board in the etching solution until the periphery is completely etched, a phenomenon called side etch will occur in the center, ensuring the necessary line width, or in some cases causing lines (conductors). may even disappear. To solve this problem, efforts are being made to develop a method for uniformly plating the entire substrate, but no method or method that is completely satisfactory has yet been found. Therefore, at present, for products that require high precision and fine patterning, it is possible to electrolytically plate a board that is two to four times the required board area, and use only the center part as a product, for example, or use an electrolytic plating machine to make the plate thinner. Or, a thin copper foil is used to cover the insulating substrate. Doing this will extremely deteriorate the characteristics of the through hole. In addition, it is necessary to protect the plating film that was previously plated on the inner wall of the hole during etching, and methods of protecting the hole by filling it with synthetic resin or tenting it with a photosensitive etching resist film are adopted. .

In the former case, with this method, the holes drilled on the entire surface of the substrate must be completely filled, and if even one hole is incomplete, it will be defective and the product yield will be extremely degraded. In the latter case, since the resist is in the form of a film, it covers the entire surface of the board, reducing the number of imperfections and defects, but heat is added during the process of exposing and developing this film, so copper foil The shrinkage of the film differs between the part that is in close contact with the hole and the part that covers the hole, which may cause cracks to form around the hole. There is also a phenomenon in which the plating film on the inner wall of the reservoir hole is etched away.

Double-sided printed wiring boards made by the above method are generally called copper through-hole boards, and they suffer from poor etching accuracy due to uneven thickness of electrolytic copper plating, and (5) poor product quality due to incomplete protection of the plating film on the inner walls of the holes. There are problems such as deterioration of the temperature and increase in the number of man-hours required.

A common method to eliminate these drawbacks is to use a solder through-hole board. This is the same process up to electrolytic copper plating as described above. Solder plating is used as an etching resist. In this case, a reverse pattern of the desired pattern is printed on the entire surface of the copper foil, and this is used as a mesh resist.
In this method, solder plating is applied to areas where there is no resist, the resist is peeled off, and then the copper is etched using the previous solder as a resist. This method basically has the same problems as the previous method, but it is not necessary to protect the inner wall of the hole.

(Objective of the Invention) It is an object of the present invention to provide a completely new fine patterned printed wiring board and a method for manufacturing the same, which eliminates the drawbacks of the above-mentioned printed wiring board manufacturing method.

(Structure of the Invention) (6) The double-sided printed wiring board and the manufacturing method thereof of the present invention provide a double-sided printed wiring board in which circuit conductors formed on both sides of a laminate are electrically connected by through-holes, in which only the inner wall of the through-hole is A double-sided printed wiring board, which is a through-hole consisting of three layers: electroless copper plating, electrolytic copper plating, and electrolytic solder plating, and a double-sided copper-clad laminate that is completely coated with a synthetic resin face on both sides to form a metsukiresist. a step of drilling a through hole at a predetermined position; a step of activating the inner wall of the through hole and sequentially performing electroless copper plating, electrolytic copper plating, and electrolytic solder plating; a step of peeling off the metal resist; This method of manufacturing a double-sided printed wiring board includes the steps of forming and etching an elastomer cyst on both sides of the foil, and peeling off the etching resist.

The most distinctive feature of the present invention is that a metal resist is provided on the entire surface of the copper foil before forming the through holes, eliminating unevenness in the plating thickness on the copper foil surface by electrolytic copper plating, and obtaining a fine pattern with good accuracy. be.

(Description of Examples) The figure shows a method for manufacturing a double-sided printed wiring board according to the present invention. (A) shows copper foil 2 on both sides of a normal laminate 1.
is formed, the entire surface is coated with synthetic resin, and a mesh resist 3 is provided (B)
. This synthetic resin needs to be a synthetic resin with emphasis on alkali resistance.

This is because electroless steel plating exhibits alkalinity with a pH of 11 to 125, but plating with steel only requires electrical conduction between the copper foils on both sides, so long as it has short-term alkali resistance. , electrolytic copper plating is PHL l~1
The plating film must have a thickness of 10 to 30 microns and must maintain sufficient electrical reliability. This is because the plating time is longer than that of electroless plating. On the other hand, solder plating has a pH of 1 to 2.
However, since it lasts for a short time, acid resistance is not required. However, the method of forming the metskiresist film may be a coating method, or a method of laminating a film-like material may be used. (C) shows the through hole 4 drilled. next(
As shown in D), electroless copper plating film 6, electrolytic copper plating film 7, and electrolytic solder plating film 8 are applied in this order, and the metal resist is removed (E).

Next, an elachinbre cyst 5 is formed by screen printing (F). It is necessary to make the diameter smaller than the diameter of the iR pattern through hole 4 in the etching resist 5 so that the copper foil underneath is completely covered. Next, apply the specified etching solution (
For example, a circuit pattern is formed by etching with ferric chloride or cupric chloride (G).

〔Example〕

A double-sided copper-clad laminate with a thickness of 1.6mm made by laminating 35 micron copper foil on a glass epoxy base material was used, and a phenoxy resin was used as the synthetic resin face using MEK.
The solution was dissolved in a 60% solution and coated to a thickness of 25 microns using a Shimodo (7) rubber roll coater. After drying, it was further coated on one side to the same thickness, and after drying, a through hole was made at a predetermined position using a carbide drill with a diameter of 0.8 mm. The entire substrate was immersed in a 12% aqueous solution of stannic chloride for 2 minutes (9), taken out, and immediately immersed in an aqueous solution of baradium chloride 4 to activate the inner walls of the through holes. Next, it was immersed in an electroless copper plating bath shown in Table 1 for 10 minutes to form an electroless copper plating layer.

Table Plating bath composition After washing with water, copper plating was performed using the electrolytic copper plating bath shown in the table to make the through holes more complete, and further solder plating was performed using an electrolytic solder plating bath to obtain an etching resist. Next, the substrate was immersed in a container heated to 30°C in an isostatic mixture of MEK and trichlorethylene (10) to peel off the Metsukiresist, and washed with a 3% aqueous solution of hydrochloric acid and smoked with water. Next, the desired grooves and turns are formed on a 250-mesh stainless steel screen, and an etching lens ink containing high acid value maleic acid resin as the main component is printed.
Drying was performed at 90°C for 5 minutes. Furthermore, one side was printed in the same manner, and unnecessary portions of the copper foil were removed using an aqueous solution of ferric chloride to form a circuit board. This confirms that the entire surface of the board is etched without any uneven etching, and the through-holes are completely etched without any protection, with no damage to the underlying copper plating due to the solder plating. It was also confirmed that it has the following functions.

(Effects of the Invention) As described above in detail in the examples, the present invention solves the problem of uneven etching time, which was the biggest problem in the conventional manufacturing process of double-sided printed wiring boards, that is, the copper plating caused by the copper plating of the holes in the through holes. This solves the difficulty in forming fine patterns due to uneven plating thickness on foil. According to the present invention, in the case of a 35 micron copper foil, a pitch of 300 microns can be obtained, and in the case of an 18 micron copper foil, a pitch of 250 microns can be obtained, and if a photographic method is used in addition to screen printing, a pitch of 200 microns can be obtained. We have also confirmed that it is possible. This is because, as mentioned above, there is no copper plating on the copper foil surface and only the initial thickness of the copper foil, so it is uniform over the entire surface and the etching time can be made constant over the entire surface, so it can be formed with high accuracy regardless of whether the wire is thick or thin. It is. Further, due to the structure of the through-hole according to the present invention, the inner wall is plated with solder, and the solder is stable in ordinary etching solutions and will not be dissolved or corroded. Therefore, unlike conventional manufacturing methods, there is no need to fill the through holes with synthetic resin or tent with Renost film.

In the future, printed wiring boards will be indispensable for devices to become smaller, thinner, and lighter, so fine patterning is an element that cannot be ignored. The present invention makes it possible to easily obtain fine patterns in printed wiring boards based on this background, and is simpler than conventional manufacturing methods, making a great contribution to the industry.

[Brief explanation of the drawing]

The figure is a diagram showing a method for manufacturing a double-sided printed wiring board according to the present invention. DESCRIPTION OF SYMBOLS 1... Laminate board, 2... Copper foil, 3... Metsukiresist coating, 4... Through hole, 5... Etching resist, 6... Electroless copper plating coating, 7... Electrolytic Copper plating film, 8... Electrolytic solder plating film. (13) Procedural Amendment Form C) Revenue Stamp Amount Yen June 13, 1980 Mr. Kazuo Wakasugi, Commissioner of the Patent Office], Indication of Case Patent Application No. 1982-22948 2, Issued
Name of Double-Sided Printed Wiring Board and Its Manufacturing Method 3, Relationship with the Amendment Case Applicant Address 1006 Kadoma, Kadoma City, Osaka Prefecture Name
(582) Representative of Matsushita Electric Industrial Co., Ltd.
Toshihiko Yamashita Phone 03 (431) 811
No. 1 (representative) 5. Date of procedural amendment order: May 11, 1982 (Shipping date: May 31, 1982)
6. Number of inventions increased by amendment 08. Contents of amendment (1) "(4)" in the third line of page 8 of the specification is corrected to read "Figure 1." (2) Same line 6 r (B) J in Figure 2)” is corrected. (3) Same line 20 r (C) Correct J to "Figure 3". (4) On page 9, line 1, ``no'' is corrected to read ``Figure 4''. (5) Same line 3 r (E) Correct J to "(Figure 5)". (6) Correct “Axis” in line 5 of the same to “(Figure 6)”. (7) Same line 10 r (G) J as “(Figure 7)”
I am corrected. (8) Page 13, line 5 “The diagram is...
" is corrected to "Figures 1 to 7 are...". (9) Correct the drawing as shown in the attached sheet. Above 12 = Figure 1 Figure 7-

Claims (2)

[Claims] (1) In a double-sided printed wiring board in which circuit conductors formed on both sides of a laminate are electrically connected through through holes, only the inner walls of the through holes are coated with electroless copper plating, electrolytic copper plating, etc.
A double-sided printed wiring board characterized by a through hole made of three layers of electrolytic solder plating. (2) The process of coating the entire surface of a double-sided copper-clad laminate with a synthetic resin face to form a metal sheet, the process of drilling through holes at predetermined positions, and the process of activating the inner walls of the through holes to perform electroless copper plating and electrolytic copper plating. The method is characterized by comprising a step of sequentially performing plating and electrolytic hunter plating, a step of peeling off the etch resist, a step of forming and etching an etching resist on both sides of the copper foil, and a step of peeling off the etching resist. A method for manufacturing a double-sided printed wiring board. C1)