JPH01321683A - Manufacture of printed wiring board - Google Patents

Abstract

PURPOSE:To prevent the generation of defectives due to resin residue completely, to obviate even the deterioration of solderability and to form an SR even to the small section of a pad clearance by forming an imidazole film onto a through-hole and a circuit pattern and applying an insulating resin. CONSTITUTION:A substrate 1 to which a through-hole 2 and a circuit pattern 3 are shaped is dipped into an imidazole solution, imidazole films 4 are applied and formed onto the through-hole 2 and the circuit pattern 3, the circuit pattern 3 on the surface and rear of the substrate is buried with a first insulating resin 5, and the insulating resin 5 on the circuit pattern 3 is removed. The imidazole films 4 applied onto the through-hole 2 and the circuit pattern 3 are dissolved and gotten rid of, and sections except the inside of the circuit pattern 3, a pad for mounting a part, the through-hole for mounting the part and a land are coated with a second insulating resin 6. Accordingly, the resin as a solder mask (SR) is not left onto the through-hole for mounting the part and the land and the pad, no defective is generated due to resin residue, solderability is not also deteriorated, and the SR can also be formed to the small section of a pad clearance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a printed wiring board, and more particularly to a method for forming an insulating resin that covers circuit patterns other than through holes, lands, and pads for mounting components.

[Conventional technology]

Conventionally, an insulating resin so-called solder mask (hereinafter abbreviated as SR) is used to cover a desired portion of a circuit pattern on a printed wiring board.
The method of forming was as follows.

First, as shown in FIG. 2(b), a liquid (dry film) photosensitive resin is applied to the entire front and back surfaces of the substrate 1, as shown in FIG. The photosensitive resin layer 7 is coated and dried (laminated).
After forming the photosensitive resin layer 7, the photosensitive resin layer 7 is exposed to light through a mask, developed, and further subjected to ultraviolet irradiation or heating, or a combination of ultraviolet irradiation and heating to harden the developed photosensitive resin layer. Then, as shown in FIG. 2(C), <SR.

They formed 8. Another method is to screen print a thermosetting or ultraviolet curing resin on the front and back surfaces of the board on which through holes and circuit patterns are formed, and then harden the resin. It is being done.

[Problem to be solved by the invention]

The conventional SR forming method for printed wiring boards described above has the following drawbacks.

1) In the so-called photo method using a photosensitive resin, a liquid photosensitive resin is applied to the entire front and back surfaces of the substrate, and then exposed to light.
This is a method of developing and removing unnecessary parts of the photosensitive resin on component mounting pads and through-hole lands. In this method, photosensitive resin may remain on the pads and lands, causing a decrease in yield and poor soldering properties.

(2) Align the screen plate or mask film to the mounting pad and through-hole land, and
Although an R pattern is formed, in consideration of the expansion and contraction of the screen plate and mask film and alignment accuracy, the design is usually such that a relief of 0.1 to 0.2 mm is provided on one side from the pad or land. However, due to the high density of mounted components,
For example, although the gap between pads has become smaller to 0.2 mm, it is now required to form an SR between pads in order to prevent solder bridging between pads during mounting. However, in the conventional SR forming method, the pad gap is 0.2 m.
For high-density packaging such as m, it is difficult to print SR between pads without covering the pads with SR.

The purpose of the present invention is to prevent resin that becomes SR from remaining on through-holes, lands, and pads for component mounting, thereby eliminating the occurrence of defects due to resin residue, achieving a high yield, and causing no deterioration in soldering properties. Another object of the present invention is to provide a method for manufacturing a printed wiring board that can form an SR even in a small area between pads and can handle high-density packaging.

[Means to solve the problem]

The method for manufacturing a printed wiring board of the present invention includes the steps of: immersing a substrate on which through holes and a circuit pattern are formed in an imidazole solution, and depositing an imidazole film on the through hole and circuit pattern; After embedding the circuit pattern with the first insulating resin, a step of removing the insulating resin on the circuit pattern, a step of dissolving and removing the imidazole coating deposited on the through hole and the circuit pattern with an acid solution, and the circuit The method includes a step of covering portions of the pattern other than the component mounting pads, component mounting through holes, and lands with a second insulating resin.

〔Example〕

Next, the present invention will be explained with reference to the drawings. FIGS. 1(a) to 1(f) are longitudinal cross-sectional views of a printed wiring board shown in a process for explaining one embodiment of the present invention.

First, the substrate 1 on which the through holes 2 and the circuit pattern 3 are formed as shown in FIG. 1(a) is immersed in an imidazole solution, and the imidazole coating 4 is applied on the through hole 2 and the circuit pattern 3 as shown in FIG. 1(b). Adhesion is formed. Next, as shown in FIG. 1C, a liquid photosensitive first insulating resin is applied to the entire front and back surfaces of the substrate 1 and dried. Next, the first insulating resin layer 5 is formed by exposing the first insulating resin in a portion other than the inner wall of the through hole 2 and the land near the corner through a mask, and removing the unexposed portion by development. The mask used in this case is desirably designed to have a dot having the same diameter as the diameter of the through hole 2 or 0.2 mm larger than the diameter of the through hole. Next, Figure 1 (d
), the front and back surfaces of the substrate 1 are polished flat to remove the first insulating resin layer 5 on the circuit pattern 3. Next, board 1
is immersed in a 10% hydrochloric acid solution to dissolve and remove the imidazole coating inside the circuit pattern 3 and through holes 2 as shown in FIG. 1(e). Next, a thermosetting or ultraviolet curable insulating resin is formed on the parts other than through holes, lands, and pads for component mounting by screen printing, or a photosensitive insulating resin is applied, exposed and developed, and the first Figure (f)
A desired printed wiring board was obtained by forming the second insulating resin layer 6 as shown in FIG.

Next, other embodiments of the present invention will be described with reference to FIGS. 1(a) to (f). First, as shown in FIG. The substrate 1 is immersed in an imidazole solution, and an imidazole coating 4 is formed on the through holes 2 and the circuit pattern 3 as shown in FIG. A thermosetting first insulating resin is screen printed on the entire surface of the through hole 2 except for the lands near the corners and the inner wall, and then hardened to form the first insulating resin layer 5 as shown in FIG. 1(c). The screen used is
The first insulating resin is designed to prevent the first insulating resin from entering the inner wall of the through hole 2 by providing a dot with a size that is the same diameter as the drill diameter of the through hole 2 or about 0.3 mm larger than the drill diameter. Thereafter, as in Example 1, as shown in FIG. 1(d), the first insulating resin layer 5 on the circuit pattern 3 is removed, and the first
Removal of imidazole film as shown in Figure (e), Figure 1 (f)
The second insulating resin layer 6 was formed as described above to obtain a desired printed wiring board.

〔Effect of the invention〕

As explained above, the present invention has the following effects.

<1) Since an imidazole film is formed on the through-holes, lands, and pads for component mounting, and the SR resin is not directly applied, there is no SR resin left, so there are no defects due to resin residue, and a high yield can be obtained. Soldering can also solve the problem of undercoating.

(2) Since the imidazole coating is used to form small gaps between pads that are difficult to form using conventional manufacturing methods, SR can be formed without being applied to the pads, making it possible to form printed wiring boards that are compatible with high-density packaging. It is possible to manufacture

[Brief explanation of the drawing]

1(a) to 1(f) are cross-sectional views of a printed wiring board shown in order of process for detailed explanation of the present invention, and FIGS. 2(a) to 2(f)
(C) is a cross-sectional view of a printed wiring board shown in order of steps to explain a conventional method for manufacturing a printed wiring board. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Through hole, 3... Circuit pattern, 4... Imidazole coating, 5... First insulating resin layer, 6... Second insulating resin layer, 7 ...Photosensitive resin layer, 8...SR.

Claims (1)

[Claims] A step of immersing the substrate on which the through holes and the circuit pattern were formed in an imidazole solution and forming an imidazole film on the through hole and the circuit pattern, and embedding the circuit pattern on the front and back surfaces of the substrate with a first insulating resin. After that, a step of removing the insulating resin on the circuit pattern, and a step of dissolving and removing the imidazole coating deposited on the through holes and the circuit pattern with an acidic solution,
A method for manufacturing a printed wiring board, comprising the step of covering portions of the circuit pattern other than pads for component mounting, through holes for component mounting, and lands with a second insulating resin.