JPH02253693A - Manufacture of printed wiring board - Google Patents

Abstract

PURPOSE:To eliminate remnants of plating resist and facilitate manufacture of a printed wiring board which has through-holes or via-holes having high contact reliability by a method wherein the parts of a photosensitive thin film covering the parts corresponding to piercing holes or recesses are cut off to form apertures beforehand. CONSTITUTION:After a photosensitive thin film for forming a plating resist film is formed on an insulting board surface, the parts of the photosensitive film corresponding to piercing holes or recesses for forming through-holes or via-holes are cut off to form apertures beforehand. As developer is made to penetrate into all over the insides of the piercing holes or recesses from the beginning of a development, resin films in the piercing holes or recesses can be dissolved and removed securely an quickly. With this constitution, remnants of the plating resist can be effectively eliminated and a printed wiring board which has patterns having high contact reliability, especially the small diameter through-holes or via-holes, can be manufactured.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a printed wiring board, and in particular, a method for developing a photosensitive resin thin film in which holes are formed in advance at locations corresponding to through holes, etc. This paper proposes a method for manufacturing printed wiring boards having through holes and via holes with excellent reliability by forming a plating resist and then plating.

[Conventional technology]

Conventionally, in the manufacture of printed wiring boards, when a conductor circuit is first formed on an insulating substrate by electrolytic plating or electroless plating, a photosensitive thin film for forming a plating resist is first formed on the insulating substrate, and then the conductor circuit is formed. A conductor circuit is formed by exposing the area other than the part to be formed, then performing a development treatment to melt and remove the photosensitive thin film in the part where the conductor circuit is to be formed, and then performing electrolytic plating or electroless plating. There is.

In recent years, with advances in electronic technology, electronic devices such as large computers are becoming more densely packed or have higher speed calculation functions. As a result, it has become necessary to reduce the diameter of through holes and via holes formed in printed wiring boards.

[Problem to be solved by the invention]

Now, in the conventional method of manufacturing printed wiring boards as described above, the photosensitive thin film for forming a plating resist is produced by applying a liquid photosensitive resin for forming a plating resist or pasting a photosensitive film for forming a plating resist. It is common to form.

However, among the photosensitive thin films for resist formation formed in this way, the photosensitive thin film for plating resist formation formed by applying the former photosensitive resin liquid is such that the resin liquid enters the through holes or recesses. Therefore, even if a development process is performed, it is difficult to completely remove the photosensitive thin film for forming a plating resist formed inside the through hole or recess in a short period of time. On the other hand, in the latter method of forming a photosensitive thin film for forming a plating resist by pasting a photosensitive film for forming a plating resist, the resin for forming a plating resist in a semi-dissolved state is removed just before the end of the development process. It is easy to get into the through holes or recesses, and in reality, in either method, residues of plating resist remain in the through holes or recesses, resulting in the formation of plating resist residues.

Residues of plating resist remaining in these holes cause poor connection of through holes and via holes. Therefore, it is important to leave as little of this plating resist residue as possible.

However, with conventional development techniques, it is difficult to completely remove the remaining plating resist in through holes and recesses, especially in the case of insulating substrates with through holes and recesses that are made small in diameter for high-density mounting. However, since such a removal operation takes an extremely long time, the resolution of conductive circuit parts other than through-holes and via-holes deteriorates, and the resulting circuit has a disadvantage that the conductivity of the circuit becomes low.

The purpose of the present invention is to solve the problem of poor conductivity caused by residual plating resist inside the holes, and to improve printed circuit boards having through holes or via holes with extremely high connection reliability. The aim is to develop a method for advantageously manufacturing a.

[Means for solving problems]

In order to achieve this objective, in the present invention, a plating resist is formed on the surface of an insulating substrate having through holes or recesses for forming through holes, via holes, etc., and conductive plating is applied thereon. In the method for manufacturing a printed wiring board, first, a photosensitive thin film for forming a plating resist is formed on the surface of the insulating substrate, and then the photosensitive thin film is coated on a portion of the substrate corresponding to the through hole or recess. We propose a method of cutting out an opening, then developing the photosensitive thin film to form a plating resist, and then forming a conductor circuit.

[For production]

In the present invention, after a photosensitive thin film for forming a plating resist is formed on the surface of an insulating substrate, the photosensitive layer is cut out at a location corresponding to a through hole or recess for forming the through hole or via hole. The feature is that the holes are provided in advance.

The reason for this is that when the unexposed portions of the photosensitive thin film are to be dissolved and removed during the development process performed to form the plating resist, the photosensitive thin film must be dissolved and removed in order from the surface thereof. However, in the method using resin liquid, the photosensitive resin liquid for forming the plating resist enters into the through holes or recesses formed in the substrate, and the resin in the holes, which has been hardened and thinned, is completely removed in a short time. It was extremely difficult to remove it. In addition, even in the method using a resin film, the resin for forming a plating resist enters the through hole or recess in a semi-dissolved state just before the end of the development process, so a phenomenon similar to that in the case of using a resin liquid occurs. Therefore, no matter which method is used, residues of the plating resist will remain inside the hole.

Therefore, by making a hole in the photosensitive thin film that covers the portion corresponding to the through hole or recess in advance,
Since the developer can penetrate into every corner of the through holes and recesses from the beginning of the development process, the resin film inside the holes can be dissolved and removed reliably and quickly, and plating resist residue can be effectively prevented.

In the present invention, the method of making a notch in the photosensitive thin film at a location corresponding to the through hole includes pin pricking, laser,
Means such as high pressure water or high pressure air can be employed. On the other hand, a laser or the like can be used to cut out holes in the photosensitive thin film in the portions corresponding to the recesses.

The size of the opening provided in the photosensitive thin film formed on the substrate in the previous step is preferably 10 μm or more. The reason for this is that if the holes formed in the photosensitive thin film are smaller than IO μmφ, the passage of the developer becomes difficult and the effect of opening the holes is diminished.

Further, as a method for developing the photosensitive thin film, a spray method or a dipping method can be applied.

It is particularly advantageous to apply the method of the present invention to wiring boards in which through holes or via holes with an aspect ratio (hole depth/hole diameter) of 3 or more are formed. The reason for this is that plating resist remains easily inside through-holes and via-holes with an aspect ratio of 3 or more; however, by applying the method of the present invention, through-holes and via-holes with an aspect ratio of 3 or more are This is because the developer can easily reach the inside.

In addition, in the present invention, it can be said that it is also effective to perform the development while applying vibrations after exposing the photosensitive resin thin film for forming a plating resist formed on the substrate.

The reason why it is preferable to apply vibration during development is considered to be as follows. In other words, if you perform development while applying vibration,
The solubility and diffusivity of photosensitive resin thin films for forming plating resists in developing solutions can be improved, and plating resists can be improved by removing air bubbles from through holes and via holes and by wetting through holes and recesses with developing solution. It can be dissolved efficiently.

Such vibrations are preferably vibrations generated by sound waves or mechanical motion, and in particular, sound waves are generated at 15 K.
Has a frequency of Hz ~ I Mllz and 0.35W/c
A material with a strength of m2 or more is effective. At the above frequency and intensity, cavitation is likely to occur and is suitable for removing air bubbles.

Furthermore, as a method for generating the sound waves, it is preferable to use a piezoelectric or magnetostrictive vibrator, to use a horn attached to the vibrator, or to use a speaker. Also, the sound waves have an incident angle of 0 to 15 with respect to the substrate.
It is desirable that the angle of incidence be given in degrees; if the incident angle is larger than this, total reflection will occur, the sound waves will not pass through the substrate, and the efficiency of vibration will decrease. Further, it is preferable that the vibration caused by the mechanical movement be applied by repeatedly moving the substrates in the same plane or by combining the substrates in the vertical direction.

The development process in the present invention is performed by immersing the substrate in a developer, spraying the developer onto the substrate, or spraying the developer while the substrate is immersed in the developer.

As the developer, an organic solvent is used in the solvent development method, and an alkaline solution is used in the alkaline development method. Such organic solvents include at least one selected from chlorocene, Eterna rR (manufactured by Fuikasei Co., Ltd.), butyl cellosolve, methyl cellosolve, butyl cellosolve acetate, methyl cellosolve acetate, methyl ethyl ketone, cyclohexanone, etc., and as the alkaline solution, At least one selected from sodium carbonate, sodium metasilicate, etc. can be used.

As explained above, by applying the present invention, it becomes possible to perform development without leaving plating resist, and it is possible to manufacture a printed wiring board having through holes and via holes with high connection reliability.

〔Example〕

Example 1 (1) 60 parts by weight of phenol novolak epoxy resin (manufactured by Yuka Shell, trade name: Ebikoat 154), 40 parts by weight of bisphenol A epoxy resin (manufactured by Yuka Shell, trade name: Epicor 1001), imidazole 4 parts by weight of curing agent (manufactured by Shikoku Kasei, trade name: 2P4MH2), fine epoxy resin powder (manufactured by Toshi, trade name: Trepar E)
Mix 30 parts by weight of P-B) and 0.1 part by weight of palladium chloride (special grade palladium chloride manufactured by Usiko Kagaku Kogyo Co., Ltd.) using three rollers, adjust the viscosity to 500 CP with methyl cellosolve, and prepare an adhesive for electroless plating. A drug was prepared.

(2) Using a roll coater, this adhesive was applied onto a glass epoxy insulating plate containing palladium chloride as a plating catalyst. Then dry and harden it to a thickness of 2.
An adhesive layer of 0 μm was formed.

(3) This substrate was coated with anhydrous chromium #800 g/l
After roughening the surface of the adhesive by immersing it in an aqueous solution, it was immersed in a neutralizing solution (manufactured by Sibley, trade name: PN 150) and washed with water.

(4) Place the NC multi-axis drilling machine (Excei) in the specified position.
Manufactured by lon Automation, product name: Mar
A through hole of 0.3 mm was made using a drill (kDrillier).

(5) A dry film of a photosensitive resin for forming plating resist (manufactured by San Nopco, trade name: DFR-400) was stacked on the substrate, and a press roller was used to press the dry film at l m/mi.
While transporting the substrate at 115℃, 2 kg/cr1
After laminating with No. 12, it was exposed with a mercury lamp.

(6) A hole was made in the through hole using a 0.3 mm diameter bottle.

(7) Next, development was performed for 60 seconds to form a plating resist, and then re-exposure and heat treatment were performed to sufficiently harden the plating resist.

(8) Electroless plating was performed to form a conductor circuit.

Example 2 (1) Prepare a photosensitive adhesive for electroless plating,
After coating the insulating substrate on which the conductive pattern was formed using a knife coater, it was dried at 70° C. to form a photosensitive resin insulating layer with a thickness of 50 μm.

(2) Next, a photomask printed with a black circle of 100 μmφ was used for exposure and development, and 10 μm diameter black circles were printed on the wiring board.
An opening of 0 μmφ was formed.

(3) Next, at 100°C for 1 hour, and then at 150°C for 10
Heat treated for hours.

(4) The wiring board was immersed in chromic acid for 10 minutes to roughen the resin surface, neutralized, and then washed with water.

(5) It was activated by immersion in a commercially available tin/palladium colloidal catalyst.

(6) A photosensitive dry film for forming a plating resist was laminated.

(71co, 6 holes of 50 μmφ were made with a laser, and then exposed.

(8) After developing for 60 seconds to form a plating resist, re-exposure and heat treatment were performed to sufficiently harden the plating resist.

(9) Electroless plating was performed to produce a multilayer printed wiring board.

〔Effect of the invention〕

As explained above, according to the present invention, no plating resist remains in the through holes or recesses during development.
It can be said that this method is extremely effective for manufacturing printed wiring boards having patterns with high connection reliability, especially small-diameter through holes and via holes.

Claims (2)

[Claims] 1. In a method for manufacturing a printed wiring board in which a conductive circuit is formed by forming a plating resist on the surface of an insulating substrate having through holes or recesses for forming through holes, via holes, etc., and applying conductive plating on the resist, First, a photosensitive thin film for forming a plating resist is formed on the surface of the insulating substrate, and then openings are provided by cutting out the photosensitive thin film at portions corresponding to the through holes or recesses in the substrate. 1. A method for manufacturing a printed wiring board, which comprises developing a transparent thin film to form a plating resist, and then forming a conductor circuit. 2. 2. The method for manufacturing a printed wiring board according to claim 1, wherein the diameter of the opening provided in the photosensitive thin film is 10 μm or more.