JP2009267173A - Printed circuit board, and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printed circuit board, small in the reflection of light from an insulating layer (resist layer) on the surface of a printed circuit board, small in the undercut of an opening of an insulating layer pattern formed so as to eliminate a spot or discoloration occurring on the mounting pad at the opening, and suitable for the mounting of a semiconductor chip for imaging. <P>SOLUTION: A manufacturing method of the printed circuit board includes a process for forming a first resist layer 2 on a substrate 3 with a wiring 4 formed thereon, a process for forming a second resist layer 1 on the first resist layer 2, an exposing process for simultaneously curing the first and second resist layers employing a predetermined mask, a developing process for simultaneously resolving the uncured parts of the first and second resist layers and a process for effecting post cure, while the second resist layer is a black resist layer for suppressing the reflection of light. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a printed wiring board, and more particularly to a printed wiring board having a black insulating layer for suppressing light reflection on the surface of the board.

Conventionally, a printed wiring board has mainly used a green or yellow photosensitive resin or a thermosetting epoxy resin for a surface insulating layer (solder resist). Therefore, when an imaging semiconductor chip such as a CCD or CMOS is easily mounted on the surface of the chip, light reflected from the insulating layer around the mounting portion is taken into the light receiving portion of the chip, causing halation, and clear. It was difficult to obtain an image.
Therefore, by adding an inorganic filler, a pigment, or the like to the resin forming the insulating layer, reflection of light on the surface of the insulating layer is suppressed, and unnecessary light intrusion to the light receiving portion of the imaging chip is prevented.

  In recent years, with the increase in the density of printed wiring boards, there has been a demand for fine patterns capable of mounting components at high density even in the insulating layer pattern on the surface of the printed wiring board.

However, when an insulating layer made of a photosensitive resin uses a resin with a pigment added to suppress reflection of light or a resin containing a large amount of filler, ultraviolet rays are exposed to the inside of the resin during exposure in the photolithography process. Because it does not reach enough, curing due to photopolymerization reaction becomes insufficient, and there is a problem such as peeling of the insulating layer formed in the predetermined pattern or large undercut due to pattern development in the next process, for high density mounting There has been a problem that the insulating layer pattern required for the printed wiring board cannot be realized.
In this undercut part, chemical components in the manufacturing process are likely to remain, causing spots and discoloration on the mounting pad, resulting in poor appearance and mounting defects in the assembly process of mounting the semiconductor chip. It was.

  In particular, when a black photosensitive resist having a high effect of suppressing reflection of light and having good visibility (see, for example, Patent Document 1) is used, the transmittance of ultraviolet rays is other green, red, yellow, indigo, etc. It is weak compared to other photosensitive resists, ultraviolet rays do not reach the deep part of the resist layer, and it is difficult for the photopolymerization to cure at the bottom of the resist layer, causing problems such as large undercuts and peeling of the insulating layer. It was.

Therefore, as a method of reducing the amount of undercut when this black photosensitive resist is used, measures against temperature rise caused by changing the wavelength while exposing with ultraviolet light having a wavelength of 400 to 500 nm having high light transmittance. Patent Document 2 discloses a method of manufacturing a printed wiring board that cools an exposure apparatus.
Japanese Patent Laid-Open No. 11-115598 JP 2003-29417 A

However, in the method of Patent Document 2 in which the inside of the exposure apparatus is cooled and ultraviolet rays having a high light transmittance are used, even if the inside of the exposure apparatus is cooled, the temperature of the printed wiring board can be suppressed completely uniformly. The printed wiring board itself may be damaged by heat.
Further, Patent Document 1 shows that good visibility can be obtained, but since the form is provided so as to cover the land, the copper foil pattern, and the first resist printing, the photosensitive resist No problems such as the occurrence of excessive undercuts and peeling of the resist layer are caused when the curable resin is cured. Therefore, nothing is indicated for the problems that are problems in the present invention.

  In view of such a situation, the present invention has little reflection of light from the insulating layer (resist layer) on the surface of the printed wiring board, the undercut of the formed insulating layer pattern opening is small, and the stain generated on the mounting pad of the opening is small. Provided is a printed wiring board suitable for mounting an imaging semiconductor chip without any discoloration.

  According to a first aspect of the present invention, there is provided a step of applying a first photosensitive resist to a substrate on which wiring is formed and drying to form a first resist layer, and a second photosensitive layer on the first resist layer. A step of applying and drying a conductive resist to form a second resist layer, an exposure step of simultaneously curing the first and second resist layers using a predetermined mask, and an uncured portion of the first and second resist layers A method for producing a printed wiring board, wherein the second resist layer is a black resist layer that suppresses reflection of light, and further includes an ultraviolet transmittance of the first resist layer. These are the manufacturing methods of the printed wiring board which is a resist layer higher than the ultraviolet transmittance of a 2nd resist layer.

  A second invention of the present invention comprises a substrate on which wiring is formed, a first resist layer provided on the substrate, and a second resist layer provided on the first resist layer, wherein the first resist layer is The second resist layer is an insulating layer having an ultraviolet transmittance higher than that of the second resist layer, and the second resist layer is a printed wiring board having an insulating layer surface that suppresses reflection of light. The layer surface that suppresses the reflection of light is a layer surface of a color that absorbs light, or a layer surface that causes irregular reflection, and the layer surface that suppresses the reflection of light of the second resist layer, It is a black layer surface.

  The printed wiring board according to the present invention has little reflection of light from the insulating layer (second resist layer) on the surface thereof, the undercut of the opening of the insulating layer pattern is small, and a stain or discoloration generated on the mounting pad of the opening The printed wiring board is suitable for mounting an imaging semiconductor chip.

Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 is a partial cross-sectional view of a printed wiring board having two insulating layers according to the present invention.
FIG. 2 is an enlarged schematic cross-sectional view of the opening portion of the insulating layer pattern, wherein (a) is composed of two resist layers according to the present invention, and (b) is composed of one conventional resist layer. .
1 to 2, 1 is a second resist layer (insulating layer), 1a is a conventional resist layer, 2 is a first resist layer (insulating layer), 3 is a resin substrate, 4 is a mounting pad, 10 is a printed wiring board, and d ₀ and d ₁ are undercut amounts.

The present invention shown in FIG. 1 and FIG. 2 (a) reflects light that becomes a second resist layer on a printed wiring board that has been first dried by applying a first photosensitive resist that becomes a first resist layer. A second photosensitive resist that has a black color to suppress the above is applied and temporarily dried. Next, after exposure through a predetermined mask with ultraviolet rays, pattern development is performed, and post-cure is performed in order to completely cure the two photosensitive resists. Finally, the resist layer, which is an insulating layer on the substrate surface, has a two-layer structure, and the undercut d ₀ (FIG. 2A) of the opening is smaller than the conventional undercut d ₁ (FIG. 2B). It becomes a wiring board.

By forming the resist layer in two stages by providing the second resist layer on the first resist layer, a resist layer having a sufficient thickness as an insulating layer is formed, and a lower layer than the second resist layer serving as an upper layer is formed. Since the first resist layer has a higher ultraviolet transmittance, the curing reaction proceeds at the lowermost first resist layer even if the amount of ultraviolet light transmitted from the upper layer is small. Therefore, the amount of undercut formed in the opening of the insulating layer by pattern development can be reduced, and thus a printed wiring board can be produced in which no impurity residue remains on the mounting pad.
Regarding the layer thicknesses of these resist layers, it is preferable that the thickness of the first resist layer is the same as or the same as the thickness of the second resist layer.

The second resist layer has a layer surface that suppresses reflection of light. As such a layer surface, a layer surface of a color that absorbs light, particularly a layer surface of a color that absorbs light, typically black, is preferable, or a layer having irregular surface irregularities that easily cause irregular reflection. Surface.
The second resist layer may be configured not only to suppress light reflection only on the layer surface but also to suppress light reflection if the entire resist layer including the layer surface is an insulating layer.
Hereinafter, description will be made using examples.

  A photosensitive resist (solar ink PSR-4000AUS308 (green)) having an ultraviolet transmittance of 29.5% is used as the first photosensitive resist on the glass / bismaleimide-triazine laminated substrate on which the wiring is formed so as to have a film thickness of 20 μm. And a first resist layer is formed at 85 ° C. for 25 minutes to form a first resist layer, and then a photosensitive resist (solar ink PSR-4000EG23 having an ultraviolet transmittance of 7.3%) is formed on the resist as a second photosensitive resist. (Black)) was applied to a film thickness of 20 μm and dried at 85 ° C. for 35 minutes to form a second resist layer.

Next, after exposure through a predetermined negative film mask with 1200 mj / cm ² ultraviolet rays, spray development was performed for 1 minute with a 1 wt% sodium carbonate aqueous solution at 40 ° C. Further, a post-cure was performed at 150 ° C. for 40 minutes to completely cure the resist layer, and a printed wiring board having a surface insulating layer having a two-layer structure and a black upper insulating layer was produced.

When a part of this printed wiring board is cut out and the opening of the two insulating layers formed is cross-sectionally observed, the amount of undercut (d ₀ ) is 8 μm on average and satisfies the requirement of less than 10 μm for the opening. It was.
Moreover, when Ni-Au plating was applied to this printed wiring board and appearance inspection was performed, defects such as spots and discoloration were not confirmed on the surface of the mounting pad in the opening of the insulating layer, and the surface condition was good. showed that.

  Next, this printed wiring board was pretreated in accordance with IPC / JEDEC Standard J-STD-020 moisture soak level 2 and then floated on a molten lead eutectic solder at 260 ° C. for 30 seconds to perform a heat resistance test, and the insulation layer was peeled off. However, defects such as peeling were not confirmed, indicating a good adhesion state.

(Comparative example)
For comparison, a photosensitive resist (solar ink PSR-4000EG23 (black)) with an ultraviolet transmittance of 7.3% is applied to a film thickness of 40 μm and dried at 85 ° C. for 60 minutes to form a single layer resist. A printed wiring board was produced in the same procedure as in Example 1 except that the layers were used.

The cross section of the produced printed wiring board was observed, and the undercut amount (d ₁ ) was measured. The average was 40 μm, nearly five times that of the example of the present invention, and the required accuracy was less than 10 μm. . In addition, after performing the appearance inspection after applying Ni-Au plating, plating stains are confirmed on the mounting pad that seems to be due to the residue of chemicals used in the manufacturing process, and as a printed wiring board on which the imaging semiconductor chip is mounted It was difficult to use.

It is a fragmentary sectional view of the printed wiring board which has two resist layers (insulating layer) of this invention. It is an expansion schematic sectional drawing of an insulating-layer pattern opening part, (a) consists of two resist layers which concern on this invention, (b) consists of one conventional resist layer.

Explanation of symbols

1 Second resist layer: Upper layer side (insulating layer)
1a Conventional resist layer 2 First resist layer: lower layer side (insulating layer)
3 Resin base material 4 Mounting pad 10 Printed wiring board d ₀ , d ₁ Undercut amount

Claims (5)

Applying a first photosensitive resist to a substrate on which wiring is formed, and drying to form a first resist layer;
Applying a second photosensitive resist on the first resist layer and drying to form a second resist layer;
An exposure step of simultaneously curing the first and second resist layers using a predetermined mask;
A developing step of simultaneously dissolving uncured portions of the first and second resist layers;
Including post-cure process,
The method of manufacturing a printed wiring board, wherein the second resist layer is a black resist layer that suppresses reflection of light.   The method for manufacturing a printed wiring board according to claim 1, wherein the ultraviolet transmittance of the first resist layer is higher than the ultraviolet transmittance of the second resist layer. A substrate on which wiring is formed;
A first resist layer provided on the substrate;
A second resist layer provided on the first resist layer;
With
The first resist layer is an insulating layer having an ultraviolet transmittance higher than that of the second resist layer,
The second resist layer is an insulating layer and an insulating layer having a layer surface that suppresses reflection of light,
A printed wiring board characterized by being.   The printed wiring board according to claim 3, wherein the surface of the second resist layer that suppresses light reflection is a color surface that absorbs light or a surface that causes irregular reflection.   The printed wiring board according to claim 3, wherein the layer surface that suppresses the reflection of light of the second resist layer is a black surface.

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