JPS6233316B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to protective plating in the production of printed wiring by pattern plating.

When producing printed wiring using the pattern plating method, electrolytic copper plating is applied to the copper surface of the copper clad laminate where there is no resist, and then protective plating with solder, gold, etc. is applied, and then the resist is removed. The exposed copper foil was removed by etching to create conductor wiring. When etching copper as described above, only the top surface (and inner walls of through-holes if there are through holes) is protected by a plating layer of solder, gold, etc., so the side surfaces are etched, resulting in so-called side etching. bring about a condition. Moreover, for this reason, the allowable range of etching time is narrow.

The rate of progress of etching differs depending on the size of the conductor spacing, so if etching is carried out sufficiently to avoid etching residue where it should be etched, severe side etching will occur, and this will cause the shape and size of the conductor to deteriorate. The shape is different from the original drawing, and the shape of the cross section of the wiring is similar to that of a mushroom. If the eaves of this mushroom umbrella fall off, it can cause an electrical short circuit. In order to avoid this falling off, methods such as melting the plated solder are used.

The thinner the copper foil in the copper-clad laminate, the shorter the time required for etching, and the smaller the side etch of patterned copper. However, extremely thin copper foils are usually thinner than 18 microns for technical and economic reasons, such as being difficult to handle, having holes that cause the resin on the back side to come out and spread, and requiring a supporting metal film. thick copper foil is used in the laminate.

By applying protective plating not only to the top surface of the pattern-plated copper but also to the side surfaces before etching, side etching of the pattern-plated copper can be prevented, and the side etch of the copper foil underneath can also be reduced, reducing the overall side etch. We thought that the size would be significantly smaller than that without side protective plating, and as a result of intensive study, we arrived at the present invention.

In other words, the present invention provides two upper and lower resin layers on the surface of the copper foil of a copper-clad laminate (the resin constituting the upper layer and the resin constituting the lower layer have different solvent resistance, and the lower layer has a resin layer that is less than 1/10 of the upper layer. After forming a resist image consisting of (with a thickness of This is a protective plating method for patterned copper sides.

According to the method of the present invention, after patterned copper plating, the resist image consisting of two types of resin layers with different solvent resistance is removed in two stages. First, the upper layer, which accounts for most of the thickness of the resist layer, is removed. Side etch can be significantly reduced by applying a protective plating to the patterned copper, then removing the thin underlayer of resist and etching away the copper foil of the laminate.

The method of the present invention will be explained with reference to the drawings. Figure 1 shows
A resist image consisting of two resin layers, a lower layer 3 and an upper layer 4, is formed on the surface of a copper foil 2 of a copper-clad laminate 1. After patterned copper plating is applied to this, patterned copper 5 is formed in the areas where there is no resist image, as shown in FIG. 2, the upper layer 4 of the resist image is removed as shown in FIG. Next, protective plating 6 is applied to the exposed patterned copper portions as shown in FIG. 4, and then the remaining resist image lower layer 3 is removed as shown in FIG. Finally, by etching the exposed copper foil 2 using a conventional method, a pattern with small side etch as shown in FIG. 6 is obtained.

A resist image suitable for the present invention may be one in which the upper layer is dissolved or significantly swollen, but the lower layer is not substantially swollen or dissolved, and can be removed by being dissolved or significantly swollen in another solvent. . Such a resist image can be created by screen printing, or by screen printing only the upper layer on a thin resin coating on the entire surface and removing the lower layer in the uncoated area, but it is possible to create a resist image with a high profile that requires side protection plating. Precision wiring is generally made using photosensitive resin. In this case, use the usual method of attaching a photomask to the photosensitive resin, exposing it to light, and developing it.
A resist image can be easily formed.

To create a resist image with the above-mentioned dissolution and swelling characteristics using a photosensitive resin, the photosensitive resin must be made of a thin film of photocrosslinkable or photocrosslinkable polymerizable resin and whose solvent affinity changes upon exposure to light (photosensitive resin). A combination of a thick film of photosensitive resin (including the case of polymerization), (for example, a combination of an upper layer of a photosensitive resin made of a polymer with an amino group and orthoquinone azide and a lower layer of a polyvinyl cinnamate photosensitive resin, etc.) ), a solvent that can dissolve or significantly swell a thick upper layer cannot do this to a thin lower layer (which does not have to be a photosensitive film), and conversely, a solvent that can dissolve or significantly swell a lower layer cannot do this to an upper layer. There are combinations of upper and lower layers such as (for example, the upper layer is a combination of the above-mentioned amino group-containing polymer photosensitive resin or a mixture of pentaerythritol triacrylate and polymethyl methacrylate, and the lower layer is a combination of polyacrylonitrile, etc.). In any combination, it is necessary that the adhesion between the upper and lower layers is sufficiently strong so that they do not peel off during operations such as development and plating (an intermediate layer may be provided to strengthen the adhesion).

When removing the upper layer of the resist image, it is desirable to remove the upper layer by dissolving it, since any operation that would damage the lower layer must not be performed. In particular, it is desirable that the lower layer can be dissolved and removed using a solvent that does not swell.
In these respects, resist images of photosensitive resins made of polymers with amino groups and orthoquinone diazide as shown in the examples can be dissolved and removed with 1,1,1-trichloroethane, which is often used as a developing solvent. Therefore, it is extremely convenient as an upper layer.
This photosensitive resin has a photosensitive group that is photodegradable, which is also advantageous for the present invention in the following respects. In other words, if the photosensitive material in the thick upper layer is a photodegradable type, the light at the photosensitive wavelength of the upper layer will easily reach the lower layer, but if it is not a decomposable type, and the overlap of the photosensitive wavelength ranges of the upper and lower layers is large, the upper layer will not be suitable for use. The exposure time is insufficient for exposing the lower layer.

A method of forming a photosensitive resin film on a copper surface to form a two-layer resist image as described above is to form the lower layer by coating and drying the copper surface, and then forming the upper layer by coating and drying. Alternatively, a separately formed upper layer film may be attached, or a film in which both the upper and lower layers are superimposed may be attached to the copper surface. An appropriate method may be adopted depending on the properties of each resin and the target type of wiring.

The lower layer needs to have good adhesion to copper, but
In particular, when a separately formed lower layer film (generally overlaid with an upper layer) is attached to a copper surface, it is important to use a material that is easy to adhere to. Further, if a lower layer is used in which a lower layer portion below a portion of the upper layer that is removed during development is removed at the same time, there is no need to separately remove this lower layer, and the number of steps is reduced.

If the lower layer is thicker, the area on the side surface of the patterned copper that is protected by plating will be reduced. Further, when the lower layer is not photosensitive and the lower layer is thick, the peripheral portion of the lower layer below the upper resist image may also be removed when the exposed portion of the lower layer is removed after development. On the other hand, if the lower layer is extremely thin, it has disadvantages such as pores and being easily damaged during operation. For these reasons, the appropriate thickness of the lower layer varies depending on the properties of the lower layer material, the method of forming the lower layer, the thickness of the upper layer, the type of wiring fabrication operation, etc., but is usually 0.3 to 3 microns, and is approximately 10 minutes thicker than the upper layer. It is often less than 1.

Most of the operations for producing conductor patterns using the method of the present invention are the same as ordinary pattern plating methods, except that the resist is removed in two stages.
There are some differences with step removal. There is no problem if the upper and lower layers are developed at the same time, but
If the lower layer remains during development, it is of course necessary to remove the exposed portion of the lower layer by a method that does not damage the resist pattern of the upper layer before performing the next plating pretreatment operation. If the lower layer is made of polyacrylonitrile, it can be removed by dissolving it with an aqueous solution of sodium thiocyanate, without damaging the resist pattern made of a so-called solvent-developable photosensitive resin. When removing the upper resist layer after normal plating pretreatment and pattern copper plating, operations such as brushing that may damage the thin lower layer must not be performed.

Generally, it is better to perform etching with an ammonium persulfate solution and acid washing as pretreatments performed before protective plating, but no problems are observed in acid gold plating even without the above etching.

Protective plating can be done in the same way as in normal cases, but if the copper foil of the copper-clad laminate has a thickness of 18 microns, the thickness of the protective plating is 2.2 microns even with solder plating, not to mention gold plating. Microns can achieve the purpose of protection. Of course, the plating may be made thicker, and this may also be used to reduce the conductor spacing.

In removing the lower resist layer after protective plating, various operations such as brushing in a solvent may be used, but if the lower layer is non-crosslinked, brushing is not necessary.

Etching of the copper foil exposed by removing the lower resist layer is carried out by a conventional method. This area undergoes side etching, but the degree of side etching is the same as etching a resist image on a copper-clad laminate. In other words, the cross-sectional shape of the conductor wiring when side protective plating is performed using the method of the present invention is the same as that of copper when a resist image (cross section is rectangular) with a thickness of several tens of microns is etched on an 18-micron copper foil. and resembles the cross-sectional shape of the entire resist. Therefore, there are no parts that easily fall off like the eaves of a mushroom umbrella.
Even if the printed wiring board surface is rubbed strongly, the peripheral portion of the wiring will not bend. It is possible to create a wiring whose conductor width and conductor spacing are smaller than the conductor height and which is not easily deformed by external force. It is thought that the demand for wiring with small conductor widths and conductor spacing will increase in the future, but even if it is possible to create a resist image with small widths and spacings and thick vertical sides, it is difficult to transfer this to a conductor image using either an additive method or a subtraction method. There are difficulties. The side protective plating method of the present invention is one excellent method for obtaining fine conductor images.

EXAMPLES The present invention will be described in more detail below with reference to Examples.

Example 1 Copolymer of methyl methacrylate, ethyl acrylate, acrylonitrile, and 2-N/N-dimethylaminoethyl methacrylate (weight ratio 55:25:
13:7) and naphthoquinone-(1,2)-diazide-(2)-5-sulfo(4'-
A solution of hydroxy)anilide in methyl ethyl ketone was applied to a 25 micron thick polyethylene terephthalate film and dried to produce a 40 micron thick photosensitive resin film. A photo-crosslinkable photosensitive resin solution "Kodatsuku Photoresist" (polyvinyl cinnamate photosensitive resin) is applied to the polished copper surface of a copper (thickness 18 micron) clad glass cloth epoxy laminate and dried to a thickness of approx. 1
On top of the micron film formed, the above thick photoresist film was thermocompression bonded, and the polyethylene terephthalate film was peeled off. A photomask film with 300 lines per inch was vacuum-adhered to the photoresist surface, exposed to an ultra-high pressure mercury lamp, developed with a spray of 1,1,1-trichloroethane at 20°C, and ammonium persulfate solution (ammonium persulfate 240g/ ,
After light etching with a room temperature spray of sulfuric acid (16g/) and washing with dilute hydrochloric acid, electrolytic plating was performed in a copper sulfate bath to a thickness of approximately 35 microns. The amino group-containing polymer was solubilized in trichloroethane by immersion in hot water for about 10 seconds, and the polymer was removed by the same operation as development. After washing with dilute hydrochloric acid, wash in an acidic gold plating bath for about 2 hours.
Electrolytic plating was performed to a thickness of microns. The remaining film of "Kodatsu Photoresist" was removed by brushing in methylene chloride, and then etched by spraying with a 30% iron chloride solution at 50°C to obtain a fine conductor image. The conductor width matched the sum of the width of the opaque part of the photomask and twice the gold plating thickness, and there were no etch marks between the conductors, and only a slight side etch was observed in the part originating from the copper foil. . Even if the upper surface was rubbed with a cloth, no reduction in the conductor width due to bending or falling off of the peripheral portion of the conductor was observed.

Example 2 In exactly the same manner as in Example 1, the polyethylene terephthalate film was peeled off from a copper-clad laminate with double layers of photoresist film, and a photomask film with 80 lines per inch was vacuum-adhered, and the center wavelength was set at 400 nm. The light was exposed to a light-emitting surface made by arranging fluorescent lamps with holders. As in Example 1, development with trichloroethane spray at 20°C, pre-plating treatment with light etching with ammonium persulfate solution and washing with dilute hydrochloric acid, and electrolytic plating (about 35 microns thick) in a copper sulfate bath were carried out. I did it. After immersion in hot water, the upper layer of the resist image was dissolved and removed using trichloroethane spray, and after pretreatment of spraying with ammonium persulfate solution and washing with dilute hydrochloric acid, it was electrolyzed to a thickness of 2 microns in a matte soldering bath. It hit me. The remaining resist was removed by brushing in methylene chloride, and etching was performed by spraying an ammonium persulfate solution at 50° C. to remove the copper foil exposed by the resist removal. Although the thickness of the solder plating in this example was much thinner than that of ordinary solder plating, etching of the patterned copper was prevented. There was no remaining etching between the conductors, and only a small amount of side etching was present in the copper foil of the substrate below the patterned copper.

Example 3 "Kodatsu Photoresist" to which 2% dodecylbenzene was added as a plasticizer was coated on a polyethylene plate and dried to form a film with a thickness of approximately 1.5 microns, and then applied on a polyethylene terephthalate film in the same manner as in Example 1. The photoresist film (thickness: 40 microns) made in 1992 was pasted face to face with a heated roller, the polyethylene plate was peeled off, and the "Kodatsu Photoresist" film was transferred onto the thick photoresist film. Example 1
The above double photosensitive film was attached to the copper surface of a polished copper-clad laminate similar to the above using a hot roller. The subsequent operations were carried out in the same manner as in Example 2, and the same results as in Example 2 were obtained.

Example 4 A dimethylformamide solution of polyacrylonitrile was applied to the polished copper surface of a copper (thickness: 18 microns) clad glass cloth epoxy laminate and dried.
A film with a thickness of microns was formed. A photoresist film on the same polyethylene terephthalate film as used in Example 1 was bonded thereon by thermocompression. After peeling off the polyethylene terephthalate film, a photomask film with 80 lines per inch was vacuum-adhered in the same manner as in Example 2, exposed to light using a fluorescent lamp, and then developed with trichloroethane spray. The developed laminate was immersed in a 52% aqueous solution of sodium thiocyanate to dissolve and remove the polyacrylonitrile in the areas not covered by the photoresist image, followed by light etching with an ammonium persulfate solution and dilute acid washing. Electrolytic plating was done in a copper sulfate bath to a thickness of about 35 microns. As in Example 1, the photoresist image was immersed in hot water, then dissolved and removed using trichloroethane spray, washed with dilute acid, and then electrolytically plated in an acidic gold plating bath to a thickness of approximately 2 microns. Summer. After washing with a 52% sodium thiocyanate solution to remove polyacrylonitrile and etching with an iron chloride solution in the same manner as in Example 1, there was no etching residue, and the side etching was only on the parts of the laminate that originated from the copper foil. A slight conductor image was obtained.

Example 5 When polyacrylonitrile is used as a thin lower layer as in Example 4, a crosslinkable polymer can be used as an upper layer. In place of the photosensitive resin film in Example 4, a cross-linked polymerizable photosensitive resin film “Riston T” was used.
-1215'' was pasted, a photomask was vacuum-adhered without removing the polyethylene terephthalate film, and exposed to collimated light from a high-pressure mercury lamp.The polyethylene terephthalate film was peeled off and developed with trichloroethane spray at 20°C, and the following patterned copper The same operations as in Example 4 were performed until plating.Different from Example 4, the photoresist image was removed by dipping in methylene chloride.The subsequent operations were performed in the same manner as in Example 4. Similar results were obtained.

[Brief explanation of the drawing]

FIG. 1 shows a cross-sectional view of a copper-clad laminate in which a resist image consisting of two upper and lower resin layers is formed on the surface of the copper foil. FIG. 2 shows a cross-sectional view after patterned copper plating, and FIG. 3 shows a cross-sectional view after removing the upper layer. Figure 4 shows a cross-sectional view when protective plating is applied.
FIG. 5 shows a cross-sectional view when the lower layer is removed. 6th
The figure shows a cross-sectional view after etching. 1... Copper-clad laminate, 2... Copper foil, 3... Lower layer of resist image, 4... Upper layer of resist image, 5...
Copper with pattern plating, 6...protective plating.

Claims (1)

[Claims] 1 Two resin layers, upper and lower, on the surface of the copper foil of a copper-clad laminate (the resin that makes up the upper layer and the resin that makes up the lower layer have different solvent resistance, and the thickness of the lower layer is 1/10 or less of the upper layer) After forming a resist image consisting of the resist image and pattern copper plating, the upper layer of the resist image is removed, a protective plating is applied to the patterned copper, and then the lower layer of the resist image is removed. Protective plating method for plated copper sides.