TWI411366B - Method of plugging high-density vias - Google Patents

Abstract

A method of plugging high-density vias includes providing a substrate having a plurality of vias; coating the substrate with a photo imagable solder mask and filling the vias with the photo imagable solder mask; making the photo imagable solder mask cross-link by exposure and removing the uncross-linked solder mask by developing, so as to leave the solder mask within the vias and covering the edge of the vias on the substrate; and removing the photo imagable solder mask from a surface of the substrate using a soft scrubber.

Description

High density through hole plugging method

The invention relates to a method of plugging a printed circuit board (PCB), and more particularly to a method of plugging a printed circuit board having high density vias.

Printed circuit boards are important components for integrating electronic product functions, and generally involve lamination, drilling, electroplating, plugging, exposure development, solder masking, and the like. However, with the rapid development of technology, the PCB industry is also moving toward the development of micro-hole, thin-line, high-density interconnection (HDI) products, which is important for the improvement of the plug-in process. As shown in Fig. 1A, the conventional plugging process mainly fills a via hole such as an epoxy resin into the via hole of the substrate 100, and forms a projection 130'. Then, as shown in Fig. 1B, the plugging agent 130, particularly the projection 130', is removed by brushing to remove the surface of the protruding substrate 100. However, the conventional plugging agent tends to be hard, so that the number of the projections 130' in the high-density through-hole region is increased and the degree of aggregation becomes high, and the epoxy resin is likely to remain on the surface of the substrate 100 after brushing (arrow A in the figure). Refers to the defect); if it is removed using a hard brushing device, it is easy to brush excessively to expose the substrate (the area indicated by the arrow B in the figure). In addition, when the surface of the substrate 100 is not flat, the brushing control is also more difficult, and the damage to the conductive layer 120 adjacent to the outer edge of the through hole is more serious.

Therefore, a plugging method is proposed to effectively fill the high-density through-holes, and the problem of resin residue and substrate exposure can be improved.

In view of this, the present invention proposes a plugging method for high density through holes. In one embodiment, the method includes providing a substrate having a plurality of electrical via holes; coating the photosensitive solder resist on the substrate; and filling the photosensitive solder resist into the electrical via; performing exposure to partially expose the solder resist Cross-linking, and developing to remove the uncrosslinked photosensitive solder mask, leaving a photosensitive solder resist covering the outer edge of the through-hole on the substrate and a photosensitive solder resist in the through-hole; removing the protruding substrate surface Photosensitive solder resist; and image transfer technology to form conductive wiring on the substrate.

The above method can solve the problem of the conductive layer which is easily over-grinded when the plug hole is formed to break the high-density via region. Moreover, performing the plugging before the image is transferred can reduce the hole breakage problem that may occur when the image is transferred and etched.

The above and other objects, features and advantages of the present invention will become more apparent from It is to be understood that the described embodiments are merely illustrative, and are not intended to limit the scope of the invention.

2A to 2F are cross-sectional views showing the structure of the substrate at various stages of the plugging method according to an embodiment of the present invention. The same component symbols in the various figures represent similar components, and are clearly drawn, and the components are not drawn to scale.

Referring to FIG. 2A, an electrical via hole is formed in the substrate 200. The substrate 200 may be an electrically insulating insulating substrate covering the conductor layer, such as an epoxy resin fiberglass plate (FR4), but is not limited thereto. The method of forming the through hole includes, for example, forming the through hole 210 through the substrate 200 at a predetermined position. The method of forming the through holes 210 may employ mechanical drilling, laser drilling, or other suitable drilling techniques. Then, steps of de-soiling, desmear, and the like are performed, and then through-hole plating is performed to form a conductive layer 220 on the inner surface of the via hole 210 and the surface of the substrate 200. Conductive layer 220 is typically a copper layer.

Referring to FIG. 2B, a solder mask (commonly known as green paint) 230 is applied to the substrate 200, and the solder resist 230 is filled in the through hole 210 to perform a plugging step. Before applying the solder mask, the surface of the copper surface and the surface of the substrate can be selectively roughened to prevent the solder paint from adhering to the inner surface of the through hole. There are many types of solder resists, such as infrared (IR) baking type, ultraviolet (UV) curing type resin, liquid photo imagable type ink, and dry film solder mask. In this embodiment, the solder resist varnish 230 is preferably a photosensitive ink. The photosensitive ink contains, for example, an oligomer or a resin, a polyfunctional monomer, a photosensitizer, a hardener, a solvent, etc., which will not be described in detail herein. The method of applying the solder resist 230 can be screen printing, roll coating, dip coating, electroposition, or other suitable coating technique. As shown in FIG. 2B, taking the squeegee technique as an example, after the single-sided plug hole is formed, the ink filling surface 232 and the convex ink surface 236 are formed on the top surface and the bottom surface of the substrate 200, respectively. The ink protruding from the convex ink surface 236 (i.e., the solder resist) is then scraped off at a low angle using a thin doctor blade. The angle of the squeegee is preferably less than 45 degrees, more preferably 30 degrees. The degree of use of the blade hardness is generally from 50 to 70 degrees, preferably from 60 to 65 degrees.

Referring to FIGS. 2C and 2D, the solder resist lacquer 230 is disposed on the outer edge of the through hole 210 and the through hole 210 on the surface of the substrate 200 by exposure development. As shown in FIG. 2D, the surface of the substrate 200 on the outer edge of the through hole 210 still has a solder resist lacquer 230 covering a portion of the conductive layer 220 at the corner of the through hole. Exposure development techniques include, for example, placing a backsheet 240 on a substrate 200, wherein the opening 242 of the backsheet 240 is sized larger than the aperture of the via 210. Next, the solder resist under the opening 242 is crosslinked by UV illumination, and the uncrosslinked solder resist is removed by etching, followed by a post-cure step. Before the exposure, the solvent of the liquid ink may be selectively dried by a pre-cure step to facilitate exposure.

Referring to FIG. 2E, the solder resist lacquer 230 on the surface of the protruding substrate 200 is removed. The removal method may be to remove the solder mask on the surface of the substrate by using a brush grinding device, for example, slightly grinding the surface of the substrate with a hard brushing device (such as a ceramic brush or abrasive belt), and then softly brushing the device (such as a non-woven brush or nylon). Brush) Continue grinding until no solder mask remains on the substrate surface. Especially in the case of removing the solder resist in the high-density through-hole area, the soft grinding is the main grinding method to avoid excessive grinding, thereby reducing the conductive layer on the outer edge of the adjacent through-hole when removed (the area indicated by the circle in the figure) The destruction.

Continuing with reference to FIG. 2E, conductive traces (eg, pads, wires) are formed using image transfer techniques, wherein the opening 252 of the backsheet 250 used herein is sized larger than the opening 242 of the backsheet 240 to ensure that the wires are conductive. Next, a conductive layer 220 as shown in FIG. 2F is formed by etching. Since the plug hole is formed before the image is transferred, the through hole is protected by the solder resist paint 230, so that the hole breakage problem which may be caused during etching can be reduced.

Next, as shown in FIG. 2F, a solder resist layer 260 is formed on the surface of the substrate 200. The solder resist layer 260 may be an IR baking type, a UV curing type resin, a liquid photosensitive type ink or a dry film type solder resist. In one example, the solder resist layer 260 is a photosensitive ink. Preferably, the photosensitive ink composition as the solder resist layer 260 herein may be similar to the solder resist 230, but has a low solid content and a high solvent content. The easiest way is to use a photosensitive ink as the solder resist 230, but reduce the content of the powder filler. The method of forming the solder resist layer 260 can employ any suitable coating technique, and the invention is not limited thereto.

The above method can solve the problem of the conductive layer which is easily over-grinded when the plug hole is formed to break the high-density via region. Moreover, the image removal is used to remove part of the anti-welding paint, and then the brush-grinding removes the anti-solder paint of the protruding substrate, thereby reducing the occurrence of the hole breakage problem or the residual of the solder resist.

While the present invention has been described above in terms of the preferred embodiments thereof, it is not intended to limit the invention, and the present invention can be modified and modified without departing from the spirit and scope of the invention. The scope is subject to the definition of the scope of the patent application.

100. . . Substrate

120. . . Copper layer

130. . . Plugging agent

130’. . . Protrusion

200. . . Substrate

210. . . Through hole

220. . . Conductive layer

230. . . Anti-corrosion paint

232. . . Silk surface

236. . . Convex ink surface

240, 250. . . Negative film

242, 252. . . Opening

260. . . Anti-corrosion paint layer

A, B. . . arrow

1A and 1B are schematic cross-sectional views of a substrate structure after plugging in a conventional method;

2A to 2F are cross-sectional views showing the structure of the substrate at various stages of the plugging method according to an embodiment of the present invention.

200. . . Substrate

220. . . Conductive layer

230. . . Anti-corrosion paint

240. . . Negative film

242. . . Opening

Claims (10)

A method for plugging holes of high-density through-holes, the method comprising: providing a substrate having a plurality of through holes; coating a photosensitive solder resist on the substrate, and filling the photosensitive solder resist into the substrate In the through hole; using an exposure and development technique, leaving the photosensitive solder resist on the outer edge of the through holes on the substrate and the photosensitive solder resist in the through holes; and removing the protruding substrate The photosensitive solder resist paint. The method of claim 1, further comprising forming a conductive layer on the inner surface of the through holes and the substrate before applying the photosensitive solder resist. The method of claim 2, further comprising, after the exposure and development technique, the photosensitive solder resist on the outer edge of the through holes on the substrate covers a portion of the conductive layer at the corners of the through holes. The method of claim 1, wherein applying the photosensitive solder resist comprises using a squeegee technique. The method of claim 1, wherein the removing the photosensitive solder resist protruding from the substrate comprises using a soft brushing device to remove the photosensitive solder resist protruding the substrate. The method of claim 5, wherein the removing the photosensitive solder resist protruding from the substrate further comprises using a hard brushing device to remove the photosensitive type protruding the substrate before using the soft brushing device. Anti-weld paint. The method of claim 1, further comprising forming a conductive wiring on the substrate by using an image transfer technique after removing the photosensitive solder resist protruding from the substrate. The method of claim 7, further comprising forming a solder resist layer on the substrate after removing the photosensitive solder resist protruding from the substrate. The method of claim 5, wherein the soft brushing device utilizes a non-woven brush or a nylon brush. The method of claim 6, wherein the hard brushing apparatus utilizes a belt or a ceramic brush.