TW201313966A - Direct plating method - Google Patents

Abstract

The present invention relates to a method for direct plating in the manufacture of printed circuit boards, IC substrates and the like. The method utilizes a conductive layer selected from electrically conductive polymers, colloidal noble metals and electrically conductive carbon particles for BMV filling and hence avoids an intermediate layer of copper deposited by electroless plating and thereby insufficient line shape and adhesion of copper tracks formed by etching in successive manufacturing steps.

Description

Direct plating method

The present invention relates to a method of manufacturing a printed circuit board. More particularly, the present invention relates to direct plating methods for fabricating high density interconnect (HDI) printed circuit boards, IC substrates, and the like.

The miniaturization of the features of ongoing HDI printed circuit boards, IC substrates, and the like requires more advanced manufacturing methods than conventional methods such as forming circuits by printing and etching.

The method known in the art begins with a bare dielectric substrate semi-additive process (SAP) after laser drilling of a blind microwell and the like, followed by deposition of a conductive layer in the patterned pattern. The copper is selectively electrolytically deposited in the opening of the resist material and the portion of the conductive layer not coated with the electroplated copper is removed. The conductive layer typically comprises a precious metal seed layer and a thin copper layer deposited by electroless plating. The main disadvantage of this SAP method is the weak adhesion between the seed layer/conducting layer and the surface of the bare dielectric substrate. This weak adhesion can result in undesirable delamination of the copper tracks during subsequent fabrication steps or subsequent use of the printed circuit board.

Another method in the art utilizes an advanced modified semi-additive method (AM-SAP) that replaces the bare dielectric substrate material with a substrate having a copper layer on the top of the dielectric substrate. The copper layer at the top of the dielectric substrate material herein refers to copper cladding. The thickness of the copper cladding is in the range of 0.5 to 10 μm. The copper cladding is typically fabricated by "thinning" of a thicker copper coating attached to both sides of the dielectric substrate.

The reason for the need for this low-thickness copper is that the copper coating that has not been electroplated with copper during subsequent processing steps needs to be removed by subsequent etching. In order to obtain a very fine and regular copper pattern by etching, the thickness of the copper cladding must be as small as possible.

The prior art AM-SAP method comprises the steps of: (i) providing a dielectric substrate (1) having a copper cladding (2) having a thickness of 0.5 to 10 μm on both sides of the dielectric substrate (1) and blindness Micropores (BMV) (3), (ii) depositing a seed layer (5a) onto the surface of the substrate, (iii) depositing a copper conducting layer (5) to the seed layer (5a) by electroless plating (iv) applying a resist layer (4) to the copper cladding (2) and patterning the resist layer (4), (v) depositing a copper layer on the conductive layer (5) by electroplating (6), (vi) depositing a resist (7) on the top of the electroplated copper (6) and removing the patterned resist layer (4), (vii) etching to eliminate the resist (7) Protecting the copper and removing the resist (7).

This method is illustrated in Figure 1. The result of this method is the copper rail (8) and the BMV (9) filled with copper.

The conductive layer (5) is required to provide electrical conductivity to the sidewalls of the BMVs composed of the dielectric substrate (1) material.

After the BMVs (3) are formed by laser drilling, a decontamination operation is required to remove the smudges and other residues from the sidewalls of the BMVs. Purification is accomplished by wet chemical de-soiling methods or by plasma. Both methods in this technology Known in.

A seed layer (5a) is then deposited onto the copper cladding (2), the dielectric sidewalls of the BMVs (3), and the metal bottom of the BMVs (3). The seed layer (5a) typically comprises a noble metal, preferably palladium. Methods and materials for forming this seed layer (5a) are known in the art.

Next, the conductive layer (5) is deposited onto the seed layer (5a) by electroless copper plating.

Both the seed layer (5a) and the conductive layer (5) are deposited onto the entire substrate surface. The entire substrate surface includes the surface of the copper cladding (2) and the walls of the BMV (3).

The microstructure (conducting layer (5)) of copper deposited by electroless plating is different from the microstructure of the electroplated copper layer (6) and the copper cladding (2). Different microstructures of copper deposited by different methods result in different etch states.

Figure 2 shows the copper rail (8) obtained by the method according to Figure 1. The conductive layer (5) deposited by electroless copper plating acts as a "boundary line" in the copper track (8): where the etching corrosion is compared to copper coating (2) and copper layer deposited by electroplating (6) The situation is strong. This results in an irregular shape of the copper track (8) which has the disadvantage of the propagation of the current and which further reduces the adhesion of the copper layer (6) on the copper cladding (2).

Accordingly, it is an object of the present invention to provide a method of avoiding or minimizing the disadvantages of an intermediate layer of copper deposited by electroless plating. In particular, the objectives are to improve the adhesion between the copper cladding (2) and the copper layer (6) by electroplating, to provide a method of fabricating a regular shaped copper rail (8) and by electroless plating. The undercut of the copper track (8) is avoided during the etching caused by the deposited intermediate layer (5) of copper.

The objects are solved by a direct plating method comprising the steps of: (i) providing a dielectric substrate (1) having copper having a thickness of 0.5 to 10 μm on both sides of the dielectric substrate (1) Coating (2) and at least one blind microwell (BMV) (3), (ii) depositing a conductive layer (5) on at least a portion of the surface of the substrate, wherein the conductive layer (5) is selected from a conductive polymer, a group comprising colloidal particles of noble metal and conductive carbon particles, (iii) applying a resist layer (4) to the copper coating (2) and patterning the resist layer (4), and (iv) borrowing A copper layer (6) is deposited onto the conductive layer (5) by electroplating.

The dielectric substrate (1) is composed of a polymeric material such as an epoxy resin, a cyanate resin, a bismaleimide resin, a bismaleimide triazine resin, a benzoxazine resin, and mixtures thereof. The dielectric substrate (1) may additionally contain a reinforcing material such as a glass reinforcing material. A copper cladding (2) is included on both sides of the dielectric substrate (1). The thickness of the copper coating (2) is in the range of 0.5 to 10 μm, more preferably 1 to 5 μm, and most preferably 1.5 to 3.5 μm. The copper coating (2) can be obtained, for example, by "thinning" thick copper coating. Thinning is usually done by different etching methods. Directly manufacturing copper cladding without the need for thinning, as appropriate.

Laser drilling through the copper cladding (2) and the material of the dielectric substrate (1) to the copper on the other side of the dielectric substrate (1) serving as the metal bottom of the BMV (3) Cover (2) to form BMV (3). Optionally, a laser radiation absorbing layer is deposited onto the surface of the copper cladding (2) prior to laser drilling.

Second, the sidewalls of the BMVs (3) are subjected to a purification process to remove drill and other residues from the laser drilled holes. The purification process can be a wet chemical desmear process or a plasma desmear process. Such methods are known in the art (for example: C. F. Coombs, Jr., "Printed Circuits Handbook", 5th edition, 2001, Chapter 28.4, pages 28.5 to 28.7).

The wet chemical desmear method comprises the steps of: a) expanding the surface of the dielectric substrate (1), b) etching the surface of the dielectric substrate (1) with a permanganate solution, and c) reducing the surface of the dielectric substrate (1) The surface of the dielectric substrate (1) removes MnO ₂ .

After the sidewalls of the BMVs (3) are desmeared, a conductive layer (5) formed of a group of conductive polymers, colloidal noble metal particles, and conductive carbon particles is deposited onto the surface of the substrate. The surface of the substrate comprises a copper cladding (2), a sidewall of the BMV (3) previously formed by drilling, and a backside of the copper cladding (2) on the back side of the substrate serving as the metal bottom of the BMV (3) .

In the case of a conductive polymer, a conductive layer (5) is deposited on portions of the surface of the substrate including the previously formed sidewalls of the BMVs. The sidewalls of the BMVs are composed of a non-conductive dielectric material.

Preferably, the conductive layer (5) comprises a conductive polymer selected from the group consisting of polythiophenes, polypyrroles, polyanilines, derivatives thereof, and mixtures thereof.

The most preferred conductive polymer is selected from the group consisting of polythiophenes, derivatives thereof, and mixtures thereof.

The conductive layer (5) comprising polythiophene, derivatives thereof, and mixtures thereof is formed by the following steps: a) contacting the surface of the dielectric substrate (1) with a solution of a water-soluble polymer, b) treating the surface of the dielectric substrate (1) with a permanganate solution, and c) using at least one thiophene compound and at least Treating the surface of the dielectric substrate (1) with an acidic aqueous solution or an acidic microemulsion of an aqueous base of an alkanesulfonic acid, the method only results in a portion of the surface of the substrate composed of the dielectric substrate material (1) (ie, A conductive organic polymer is formed on the side wall of the BMV (3). No conductive polymer is formed on the surface of the copper coating (2).

The water-soluble polymer used in the step a) is selected from the group consisting of polyvinylamine, polyethyleneimine, polyvinylimidazole, alkylamine ethylene oxide copolymer, polyethylene glycol, polypropylene glycol, ethylene glycol and A copolymer of polypropylene glycol, polyvinyl alcohol, polyacrylate, polypropylene decylamine, polyvinylpyrrolidone, and mixtures thereof. The concentration of the water-soluble polymer is in the range of 20 mg/l to 10 g/l.

The solution of the water-soluble polymer may additionally contain a solvent selected from the group consisting of ethanol, propanol, ethylene glycol, diethylene glycol, glycerin, dioxin, butyrolactone, N-methylpyrrolidone, dimethylformamide, and dimethyl A water-soluble organic solvent of a group consisting of acetylamine, a half ether of ethylene glycol, and a half ester. The water-soluble organic solvent can be used in pure form or diluted with water. The concentration of the water-soluble organic solvent is in the range of 10 ml/l to 200 ml/l. During step a), the solution of the water-soluble polymer is maintained at a temperature in the range of 25 ° C to 85 ° C, and the dielectric substrate (1) is immersed in the solution for 15 s to 15 min.

Next, in step b), the surface of the dielectric substrate (1) is treated with a manganate solution. The source of permanganate ions can be any water soluble permanganate compound. Preferred sources of permanganate ions are selected from the group consisting of sodium permanganate and potassium permanganate. The concentration of permanganate ions is in the range of 0.1 mol/l to 1.5 mol/l. The permanganate solution can be acidic or basic. Preferably, the permanganate solution has a pH in the range of 2.5 to 7. A layer of MnO ₂ is formed on the sidewall of BMV (3) by step b).

The surface of the dielectric substrate (1) is then contacted with a solution comprising a thiophene compound and an alkanesulfonic acid in step c).

The thiophene compound is preferably selected from the group consisting of 3-heterosubstituted thiophenes and 3,4-heterosubstituted thiophenes. Most preferably, the thiophene compound is selected from the group consisting of 3,4-extended ethyldioxythiophene, 3-methoxythiophene, 3-methyl-4-methoxythiophene, and derivatives thereof. The concentration of the thiophene compound is in the range of 0.001 mol/l to 1 mol/l, more preferably in the range of 0.005 mol/l to 0.05 mol/l.

The alkane sulfonic acid is selected from the group consisting of methanesulfonic acid, ethanesulfonic acid, methanedisulfonic acid, ethanedisulfonic acid, and mixtures thereof. The concentration of the alkane sulfonic acid is set by adjusting the desired pH of the solution used in step c). The pH of the solution is preferably set to 0 to 3, more preferably in the range of 1.5 to 2.1.

In step c), when the acidic aqueous solution or the acidic microemulsion acidic contact dielectric substrate (1) containing at least one thiophene compound and at least one aqueous substrate of an alkanesulfonic acid is used, the thiophene compound is in step b) The deposited MnO ₂ is polymerized upon contact. The conductive layer (5) is then formed by polythiophene and derivatives thereof obtained by the thiophene compounds.

This method only results in the formation of a conductive organic polymer on the portions of the surface of the substrate composed of the dielectric substrate material (1), i.e., the sidewalls of the BMVs (3). The surface of the copper cladding (2) does not contain the conductivity as a conductive layer (5). Machine polymer.

Electrochemicals has developed a method involving the use of conductive carbon particles and is commercially available, for example, under the trade name "Shadow". Another method known in the art is the "black hole" method developed by MacDermid. Suitable conductive carbon particles are, for example, graphite and its derivatives (Printed Circuits Handbook, 5th Edition, 2001, C. F. Coombs, Jr., eds., pp. 30.4 to 30.6). The substrate surface is first adjusted and then coated with conductive carbon particles. The carbon coating is then dried and the portion of carbon particles deposited on the copper coating (2) is removed. This carbon coating acts as a conductive layer (5) and is suitable as a surface for electroplating copper.

In another embodiment of the invention, the conductive layer (5) is formed from a colloidal precious metal (Printed Circuits Handbook, 5th Edition, 2001, C. F. Coombs, Jr. eds., pp. 30.2 to 30.4). Shipley Ronal and Atotech have developed methods involving the use of colloidal palladium particles and are known, for example, under the trade names "Crimson", "Conductron" and "Neopact", respectively. The conductivity of the colloidal palladium particles can be increased by, for example, providing a "bridge" of vulcanization between individual colloidal palladium particles adsorbed on the surface of the substrate. The conductivity of the adsorbed colloidal palladium particles is then sufficiently high to act as a conductive layer (5) for continuous electroplating of copper.

An embodiment using conductive carbon particles or colloidal precious metal particles as the conductive layer (5) is shown in FIG. The formed copper rail (8) is shown in Fig. 6.

Next, the surface of the dielectric substrate (1) is rinsed and then applied to form a copper track (8) and a copper-filled BMV (9) by copper plating.

Plating solutions suitable for copper deposition in step (iv) have been used in the art know. It is preferred to use an acid copper plating bath comprising copper ions, an acid, an organic additive, and chloride ions. This copper electroplating bath composition is disclosed, for example, in C. F. Coombs, Jr., "Printed Circuits Handbook", 5th edition, 2001, Chapter 29.4, pages 29.4 to 29.15.

The advantages of the method according to the invention in relation to the AM-SAP method known in the art are diverse: due to the lack of a conductive layer (5) comprising a copper layer deposited by electroless plating, The adhesion between the copper layers (6) deposited by electroplating on the copper cladding (2). Moreover, after etching, the shape of the copper track (8) is comparable to the AM-SAP method known in the art (which includes intervening between the copper cladding (2) and the plated copper layer (6) The copper track (8) obtained by electroless plating of the deposited copper layer (Fig. 2)) is more regular (Figs. 4 and 6).

The following non-limiting examples further illustrate the invention.

Instance Example 1 (comparative)

First, immerse the dielectric substrate (1) with a copper coating (2) having a thickness of 2 μm attached to both sides of the substrate and BMV (3) (having a diameter of 60 to 130 μm and a maximum aspect ratio of 1.1) at 30 ° C. The following includes H ₂ SO ₄ cleaner (Securiganth ^® Etch Cleaner SPS, product of Atotech Deutschland GmbH) for 30 s. Next, a seed layer (5a) comprising palladium is deposited. A thin layer of copper acting as a conductive layer (5) was deposited by electroless plating (Printoganth ^® U Plus, product of Atotech Deutschland GmbH, T = 35 ° C, t = 360 s). A copper layer (6) is deposited on the conductive layer (5) by electroplating (Cupracid ^® HL, product of Atotech Deutschland GmbH).

After the tin resist is applied, the resist layer (4) is removed, and the etching is eliminated. The conductive layer (5) and the portions of the thin copper cladding (2) coated by the deposited copper layer (6) are plated. A cross section of the dielectric substrate was prepared and investigated by optical microscopy.

Thus, the copper track shows an undesired undercut of the conductive layer (5) containing electrolessly plated copper (Fig. 2).

Example 2

First, immerse the dielectric substrate (1) with a copper coating (2) having a thickness of 2 μm attached to both sides of the substrate and BMV (3) (having a diameter of 60 to 130 μm and a maximum aspect ratio of 1.1) at 30 ° C. The following includes H ₂ SO ₄ cleaner (Securiganth ^® Etch Cleaner SPS, product of Atotech Deutschland GmbH) for 30 s. Secondly, by a) immersing the surface of the dielectric substrate (1) in a solution comprising a water-soluble polymer (Seleo ^® CP Conditioner Plus, product of Atotech Deutschland GmbH, T = 30 ° C, t = 30 s), b) Immersing the surface of the dielectric substrate (1) into a solution comprising permanganate ions (Securiganth ^® P 500, product of Atotech Deutschland GmbH, T = 90 ° C, t = 70 s), and c) dielectric substrate ( 1) The surface was immersed in a solution comprising a thiophene compound and an alkanesulfonic acid (Seleo ^® CP Plus, product of Atotech Deutschland GmbH) at T = 20 ° C for a continuous t = 90 s deposition of the conductive layer (5).

The copper layer (6) is deposited by electroplating (Cupracid ^® HL, product of Atotech Deutschland GmbH) into the conductive layer (5) and the copper cladding (2) not covered by the patterned resist layer (4) On those parts.

After applying the tin resist, removing the resist layer (4) and etching the conductive layer (5) not covered by the copper layer (6) deposited by electroplating and the copper cladding (2) After the equal portion, the cross section of the dielectric substrate is prepared and optical microscopy Mirror research.

Therefore, the copper rail (8) shows the desired regular shape (Fig. 4).

1‧‧‧ dielectric substrate

2‧‧‧copper cladding

3‧‧‧BMV

4‧‧‧Resist layer

5‧‧‧Transmission layer

5a‧‧‧ seed layer

6‧‧‧ copper layer

7‧‧‧Resist

8‧‧‧Bronze track

9‧‧‧BMV filled with copper

Figure 1 shows a prior art method for obtaining copper tracks (8) and BMV (9).

Figure 2 shows a schematic cross section of a copper rail (8) obtained by the method according to the prior art of Figure 1.

Figure 3 shows a method according to the invention for obtaining copper tracks (8) and BMV (9).

Figure 4 shows a schematic cross section of a copper rail (8) obtained by the method according to Figure 3.

Figure 5 shows another method according to the invention for obtaining copper tracks (8) and BMV (9).

Figure 6 shows a schematic cross section of a copper rail (8) obtained by the method according to Figure 5.

1‧‧‧ dielectric substrate

2‧‧‧copper cladding

3‧‧‧BMV

4‧‧‧Resist layer

5‧‧‧Transmission layer

6‧‧‧ copper layer

Claims (15)

A direct plating method comprising the steps of: (i) providing a dielectric substrate (1) having a copper cladding having a thickness of 0.5 to 10 μm on both sides of the dielectric substrate (1) (2) And at least one blind microwell (BMV) (3), (ii) depositing a conductive layer (5) on at least a portion of the surface of the substrate, wherein the conductive layer (5) is selected from the group consisting of a conductive polymer, comprising a noble metal a group of colloidal particles and conductive carbon particles, (iii) applying a resist layer (4) to the copper coating (2) and patterning the resist layer (4), and (iv) by electroplating A copper layer (6) is deposited onto the conductive layer (5). The direct plating method of claim 1, wherein the portion of the substrate surface includes sidewalls of the at least one blind microwell. The direct plating method of claim 1, wherein the colloidal particles comprising a noble metal are colloidal palladium particles. The direct plating method of claim 1, wherein the conductive carbon particles comprise graphite or a derivative thereof. The direct plating method of claim 1, wherein the conductive layer (5) comprises a conductive polymer selected from the group consisting of polythiophene, polypyrrole, polyaniline, derivatives thereof, and mixtures thereof. A direct plating method comprising the steps of: (i) providing a dielectric substrate (1) having a copper cladding having a thickness of 0.5 to 10 μm on both sides of the dielectric substrate (1) (2) ) and at least one blind microwell (BMV) (3), (ii) depositing a conductive layer (5) on at least a portion of the surface of the substrate, wherein the conductive layer (5) is selected from the group consisting of conductive polymers, colloidal particles comprising noble metals, and conductive carbon particles, wherein The following steps form the conductive layer (5) in step (ii): (ii) a) contacting the surface of the dielectric substrate (1) with a solution of a water-soluble polymer, (ii) b) using a permanganate solution Treating the surface of the dielectric substrate (1), and (ii) c) treating the surface of the dielectric substrate (1) with an acidic aqueous solution or acidic microemulsion containing at least one thiophene compound and at least one aqueous substrate of an alkanesulfonic acid, (iii) applying a resist layer (4) to the copper cladding (2) and patterning the resist layer (4), and (iv) depositing a copper layer (6) onto the conductive layer by electroplating ( 5) Up. The direct plating method of claim 6, wherein the water-soluble polymer is selected from the group consisting of polyvinylamine, polyethyleneimine, polyvinylimidazole, alkylamine ethylene oxide copolymer, polyethylene glycol, polypropylene glycol, and B. a copolymer of a copolymer of a diol and a polypropylene glycol, a polyvinyl alcohol, a polyacrylate, a polypropylene decylamine, a polyvinylpyrrolidone, and a mixture thereof. The direct plating method of claim 6, wherein the concentration of the water-soluble polymer is in the range of 20 mg/l to 10 g/l. The direct plating method of claim 1 or 6, wherein the permanganate ion concentration is in the range of 0.1 mol/l to 1.5 mol/l. The direct plating method of claim 1 or 6, wherein the at least one thiophene compound is selected from the group consisting of 3-substituted hetero-substituted thiophenes and 3,4-substituted hetero-substituted thiophenes a group of people. The direct plating method of claim 1 or 6, wherein the concentration of the at least one thiophene compound is in the range of 0.001 mol/l to 1 mol/l. The direct plating method of claim 1 or 6, wherein the at least one alkane sulfonic acid is selected from the group consisting of methanesulfonic acid, ethanesulfonic acid, methanedisulfonic acid, ethanedisulfonic acid, and mixtures thereof. The direct plating method of claim 1 or 6, wherein the pH of the solution comprising the at least one thiophene compound and the at least one alkanesulfonic acid is in the range of 0 to 3. The direct plating method of claim 1 or 6, wherein the thickness of the copper coating (2) is in the range of 1 to 5 μm. The direct plating method of claim 1 or 6, wherein the thickness of the copper coating (2) is in the range of 2 to 3 μm.