# US 4,398,993 A · Neutralizing chloride ions in via holes in multilayer printed circuit boards

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- Number: US 4,398,993 A
- Document ID: US4398993A
- Status: Granted
- Kind: A
- Application number: 06/392,849
- Filed: 1982-06-28
- Granted: 1983-08-16
- Earliest claimed: 1982-06-28
- Assignees: International Business Machines Corporation
- Inventors: David W. Hume, Jr.; John Rasile
- Web page: https://patentgrep.com/patent/US4398993A

## CPC

- H05K 3/26: Cleaning or polishing of the conductive pattern
- H05K 3/0035: {of blind holes, i.e. having a metal layer at the bottom}
- H05K 3/025: {by transfer of thin metal foil formed on a temporary carrier, e.g. peel-apart copper}
- H05K 2201/0355: Metal foils
- H05K 2201/09509: Blind vias, i.e. vias having one side closed
- H05K 2203/0152: Temporary metallic carrier, e.g. for transferring material
- H05K 2203/0554: Metal used as mask for etching vias, e.g. by laser ablation
- H05K 2203/0723: Electroplating, e.g. finish plating
- H05K 2203/0726: Electroforming, i.e. electroplating on a metallic carrier thereby forming a self-supporting structure
- H05K 2203/0766: Rinsing, e.g. after cleaning or polishing a conductive pattern
- H05K 2203/0786: Using an aqueous solution, e.g. for cleaning or during drilling of holes
- H05K 2203/1388: Temporary protective conductive layer
- H05K: PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS

## Abstract

A neutralization process is provided for neutralizing chloride ions in etched via holes in multilayer printed circuit boards. The process comprises two dip operations of the board in a Neutra-Clean and water solution which is continuously re-circulated. This is followed by subjecting the board to a heated de-ionized cascaded water feed, an ambient overflow de-ionized water rinse, and conveyorized air drying. The Neutra-Clean solution has the ability to penetrate down to the bottom of the via hole and to attract the free chloride ions from the etchant residue. The de-ionized water feed and rinse steps rinse out and remove the Neutra-Clean solution and any residuals formed by chemical reaction.

## Claims

### Claim 1

The process of drilling blind via holes in a printed circuit board composite which consists of a peel-apart-copper layer covering an epoxy substrate which consists of the steps of:
etching holes through the peel-apart-copper layer;
subjecting said holes to a circulating Neutra-Clean solution;
cleaning said holes to remove said Neutra-Clean solution; and
utilizing a laser drill to extend said etched holes into the epoxy substrate.

### Claim 2

The process of drilling blind via holes in a printed circuit board composite which consists of a peel-apart-copper layer covering an epoxy substrate which consists of the steps of:
etching holes through the peel-apart-copper layer with a cupric chloride etchant containing HCl acid;
subjecting said holes to a circulating solution of Neutra-Clean and water to neutralize chloride ions in the etchant residue in said holes;
cleaning said holes with de-ionized water to remove said Neutra-Clean solution and any residuals due to chemical reaction; and
utilizing a laser drill to extend said etched holes into the epoxy substrate.

### Claim 3

The process of drilling blind via holes in a printed circuit board composite which consists of a peel-apart-copper layer covering an epoxy substrate which consists of the steps of:
etching holes through the peel-apart-copper layer with a cupric chloride etchant containing HCl acid;
first and second 5 minute dip operations of said holes in a solution of 50% Neutra-Clean and 50% water at 120.degree. F.;
subjecting said holes to a 2 minute heated de-ionized cascaded water feed at 100.degree. F.
subjecting said holes to a 2 minute ambient overflow de-ionized water rinse; and
utilizing a laser drill to extend said etched holes into the epoxy.

### Claim 4

A process for neutralizing chloride ions in etched via holes in a multilayer printed circuit board, wherein said via holes are etched by a cupric chloride etchant containing HCl acid, said process comprising the steps of:
first and second dip operations of said via holes in a solution of Neutra-Clean and water which is continuously re-circulated;
subjecting said via holes to a heated de-ionized cascaded water feed;
subjecting said via holes to ambient overflow de-ionized water rinse; and
air drying the board.

### Claim 5

A process for neutralizing chloride ions in etched via holes in a multilayer printed circuit board, wherein said via holes are etched by a cupric chloride etchant containing HCl acid, said process comprising the steps of:
first and second dip operations of said via holes in a solution of Neutra-Clean and water which is continuously re-circulated, said solution containing ammonium chloride and sodium chloride which attract free chloride ions from etchant residue in said via holes;
subjecting said via holes to a heated de-ionized cascaded water feed;
subjecting said via holes to an ambient overflow de-ionized water rinse, said water feed and water rinse removing the Neutra-Clean solution and any residuals due to chemical reaction from said via holes; and
air drying the board.

### Claim 6

A process for neutralizing chloride ions in etched via holes in a multilayer printed circuit board, wherein said via holes are etched by a cupric chloride etchant containing HCl acid, said process comprising the steps of:
first and second 5 minute dip operations of said via holes in a solution of 50%
Neutra-Clean and 50% water which is continuously re-circulated at 120.degree. F.;
subjecting said via holes to a 2 minute heated de-ionized cascaded water feed at 100.degree. F.;
subjecting said via holes to a 2 minute ambient overflow de-ionized water rinse; and
conveyorized air drying of the board.