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Method for Making Reliable Multiwire Plated Through Holes

IP.com Disclosure Number: IPCOM000053076D
Original Publication Date: 1981-Aug-01
Included in the Prior Art Database: 2005-Feb-12
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Underkofler, WL: AUTHOR [+2]

Abstract

In the multiwire circuit board process, insulated copper wires are embedded in an adhesive layer by a wiring machine. A layer of epoxy glass prepreg is hot pressed over the wires and adhesive to encapsulate the wires. Electrical connections to the wires are made by drilling through the board and wires and making a plated through hole with plated connection to the end of the wire. The plated through hole is made by catalytically seeding the hole wall followed by electroless copper plating.

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Method for Making Reliable Multiwire Plated Through Holes

In the multiwire circuit board process, insulated copper wires are embedded in an adhesive layer by a wiring machine. A layer of epoxy glass prepreg is hot pressed over the wires and adhesive to encapsulate the wires. Electrical connections to the wires are made by drilling through the board and wires and making a plated through hole with plated connection to the end of the wire. The plated through hole is made by catalytically seeding the hole wall followed by electroless copper plating.

Intermittent problems can occur relative to the quality of the plated joint between the hole and the wire end and the formation of nodules and spongy copper. Joint separation would occur with solder shock.

The following process cures these problems and creates a sound plated through hole to wire joint. Key operations of the process flow are: 1. Laminate FMY38 adhesive (product of American Cyanimid Co.) to an epoxy glass laminate. 2. Insert the insulated wires into the adhesive panel. 3. Cure bake the adhesive for 1 hour at 250 degrees F. 4. Laminate the semi-cured epoxy glass prepreg. 5. Laminate POLY-SPOT-STICK* (rubber mask) to protect the prepreg from chemicals, seeder, and unwanted plating. 6. Drill holes. 7. Vapor blast, heat shrink POLY-SPOT-STICK, and vapor blast. 8. Chemical hole clean. a. Pyrrolidone, Chromic-Sulfuric acid b. Sodium Permanganate (4 minutes) flow through. 9. Vapor blast. 10. Seed (tin-palladium ca...