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Rounded Plated Through Holes

IP.com Disclosure Number: IPCOM000091004D
Original Publication Date: 1969-Sep-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Spannhake, HK: AUTHOR

Abstract

In fabricating multilayer printed circuit boards with plated through-holes, the hole platings, when stressed, tend to crack at edge junctures between interior hole surfaces and exterior board surfaces. Such cracking is avoided by rounding the edges before the holes are plated. Starting with a metal foil clad multilayer structure 1 as in drawing A, with predrilled, burr-free and debris-free through-holes 2, the exterior foil surfaces are subjected to localized milling action, drawings B and C. Such milling occurs at least until hole edge regions 3 are rounded to desired states of curvature 4. Smoothed holes 2 are then over-plated, drawing D, by electroless and electrolytic techniques.

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Rounded Plated Through Holes

In fabricating multilayer printed circuit boards with plated through-holes, the hole platings, when stressed, tend to crack at edge junctures between interior hole surfaces and exterior board surfaces. Such cracking is avoided by rounding the edges before the holes are plated. Starting with a metal foil clad multilayer structure 1 as in drawing A, with predrilled, burr-free and debris-free through- holes 2, the exterior foil surfaces are subjected to localized milling action, drawings B and C. Such milling occurs at least until hole edge regions 3 are rounded to desired states of curvature 4. Smoothed holes 2 are then over- plated, drawing D, by electroless and electrolytic techniques. When not rounded in this manner, the deposited plating 7 has a tendency to form cracks 8 along edge regions, drawing E, when placed under stress as by subsequent filling of the holes with solid matter. In the edge rounding process, the etching phase, drawing B, is carried out in an etchant such as ferric chloride for a time just sufficient to cause dissolution of surface metal 9 at sites 10 adjacent hole edges 3 without damage to other parts of the surface metal. The subsequent vapor blasting phase, drawing C, is also controlled in intensity and time duration to produce the desired curvature at edge regions 3.

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