SMTA International Conference Proceedings

Controlling High Copper Roughness for Enhancing Immersion Metal Surface Finish Performance

Authors: Lenora Toscano, Aaron Karoly, Ernest Long, Ph.D.
Company: MacDermid
Date Published: 9/28/2014   Conference: SMTA International

Abstract: PCB proprietary chemical suppliers rely on chemical processes that generate high surface roughness to promote soldermask adhesion to copper. This is in response to PCB applications which require high thermal resistance, line and space reduction, compatibility with all surface finishing and high temperature localized assembly. All of these conditions benefit from a strong bond between the copper and soldermask, especially at the soldermask/pad interface locations.

The surface preparation for soldermask application involves a chemical process that modifies the copper topography, creating a high roughness and high surface area structure which anchors the soldermask to the copper for superior adhesion. Unfortunately, very high copper roughness can lead to performance challenges related to the surface finish including difficulty in achieving surface cleanliness and degraded solderability. This is especially true for those finishes that are designed to produce thin deposits such as immersion metal plating.

This paper addresses the issue of high copper roughness in conjunction with thin surface finish plating such as immersion silver and immersion tin performance. It will propose a microetch chemistry to reduce the real surface area roughness associated with traditional heavy soldermask adhesion promoters. It will show how this newly developed etch chemistry then enhances the performance characteristics of the final finish which had been degraded by high copper roughness.

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