Reducing Solder Voids with Copper-Filled Microvias

Stafstrom, Eric; Singer, Adam; McLenaghan, James; Nishu, Keisuke
April 2003
Circuits Assembly;Apr2003, Vol. 14 Issue 4, p22
Trade Publication
The article presents a study which seeks to find out the frequency, location and size of voids with and without copper-filled vias. The purpose of this study was to determine the effect of via filling on void formation in solder joints. Utilizing microvias in surface-mount pads on printed wiring boards (PWB) has created unique challenges for both PWB fabricators and assemblers. Implementation of microvia-in-pad technology into PWB designs allows for tighter spacing of ball grid arrays (BGA) and stacked via build-up techniques to eliminate less reliable plated through holes. Based on x-ray imaging, the IPC-7095 standard specifies three categories for void size for BGA solder joints. These categories are based on the percentage of joint cross-sectional area occupied by the void. The study compared conformal copper plating to partial and full via filling with copper. Different solder paste chemistries and reflow profiles were selected to provide a range of potential solder voids. Both cross section and x-ray analysis were performed to measure void size, occurrence and location.


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