Authored By:
Georgie Thein, David Geiger, and Murad Kurwa
Flextronics International
Milpitas, California
Summary
In this study various printed circuit board surface finishes were evaluated, including: organic solderability preservative (OSP), plasma finish (PF), immersion silver (IAg), electroless nickel / immersion silver (ENIS), electroless nickel / immersion gold hi-phosphorus (ENIG Hi-P), and electroless nickel / electroless palladium / immersion gold (ENEPIG). To verify the performance of PF as a post-treatment option, it was added to IAg, ENIG Hi-P, and ENEPIG to compare with non-treated. A total of nine groups of PCB were evaluated. Each group contains 30 boards, with the exception on ENIS where only 8 boards were available.
The PCBs were subjected to various pre-conditioning to simulate different conditions of the surface finish. After pre-conditioning, the PCB was printed with lead-free SAC305 solder paste and SMT components placed. The PCB was reflowed using a typical reflow profile for a lead-free process.
After reflow, each surface finish under various pre-conditioning was rated for solder spread on pad, voiding performance of BGA and QFN devices, followed with cross sectional analysis. The results were tabulated by each pre-conditioning group and a summary table was provided. A summary was provided to rate each surface finish for use under three conditions: 1) fresh condition, 2) three times reflow, 3) storage simulation.
Conclusions
New board surface finishes evaluated for this study were Plasma Finish (PF), Electroless Nickel / Immersion Silver (ENIS), Electroless Nickel / Immersion Gold Hi-Phosphorous (Hi-P ENIG), and Electroless Nickel / Electroless Palladium / Immersion Gold (ENEPIG).
Surface finishes with Organic Solderability Preservative (OSP) and Immersion Silver (IAg) were also tested. In addition, plasma finish was added as the top coat protection to IAg, Hi-P ENIG, and ENEPIG to verify any performance differences.
A total of nine groups of PCB surface finish were evaluated. PCBs were subject to various pre-conditioning prior to assembly to simulate possible scenarios during typical assembly processes (for example: reflowed in air, baking, misprint, etc). Other pre-conditioning simulated storage and shelf life, and more pre-conditioning simulated extreme processes (1x, 2x, 3x reflow prior to assembly). In total, each group of PCB surface finishes had 30 pieces available with 3 samples per pre-conditioning, except for ENIS where only 8 pieces were available.
Based on the results from the solder spread test, there was no significant improvement observed on the surface finish with OSP versus PF, or the surface finish with PF added as a top coat protection.
Initially Published in the IPC Proceedings
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