| After switching from No-clean flux to Water soluble (Kester)we encountered voids problem (X-ray and microsectioning). Reducing the apperture sizes made the voids smaller but did not eliminate them. So we had to go back to No-clean. Any idea why voids occur? | Will appreciate any answer. | Voiding occurs with almost all solder paste applications. It sounds like you know some serious stuff as you are capable of both X-Ray and X-Sectional analysis and apparently have serious reliability concerns as well. Therefore, I'm sure you also know voiding isn't always a bad thing.
First, how much voiding? Second, how many voids in what locations? If you're in the 20% arena, you are doing pretty well according to some in industry and I agree with most of what is said regarding this percentage.
If you can do the analysis, are you correlating results with shake and bake and cycles to failure? I have seen very high cycle numbers with and without paste. Fewer at times without paste as there are no voids formed.
Earl Moon
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