Sunday, December 22, 2013

It's all about the paste

I finished building the last few BGA test boards today and learned a bit.  Here's an overview of my results including all six cards per component:

Part Type Total Qty Qty Failed Yield
0805 18 0 100%
0603 12 0 100%
0605 (LED) 48 2 95.8%
0402 24 0 100%
QFN (0.65mm pitch) 6 0 100%
BGA (0.5mm pitch) 6 1 83.3%

I was able to correct the LED soldering issues by hand; I think that the parts were a little misaligned when I placed them.  The BGA issue looks like a short.  I'll do some more testing to try to confirm that.

Fortunately I was able to improve my assembly process and the last three boards built were trouble-free.  The most important improvement that I made while building the last three cards was to secure the stencil on only one side so that I could remove it quickly and avoid smearing the paste:

This method allowed for a very clean application of paste:

Better assembly led to prettier pictures:

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