My problem is dropping solder ball from BGA devices after ball attachment process.
First, I suspected the tempareture of reflow oven, but that was sufficient to melt
solder ball. After reflow, some balls(5-10% of strip) are missing, and empty pads
are not wetting or partialy wetting.
I found voids in flux on pad before placing ball, so I guess the void will expand
in reflow furnace, and ball dosen't touch to pad. I use dispensing system to provide
flux, which sometimes contaminates air void to flux on pad.
Does anyone have any experiences and suggestions to solve this problem ?

Thanks in advance.
---------------------
Fumiaki Shigeoka
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