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With my previous work developing rework processes for ceramic BGAs (1st
level package rework, not card rework), I played around with inverting the
BGA at temps of 200C while securing the 90/10 balls in hopes of separating
the two. I found that even inverted you still had to apply a significant
amount of force to separate them. The surface tension effects of the molten
eutectic solder were quite large, enough to support a heavy CBGA inverted.
If you are using a PBGA, they should be able to undergo a 2nd reflow
inverted without any harm. In fact you will elongate the joints some, making
them even more reliable (never thought you would see a bonus of a second
reflow!). The question is how far are you from the cliff when you include
belt vibration and other factors.
It may be worth experimenting with rather than having to use epoxy to glue
component down.
Don Foster
Symbios Logic
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