I once watched a real time x-ray video, produced by Phoenix X-ray. The video
was a 9 minute reflow of a BGA package. In the sequence one could observe
the initial wetting and second drop of the BGA package (reminiscent of the
Ersa real time view from a side mounted camera). Immediately after the
second drop the solder fillets were nearly perfect with negligible voids.
During the following few minutes voids began to form within the balls. They
began small and grew larger, quite large. Subsequently, they voids broke up
forming many small voids. The package spent about 5 minutes ramping to
reflow and about 4 minutes in reflow. Everything looked perfect until about
150 seconds into reflow.

I really don't know mechanisms behind the phenomena. But, wonder if you
aren't seeing something related to an extended  it.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Saul MorenoRodriguez
Sent: Wednesday, March 09, 2005 10:15 PM
To: [log in to unmask]
Subject: [TN] Voids


Hello Technetters:

In a recently running we had a problem with voids in Micro BGA's.
We resolved succesfully only increasing the preheat and the soak time,
this to dry the humidity correctly in the devices.

But my doubt is here:
The Micro BGA's are placed on first side and in first reflow we didn't
have problems,
all was ok, but voids showed up in the second reflow .
We detected them in 5DX.

Could you tell me why this happened ?

Thanks in advance..

Saul Moreno R.
Process Engineer

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