Sorry for delay Guy:
First thank you for your interesting description.
We use 3 min preheating, 1 min to soak
and 1min in reflow. It s to no clean solder paste.

Thanks..
saul

>>> "Guy Ramsey" <[log in to unmask]> 3/11/2005 10:37:46 AM >>>
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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