Rick,

Plastic BGAs as you describe are classified as moisture-sensitive
components. The main concern has to do with potential internal defects if
the parts have absorbed too much moisture from the ambient air prior to
reflow (rapid vaporization of entrapped moisture will create high stress
causing cracks and delaminations inside the package).

Another moisture-related phenomena that is unique to PBGAs is that they also
have a tendency to warp due to moisture absorption, even prior to any
temperature cycle like reflow. This is because moisture tends to swell the
different materials at different rates (i.e. the BTU laminate and the
plastic overmold). In most cases however, the corners tend to warp up, not
down as you explain.

Try to bake the components prior to reflow to see if the problem goes away.
If it works this means that your components have absorbed too much moisture
and you should also be concerned about potential reliability damage due to
internal cracks and delaminations.

Francois Monette
Cogiscan Inc.
50 De Gaspe, Suite A5
Bromont, Quebec, Canada, J2L 2N8
Tel : (450)534-2644
Fax: (450)534-0092
www.cogiscan.com


Date:    Wed, 23 May 2001 09:19:18 -0700
From:    Rick Thompson <[log in to unmask]>
Subject: Altera BGA Reflow Problem

Hi,

We have an Altera fine pitch BGA that I'm having difficulty placing &
soldering.  I'm hoping someone may have experience with this particular part
or can offer some suggestions.  The part in question is an EP20K300 series
in a 'thermally enhanced' 672 ball package. Pitch is 1mm.  The package looks
like an FR4 substrate with a layer of some sort of bonding material on top.
I think it's probably the same as the 'glob-top' material except it covers
the entire area of the part.

The problem we're having it that the part appears to be 'cupping' down at
the corners, causing shorts at the corners. Complicating this is the fact
we're placing this on .018"  thick PCB's.  I've looked at our profiles on
top and bottom and don't believe that the top is heating too much but we
still get the cupping effect.

Any experience with this chip or suggestions in general would be greatly
appreciated.

Thanks,


Rick Thompson
Ventura Electronics Assembly
2655 Park Center Dr.
Simi Valley, CA 93065

+1 (805) 584-9858   x-304  voice
+1 (805) 584-1529 fax
[log in to unmask]

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