Rick,

Do you happen to have uneven copper balance throughout the thickness of the
board - maybe some heavy-weight copper towards one outside layer and no
counterbalance in the corresponding layer on the other side? Are you using
top and bottom heating? Are you heating too fast - bear in mind how long it
takes to heat the BGA contacts under all that sunshade (aka BGA component
body).

To me, it could be that you're heating too quickly at too-high a
temperature. Reduce the heat, but have a longer soak and see if that helps
keep the board flat.

Peter




                    Rick Howieson
                    <RHowieson@DELTAGRO        To:     [log in to unmask]
                    UPINC.COM>                 cc:     (bcc: DUNCAN Peter/Asst Prin Engr/ST
                    Sent by: TechNet           Aero/ST Group)
                    <[log in to unmask]>          Subject:     Re: [TN] BGA/Vias


                    01/17/02 03:40 AM
                    Please respond to
                    "TechNet E-Mail
                    Forum."; Please
                    respond to
                    RHowieson






I probably didn't make myself clear. The problem is the board itself
collapses/sinks/"potato chips"...in the area being heated, i.e. BGA
location.
Rick

-----Original Message-----
From: Earl Moon [mailto:[log in to unmask]]
Sent: Wednesday, January 16, 2002 11:36 AM
To: [log in to unmask]
Subject: Re: [TN] BGA/Vias


Agree with that. Without board reaching equillibrium (spelling?) top to
bottom, no even solder joint formation (in the case of BGA's - ball
collapse) possible. Uneven "sinking" (collapse) bound to occur but usually
within nanoseconds of others - depending on thermal conditions.

MoonMan

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