What type of package is it?  Outside of popcorning, sometimes glob-top BGAs "potato chip" under temperature, then flatten back out when cooled.  The result is center shorts and strained ball attachments at the corners (BGA substrate moves as it cools).  The effect isn't always consistant within batches of BGAs.

> Larry Jindra
> TRW/Avionics Systems Division
> mailto:[log in to unmask]   ph (858) 592-3424   fax (858) 592-3606


-----Original Message-----
From: Brad L. Matthies [mailto:[log in to unmask]]
Sent: Monday, June 26, 2000 6:21 AM
To: [log in to unmask]
Subject: [TN] Reflow Oven Causing Bridging???


TN,

I have been asked to take a look at our convection reflow ovens to
verify that they are not causing bridging on an array packages?!?  The
ovens have recently been relocated and the CFM is slightly less than
what the previous set-up had, but is still above what the equipment
manufacturer requires.  The array package has recently begun to show
bridging between pins (not always the same two pins) on the center
grouping of balls on only one of the three array packages.  There are
two other array packages on this same board, and they show no bridging.
We are using a x-ray to view these three compontents post reflow.  Our
analysis indicates that the stencil is showing signs of wear and needs
to be replaced, but I have been asked to look at the reflow profile as
well.  I have no idea if a reflow oven (convection) can cause the type
of bridging we are seeing.  If if could, wouldn't the bridging present
globally or randomly rather than in the same location on the same
component ID?  I am also wondering if a Wave profile can cause
re-reflowed joints that would result in bridging on array packages.  Any
thoughts would be greatly appreciated.

Regards,
blm

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