Bill,
That is a lot of warp.  I guess I would try to get the vendor involved.
With that much warp over temperature there may be a temp cycle reliability
issue.  Many suppliers buy standard carriers and attach their custom die.
Maybe there is a die attachment problem.
If you have to use those parts, maybe a 'hershey kiss' paste shape on the
pads (obtained from a dispensor) may be more forgiving than a flat shape
from a stencil printer.
Just a few thoughts,
Jim Kittel

-----Original Message-----
From: Bill Raymond [mailto:[log in to unmask]]
Sent: Thursday, September 06, 2001 7:21 AM
To: [log in to unmask]
Subject: Re: [TN] BGA Warp


Jim, thanks I'll start looking into this today!  However, it appears from
testing we are doing that the warp occurs during ramp up - we have heated
some of these chips in an oven to 125 deg C, allowing them to stabilize,
and we measure warp upwards of 6 to 8 mil ... at this point, the solder
balls of the BGA are not even touching the solder paste.

Bill...

At 06:48 AM 09/06/2001 -0600, you wrote:
>Bill,
>If you have not already, look at the cooling rate on your reflow oven.  I
>solved a similar similar warpage problem by reducing the solder cooling
rate
>to 1 deg C/second.  I had to modify the blowers in the cool down section to
>achieve that rate.  I found my oven was designed to blast the top of the
BGA
>with cold air while the solder was still liquidus.  It provided for high
>speed production, but was warping some of the BGA's.
>
>Jim Kittel

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