Werner,

Thermally asymetric? Does this mean in the Z axis as a primary function of
the Al heat sink and the Silicon chip placed on a BT substrate, or?

Earl

----- Original Message -----
From: <[log in to unmask]>
To: <[log in to unmask]>
Sent: Saturday, February 09, 2002 2:29 PM
Subject: Re: [TN] Different CTE materials, what is the safe tolerance ?


> Hi MoonCaveMan,
> I had thought YOU had come out of your cave. I am currently babysitting
for
> my 3 granddaughters in NC.
> Steve says: it is a 384-ball .8mm pitch PBGA with a heatslug on the top...
> If it is in fact a PBGA with a heatslug on the top, than it is a
SBGA--these
> are notorious for warping when you change their temperature because they
are
> of a thermally asymetric design. I have seen solder balls ripped of the
pads
> and soldering pads ripped out of the PCB.
> You could also be right about the silicone affecting the global expansion
> mismatch with the PCB. TI has just agreed to license their microStarBGAs
> under Tessera's patents to avoid infringement [Sharp's CSPs were found to
> infringe Tessera's patents]. But it is not just CSPs that might have their
> BLR affected by the die; larger BGAs that are thin can suffer from the
same
> problem.
>
> Werner Engelmaier
>
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