Chris,
This sounds very similar to a problem we had.  The board
worked when the main chip was in a socket, but when soldered
down, it only worked when the chip was pressed down.  Our
first thought was that it was a warpage problem with the PCB
but it turned out to be a packaging problem with the chip
itself.  We got a new package for the chip and it worked
with the same PCBs that had failed earlier.
Just a possibility to consider.
John Woodford



>From: Chris Ball <[log in to unmask]>
>Reply-To: "DesignerCouncil E-Mail Forum." <[log in to unmask]>,
>[log in to unmask]
>To: [log in to unmask]
>Subject: [DC] DC - Tolerable Rigid Board Flexing after final assembly
>Date: Tue, 19 Sep 2000 16:51:01 -0400
>
>Hi-
>Is anyone familiar with any formal documentation saying how much you can
>flex a
>rigid PCB after assembly? Before you hurt it, I mean. I know this sounds
>like a
>stupid question, but "none" isn't a valid answer. And "as little as
>possible"
>doesn't sound very scientific.
>
>I'm familiar with the bow/twist spec for bare boards. That's not what I'm
>looking for. We're seeing failures on finished assemblies at the customer.
>When
>they dismount and ship 'em back, they work. But if we flex the housing (and
>therefore, the PCB) we can re-create the failure. When we tell the customer
>it's
>because of how they stress the PCB when they mount it, they'll ask what
>amount
>of stress is acceptable. Can anyone quantify that for me?
>
>Best Regards,
>-Chris Ball
>
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