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Date: | Fri, 2 Jul 2010 11:40:18 -0400 |
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Our friends at Rockwell have a chart in one of their presentations that show
CTE of various common laminates up to a typical reflow temp.
At room temp CTE of them is about 25ppm /degree C. But, by 150 C things get
less predictable. And can be 75 ppm / degree.
The thing is you are trying to attach a flex. What is its CTE. The
difference between the two? It is important.
Part two of your question The Z axis expansion of the woven substrate will
be higher than the "x-y" advertized CTE. So, no I would not expect the
material to shrink. What happens of the flex expands wildly above 100 C, you
might think the substrate shrank . . .
Guy
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Eric Christison
Sent: Friday, July 02, 2010 11:12 AM
To: [log in to unmask]
Subject: [TN] Question about FR4 Curing
I'm wondering about an issue we have with the dimensional stability of a
substrate made of FR4.
We're finding it's deforming during a flex attach operation, not by much
but enough to cause us a problem. We use ACF and a hot bar. The
substrate sees a temperature of 155 deg C for about 10 seconds. Someone
suggested that the movement may be due to incomplete curing of the
substrate.
I'm wondering if a temperature of 150 deg C for 10 seconds is likley to
have any effect at all on the matrix.
If it did, would the volume of the matrix increase, decrease or stay
much the same?
I realise that we'll see deformation due the application of pressure as
well but in some instances the substrate seems to be moving in the wrong
direction.
Thanks,
--
Eric Christison
Consumer& Micro group
Imaging Division
STMicroelectronics (R&D) Ltd
33 Pinkhill
Edinburgh EH12 7BF
United Kingdom
Tel: +44 (0)131 336 6165
Fax: + 44 (0)131 336 6001
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