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July 2010

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Subject:
From:
Guy Ramsey <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Guy Ramsey <[log in to unmask]>
Date:
Fri, 2 Jul 2010 11:40:18 -0400
Content-Type:
text/plain
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text/plain (93 lines)
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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