Standard available Tg FR4 laminates are capable of the higher soldering
temperature used by Pb free solders, however, the rate of X,Y and most
importantly Z axis expansion where higher layer count multilayers are
concerned are likely to be the most affected by the increase in Z axis
expansion. I would prefer to use a higher Tg FR4 where I knew that higher
temperatures are going to be used.
Normal rate of expansion above the Tg of materials is in the region of
60-70ppm per degree Celcius rise. If a higher Tg material is used, then this
overall expansion is lessened. An even better way to go is to use a filled
version of a high Tg FR4, such as PCL370HR (Polyclad), which is described as
being "Bullet-Proof". Of course there are other materials available from
other suppliers. As with all good things, however, comes a premium, so cost
would need to be factored in.
Regards,
Colin McVean
Circuit Manufacture Ltd
Unit 9-12
Rowleys Green Lane
Longford
Coventry
CV6 6AG
Tel: 02476 666168
Fax: 02476 637089
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of McCall,Doug
Sent: 19 May 2004 08:02
To: [log in to unmask]
Subject: [TN] Pb-free and laminate Tg requirements
Hi,
What is the general thinking on the glas transistion temp (Tg) for FR4 being
used for Pb-free PCBAs. I guess that the 'standard' is 140 deg-C and is it
sensible (and required) to go for a higher Tg?? Is it a good idea to use a
higher
spec laminate??
Any thoughts will be very interesting.
Thanks,
> Douglas I McCall
> Printed Circuit Board Assembly Engineer,
>
> /// /// /// BOC EDWARDS
H BOC Edwards, 15 Marshall Road, Eastbourne, East Sussex, England, BN22
9BA
> * +44 (0)1323 501147
* +44(0)1323 509824
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