Werner,

I had a recent incident where my customer complained about delamination that
led to open circuit. The boards, after assembly,  failed in-circuit test.
The failure occurred at the pins of a connector that was soldered using
selective wave. When examining the location of the failure I could see
measling between the pins of the connector and in some sever cases I could
see delamination. When cross sectioned, there was clearly delamination
between layer 2 and the prepreg on top if it. We found out that the customer
had to use 296? C. for 7 seconds to be able to solder the connector using
selective wave. There was no way to change these parameters because of the
thermal mass of the connector. The fact that we used 170 Tg laminate had no
effect on this problem. Our laminates' supplier told us that the laminate we
used had Td (Temperature to decomposition) of 300? C. which was too close to
the selective wave solder temperature. They recommended using laminate that
has Td of 350? C. which we used and it took care of the problem.

It seems to me that this Td parameter will become more important with the
Lead free process. I was not aware of its importance until I encountered
this problem.

Because of the increased cost of this laminate I'm considering the idea of
using 350 Td only next to the outer layer that gets exposed to the selective
wave and 300 Td for the rest of the laminate and pre-preg. Off course this
idea has to be tested first.


Sherif Refaat, Eng.

Technology Roadmap Consultants Inc.

E-mail: [log in to unmask]

Tel. (514) 624 9842

Fax (514) 624 0091



----- Original Message -----
From: "Werner Engelmaier" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, October 20, 2004 3:43 PM
Subject: [TN] Td questions


> Hi 'Netters,
> Has anybody looked at the Td's for the various materials used in
> components
> and PCBs relative to the higher soldering temperatures needed for
> LF-soldering?
> Can this info be shared?
> What kind of damage/failure modes and mechanisms can we expect because of
> this?
>
> Regards,
> Werner Engelmaier
>
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