Remember that TD is complete package failure and certain conditions that
precipitate electrical failure modes will be in effect at a point some
where in the gradient to the TD level. 



Jeffrey Bush
Director, Quality Assurance and Technical Support

                          76 Technology Drive - POB 1890
                             Brattleboro, Vermont 05302-1890
                                Tel. 802.257.4571.21 Fax. 802.257.0011
                                    [log in to unmask]
                              http://www.vtcircuits.com	


-----Original Message-----
From: Sherif Refaat [mailto:[log in to unmask]] 
Sent: Wednesday, October 20, 2004 5:14 PM
To: [log in to unmask]
Subject: Re: [TN] Td questions
Importance: High

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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