Many thanks to all who responded to my question on the above subject, a 
couple of which confirm my own theories.

It seem that parts with Pt/Ag (and for that matter others with a Silver 
content) terminations are susceptible to Silver leaching from the component 
metallisation into the bulk solder and that this is exacerbated by higher 
process temperatures.

Now I am not a metallurgist so correct me if I am wrong - we used to employ 
62Sn/36Pb/2Ag solder on hybrid assemblies to mitigate this type of problem 
back in the good old non-RoHS days. The theory being that the 2% Ag in the 
solder slowed the dissolution rate. As we are now using a solder with 3.5% 
silver should this not improve the situation, or do the higher process 
temperatures used just cancel this out?

Dave Hillman has said that using these parts with SAC305 CAN be done with 
careful attention to the soldering process profile. We have done our best to 
minimise the TAL and the peak temperature, mindful of getting all the other 
components on the assembly reliably soldered also. The problem parts 
concerned are on both sides of a double sided assembly and those on the side 
that is reflowed twice are definitely much worse so I guess this confirms 
that they are not really suitable.

Bit of a problem really as there is not an alternative part. Oh well  - As a 
responsible contractor we will now inform our customer and await their 
response.



-----------------------------------------------------------------------
Peter Barton
Senior Process Engineer
ACW Technology Ltd
Dinas Isaf West
Tonypandy
Mid Glamorgan. CF40 1XX  Wales

Tel: 01443 425275 (direct)
Fax:  023 8048 4882
International Tel : +44 1443 425200
International Fax : +44 23 8048 4882
Website/URL:  www.acw.co.uk

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------