Hi Ioan - what is the assembly surface finish?

Dave Hillman
Rockwell Collins
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From:   Ioan Tempea <[log in to unmask]>
To:     <[log in to unmask]>
Date:   03/01/2013 10:40 AM
Subject:        [TN] Conductive path failure in thermal cycling
Sent by:        TechNet <[log in to unmask]>



Dear Technos,

RoHS assembly, soldered with SAC305 alloy, 0.075" thick 14 layers PCB, 
failing after 250 cycles (-20 C to 125 C).

Failure mode is crack between the traces and pad at 3 places. Happens on 2 
TH components. Traces are 0.0055" wide, pads are 0.022" in diameter on the 
via side or 0.065" on the component side. There is no tear dropping.

Should I bother figuring out if manual soldering of the TH component 
fragilizes the trace-pad junction, or this is an obvious case of design 
induced failure?

Thanks,

Ioan Tempea, ing.
Ingénieur principal de fabrication / Senior Manufacturing Engineer
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