Dave,

You might ask the soldering personnel how they held down the resistor while they soldered it in place... If the pads were pre-bumped by the SMT process and they held them down with tweezers while they soldered each end in place they may have cracked them when the soldered down the 2nd end... You might be able to determine when they cracked ( first or second end) by look to see if the crack started from the top or bottom of the part...

Paul   

Paul Edwards
Surface Art Engineering


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dave Connitt
Sent: Monday, October 26, 2009 3:05 PM
To: [log in to unmask]
Subject: [TN] Question regarding 0402 resistors and ceramic capacitors

Hi Everybody,

I think I know the answer to this but here goes..

We recently started using 0402 resistors and ceramic capacitors on a
development project. Yes, it is our first time going this small...

Everything was progressing OK until this morning when it I found out a
couple of resistors cracked during temperature cycle testing (-70F to
+150F). I also found out that these parts were soldered by hand. Both
cracked parts are located in the same area, in fact I think they are the
same parts in both instances. We can't really determine when the parts
were cracked but it sounds like they may have been cracked at assembly
as they were found during trouble shooting of the circuit.

My question is could this failure be a result of trying to hand solder
these parts? I am wondering if they were pushed beyond their maximum
temp and time duration during soldering?

We should have ran these through our SMT line but time didn't allow for
it. You how it goes, there is never time to do it right the first time
but there is always time to do it over....

If someone has another possible scenario I could investigate, I would
appreciate any help.

Thanks,



Dave Connitt CID+

Printed Circuit Designer



A Wholly Owned Subsidiary of:

L3 Communications

3975 McMann Road

Cincinnati, Ohio 45245

Ph. 513- 943-2010   Fax 513-943-2288




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