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October 2009

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Subject:
From:
Werner Engelmaier <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Werner Engelmaier <[log in to unmask]>
Date:
Mon, 26 Oct 2009 18:22:23 -0400
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text/plain (101 lines)
 Hi Dave,
The most likely time for the cracking is during cooling from soldering. I bet these RCs have larger solder fillet than non-cracked chip components. You combine large CTE-mismatch [ceramic vs. FR-4], more rapid cooling after manual soldering, large solder fillets acting like vice grips—and you have a potent brew for trouble. Of course, if all of this is Pb-free—the worse.
Werner

 

 

-----Original Message-----
From: Dave Connitt <[log in to unmask]>
To: [log in to unmask]
Sent: Mon, Oct 26, 2009 6:05 pm
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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