Hi,

  Another possible reason for cracked 0402 resistors:

  These parts are thin pieces of a brittle material. When you hand solder
the first end the part almost never is flat on the PCB. If you touch the
iron to the unsoldered end you can easily cause a moment and cause a crack. 

  Operators need to avoid stressing the parts. 

 It is like grapping a piece of microscope cover glass by the corner with
steel tweezers. It is hard not to break the glass. Coupled with thermal
stress things are easy to crack.

Bob Kondner

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Tuesday, October 27, 2009 9:16 AM
To: [log in to unmask]
Subject: Re: [TN] Question regarding 0402 resistors and ceramic capacitors

Hi Dave - as always, the TechNet crew is providing some great information. 
I just wanted to add support to Rich Stadem's detailed comments - 
incorrect manual soldering practices. The optimum solder process for 
ceramic resistors and capacitors would be reflow/hot air methods. However, 
thousands of chip Rs&Cs are manually soldered every day in the electronics 
industry very reliably. There is one major issue - if the soldering iron 
comes in contact with the resistor or capacitor termination then there is 
a high potential for having induced a crack that will  not be immediately 
apparent.  I recommend you review the operator manual soldering procedure 
and emphasize the importance of not touching the component termination 
during soldering. AVX has a technical paper authored by John Maxwell 
titled "Cracks" The Hidden Defect" which is very good on describing 
cracking root causes. Good Luck.

Dave Hillman
Rockwell Collins
[log in to unmask]




Dave Connitt <[log in to unmask]> 
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10/26/2009 05:05 PM
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[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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