Based on the information in the original posting, and my own extensive
experience with this type of defect, it sounded like these particular
components were probably cracked from the hand soldering process but did
not fail electrically until stressed during temperature cycle testing. I
have seen far more reliability issues with these parts as a result of
hand soldering than any other of the root causes described within the
excellent AVX paper that John Maxwell wrote. Not that de-paneling can't
be ruled out, or any other root cause(s) as well.
Were they cracked as a result of too much solder from the manual
soldering process, or were they cracked as a result of thermal shock
from being touched with a 700 deg. F. iron, or was the root cause a
combination of too much solder, thermal shock, value-related design
characteristics of the components, or some of several other potential
causes such as de-paneling, flexure during handling/testing/subsequent
assembly processes, pick/place pressure, or ?................
Chances are the root cause was thermal shock, but may have been
compounded by the solder restraint issues that Werner described. They
probably cracked during the hand soldering operation, but did not fail
electrically until they were cycled.
Probably.
The only way to know for sure is to perform a DOE or a careful failure
analysis, or both.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Chris Mahanna
Sent: Tuesday, October 27, 2009 10:12 AM
To: [log in to unmask]
Subject: Re: [TN] Question regarding 0402 resistors and ceramic
capacitors
Dave,
Assuming that you have other hand soldered 0402s on the PBA, the tidbit
that the resistors are in the same location causes my money to land on
depanelization.
Chris
-----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]>
Sent by: TechNet <[log in to unmask]>
10/26/2009 05:05 PM
Please respond to
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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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