Hi, Dave,
Werner is correct, 0402 chip capacitors and resistors are easily cracked and often go undetected if they are hand soldered. I would suggest you buy a Hakko FR1012B infrared preheater and a Hakko 802 hot air wand. This combination costs just $2500 (and you get a third item free!), and is the most useful and versatile system for quickly soldering chip caps and resistors, small QFNs, belly pad components, glass-bodied SMT diodes, and similar components. Using a hot air wand to perform rework and manual soldering works like downtown, instructions are in IPC 7711/7721 section 5.3.1. And, as Dave Hillman of Rockwell pointed out in this forum recently, the Hakko system can be used for many other things, such as underfill cure, etc. I most recently used our system to perform BGA reballing in a somewhat exotic process, and it worked beautifully.
Until then, open up IPC 7711/7721 and carefully read the steps listed in section 5.3.2, where it shows how to safely hand solder ceramic chip caps and resistors by first applying a small amount of solder to one pad. You then place the chip carefully and touch ONLY THE PAD, NOT THE PART with the solder iron, thus reflowing the solder on one end. You then apply the iron to the other PAD and add a little solder.
Do not use tweezer style irons to solder chip caps and resistors. These are intended only for removal of parts to be replaced.
Do not use U-shaped tips to solder chip caps and resistors. These are also intended only for removal of parts to be replaced.
Both of the above methods, as well as touching these types of a component directly with an iron tip will crack the parts.
If you cannot trust the operators to never touch a part with the iron tip, then buy the Hakko and force them to learn to use it. Once they know how, they will never go back.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Monday, October 26, 2009 5:22 PM
To: [log in to unmask]
Subject: Re: [TN] Question regarding 0402 resistors and ceramic capacitors
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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