Paul
Reading between the lines, you are using a water-soluble chemistry. If
you are obtaing incomplete cleaning, then yes, you are going to have
problems, such as you describe.
Spacers are no use with LCCCs: you won't make a solder joint. I'm not
too sure about adhesives, either, as you would have to use them as a
kind of underfill: dosing the excta amount and place to seal out the
flux but not interfere with the soldering would be hairy.
Many years ago, when LCCCs were more popular that they are today,
special lead frames were available, dunno whether they still are. These
were soldered onto the LCCC with a high-temp paste and the component was
then placed in a press which cut the frames and formed them, turning
them into a J-lead device. This eased all the soldering and cleaning
problems and, at the same time, lo and behold, no TCE mismatches, as the
leads were sufficiently flexible to take them up! Just an idea...
Brian
Paul Baine wrote:
>
> Hello. This is the first time I have used IPC TechNet, so please forgive
> me if this question has been asked before.
>
> Our company has built some SEM Modules (Standard Electronic Modules) for a
> customer who recently reported failures in the field with these Modules.
> These types of Modules have Leadless Chip Carrier ICs with castellated
> terminations on them. The solder pads are underneath the IC packages. As
> part of the failure analysis performed by the customer, some of these LCCs
> were removed, and they noticed an off-yellow coating on the bottom of the
> LCCs which they feel is solder flux. They theorize that the solder flux
> has hardened over time and has become conductive.
>
> Our Production Manager thinks that this problem is caused by the fact that
> these LCCs sit flat on the substrate and therefore the solder flux gets
> trapped under the LCC during reflow and cannot be cleaned out. He proposes
> two possible solutions:
>
> - put adhesive under the LCC
>
> - put a spacer under the LCC which is dissolvable in water (i.e. during
> cleaning)
>
> I was wondering if anyone had experienced a similar problem and knew of
> an "industry standard" solution, or any solution. Thank you in advance.
>
> Best regards,
>
> Paul Baine
> Q.A. Manager
> C-Tech Ltd., Cornwall, Ontario, Canada
>
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