In a message dated 3/1/99 11:30:27 AM Pacific Standard Time,
[log in to unmask] writes:
<< Dear experts,
We are building electronics for automotive industry. We have a number of
boards where 0805 package resistors were
placed and reflowed on the 0603 pads. As the results there is no side
concave solder fillet, only under the component
terminations.
What options other than scrapping the boards would you suggest? ( Rework:
remove and replace. Do some testing
(vibration, pull test??).
Please, help
Thank you, very much
Stella N >>
Stella,
Boy-O-Boy, sounds like ya' got yourself in between a rock and hard place
huh? No doubt the resistors in question only go a bajillion times per board
instead of 1 or 2 per...that's the way it would be if it were happening to
me...I think "Murphy" wrote his book of "Laws" after following me around a
while.
Anyways, you don't have even a teensy bit of fillet along the ends? Sure
must have made the 0603 pads small and squished together if ya don't...you
should have a little bit...enough to look and tell that you've got good
wetting and solder underneath anyway.
Anybody can correct me if I'm wrong, but I remember Werner or somebody
saying at one time that we all have way too big fillets on passive components
to begin with. I remember whoever said that saying that big fillets can
sometimes lead to, or contribute to, capacitor cracking. Because a big
honkin' fillet doesn't have the "give" that a less massive fillet does.
I've built motherboards for a fairly large company that purposely laid
pads out that were quite small...just barely big enough for the part. The
bottomside pads for wave also looked like this:
___________
__| |__
|__| |__|
|__________|
That ain't autocad, but you get the idea. I've always understood too, that
most of the strength of a joint comes from the bond that forms in the
interface between the top of the pad and the bottom of the lead, the side
fillets do add strength, but not as much as some people may think. I remember
also being taught by a salty ol' QA guy that one of the big reasons that one
looks for the fillets on the sides is to feel comfortable that there is good
wetting and a good bond where you can't see (underneath).
With all that being said, your boards are going into cars, I think I would
wanna cover my fanny on this one. But again, if this isn't a real critical
thing (stereo system, etc...) I might give a little thought to it before I
started changing all them resistors...
(...and I thought my Monday started off in the toilet!!)
-Steve Gregory-
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