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April 1999

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Subject:
From:
"Stephen R. Gregory" <[log in to unmask]>
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Date:
Sat, 10 Apr 1999 21:46:14 EDT
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In a message dated 4/10/99 5:39:43 PM Pacific Daylight Time,
[log in to unmask] writes:

> Hi Technetters,
>
>  I would like to post the question to the members, is toothpick test to
>  check on the unsolder connection of QFP lead, cause reliability issue ?
>
>  Poh

Hi Poh!

Well, I'd much rather see someone use a toothpick to check whether or not a
lead is soldered than a stainless steel dental pick (which I've witnessed a
time or two... I shudder to even think about it!)

There's probes called "orange sticks" that are made from wood that are used
for that purpose and if one realizes that it doesn't take much force at all
to stress the joint enough to create a fracture, there shouldn't be much
concern for a reliabilty issue.

There have been times myself that by just looking at a joint it appears to be
fine, but with just a little pressure it is apparent that (for whatever
reason) the metalurgical bond isn't there...the foot moves. If you are seeing
that problem you really need to go back into the process to find out why,
because there definately IS a problem.

I recall the times I've experienced the problem it has been during wave
solder that it was happening. The joints were fine out of reflow during
surface mount, but re-reflowed during wave because there were vias very close
to the pads connected by a very short trace. Heat transfer during wave caused
the joints to re-reflow at the interface between the bottom of the foot and
the top of the pad, and the fillets would stay attached to the leads. It was
very difficult to see that visually. You would easily notice the problem when
a slight bit of pressure was applied to the lead and it moved.

Have your ladies doing this instead of the guys, they tend to have more of a
"delicate touch" that won't damage things when checking them....(GRIN)

-Steve Gregory-

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