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July 2000

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Subject:
From:
"Stephen R. Gregory" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 26 Jul 2000 20:32:06 EDT
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In a message dated 7/26/00 2:39:33 PM EST, [log in to unmask] writes:

<< We are experiencing problems with soldering of PLCC's.

 We find that a significant number of these devices are received from the
vendor with non-coplanar leads.  The lack of co-planarity causes open solder
joints.

 Investigation has resulted in the knowledge that approximately 5% of the
PLCC device we receive are not within the 0.004" co-planarity requirement.
We find some to be out as far as 0.012".  I cannot currently define the point
at which the lack of co-planarity becomes an issue.

 The supplier is a major manufacturer of these devices.  The parts are on
tape and reel.  We have inspected them prior to any processing at our
facility, so we know that it is not a question of in-house handling,
placement, etc.

 1) Does anyone else see co-planarity problems with PLCC's?

 2) What steps have you successfully taken to correct this problem, and what
was the result?

 3) Are there pieces of equipment I can put inline to screen <*gasp*> out
these devices?

 4) Any assembly or processing tricks you have used successfully to
compensate?




 Thanks,

 Lang
 x5046 >>

Hi Lang!

I would agree that there is something in either the testing or programming
process of the devices that is causing coplanarity problems...that's been my
experience anyway...

Tape and reeling can also introduce problems if the tape and reel machine
isn't set up properly...there are guides for the tape after the part is
sealed into the carrier tape, that guide the tape up on to the reel. If that
isn't set up correctly, it will bend the leads...you can see if that's the
problem by looking at the pocket for each part to see if it's been deformed
or not. Usually the same leads on every part will be bent.

As far as being able to compensate for the coplanarity of the leads in the
assembly process, as a general rule, your solder paste print will provide a
fillet of 50% the printed height. So if you're seeing a coplanarity of
12-mils, that means you have to print 24-mils of paste to compensate for
that....not likely. There are options on pick and place machines that will
check for coplanarity, but add 5 or so seconds to each placement that does a
coplanarity check (laser based usually).

Thing to do in my opinion is to square your supplier up...PLCC's are normally
pretty robust. To get things out that far they've been mis-handled somewhere
along the line, or a machine set-up wasn't done correctly...

-Steve Gregory-

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