Dear Graham,
We have a programmable lead straightening system which we built for in-house
use. It uses tooling which gently forms the leads in, out, up, and down.
It cannot change the location of the shoulder bend nor can it magically make
the leads any longer but we can teach it to put the foot wherever we want it
(within reason). We use this system to repair bent leads on high
reliability
components (ceramic and plastic). Its designed for QFPs but with some
programming tricks we have done
SOs. Perhaps you could send a sample unit or two and we will give it a try.
We will need to know the minimum standoff you can tolerate and the minimum
tip to tip dimension you are trying to achieve.
Don't quit that big bucks job just yet! No promises but we will give it a
shot.
Also, most any lead straightening house with a "Ruud" lead straightening
system should be able to do the same thing. A company called Tekcom with
plants in AZ and CA at one time bought the rights to this system and took it
off the market (internal use only). I don't know who has one but Tekcom in
San Jose is
a good place to start.
After straightening you can check the part with an acoustic microscope to
verify that the molding compound has not separated from the lead fingers.
Sonoscan in San Jose is one good source for this service. Several others in
the Technet
archives. If the die is small the chances are good that the leads are well
anchored
inside the package. This also depends a lot on the manufacturer of the
component and their choice of leadfames.
Don't forget to fix the board. This is not something you want to make a
habit of. Also, you will likely go out of bounds on the Jedec specs and the
manufacturers recommendations so you will probably need your customers
approval. I guess that just depends on how much vacation time you got saved
up.
Russ Winslow
Six Sigma
1940 Concourse Dr.
San Jose, CA 95131
(408) 526-1350
-----Original Message-----
From: Collins, Graham <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Wednesday, August 26, 1998 5:01 AM
Subject: [TN] reforming a SOIC
>Technetter's
>Let's say a customer designed a board with the wrong pad size, too far
>apart, such that a gull wing lead placed on the pad doesn't have a heel
>fillet. Obviously a bad thing. A redesign is in progress, but in the
>interim it has been proposed that the part be reformed to spread the feet a
>bit further apart (by about 20 thou). Component is a 20 lead SOIC.
>
>My questions and concerns are:
> - the bend will have to occur at the point where the lead enters the
>component body, otherwise there will be no clearance between the part and
>the board. How dangerous is this from a reliability perspective (class 3
>product, conformally coated)? Should I take the next few weeks off? Flee
>the country? Anyone have job openings?
>
> - do any technetters have suggestions of a half decent way to reform
these?
>I'm currently faced with doing it to about 100 to 150 parts, and doing it
by
>hand does not appeal to me due to the variability.
>
>Any other suggestions? I did consider borrowing some of the Freeze-it that
>Steve's using on his diodes, and shrinking the boards, but the reflow
>process might disagree with that...
>
>thanks!
>
>Graham Collins
>
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