Mr. Jeremy Drake
Sorry to interrupt your topic. Since it is of my interest I chipped in.
We manufacture SMD transformers. The SMD bobbins have Gullwing pins. We have to solder the wires of the transformers to these pins and solder at about 430degrees. This puts stress on the pins and the pins loose their coplanarity. We have to maintain a coplanarity better than 0.1mm. 

Since your topic is similar I needed some advice  how to adjust it (presently we are adjusting manually which is VERY tiresome and difficult). Could you let me know if you have come across a machine which can do this job or any tool maker who can develop a tool for this adjustment??

Thanks.

V.B.Venkatesh
http://www.hical.com

-----Original Message-----
From:   Jeremy Drake [SMTP:[log in to unmask]]
Sent:   Wednesday, August 26, 1998 6:49 PM
To:     [log in to unmask]
Subject:        Re: [TN] reforming a SOIC

Graham,
     I wouldn't be happy hand reforming gull wings. You say that the bend
will have to start at the component body. This means that a lot of stress
will be put on the plastic to metal bond during the bending. Plastic mould
compound doesn't have a particularly strong bond to leadframe metals at the
best of times. This hand bending of the leads is likely to lead to
delamination, giving an easy path into the package interior, wire bonds and
die for corrosive contaminants.

     Gull wing leads are originally formed by die sets that grip the leads
before making the bend. The tooling doesn't grip the package at all. This
prevents stressing the lead to plastic package interface.

     Ideally I wouldn't do this. If I had to I would do some die
penetration checks on some re-formed parts to see if there has been any
delamination. If this shows no problems and you can be sure of the
consistancy of the bends you make then it might be ok.

You also need to consider the effect of the change in the lead shape on
solder joint fatigue. The compliance of the lead is protecting the joint
from the differential strains between the package and the board. Changing
the lead profile will change the lead compliance. If it makes the lead too
stiff then again there could be long term reliability problems.

regards,
Jeremy Drake
Celestica
---------------------- Forwarded by Jeremy J Drake/HQ/CUK/Celestica on
26/08/98 13:15 ---------------------------


"Collins, Graham" <[log in to unmask]> on 26/08/98 12:54:26

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
      to "Collins, Graham" <[log in to unmask]>



 To:      [log in to unmask]

 cc:      (bcc: Jeremy J Drake/HQ/CUK/Celestica)



 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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