Chris,

Your req for 0.020" max is very tight indeed,   I can see more
serious problem of solder joint fractures with shaving off board
surfaces.
I think IPC610 specifies min 0.040", being 0.060" is typical.
Check section 3 or 4.  I don't think you can get repeatable
process with the tight requirement.  Remember boards get
warped one way and another after wavesoldering.

Some of things you can do; - provide more support pins, so
boards stays even during leadtrimming, - move the trimming
blade at a constant and controlled speed (slower is better), -
avoid cutting heavy leads, - use a new blade when you see a first
sign of flagging and bending of leads being cut.

regards
Matthew
NII, Norsat




>>> Chris_Smith <[log in to unmask]> July 16, 1998  11:39
am >>>
     All,
        I have a lead trim operation that uses a Q-corporation LOM II
     trimming system with a vacuum fixture.  We are using the
standard
     cutting rings with a 30 degree angle.  The Vacuum fixture
being used
     is quite snug and there is very little vacuum loss in the
process.
        The issue I have is the height requirement we're trying to
meet is
     .020" max length.  This strict requirement is resulting in pcbs
being
     cut into and damaged, some flagging, and some solder
fractures.  This
     seems to be a very operator dependent operation and costly if
not done
     correctly.  I have tried varying the speed the cutter is moved
across
     the board, having Q-corp sharpen the blades instead of us
doing it and
     using a QB-1 PCB brusher which was purchased for this
product.
        Is there anyone out there with a similar trim height
requirement
     and what types of things do you perform to insure a
repeatable
     process?  Also anyone with suggestions please let me, I
need to get
     this resolved if at all possible.

     Thanks
     Chris Smith
     Manufacturing Engineer

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