Hi Don:

I just looked at a bunch of boards under a microscope and can see some 
type of sub surface disturbance (fracture?).  On those boards the cut 
lines are actually traces that are 0.006" wide.  I cut these just by 
eyeball alignment and in the vast majority of cases the cut line is to 
either side of the trace.  (I'd like to do be able to cut exactly on the 
cut line, but so far have not found a good way to position the boards.)  
Those cut line traces, are in tact except where the cut line crosses the 
trace.  So if by fracture you mean a crack on the top surface that would 
cause an open circuit trace then I'd say no.

When using tin snips where the distance between the hinge and active cut 
is a few inches the fracture effect is much stronger.  Just past the cut 
the two sides get rotated relative to one another putting a lot of 
strain on the material at the cut point.  When using the 12" shear 
there's so much leverage that cuts can be made at the very front of the 
blade which is over a foot from the hinge so the angle between the two 
cutting edges is very small, hence much less strain on the PCB.
http://www.prc68.com/I/12InShear.shtml

Have Fun,

Brooke Clarke
http://www.PRC68.com




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