Hi Tony!

How old is the stencil? I think for it to stretch it would have to quite old
and have been used to print thousands of boards...stainless steel (which is
the standard) doesn't stretch that much...

What it could be is that the tension of the stencil within the frame is not
what it should be, and along with high squeegee pressure, is pulling the
stencil off registration in the direction of the print stroke. I've seen that
happen even with a fairly new stencil when there has been to much squeegee
pressure set in the printer program...

I can just about bet it has something to do with either machine set-up, or a
loose stencil...and NOT the board.

-Steve Gregory-


> Ladies and Gentlemen,
>
> We are having a major problem with an assembly house with registering
> the solder paste to surface mount features prior to pick and place. They
> are claiming that the boards are growing/shrinking some 15-20 mils.
> We have done extensive measuring on unpopulated boards in-house
> and cannot see more than 3-5 mils misregistration. The panel size
> is approximately 14.00 x 16.00 inches, 20-24 mil pitch, and 15 BGA's
> throughout the panel. Overall thickness .080. Is it possible that the mesh
> screen that they are using can expand/contract over time? has anyone
> heard of this experienced this situation before. Any information would be
> greatly appreciated.
>
> Thanks
> Tony Steinke
> AIT-Atlanta
>