This
sounds almost like the mesh that holds the
stencil in the frame is becoming weak and stretched
allowing for extensive movement of the stencil during
the
printing operation. IMHO.
Barry.
We have only seen stretch on our stencils
cause a problem when they are old and very used. At this point it is best to
purchase a new stencil, as it will pay for itself with reduced defects almost
immediately. It may be worth while to see how the board is fixtured, as it can
sometimes shift during the print cycle from time to time and cause problems.
Hope some of this is useful.
Ed
At 10:48 AM
3/29/2002 -0800, you wrote:
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
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