A movement of smt component is caused by solder tension
during reflow stage.  You could have two issues, reflow profile
and board design layout.

If a reflow profile is not good, it causes too much temperature
delta difference among smt pads/ components.  This means
pads will be reflowd at different times.  Please check your oven
profile / your solderpaste mfg oven profile guideline and make
sure boards don't get heat up too fast.

If some of your R- pack component pads are too closely
connected to heavy ground plane, th holes or heavy traces, it
could again cause unequal thermal mass and cause pads to
reflow at different times.  Also pad size and geometry could
cause component movement.  Check board layout is acceptable
for manufacturability (or follow IPC-782 guideline)

If you are still using IR or vapor phase oven, the problem can be
worse.  Are you sure you have a good solder mask dams around
smt pads?

regard
Matthew
NII-Norsat International Inc.


>>> Angie Marques <[log in to unmask]> June 10,
1998  8:22 am >>>
To all,

My R packs have a mind of there own,  at pick and place they are
aligned
then during reflow they decided to move. What causes this and
how can I
prevent this?

Thank you in advance
Angie

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