Can someone help me with a formula to approximate my design rules to 
solve the problem of falling chips on second side reflow. The chips on 
the second side of the board seem to be to heavy for the superficial 
tension that is supposed to hold them down while going through the reflow 
oven for the second time.  I want to set PCB  design rules depending on 
the weight of the chip, surface area of the chip's leads and pad sizes. I 
know that there are many more variables to consider but a simple rule of 
thumb formula will do.  Or if anybody knows about the exact science to 
deal with this problem I will appreciate the feedback. (Can't use Glue)

Thank you much.
P.S.  This is my first time in ThechNet and I thank you all for the 
forum.

Alex Basauri
SMT Engineering
Trimble Navigation LTD
The GPS Solution!!
Sunnyvale, CA
[log in to unmask]
(408) 736-4924

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