I agree, except pads that are big enough to provide fillets on the side have
been known to cause skewing, no?
James 
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> Hi John,
> The reason tombstoning occurs at all is that the outer edges of the pads
> protrude too much beyond the chip components--if you have no large solder
> fillets you will not get tombstoning because the required surface tension
> forces that cause tombstoning exist only with large fillets and unsymmetric
> position. In reflow soldering these components there is really no need for
> protruding pads (to be touched by the wave) and the resulting fillets at all.
> These components are so small, that certainly there is no need for fillets
> for reliability reasons. 
> Some people also found success with narrower pads which diminish fillet size,
> but the best way is to have pads that essentially are only underneath the
> components-- if you really want fillets put them to the side of the
> components.
> 
> Werner Engelmaier
> Engelmaier Associates, Inc.
> Electronic Packaging, Interconnection and Reliability Consulting
> 23 Gunther Street
> Mendham, NJ  07945  USA
> Phone & Fax: 973-543-2747
> E-mail: [log in to unmask]
> 
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