----- Original Message -----
Sent: Tuesday, January 21, 2003 2:17
PM
Subject: Re: [TN] Formula for
weight/surface tension to keep bottomside parts on?
There are two methods. Joint Perimeter Length and
land area.
The
rule for land area is 30 g / sqin (about 47 mg /
sqmm). This conservative estimate works unless the component
lead is much smaller than the land.
The
Joint Perimeter Length rule is 188 mg per cm of JPL. This optimistic method
works if the lead to land interface is about equal and wetting is good and
strong. Remember is not just surface tension that holds the part on the board,
wetting plays a part as well. If part of the interface is not solderable . . .
plunk.
Does anyone know the formula for calculating
(weight versus contact area) whether a component will stay on the bottomside
of a PCB?
Thanks
John Belcher
Hunter
Technologies
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