I plucked this tidbit off Technet some time ago, seems to work fine for me:
Use the component weight to pad surface area ratio.
1) Total up the pad surface area (in^2) available for the part (pad area X #
of leads)
2) Weigh the part (grams)
3) Divide the weight by the surface area.
4) If the ratio is less than 30 grams/sq. in. - it won't fall off.
Caveats are that this requires:
1) Good solderability
2) A decent reflow profile
3) A smooth running oven conveyer
4) A board that doesn't bow during reflow
Kevin Glidden
Manufacturing Engineer
Luminescent Systems Inc.
-----Original Message-----
From: Kane, Amol (349) [mailto:[log in to unmask]]
Sent: Tuesday, February 26, 2008 3:17 PM
To: [log in to unmask]
Subject: [TN] Component Suitability for Second Side Reflow
Dear Technetters,
Where would I be able to find guidance on the suitability of a particular
component for second side reflow?. Obviously, the weight of the component on
the bottom side has to be <= by the solder surface tension force to prevent
the component from falling off the board during reflow. Is there literature
available for calculation of the maximum wt of a component that can be
safely put on a pad, knowing the pad geometry, solder volume and lead
surface area?
Sounds simple enough....until you go to do the actual calculation.
Any pointers would be greatly appreciated.
Thanks,
Amol
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