One of the MANY useful rules-of-thumb I have gleaned from Technet.....
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.
You can use the reverse to find the necessary weight...
Kevin Glidden
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of bob wettermann
Sent: Tuesday, September 12, 2006 7:19 AM
To: [log in to unmask]
Subject: [TN] Surface Tension of Solder vs Part Mass in Reflow
Dear Technetters:
I have a thought question for you SMT process engineers out there.
We are attempting to have a part selectively drop off in a reflow oven on
a 2-sided l-f SMT assembly. In order for this to happen we will have to make
sure during the reflow cycle that the part in question falls off while the
others remain.
The question is how does one calculate the force due to surface tension
holding a part to the PCB while the solder is in the liquidus phase? If we
know this then we believe we have a method to attach the right amount of
weight to the device to make it fall off.
\
Thanks .
BWET
Bob Wettermann
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