Bob,

if you want to make it fall, why do you need to compute? Just attach something really heavy to it and it will fall.

There is a formula indeed for leaded solders, which I always have trouble finding, but it most likely not apply to LF, where the surface tension is supposed to be higher.

Regards,

Ioan

-----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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