In a message dated 6/4/99 3:44:39 AM Central Daylight Time,
[log in to unmask] writes:

<< One last one...

                I have been working on 0603 tombstoning mostly from the pad
                                stack/placement point of view .

Hello Vishy

Since you are dealing with such a small device my suggestion is to look for a
heat sink on the slow reflow end that is drawing the heat away from the
solderpaste or one that is holding the temperature high on one end so as to
keep the solder molten as the other pad cools quicker and forms a solder
joint first.

                One nagging suspicion is that the solder is NOT melting at
the same instant
                on both the terminations . I want to analyze if the solder
melting on the
                two termination's of the 0603 is instantaneous or not. How
can I do this?
                Are there thermocouples in the market with such resolutions
which can show
                this clear enough? I am pretty new to the reflow technology
stuff and would
                like some recommendations on how to do this.

I would place thermal couple on both ends of the 0603 so as to understand the
thermal energies in the area of the tombstoning part.  I am not aware of the
thermal couple technology to measure solder melting as you describe, but it
is my belief that if you use a standard thermal couple (mole, Kic) that you
can attach to the pads and understand the timed delta between pad end near
the reflow temperature and during the cooling phase.  With this information
in hand then you can modify your reflow preheat and ramp rates to compensate
for this thermal delta between the pads.  The key to eliminating tombstoning
is to have all pasted areas melt at the same instant and then cool at the
same instant during the forming of the solderjoint.

 Regards,
Terry Munson
CSL Inc.
[log in to unmask]
765-457-8095
  >>

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