this is definitely the reason for tombstoning.  the surface tension of
the melted solder on one side pulls on the component and the unmelted
side cannot pull back.  There are any number of suppliers of extremely
fine wire thermocouples but I don't think you need to go to such lengths
to prove it.  Your suspicions are correct.  look for uneven heat
distribution in your oven, incorrect paste placement, incorrect
component placement, bad paste, shadowing from taller components and
last but not least, solderability problems with your components.  good
luck

>-----Original Message-----
>From:  Narayana Vishy-CVN002 [SMTP:[log in to unmask]]
>Sent:  Friday, June 04, 1999 1:39 AM
>To:    [log in to unmask]
>Subject:       [TN] Thermocouple technology
>
>One last one...
>
>I have been working on 0603 tombstoning mostly from the pad stack/placement
>point of view .
>
>One nagging suspicion is that the solder is NOT melting at the same instant
>on both the terminations . I want to analyse if the solder melting on the
>two terminations 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 .
>
>
>Regards,
>Vishy
>
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