If you are restricting yourself to changing paste, dot size and process
parameters then  you should be thinking in terms of speed of wetting. This
will be effected by profile, paste  type and atmosphere.
Adjustments should be to slow the rate of wetting down whilst still achieving
the total activity needed for joint formation. So go for air and a higher
solids type no clean. Adjusting your profile accordingly. [Some manufacturers
- vertantly or inadvertantly - have "slow pastes" but generally if they do
they will tend to be the higher solid ones]


Mike Fenner
.....
> Hi All,
>        I am looking for any information concerning the reduction of
>tombstoning.
>
>        The only parameters that we can adjust are the size of the paste
>dot, the type of paste used (any composition as long as it is eutectic
>  PB/SN), and the reflow profile (two atmosphere choices).
>
>          Since the physical pheomeonon is centered around surface tension I
>  am very interested to read about any study that was done that resulted in
>  reduced surface tension.
>
>          Currently the process is in the fractional percentages, the goal
>  is to go below 100 DPM.
>
>  Thanks,
>  Paul Gill
>  Process Engineer
>

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