Paul,

   Five years ago we conduct a study to better understand tombstone at
0603 components ( we had a big problem that time !!! ), but I moved from
that company and could remember only the highlights, may be with this
information you can apply some experiments to 0402.
   The experiment were conducted with prototype boards with 11 different
pad configuration and 3 types of solder paste

    Results

    Capacitors are more sensitive to tombstone than resistors

    Solder Paste with same comercial characteristcs ( Type 3, 63/37 , No
Clean ) gave different results, at that time the best result we get with
Alpha Metals 390 DH4

    Pad design with more solder volume applied get more tombstone
results

    Pad design with more distance between the two components pads (
center to center ) get more tombstone

    Different solder profile were not tested but be carefull with fast
ramp up.

    With this experiment we choose the better pad pattern with the
better solder paste to solve our problem. You can easily start
evaluating different solder paste than goes to pad design.
    I believe with 0402 you have to be concerned with placement accuracy
also.

    Until the changes at our process were not made we had to use glue at
top side process ( we applied solder paste and then glue with a siringe
dispense machine ) to avoid tombstone at 0603 component.

     Like americans says " This is my two cents ... "

Jorge Dourado de Santana
Maintenance / Process Engr
Microtec - Brazil







> -----Original Message-----
> From: Paul [SMTP:[log in to unmask]]
> Sent: 10 de Maio de 1999 19:47
> To:   [log in to unmask]
> Subject:      [TN] Tombstoning 0402 caps.... Help needed.
>
> 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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