The number one source of tombstone defects is too much solder followed by
solder mask beneath the part.

On Thu, 24 Jul 2014 19:57:55 +0000, "Vargas, Stephen M"
<[log in to unmask]> wrote:
> Hello All:
> 
> We are experiencing a high rate of tombstoning on two particular package
> styles (0508 and 0612 capacitors) on an assembly here. The rest of the
> board solders at a normal defect rate. Here are some of the things we
have
> looked at and some aspects of our process:
> 
> I've tried using two different profiles (straight ramp to peak and a
ramp,
> soak, spike).
> I've moved the parts from our high speed chip shooter to our flexible
> placement machine to optimize placement accuracy.
> The pad layout (which is not an option for change due to the product
> having already been qualified by our customer) is very close to the
> manufacturer's recommended layout and the board finish is immersion
silver.
> We are printing 1:1, no aperture micro-modifications.
> Stencil thickness is 6 mils. I'm concerned about moving to a thicker
> stencil due to having 20 mil pitch parts on the board.
> Our paste is a low residue / pin probe-able no-clean 63/37 (again not an
> option for change).
> We also looked at which side of the device is connected to ground,
> assuming that this side of the device would heat up more slowly causing
a
> tombstoning condition pivoting at the non-ground side. But there was no
> trend indicating that this was the case.
> Solder mask height measured in between the two pads and it was
determined
> to be at the same height as the pads
> 
> I've attached a link to the datasheet for one of the devices for
> reference. I'm wondering if the forces of physics make this part more
> susceptible to tombstoning due to the terminations being on the long
side
> of the device. Any ideas on how we can improve our yields? Thanks.
> 
> http://www.avx.com/docs/Catalogs/licc.pdf
> 
> Regards,
> Steve Vargas
> 
> If you don't have time to do it right, when will you have time to do it
> over?
> John Wooden
> 
> Polaris Contract Mfg Inc
> 15 Barnabas Rd
> Marion, MA 02738
> 774-553-6192
> [log in to unmask]<mailto:[log in to unmask]>
> 
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