Tombstone

As a high-level PCBA service vendor, Makefabs always takes the quality to the top importance in our works(er... not the excuse of the many projects delay...), there are many checkpoints for quality in the soldering, that we always get confident about our products as shipping them out to customers.

But, recently we got a customer’s complaint, about the capacitor tombstone!~

As the customers complain, there are up to 5 pcs at least, the same problem at the same place.

Absolutely a bad accident, why such a problem in our production, and more seriously, we don’t check them out in our checking?

1. Why we do not check them out, with Makerfabs 3 checkpoint?
For the PCBA production, there 3 checkpoints to check the soldering quality:

1. Visual checking in the SMD soldering, to check the pick-n-place working status and if the tins are OK, after the reflow soldering;

2. AOI checking. All production >50 pcs will be checked by AOI;

3. Visual checking again, after the functional testing( if there is)and the THT soldering

For this project with the tombstone problem, we found that the circuit is enclosed by the EMC shield cover, which is the reason of not checking out:

The shield is placed in the SMD soldering, and the AOI/workers can't check the problem there… There also impossible to manually solder the shield after the reflow soldering…...

2. The root cause of tombstone?
In this board, the package of the components with tombstone, a 0402 capacitor:

We found the inner distance is 20 mils, as the total length of a 0402 capacitor is 40 mils, that is , there only 10 mils each side, for the pins soldering.
This should be the root cause for the tombstone, we suggest the designer modify the package as:

The newly updated version boards are still in production, the same tombstone problem will not happen again. Of course, if anyone knows a method to check the components in a shield cover, please kindly suggest.