Hi All,

We are manufacturers of bare PCBs and as a part
of PCB processing we have Plasma desmearing step.

Recently we're having some problem in getting etchback
in PTH consistently. We have a plasma desmearing machine,
where the loading of the panels is done horizontally.
The plasma desmearing is done in 2 cycle steps...
a) First cycle is done by purging O2
b) Second cycle is done by purging O2 & CF4

The volume of the gas and the duration of desmearing
is set based on the material type and the thickness of the PCB.

Our processing parameters are set since quite some time and we
didn't had any issues in getting etchback consistently. We've not
changed any process parameters and/or the supplier source.

We are checking the level of desmearing by conducting desmearing on
bare epoxy sheets and checking the weight loss. The results of
the weight loss are also not consistent. The results are similar
in the PCBs  also, the etchback is not consistent.

It would of great help if anyone can share the possible causes
of the problem and suggest remedies for the same.

Thanks in advance!

Best Regards,
U.Nagaraj


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