Hi All,

Further to my query sent previously, I got several
responses, based on which we had verified the gas flow
meters and RF power and they were found to be ok.

However, the results are still inconsistent.
I've posted some photos in the link below....

http://ipc-technet.groupsite.com/gallery/20924

In this trial we had purposely increased the gas flow
and the timing. The drilled hole wall is very uneven
due to plasma etchback. However, it can be seen that
near the IL Copper the epoxy is not "etched back".
This phenomenon is randomly seen (no specific trend).

I don't know how significantly the temperature inside
the plasma chamber affects the performance of plasma.

Any valuable inputs on the suspected cause and possible
solutions would be of great help.

Thanks & Regards,
U.Nagaraj


---------------------------- Original Message ----------------------------
Subject: Query on Plasma Desmearing
From:    [log in to unmask]
Date:    Thu, July 28, 2011 10:32 pm
To:      [log in to unmask]
--------------------------------------------------------------------------

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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