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July 2011

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Subject:
From:
Chris Mahanna <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Chris Mahanna <[log in to unmask]>
Date:
Thu, 28 Jul 2011 13:30:11 -0400
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Using plasma desmear for conformant effective positive etchback is an art form.
My guess is that someone is asking you to look more closely than you did before.  There is always a good deal of variation.
Are you 100% sure that you are working against the same resin formulation?

Chris

Chris Mahanna
Robisan Lab

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Uppina Nagaraj
Sent: Thursday, July 28, 2011 1:01 PM
To: [log in to unmask]
Subject: [TN] Query on Plasma Desmearing

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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