Patricia,
Thanks for the input. But as mentioned I had all my process in place,
pre-conditioner (sweller), rinse, manganates, rinse, rinse, reducer,
rinse and then....
For PCBs with <.016 or PTFE I used a Zinc, metal chealating chemistry
called (Neutraganth) that allowed for good hole wall smear removal and
ate the hell out of Teflon for uniform copper deposition. Granted
extra chemistries and hardware (vibrators/tanks/large footprint) were
required to achieve this result, but small footprint Plasma units
could not be justified for cost reasons. Its been 8 years since I
last saw a Plasma unit anyway. But thanks for the in-sight and I
would like to have current data on the advantages of Plasma.
John Gulley - QA
p.s. Although messy, you got to admit there are millions of PCBs
running through the world that have gone through Permangante versus
Plasma (100:1).
______________________________ Reply Separator _________________________________
Subject: Re: Plasma
Author: "Goldman; Patricia J." <[log in to unmask]> at Internet
Date: 1/27/97 1:46 PM
John,
Gosh, where did you get this info from? Plasma desmear processing uses
small amounts of about 3 different, very pure gases (O2, N2 and a
fluorocarbon, usually). No other chemicals that I am aware of. The only
waste is the small amount of gases that are discharged. The plasma desmear
is done under vacuum, hence the small amount of gases used/discharged.
It is considered more expensive because there is a larger capital equipment
cost, I believe. In the past, uniformity of desmear and etch was a problem.
That is no longer much of an issue with the much improved equipment now
available. APS in Florida has done much in the development of their
equipment (reverse gas flow and circulation, better electrode and panel
placement, etc.) to eliminate variability. The process is essentially a
batch one and is longer than the other methods (permanganate, sulfuric). On
the other hand, it is clean, with minimal waste, and it will work on all
material types, even PTFE (different gas required) and flex.
Permanganate is great if you have the right set-up: three process tanks and
3 double rinses. There are 3 process steps: solvent clean/swell/sensitize;
permanganate (runs hot, needs SS or better tank); neutralizer; each needs a
good rinse. The permanganate bath needs to be regenerated, either
electrically or chemically, or it will soon fall apart (precipitates MnO2).
Works on epoxy and polyimide substrates, but not flex. There are many
suppliers of good processes, ask any board manufacturer.
Sulfuric acid process requires hot, concentrated sulfuric acid. It is
dangerous and messy and works only on standard difunctional epoxy materials.
Often produces a substandard desmear (esp. when sulfuric concentration
drops slightly). Because of the viscosity of the acid, small, high aspect
ratio holes cannot be reliably processed. Not Recommended!
Way back when, I worked with plasma in a board shop and it was a bear, but
that was 15 years ago with first generation equipment. Those that have the
new generation equipment think it is the greatest thing since, well you
know. Talk to Advanced Plasma Systems in FL - they know and understand a
lot about the process. Ask for customers to talk to, if you need more info.
I swore by permanganate for many years (esp. when I was on the supply side)
but nowadays, if I were setting things up, I would take a real good look at
plasma, the only dry desmear/etchback process for multilayer holes and vias.
Patty
----------
From: John_Gulley
To: Hound; technet
Subject: Re: Plasma
Date: Friday, January 24, 1997 6:49PM
Gaylor,
Not sure where you are hearing that Plasma is good, but past fab shop
I've worked for or surveyed from the customer end, have moved away
from using plasma. I could be wrong and someone in the forum may
correct me, but this has been the underlying trend.
Several reasons are:
1. Cost, the dry-chemicals are very expensive.
2. You typically have non-uniform smear removal of the hole wall.
3. Check your local city and state ordinance on chemicals.
4. Expensive equipment.
5. Proper air ventilation in-place
If you have low volumes, use sulfuric acid, but have safe and
preventive measures in place.
For higher volumes, I would highly recommend using Permanganate for
smear removal. The advantages outweigh the disadvantages of using
this make-up. Once you have your two chemistries mixed, just add DI
or replace evaporated water.
Regards,
John Gulley - QA
Inet Inc.
Plano, TX 75075-7270
______________________________ Reply Separator
_________________________________
Subject: Plasma
Author: [log in to unmask] (Timothy Gaylor) at Internet
Date: 1/23/97 11:25 PM
I am interested in the Plasma desmear process. I have been reading alot
about this type of desmear technique and dont quite understand the
variables involved.
>From what I understand there is a combination of three gasses that
combine to create the "plasma" state ( the most common oxygen, nitrogen
and tetraflouromethane).
How are these gasses controlled and what effects do the ratio of the
gasses effect the etchrate?
T.A. Gaylor
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