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January 1997

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Mon, 27 Jan 1997 16:37:59 -0600
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     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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