Peter: In a perfect world, I would agree with you...
But given that I am proposing going from little control, (Baume' ONLY) to reasonable control.. (if not perfect as you suggest), and that to go to your level of control would be quite expensive, and would then bring up the issue of what do you do with the information. In other words, your proposed method of controlling metal by direct measurement, then brings up the issue, that if you are going to be this precise, you really want to monitor and control Chloride as well, and the whole thing starts to snowball in expense and difficulty....
Whereas what I am proposing is not perfect, it is so much an improvement over current methodology, and is only slightly expensive...
So, in a perfect world, I would agree with you completely, this week, it is beyond our industries reach economically, and far too complex.
Rudy Sedlak
RD Chemical Company
peter blokhuis <[log in to unmask]> wrote: I don't agree that the temperature has much to do with the factors that determine the ability to etch extremely fine lines: yes it will influence the rate of etching, but if the spray at all nozzles is at the same temperature (a given) then then I don't see the benefit in going crazy with temperature control more accurate than +/-1 degree.
To Rudy's points about SG control: I agree with the need to control pH. However controlling the metal by SG alone is impossible as the chloride molarity affects density directly. In other words, what you are measuring witha SG controller is the combination of metal content plus Chloride molarity.
So that leaves real-time metal analysis as the only way to control metal concentration which would be impractically expensive.
Peter Blokhuis
Edward Szpruch wrote:
Rudy,
Two additional points, both of crucial importance :
- tight control of temperature
- tight control of spray pressures ( upper and lower spray , across etching chamber and real exact jobs - post etch spray nozzles )
Regards
Edward
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of R Sedlak
Sent: Wednesday, September 13, 2006 12:01 PM
To: [log in to unmask]
Subject: [TN] Ammoniacal Etch
Joe, Wayne, and others...
A couple of words about ammoniacal etch which might help shed some light on the situation.
90+% of the pcb fabricators control ammoniacal etch using only density (Baume').
This was adequate when we called 10 mil line and space "fine lines", but really is not adequate for today's world...
Think about the fact that Cupric etch has three conditions which are monitored:
Metal content (By density)
Acidity (Usually by conductivity)
Cuprous Content (By ORP)
If you were going to control ammoniacal with the same precision you would control by the following
Metal Content (By density)
pH (Comparable to Acidity in the Cupric etch)
Cuprous Content (which is controlled by air flow through the chamber)
So, in many ways the ammoniacal etch today could be considered to be operating on luck. The system works best when it is used continuously. The system is pushed to its limits when operated intermittently.
Rudy Sedlak
RD Chemical Company
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