Date: Mon, 14 Sep 1998 10:13:36 -0400
At the PWBRC, we are working on regulatory tools that will cover air, water, solid/haz. waste, and
chemical reporting. Over the weekend, I used a couple of the Internet-based TRI databases (e.g.,
http://www.epa.gov/enviro/html/tris/tris_query_java.html) and studied summaries of pollutant release reports for 64 facilities in SIC 3672, randomly selecting contract PWB manufacturers.
I'm trying to come up with some lists of commonly reported chemicals that facilities could use as a
guide. Could someone shed light on something that I noticed.
Of the 64 companies, only twelve reported releases of ammonia to the environment. The releases
ranged from 5 to 32,000 lbs./year (for fugitive and stack releases to the air). I know from
previous work that the majority of PWB manufacturing facilities use ammoniacal etchant.
How are releases avoided at the remaining facilities?
Another area where there were significant differences was with "certain glycol ethers," that
may be associated with many liquid photoimageable soldermasks. Only four companies reported
releases (avg. of over 3,000 lbs./year to the air). Again, how are releases avoided?
Thanks,
George Cushnie
Date: Tue, 15 Sep 1998 11:01:23 EDT
I am a consultant in the environmental field with experience in the pcb
industry. There are a couple of ways that ammonia releases may be minimized
to the air.
One method is to route the ammonia which is vented from the etchers through a
wet scrubber. Water absorbs the ammonia readily but becomes loaded fairly
quickly at which point any reduction in the ammonia concentration is very
small. A high efficiency wet scrubber will normally need a pH control system
to chemically control the pH of the scrubbing solution. Control efficiencies
of 95 - 98% are common with chemical control. A 4-20mA output from a pH
controller is used to drive a proportional chemical metering pump (normally a
diaghram pump rated for sulfuric acid). Sulfuric acid is used with the pump
and the pH is controlled in the 4.0 - 6.5 range. The sulfuric acid combines
with the ammonia to produce ammonium sulfate which is then transferred to the
facility water treatment department. The scrubber, pump and associated
equipment must be able to withstand the sulfuric acid. Sulfuric acid of 66 Be
is normally used directly from the shipping container with proper backflow
valves to prevent water enterring the drum. Make-up water is bled into the
scrubber at a sufficient rate to prevent ammonium sulfate from crystallizing
on the scrubber media surfaces. The ammonium sulfate may act as a chelator and
should be waste treated accordingly (there will also be copper from etchant
which was in the air stream as well).
Another method that I have heard has been used is to place condensing coils
in the exhaust vents. The corrosive nature of the fumes (which will include
some etchant) will probably require titanium condensing coils. Running
chilled water through the coils will cause the ammonia to condense and run
back into a collection chamber and back into the etcher. The velocity of the
exhaust must not be too high as this will cause the condensed droplets to re-
enter the air stream.
Evaluating the amount of ammonia in the air exhaust can be approximated with
a Draeger tube or by contacting an environmental lab to perform the test. The
results will vary widely based on the current conditions that the etcher is
operating under. Some companies do not consider that a significant amount of
ammonia could be exiting the etchers to the environment. Only a test will
determine the volume of ammonia being released.
Glycol ethers are also found in resist strippers and cleaning solutions
("soaps" found on copper electroplate lines may have a glycol component). The
rate of glycol ether released to the environment is based on the temperature
of the solution, the volume of air exhausted, the size of the bath, whether or
not the material is sprayed, and the physical properties of the specific
glycol ether. Companies that are required to perform an annual emissions
inventory (due to VOC annual releases or for permit compliance) must determine
the amount of glycol (VOC) which is released from all compounds. If a
facility is below certain thresholds, formal reporting of VOC releases is not
required.
I hope this helps out.
David Miller
George,
The reporting threshold for NH3 is quite straightforward. Most fresh
ammoniacal etchant is about 97 gpl free NH3. This equates to about 8.8% of
the weight in each gallon of fresh etch. Adding 10% of the ammonium
compounds in the typical chloride based ammoniacal etchant raises the NH3
for reporting purposes to 9.56%, or about 0.87 lbs/gal. Dividing this into
10,000 lbs reporting threshold for otherwise use, yields 11,406 gallons. In
other words, if a PWB shop uses 11,406 gallons of chloride based ammoniacal
etchant per year, they are subject to the ammonia reporting requirements of
SARA Title 313. This volume equates to 207 55-gallon drums or about four
drums per week. Besides ammoniacal etch, there are other potential PWB raw
material sources of ammonia.
You're also correct in the glycol ether category. "Certain glycol
ethers" essentially are ethylene glycol ethers and their acetates. While
the major source of these can be the LPISMs, there are other process raw
materials such as HASL flux material, some screening inks and a few others.
Since LPISMs generally fall into two categories - screen coated and curtain
coated, it is important to understand the solvents contained in each, as
they do vary by product. For example, Enthone's 3241 material has about
26.2% VOC content, but only 17.3% is SARA reportable glycol ethers. If a
shop used this LPISM, its reporting threshold would be 5485 gallons. Shops
using Probimer 52M know that over 50% of this coating is SARA reportable,
but if they use 65M, none of it is (all solvent is propylene glycol ether
or its acetate). While there are several control devices that can
effectively remove GEs from air exhausts, water scrubbing is the least
expensive, as both ethylene and propylene glycol ethers are water soluble
and biodegradeable. Scrubbing efficiencies of 96-97% are not uncommon.
This last point raises an interesting footnote, as larger shops which
have control devices could very well emit fewer GEs than smaller shops w/o
control devices. Of course, this comparison can't be made if everyone isn't
reporting above the usage thresholds. Lee
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From: George Cushnie
Subject: Chemical Reporting Questions
PWBRC Staff
http://www.pwbrc.org
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From: David Miller
Subject: Re: Chemical Reporting Questions
X-To: geoc@CAIWEB.COM
George,
Miller Research Inc.
Dmiller525@aol.com
Date: Tue, 15 Sep 1998 14:40:05 -0400
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From: Lee Wilmot
Subject: Re: Chemical Reporting Questions
X-To: George Cushnie
Good catch. I think the main reason is that many reporting are not
calculating either the reporting thresholds correctly, or are not reporting
the releases properly. Please note that even with David Miller's response
of 95-98% removal efficiency for a nominal ammonia scrubber, that there is
still 2-5% of NH3 released. This point is probably reinforced by the site
that reported 5 lbs/yr air emissions. Low (or no) emissions do not exempt a
site from reporting once the threshold is surpassed.