Dear Mr. McGregor:

I would like to submit a rebuttal and supporting data regarding the
benefits and cost of "feed and bleed" maintenence of the resist
stripping process, as they pertain to your questions D. and F..

STRIPPING

The "feed and bleed" mode of operation can be applied to both
proprietary and caustic chemistries.  Based upon the dry film employed,
it is possible to measure, relatively accurately, the volume of
chemistry consumed per square foot of dry film being stripped.  Once
determined, the stripper chemistry and the proper volume of water to
dilute the chemistry to within the operating range, can be added based
upon panel count.  We have had success making frequent, low volume
additions of diluted resist stripper chemistry, on the order of 0.5
gallons of diluted chemistry (stripper at 5% v/v in water) every 20 - 25
panels.  And I am assuming 18" x 24" panels with 70% resist coverage at
this rate of addition.

This type of feed and bleed system has been in use for more than 3 years
and successfully implemented with DuPONTS TM and PM series, ENTERECS
7200 series, and DYNACHEMS HG, GA, FL, and AX series.  (I am sure others
have found "feed and bleed" processing applicable to other films as
well.)

Similar to operating developer on an automated "feed and bleed" basis,
there are several advantages including:

a) consistant speed of processing while maintaining stripping
performance;
b) reduced batch dump frequency and heat-up times; and
c) simplified waste treatment.

I will cite specific examples to clarify.

1.  DYNACHEM FL, 1.3 mil
        - conveyor length, 8 feet
        - speed 51 ipm
        - breakpoint 40%
        - dump frequency, once per month
        - surface square feet processed between dumps, @144,000
        - COST (assuming 70% resist coverage) $0.0118/square foot

2.  DuPONT PM Series
        - conveyor length, 6 feet
        - speed, 34 ipm
        - breakpoint, 50%
        - dump frequency, once per month
        - square feet processed between dumps, @112,000
        - cost (assuming 70% resist coverage), $0.141/square foot

3. DYNACHEM GA
        - conveyor length, 8 feet
        - speed, 60 ipm
        - breakpoint, 55%
        - dump frequency, once/two weeks
        - square feet processed between dumps, @96,000
        - cost (assuming 65% resist coverage) $0.0124

Each of the above systems employed continuous resist particulate
filtration during processing.  Filtration is required to successfully
employ "feed and bleed" processing and is the MAIN FACTOR in lowering
the operating cost of stripping, and is also the primary factor driving
the frequency of dumping.  Additionally, the copper concentration of the
resist stripper "bleed" was measured in each of the above systems and
never exceeded 14 mg/L.

We have also assited in the installtion of "feed and bleed" stripping
employing 50% w/w sodium hydroxide employed at 1.2 - 2% by volume.  As
previously addressed in other responses, it was necessary to address
copper oxidation when stripping sodium hydroxide.  While I do not have
the exact operating costs of this system, it was obviously less
expensive than using a proprietary stripper, as 50% w/w sodium hydroxide
is about $2.00 gallon.  However, when employing caustic the rates of
addition must be increased.

WASTE TREATMENT

All of the proprietary strippers I am aware of contain monoethanolamine
(MEA) as a component.  This material is defined as a complexing agent
(containing a single donor atom - "monodentate ligand") versus a
chelating agent (containing more than one donor atom - "polydentate
ligand" such as EDTA which contains 6 donor atoms).  It is inherently
easier to waste treat complexing agents because they typically form
weaker bonds with metal ions.  Depending upon regulatory requirements,
the bleed from a feed and bleed system can often be treated by primary
pH adjust.  Factors determining if this is an applicable waste treatment
method included COD (Chemical Oxygen Demand) and copper regulatory
levels in your waste stream.  Depending upon the gpm of effluent one
generates, it is possible to determine if the bleed can be treated
solely by pH adjust.

If it is necessary to treat the bleed separately, it is often possible
to combine this effluent with other alkaline wastewater streams due to
the low volume periodically generated.  I am aware of one situation
where the bleed is combined with high copper (greater than 10 mg/L)
rinse water effluent and treated by membrane ultra-filtration.  Because
the resist particulate is dosed into the system at low levels, the
resist particulate does not appear to adversely affect the holding
capacity or life of the filter.

I apologize for the long winded reply.  Yet, because most pcb
manufacturers have unique and different requirements for resist
stripping, it is difficult to cover all possibilities.  If you have
additional questions, please feel free to contact me.

Regards,
Ted Stern

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