Health and Environmental Benefits: Non-halide fluxes do not contain
regulated hazardous air pollutants, therefore greatly improving
environmental conditions and providing health benefits for employees.

Click here for a complete copy of this presentation or to discuss
SURCOTE VL non-halide fluxes.

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ANTIFOAM - The necessary Evil!

By Scott Griggs

Antifoam is unfortunately a necessary evil for developing and resist stripping spray processes. I say unfortunate because antifoams are typically petroleum based products that we do not want on the panel. 
However, the surfactants which are in the resist are dissolved into the developer or resist stripper bath and must be controlled. If this foaming isn’t controlled, it can lead to not only a mess, but a loss of spray pressure, due to pump cavitation.

Too much antifoam can cause the redeposit of the antifoam onto the panels by having it sucked-up through the pumps and sprayed through the nozzles. Too little, or ineffective, antifoam has its obvious issues.
In order to make a good decision about antifoam use, I follow these guidelines:

1) Avoid Manual Additions
It is very important that antifoam not be added in large amounts in order to avoid the potential deposition onto the panels.  I always suggest avoiding manual adds. Start by using a feed pump to intermittently add small amounts of antifoam on a continuous base. Commonly, the feed pump on/off can be activated on a timer ran off of the control panel. Low flow metering pumps or peristaltic pumps work well for this function, as they can be set to add less than a liter/hr. The least desirable scenario is having an operator add antifoam directly to a bath from the five gallon container. 

2) Avoid Alcohol Based Antifoams
Alcohol based antifoams are typically less expensive than antifoam concentrates, but the lasting power is short lived. Alcohol base antifoams appear to do a good job because they are very quick. This is achieved by lowering the surface tension of the bath. However, as the alcohol is absorbed into the solution, there is an immediate need for more additions. I have had customers decrease their usage by 10 fold simply by switching to a concentrated non-alcohol based antifoam. 

3) Some Foam is Good
When determining if you are using too much or too little, I use this rule of thumb; a little foam is a good thing. If the feed frequency is set up correctly, there will always be a small amount of foam on the surface. I shoot for approximately a half inch to one inch of a foam blanket across the top of the sump. If this is maintained over time, the usage is correct. Keep in mind that if the resist brand is changed, or loading is increased, the foaming will change accordingly and adjustments will be needed.

4) Floating vs. Miscible
I normally recommend floating antifoams for three reasons: they tend to be more effective and last longer, the surface is where the foam is, and I don't like the thought of spraying antifoam onto the panels along with the process solution.

5) Avoid Silicone Based Products
Some antifoams contain large amounts of silicone and should be avoided. If this silicone is deposited onto the panels it can be very difficult to remove and if this happens in the outerlayer developer, it can lead to plating issues.

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Feed and Bleed with NPS 3000

More and more board shops are interested in running the tin stripper on a feed and bleed system. This method gives more consistent performance and reduces the downtime for dumping and changing the solution. The system can be controlled either by specific gravity or panel count as illustrated in the charts below.

For our research, we started with NPS 3000 at 85% concentration in spray. This was replenished with 100%.

Tin Strippers Capability Charts

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Ask Rob about High Aspect Ratio Boards

Ask Rob…

Rob Coleman, our Director of Sales and Marketing, has been in the business for many years.  He will answer your questions in this column or find someone else who can!

Hey Rob, my tin stripper works great most of the time.  However, when I run high aspect ratio boards greater than 8:1, I am seeing tin in the hole.  What’s wrong?

In an effort to reduce overall operating cost for the tin stripper, my shops set their specific gravity controller to cycle on and off at a Specific Gravity (SG) of 1.355.  This is great for reducing cost and maximizing loading, but the higher SG is also what is contributing to the residual tin left behind on panels with a high aspect ratio.  As the SG is increased, the density of the material rises, thus making the solution more viscous.  The more viscous the solution, the more difficult it is to flow through small holes.

To avoid residual tin left behind, run the panels at a lower SG setting.

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Cleaning Innerlayers

The trend to finer lines and spaces continues to challenge processors of innerlayer material. With thinner core laminate and thinner copper foil, mechanical cleaning, the cleaning method of choice for years, is no longer an option.

Dry film photoresists will have trouble conforming to grooves and gouges left by pumice, creating the potential for reduced line width or shorts after etching. Mechanical cleaning can also cause distortion of the layers, and the layers can be creased and crumpled in the machine, creating scrap. Chemical cleaning eliminates these problems, maintains the dimensional stability of thin core layers and has become the standard process at many shops.

There are several types of cleaning that must take place during innerlayer processing. The first is to remove the chromate conversion coating from the copper foil. Acid organic cleaners work well for this application, along with handling soils and fingerprints in preparation for photoresist lamination.

RBP Layer Clean CR is an acidic, organic, water-soluble cleaner containing ingredients specifically designed for cleaning innerlayers. It is very effective for removing the chromate conversion coating prior to resist lamination. Its non-chloride formulation offers an advantage in waste treatment.

Chloride based cleaners form copper complexes that need special treatment; Layer Cleaner CR can go directly to a standard ion exchange column for treatment. When used on drum side treated foils, Layer Cleaner CR provides effective cleaning of the foil, and since no microetch is needed, the cost of the cleaning process is significantly reduced. For use in spray or soak applications, it is effective at removing handling soils and tarnish and rinses easily with warm water.

Following this cleaner, most photoresist manufacturers recommend a 20 to 40 microinch microetch before resist lamination. This enhances resist adhesion by creating an increased surface area.

RBP Quantum Etch, a stabilized peroxide solution, provides a consistent and controllable etch rate throughout the life of the bath. When compared to sodium persulfate, it offers a significantly higher capacity, as well as a reduced need for waste treatment.

A second process where innerlayers require cleaning is prior to oxide treatment. Proper cleaning of the copper removes organic and inorganic contamination, such as resist residues and tarnish, and is critical to ensuring that the oxide coating formed is consistent and uniform.

Cleaning is especially important with lighter oxide and oxide replacement systems. Fingerprints, tarnish and resist residues must be removed to allow the surface treatment to form. Ultraclean NF is an alkaline soak cleaner that has the capability to ensure that the cleaning process is effective.

Another cleaning issue for innerlayer processing comes with the increased popularity of double treated (DT) foil. The use of this foil eliminates the oxide treatment process and reduces the need for cleaning prior to photoresist lamination. However, it is still important to ensure that the material is free of contaminants before lamination with a thorough cleaning.

DT copper foil must be cleaned with an alkaline based cleaner. Copper foil manufacturers caution against using an acid cleaner as it can attack the DT surface, which will affect lamination peel strength. For effective removal of organic contaminants use alkaline cleaners such as Ultraclean NF for spray or soak applications, respectively.

To ensure cleanliness and the removal of the chromate conversion coating, a test using ammonium sulfide solution can be done to evaluate the effectiveness of the cleaning process on the copper foil surface before further processing. For additional information on this test, contact a RBP technical service representative.

Chemical cleaning of inner layers produces consistent results and allows the process to be conveyorized for more control, greater efficiency and higher throughput.

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Resist Strippers Capability Charts

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Ask Rob about Low Operating Costs

Ask Rob…

Rob Coleman, our Director of Sales and Marketing, had been in the business for many years.  He will answer your questions in the column or find someone else who can!

Hey Rob, with all of the different selling prices and different concentrations used from one resist strip supplier to the next, how do I know whether I am getting the lowest operating cost?

That is a good question. It can be very confusing as to whether you are getting a good deal or not. Each supplier has different unit costs and different concentrations and each bath performs differently. One product may have the lowest selling price, but could be used at a higher concentration or not last as long, could therefore end up costing you more. This makes it hard to determine overall lowest operating cost.

Here is what I do. I focus on loading in mil-sq.ft./gallon of concentrate. It is the best measurement that takes into account each suppliers’ price and concentration and puts the emphasis on the life of the bath or loading. You need to determine how much resist in mil-sq.ft. can you load per gallon of concentrate used before the bath is spent.

Example:

Loading:  10,000 panels run x 1.5 mil film x 70% area  = 10,500 mil-sq.ft.
Cost:  20 gallons of resist stripper used x $12.00/gallon = $240.00
Cost/mil-sq.ft.:  $240.00 / 10,500 mil-sq.ft. = $0.023/mil-sq.ft.

Shop based on cost/mil-sq.ft./gallon of concentrate and you will never make a bad decision.

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Ask Tony about Trapped Resist

Ask Tony…

Tony Jackson has been the Electronics Sales Manager for RBP Chemical Technology for the past 13  years servicing Canada, New England and the Midwest Region.

My outer layer resist stripper process works fine until I run jobs with very fine lines and spaces.  The dry film sometimes gets trapped between circuits causing etching problems.  How can this situation be avoided?

Good question.  In today’s market, it is quite common to have traces or spacing of less than 2 mils.  If the bulk of your work is typically 4 mil lines and spaces, a particle size of 100 microns would most likely be sufficient.  But when spacing drops to 50-75 microns or the traces are over plated and trapping the resist, the same resist strip parameters will most likely not work.

What needs to be done is to set the process up for the smallest particle size you will need, not a process that addresses the bulk of the work.  The process needs to generate a particle for the most difficult of applications, or putting it simply, a particle size that is smaller than the spacing.

First of all, you need to work with a resist stripper that is designed to generate smaller particles.  Many of the products on the market are old and outdated and were developed 5-10 years ago when typical spacing was 8-12 mils.  Once you have identified the stripper that is compatible with today’s films and board designs, you are ready to begin testing.

Run 3-4 different concentrations and temperatures to see which parameter creates the best particle size for your needs. Once you have identified the right chemical parameters, a good horizontal spray machine will do the rest of the work.  Make sure you provide adequate contact time allowing for a break point of 40-60%.  Very high spray pressures of 2.5-4.0 bar are preferred in these situations.  Fan shaped nozzles should be aligned properly to insure the chemistry is uniformly distributed over the panel.  If this is all done well, you should have successfully eliminated any possibility of problems etching the copper from between traces.

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Preventive Maintenance on the Line

The shop is swamped and orders are pouring in. There just isn't any time to clean the equipment or scrub a tank - right? WRONG - a critical mistake made by some PCB manufacturers is to wait until a process is out of control rather than perform regular preventive maintenance (PM) procedures throughout their operations.

This can result in sudden breakdowns, work stoppages and the need for rework, all of which results in loss of money, time and energy. Planning and managing downtime through routine PM procedures is a much smarter and more effective approach to ensuring high yields and on-time shipments.

PM should be addressed in all aspects of the manufacturing process. The first and most critical area of concern is IMAGING. Problems here can result in shorts and open circuits that may not be detected until the end of processing. A lot of wasted time, labor and chemistries along with the expense of rework, make mistakes in this area very costly.

In addition to the stringent environmental controls required in the imaging area, RBP recommends using high quality, anti-static film cleaner applied with a lint-free cloth to the film. The cleaner should be dispensed from a container whose properties are not attacked by the cleaner itself. Nylon is typically a good choice. We do not recommend a polyethylene based container, as the plastic can dissolve into the cleaner and cause hazing problems. Reuse of containers can cause buildup of the antistatic agent which can also result in hazing.

In the DEVELOPING PROCESS, it is imperative that the equipment be properly maintained following manufacturers' recommendations. It is especially important to check and periodically replace worn nozzles.
They reduce the spray pattern area and produce an irregular flow. This can leave areas with less solution impingement and cause uneven developing or stripping of panels. Stainless steel nozzles generally perform
much better than plastic.

It is also critical to clean equipment to prevent residue build-up. The use of proprietary developing chemicals with cleaning agents can help to combat carbonate and polymer residues. A dirty developer results in greater chemical usage, poor developing quality, erratic or reduced developing speed and the need for excessive rinsing to fully clean panels.

BLEED AND FEED SYSTEMS must also be properly calibrated and continually monitored for residue buildup. A dirty system will not release the correct amount of replenishing solution at the right time, reducing the developing speed and effectiveness. It can also cause chemical imbalances such as too much carbonate or antifoam in the solution. These can build up quickly and create the need for additional cleaning. The possibility of an antifoam problem can be reduced by using a highly concentrated, high purity product that will not build up as quickly.

PM in the RESIST STRIPPING PROCESS should be handled much the same as with developing. Equipment needs careful cleaning, monitoring and maintenance.

The critical issue here is to ensure a good match between the stripper and the resist. This results in optimum loading capacity, strip time and particle size. Matching the particle size created by a particular stripper/ resist combination with the capability of the filtering system reduces the potential for clogged nozzles and incomplete
stripping.

In the TIN/LEAD STRIPPING PROCESS a buildup of tin/lead residues can contribute to overheating, premature depletion of the stripping solution and excessive chemical consumption. This results in incomplete stripping and lead salt residues being deposited on panels. Again, PM is a necessary aspect of ensuring efficient processing.

It is apparent that many aspects of the PCB manufacturing process can benefit from a carefully planned PM program. Along with this, RBP also offers several other tips that can help prevent problems:

• Always follow manufacturers' recommendations on operation and PM of
  equipment
• Use “value added,” proprietary chemicals to increase efficiency and minimize
  production and labor costs.
• Use recommended amounts of chemicals to avoid unnecessary build-up and
  cleaning problems.
• Make sure chemicals and processes are compatible to avoid additional
  waste or residue.

Following a few guidelines and committing to a PM program can lead to higher yields, less rework and more cost-effective operations. Contact RBP direct for assistance in setting up a preventive maintenance program that will work for you.

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VOC Considerations in Printed Board
Fabrication Process Chemistry
Presented at IPC Printed Circuit Expo

History and Background

On November 15 1990 President George Bush signed the Clean Air Act into law, legally restricting the output of selected air pollutants by cities and industry. The Act addresses multiple sources and types of air pollution, but for the purposes of this discussion, we will deal with the "VOC" [volatile organic compound] component of "ground level ozone", resulting from the material choices and methods used in Printed Board fabrication. "Ground-level ozone (O3) is the major component of smog. Ozone is not emitted directly into the air, but is formed through complex chemical reactions between precursor emissions of volatile organic compounds (VOC) and nitrogen oxides (NOx) in the presence of sunlight.". A simplified schematic of the reaction follows:

This presentation is the direct result of an occurrence at one of our customers that illustrated several widely misunderstood aspects of VOC regulations, measurement and calculation, and operational considerations. These misunderstandings potentially can result in suboptimal process choices and/or excessive costs. We felt that a brief review in open forum would benefit all of us in the industry.

Impact of Regulation and Response Alternatives on Operations
The Clean Air Act and the accompanying regulations provide for variations in both the degree and implementation schedule required depending on the degree of "attainment" (i.e. the degree of compliance with the targeted levels of ground level ozone), as illustrated below.

Classification of Ozone Nonattainment Areas

Marginal

• Deadline to Attain (from Nov 15, 1990) – 13 years
• Design Value (ppm) – 0.121 - 0.138

Moderate

• Deadline to Attain (from Nov 15, 1990) – 6 years
• Design Value (ppm) – 0.138 - 1.160

Serious

• Deadline to Attain (from Nov 15, 1990) – 9 years
• Design Value (ppm) – 0.160 - 0.180

Severe

• Deadline to Attain (from Nov 15, 1990) – 15 years
• Design Value (ppm) – 0.180 - 0.190
• Deadline to Attain (from Nov 15, 1990) – 17 years
• Design Value (ppm) – 0.190 - 0.280

Extreme

• Deadline to Attain (from Nov 15, 1990) – 13 years
• Design Value (ppm) – Above 0.280

Areas that are likely to be classified as Extreme, Severe, or Serious as of late-1990 are presented below.

Ozone Nonattainment Areas

Extreme (1 area)

• Los Angeles-Anaheim-Riverside, CA

Serious (16 areas)

• Atlanta, GA; Bakersfield, CA; Baton Rouge, LA; Beaumont-Port Arthur, TX;
  Boston, MA; El Paso, TX; Fresno, CA; Hartford, CT; Huntington-Ashland, WV-KY-OH;
  Parkersburg-Marietta, WV-OH; Portsmouth-Dover-Rochester, NH-ME; Providence, RI;
  Sacramento, CA; Sheboygan, WI; Springfield, MA; Washington, DC-MD-VA

Severe (8 areas)

• Baltimore, MD; Chicago, IL-IN-WI; Houston-Galveston-Brazoria, TX; Milwaukee-Racine, WI;
  Muskegon, MI; New York, NY-NJ-CT; Philadelphia, PA-NJ-DE; San Diego, CA

In addition, there is the usual provision allowing local governmental entities to apply more
(but not less) stringent limits on emissions.

Most process areas of printed wiring board fabrication operations have potential contributors to
VOC emission (various film, surface, and screen cleaners, fluxes, etc.). This illustration is limited to
the photoresist stripping operation.

Photoresist stripping concentrates (proprietary variations on the "aqueous" stripping chemistries) vary
from near 0#/gallon VOC (on a formulary basis) for ~100% inorganic [caustic] formulations to over
6#/gallon for 100% organic [amines, stabilizers, surfactants, etc.]. The actual reportable VOC content
for such concentrates is most commonly measured using a method described in 40 CFR Part 60
Method 24, generally shortened in conversation to "Method 24". This is the value typically reported
on the MSDS for the concentrated material.

This method is essentially a weight loss determination at specified time and temperature,
mathematically deducting the water content (most properly determined using a Karl-Fischer titration)
and assuming that the remainder of the weight loss is due to VOC content. Several factors can result
in a difference between the actual (formulary) VOC content and the reportable (by analysis) VOC content,
including interactions between constituents, volume/surface area ratio of the glassware selected, etc.

The actual VOC emissions required to be reported must be determined by examining the air discharge
permit at the location in question. The simplest (though neither the most technically correct nor in many
cases, the wisest) method is to assume that ALL the VOCs contained in the incoming concentrate are
emitted as reportable VOC’s. This is the worst-case scenario, and can result in reporting quantities
many times higher than actual emissions.

There are at least two factors contributing to these possible discrepancies:

• Partial-pressure effects on volatilization, and

• Distribution of VOC constituents in non-volatile matrices/non-reportable waste streams.

Partial pressure calculations can be used to estimate the equilibrium concentration of a material split
between the liquid and vapor phase. Perhaps more importantly (from a practical standpoint) is the
distribution of the organic fractions of a process chemistry between the various input and output
streams of a process.

The quantity of VOC emissions to be reported can be very different depending on how
the permit is structured, and dependng on how detailed an analysis the user is prepared to undertake.
If no reasonably well-documented accounting for the various exit streams is documented, it will be
extremely difficult to justify any deviation from the simplest assumption, i.e. the gross-pounds-of-VOC-
content imported to the operation equals the reportable VOC emission. At the very least, the operator
must work closely with the local air-emissions regulatory body (in the US, the EPA or it’s local designee)
to structure an acceptable means of accounting for actual or calculated losses.

Responding to a Process VOC Challenge: A Case Study

In the specific case that inspired this discussion, a high volume commercial operation was faced with
a requirement to significantly reduce the reported quantity of VOC emissions from their photoresist
stripping operation, after an audit by an environmental consulting firm. The production operation was
happy with the operational performance of the chemistry in use, but a less functionally desirable
alternative chemistry was available. A sample (of unknown pedigree) of the alternative chemistry
was analyzed by the contractor, and was reported to be much lower in VOC content than the
incumbent product. The printed boards in production at this facility were primarily SMOBC,
using tin as the etch resist, and a signficant proportion started with two ounce or greater foil.
In this operation, that meant multiple passes through the entire strip-etch-strip line for the
heavier copper panels, to avoid line purges and the attendant production interruptions.

Process changes were not acceptable, for capital and training reasons. The immediate request from
the operator was for "…a product that works just like the one we’re using, just lower the VOC content…".
Reportedly, no cost increases would be tolerated. In descending order of priority were yield, speed,
cost per gallon, copper finish, and finally, loading. Simplicity and consistency in operation were
more important than chemical "efficiency" to this operation.

In the classic custom formulation approach, this would suggest substitution of inorganics for some
portion of the organic sources of alkalinity, but it was soon determined that the tin deposit/registration
issues interactions were insufficiently robust to tolerate multiple passes through a higher-causticity
resist stripper without increases in etchouts. This was shown to be true despite incorporation of
several alternative metal protection chemistry "packages", within the "no cost increase" constraint.

Given the emphasis on speed and simplicity of control, and with some careful balancing of the
various amine species for optimized results, it was possible to formulate an all-organic resist stripper
meeting their VOC target, while maintaining speed, finish, and yield. The trade-off was loading capacity,
which (while it might not have been detectable in the operation as normally configured) was unacceptable
to us in terms of "value for money". In reporting this to them, we reiterated the possibility of determining
actual VOC emissions (vs. the simple "total VOC in = reported emissions", worst case approach). On this
hearing, and now realizing more clearly the trade-offs involved, a cooperative approach involving stack
sampling by the environmental consulting firm, stabilized (baseline) operation by the operator,
and chemical monitoring by the supplier was agreed upon.

This is not without a cost, as the stack monitoring and analysis, and calculation of fugitive emissions
will be time (read "money") consuming for all parties. In this case, the benefits of the possibility of
continued operation with a well-understood, high-performance chemistry outweighed the costs
associated with the analysis. In another situation (for example, an operation where the scrubber
was inadequate, or a smaller operation), it might have required a chemistry or procedural change.

Future Considerations

The possibility of enforcement "speed-up" or "stretch-out" in various regions as attainment levels
are met, compliance targets are changed, or the political climate varies always exists. It is reasonable
to assume that geographic areas not currently emphasizing VOC emission targets will do so in the future.
As to future regulation, who can tell?

Conclusion

It is possible to meet stringent VOC content targets by customized formulation, optimizing for a
specific location’s requirements. However, consideration of the "big picture", and open, cooperative
communication between all parties is needed to achieve the "best" balance between operational,
environmental, and cost considerations.

Personal conversations, RBP laboratory personnel, December 1999-February 2000

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RBP Chemical Technology, Inc. – The Intelligent Choice ™
150 S. 118th Street
Milwaukee, WI USA 53214-0069
1-800-558-0747
Outside USA: 1-414-258-0911

© Copyright 2006 RBP Chemical, Inc.
All Rights Reserved.

Industry Related links:

IPC

California Circuits Association

Printed Circuit Design and Manufacture

Circuit World

Etchomatic

Uyemura International Corporation (UIC)

IPCA (India Printed Circuit Association)

KPCA (Korean Printed Circuit Association)