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April 17, 2006

Batch Washing Machine Request

We are looking for a reliable batch washing machine for cleaning PWB assemblies prior to conformal coating. Our batch sizes are typically 30 to 40 assemblies.  Our current machine uses a 75/25 alcohol/water mix with a resistivity monitor.  Since we use RMA flux on the assemblies, we need either an alcohol mix or a saponifier/water wash system. What is available on the market?



Tom Nedlik

Experts Comments

There are several manufacturers of batch-format de-fluxing systems on available today. My reply will address two aspects of your questions. First, the easy answer:

Manufacturers of batch format de-fluxing systems:

Aqueous Technologies
www.aqueoustech.com

Austin American Technology
www.aat-corp.com

EMC Global Technology
www.emcgti.com

Unit Design
www.unitdesign.com

Now, let's discuss the other aspect of your question. That is the issue of what type of cleaning media to use. Basically you choices are the following:

Solvent
Semi-aqueous (solvent wash plus water rinse)
Aqueous (water-based chemical mixed with water)

In earlier days, the most common de-fluxing product was a vapor degreaser and a CFC-based solvent such as Freon TMS or 111 Trichlorethene. In those days, it was the solvent that did all of the work, not the cleaning equipment. In fact, all a vapor degreaser basically had to do was to heat and re-condense the solvent.

The Montréal Protocol ended the reign of solvents and aqueous-based technologies took the spotlight. Early aqueous-based chemicals, although effective flux removers, were not without blemish. Dull leads were a common side-effect of early aqueous chemicals such as saponifiers.

Fast-forward twenty years and aqueous-based cleaning is now the benchmark cleaning process in post-reflow de-fluxing. Modern aqueous chemistries produce cleanliness levels far exceeding the best solvents and cosmetic results only dreamed of in earlier days. Modern aqueous de-fluxing equipment provides features and benefits only dreamed of in the 1980's. Today's water-based de-fluxing chemicals are complex blends that include cleaning agents, corrosion inhibitors, de-foamers, etc. Water-based chemicals are fully compatible with all flux types including water-soluble (OA), Rosin ('R', 'RA', 'RMA'), and no-cleans. The newest water-based de-fluxing chemicals are extremely effective both lead and lead-free post-reflow flux residues.

"I've been told that we have to use solvent because of a Mill-STD". We hear this question frequently. The fact is, there is no military specification that mandates the use of solvent. In fact, many of the cleaning solvents sold today are illegal to operate in several US States due to ever more stringent VOC restrictions (IPA included). Today, military and IPC ('J'-Standards) no longer specify the cleaning media rather they specify the cleanliness results.

There are but a handful of equipment manufacturers that still offer solvent-capable de-fluxing equipment. There are several reasons for the declining availability of solvent-based machines including:

1. Solvent-based machines frequently do not provide cleanliness levels equal to aqueous-based equipment.

2. Solvent-compatible cleaning equipment costs more than their aqueous counterparts.

3. Solvent-based cleaning equipment frequently require fire-suppression devices due to the flammable nature of many solvents. The liability of operating a solvent system is greater than an aqueous process.

4. Solvent based equipment and chemicals generally provide lower degrees of environmental compliance compared to aqueous-based solutions.

5. Solvents are generally less operator-safe than aqueous solutions. Solvents frequently require greater care with storage, use, and disposal compared to aqueous chemistries.

IPC initiated a study entitled Phase II Testing. In this test, aqueous chemicals were tested against solvents. Results of the Phase II testing indicated the superiority of aqueous-based solutions compared to traditional solvents.

In almost all de-fluxing applications, the wash solution (aqueous or solvent) must be thoroughly removed from the assembly. The rinsing process is considered an integral part of the de-fluxing process. Because solvents by nature are not soluble in water, the rinsing process is normally conducted in a separate machine. That means at least two machines are required for solvent-based de-fluxing. One machine for wash, another for rinse and dry (in some cases, three machines are required, one for wash, one for rinse, and another for dry).

In an aqueous-based process, wash, rinse, and dry are accomplished in the same machine, eliminating the need for product transfer and providing a faster overall cycle time.

To conclude, aside from the few legitimate justifications for a completely "waterless" process, aqueous processes provide superior cleanliness, increased environmental and operator safety, lower chemical and equipment costs, and faster cycle times. Aqueous processes meet and exceed all military and IPC cleanliness standards. Aqueous cleaning processes represent the conventional wisdom in circuit assembly de-fluxing practices and procedures.

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Mike Konrad
President
Aqueous Technologies
Mr. Konrad has been in the electronic assembly equipment industry since 1985. He is founder and CEO of Aqueous Technologies Corporation, a manufacturer of automatic de-fluxing equipment, chemicals, and cleanliness testing systems.

Regarding Mr. Nedlik's question about a batch cleaning machine using IPA and water, once again people have forgotten about a proven, reliable and fast cleaning method that industry has been using for sixty years: the vapor degreaser.

A vapor degreaser is an ideal choice for this application. Let's assume he's removing light oils, fingerprints, maybe a solder ball or two, and some odd flux residues here and there. A vapor degreaser could clean a batch of those boards (assuming reasonable size) in under 5 minutes. The boards will come out clean, dry, and ready to coat. Any IPA, water, or semi-aqueous system is going to be slower, generate a substantial waste stream, use more electricity, and not do as well in the smallest corners and spacings. In addition, there will be problems drying the boards, to ensure that no water gets trapped under the coatings.

Most people are under the impression that vapor degreasers are environmentally unsound and damage the ozone-layer. This is untrue, and was merely a function of the solvents used during the Cold War era, specifically the CFCs. Today there are a number of companies selling ozone-safe solvents engineered for vapor degreasers, and (while it pains me to admit this) most of them work pretty well.

So how does a vapor degreaser work? Basically, it's a still -- just like a still used to make whiskey.

You have your solvent in the bottom of the machine, which you heat it to boiling ("A"). While heating water is slow and energy-intensive, these solvents are "low boilers." This means they basically boil just above room temperature, say 90-100 degrees F, so the energy required is minimal.

The boiling solvent turns into vapor and tries to jump out of the machine in to the atmosphere. But the machine is designed to capture the vapors. The vapors are held in place by a "cold trap" - - simply refrigeration coils wrapped around the top of the machine ("D" and "F"). This vapor "blanket" hovers over the boiling solvent and, when chilled, is recycled back into the machine.

The cleaning starts when a "cold" part is immersed in to the vapor blanket . The solvent condenses on the parts like fog on a windshield on a damp morning. The solvent dissolves the residues and contamination, eventually dripping off back into the machine (specifically, back into Sump "A").

Some of the vapors actually touch the cooling coils, where they instantly condense into liquid and drain back into Location "B". This is the distillation process, and remember that a distilled liquid does not carry any contamination with it. So not only have we prevented the solvent from leaving the machine, we have distilled it, purified it, and now return it back to be used again. Most vapor degreasers go 3-6 months before they are shut down and cleaned out, a process that takes 3-4 hours at the most.

(The main options on a degreaser are shown in the cutaway as well. Location "C" isa water separator while locations "E" and "F" are extra cooling to better retain the solvent in the machine. Also, ultrasonics can be added to Sumps "A" and "B" if even stronger cleaning is required. Lastly, some customers buy hoists (not shown) to automate loading and unloading, which frees up workers for other chores.)

Importantly, this is an inherently simple and elegant process. There are no filters, waste treatment systems, or other collateral systems such as those found on water-based cleaning machines. Solvent consumption is minimal. Versatility and quality is maximized.

What are the benefits of this technology?

A vapor degreaser such as the one shown here will cost perhaps $25k to buy and install. It's about the size of a lateral file cabinet. There's no extra power or waste treatment machinery to buy, no drums of hazwaste to dispose of. The biggest vapor degreaser I have seen recently cost $125k, and it had every whistle and bell on the planet. The only problem with degreasers is they are not permitted in Southern California unless you are using low-VOC solvents which generally means they must be ozone-depleters (hard to believe, but true).

Some specifics:

A medium-sized vapor degreaser averages cleaning cycles of 3-10 mins., depending upon the contamination, the solvent and the cleanliness required.

A medium - sized vapor degreaser is so energy efficient it can run off a 110-v circuit. Try that with any water-based cleaning machine and you'll blow fuses into the next ZIP code.

Any vapor degreaser will clean under tight stand-offs better than any water-based system. This limit is due to the inherent nature of a molecule water (surface tension, latent heat of evaporation, etc.) and cannot be substantially improved no matter how many additives you put in to the water or pumps you put into the system.

A medium-sized degreaser will typically use a quart of solvent a week, plus or minus, depending upon the volume of useage, the training of the people using the system and the accesories bought with the system. While the solvents are expensive when filling the machine, the real issue is not the cost to buy, but the cost to use. If we're cleaning and coating several hundred boards each week perfectly, with no rework, then $25 or $30 of solvent is pretty cheap cleaning.

For solvents, I suggest he check with 3M Novec or DuPont's Vertrel (the latter of which we sell, so my bias is strong). For cleaning machinery, Branson Ultrasonics (818) 707-7001, and Ultronics (800) 553-7881, make excellent machines, as does Tiyoda Serec, 502-212-9226. Branson and Tiyoda also make water-based cleaning machines, but despite the quality of the machinery they have all the same problems inherent in any cleaning system that uses water.

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Mike Jones
Vice President
Micro Care
Mr. Jones is an electronics cleaning and stencil printing specialist. Averaging over one hundred days a year on the road, Mike visits SMT production sites and circuit board repair facilities in every corner of the globe, helping engineers and technicians work through the complex trade-offs today's demanding electronics require.
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