I would not be too thrilled with a process that cleans with ordinary soap. A special saponifier is more appropriate.

Yes, water can be a problem. You do not say what the quality of your water is, so I will assume its 14meg ohm DI water. If you are using anything less then you have the chance that trace minerals will be left on the board such as Chlorine and this is corrosive.

It's interesting that you say you clean the flux with Alcohol, does this mean the flux is not a water based flux? If so why are you cleaning with water?

Its an interesting discussion to talk about cleaning like this, but if you have a system in place and your customers have never complained, then I suggest you keep doing what is working for you. However if I was new customer I would be concerned about this?

The problem with water is the capillary forces that pull the water in to tight spaces and makes it very difficult to remover. This is not just a drying issue but a rinsing issue. It is essential that the contaminated wash water is removed with DI water to prevent potential corrosion problems.

Once the assembly has been effectively rinsed then it must be effectively dried, residual water will also pose a potential reliability risk to the assembly. If all of this is done correctly there is no reason why assemblies can't be cleaned in an aqueous or semi-aqueous process.

Let me start with this quote from George Santayana.

"Those who cannot learn from history are doomed to repeat it."

Cleaning electronic products with water has been around for at least 35 years and yes the boards were cleaner than cleaning with any solvent we ever used, and we used some beauties.

The materials of choice were Chlorinated Hydrocarbons such as Methyl Ethyl Ketone (MEK), Trichloroethylene (TRI), carbon tetrachloride, Chloroethane, 1,1,1-trichloroethane, then the industry progressed to Fluorinated Hydrocarbons such as Freon’s ( TMS, TMC), and even plane alcohol, then to water with and without saponifier.

The issue with cleaning with water was the conversion of the mental concept that electronics and water do not mix. To some degree that is correct, we do not want to run any electronic products that are wet with water.

That being said, if the product is dry, then there is zero problems as cleaning with water has been done, is being done and will continue to be done due to all the environmental requirements being imposed on the industry on solvent discharge and recycling etc.

However, cleaning with soap and water and rising is the issue to address. The soap residues must be removed and this should be tested to make sure the residues are removed as they could be susceptible to the absorption of moisture which could impact the functionality of the product.

You need to make sure the soap is designed to remove the flux residues and is not designed to clean laundry, there are differences. Check with your flux suppliers to get the proper Aqueous Cleaning Solvent to clean your particular flux residues.

I strongly recommend the IPC-AC-62A, Aqueous Post Solder Cleaning Handbook, as this document is intended to provide a basic understanding of the use of aqueous cleaning process and provides test methods to verify the goodness of the cleaning process.

As usual, the answer to a broad, all encompassing question starts out with "…It depends..". Water is an excellent solvent for many materials, both inorganic and organic.

Water will dissolve traces of ionic materials which may be localized in one place, and through the dissolution, result in spreading the now-dissolved materials into many other places. Oftentimes water will dissolve materials which organic solvents will not, hence its "schizophrenic" nature.

If we want it to dissolve the material, it’s useful as a cleaner. If we don’t want it to dissolve material, it’s a contaminant, hazard, or even a chemical reactant.

Water can react with chemically active materials resulting in evolution of hydrogen gas. Moreover, water can evolve hydrogen when an electric current is passed through it.

However, each of these circumstances is unique, identifiable and controllable. I have never heard of any instance of these anomalies occurring in the manufacture of electronic products.

Notwithstanding all of the above, I would say that water can become a problem under any of several circumstances:

1. If the water is not 'ultra-pure' in the final washing stages, any dissolved solids will remain on the newly cleaned product as the water is dried off. Think of water spots on glasses coming from the dishwasher.
2. Water is harder to dry by evaporation due to its strongly hydrogen-bonded structure. In thermodynamic jargon, the latent heat of vaporization for water is very high. The higher temperature required for complete drying (compared to alcohols or other low boiling organic solvents) may result in thermal shocks to components.
3. Because of its polar nature, water forms very strong bonds with polar surfaces, such as found in silicon products. The packets of 'silica gel' which we often find inside products to keep them dry during shipping, work on that principle. They adsorb water vapor and bind it very tightly, thereby lowering the %RH inside the compartment/container, etc. So, the question is "how dry is dry enough" for the products at hand which you routinely deal with?
4. The practical side of my nature says "if you've never had a problem before" you probably won’t now…assuming that you use highly pure water. However, the new RoHS/WEEE requirements have required the use of new and different solders, which may have implications for interference with desired cleaning results due to interactions with water.

In summary, the key is to use the cleaning properties of water to remove the residues, but dry the newly cleaned products as quickly and gently (thermally) as possible.

By the way, there are chemical methods available (known as the Karl Fischer test) to quantitatively analyze water content on solids, or in liquids, if it is suspect as a cause for a product failure.

I would be interested to know any specific experiences that the quality engineer has encountered regarding the negative effects of water, beyond the scope of my comments. I hope this is useful

Wow. Simple question, but it requires a complex answer. Let’s start with the basics—

In general, you should never have to rinse your boards once you have cleaned them with alcohol. Since you have this requirement, that tells me you are using dirty alcohol and dirty brushes, probably in a plastic pump bottle. This simply isn’t going to get it done with modern PCBs. For more details, see: http://www.microcare.com/faqdetails.aspx?faqid=98

You see, contamination migrates! If you MUST use alcohol, change it every day and wash the brushes and the dispensing bottles. If that's not possible all you're doing is moving the contamination from one PCB to another. A much better tool is to use fresh, clean alcohol from an aerosol container.

Now, what about your water problem? There are three general grades of water: tap water, distilled water and deionized (DI) water. In terms of precision cleaning, neither tap water nor distilled water are sufficiently pure to handle the job as both are contaminated, to greater or lesser degrees, with minerals and organics. So if you want to use water, you must jump to DI-water.

Tap water, especially tap water mixed with detergents, should never be used for cleaning circuit boards. It generally will not remove the contamination and almost certainly will deposit soapy residues on the PCB.

But DI water can be tricky. The quality of DI water usually is measured by the water's resistance to electric current (in OHM-cm). Now, how pure is that?

• 50 kOHM is pretty standard and can be produced easily and inexpensively by many in-house deionizing systems.
• 1 megaohm of resistivity is the minimum required for true precision cleaning.
• In the really high-end world, such as the semiconductor industry, 20 megaohms is the norm. 20 megaohm water is so hungry for ions it will cut through steel.

Obviously, the cost, energy consumption, through-put and handling issues all jump exponentially as the purity of the water increases. The more pure the water, the more hungry it is for ions, so it will clean better but be more tricky to handle.

The only viable option is a tightly-sealed, closed-loop system which purifies the water, performs the cleaning task, and then recycles the water. These tend to be expensive, energy-hungry, and relatively slow in through-put. DI water on the benchtop is futile.

So what are your other choices?

Given the complexities of using water, many PCB makers and repair shops have switched to cleaning with solvents. On the benchtop, they typically use solvents in aerosol packages. If they have bigger cleaning jobs, the proper tool is a vapor degreaser.

The perfect solvent would be strong enough to remove the contamination, but mild enough to not attack any plastic components. It would be nonflammable, fast-drying, have no aroma, be safe for people and the environment, and affordably priced.

In today's world, the most popular products that meet these criteria are aerosol cleaners from MicroCare, Chemtronics and TechSpray. All are available from quality distributors anywhere in the country.

The benefits of using nonflammable, fast-drying solvents are numerous:

• They are Versatile: They remove a wide variety of contamination. The strength of the cleaner can be tailored with different additives, so you can get very mild to very strong cleaners.
• They Work In Tight Spaces: Because of their low viscosity, high density (130% the weight of water) and low surface tension, these cleaners easily get into and around BGA chips which have extremely tight spacing or narrow stand-offs.
• They’re Speedy: Because they are strong, uncontaminated (never exposed to air until used), and they dry fast, your techs will clean fast.
• They Don’t Stick Around: Because the solvents evaporate so quickly, the liquid quickly removes itself from under chips, out of blind vias, and from inside connectors where slow-drying solvents could be trapped. This keeps costs down and quality up.
• They Don’t Leave Residues or Spots: Water often leaves unacceptable spots which solvents rarely, if ever, leave.
• Broad Compatibility: Solvents are highly suitable for use with most components and plastics because the ingredients in the solvents can be tweaked for different materials profiles. For example, MicroCare sells a Contact Cleaner C which is so mild it can be sprayed on polycarbonate, but the same solvent with a different additive will remove even tough conformal coatings.
• Highly Effective: Modern solvents can easily clean almost every type of contamination, up to and including heavy greases, oils and even waxes.
• They're Safe for People. Modern, nonflammable cleaners have been thoroughly vetted by TSCA, ACGIH and other agencies. Properly used, they will give you years of safe cleaning with virtually none of the health risks of old-style solvents.
• Superior Environmentally: Modern solvents are very gentle on the environment. In terms of air quality issues, the solvents vary considerably, but MicroCare Contact Cleaner C (for example) is completely ozone-safe, VOC exempt and only a moderate global warmer. You don't get much better than that!
• Low Costs: Properly used, solvents are inexpensive to purchase and use, normally less than a dollar a day per technician.

In short, solvent cleaning on the benchtop delivers the highest quality cleaning in the shortest possible time, with the least risk of damage to the boards, components or the environment.