Ask the Experts
April 13, 2018
Can Water be Harmful to Electronics Components?
We have been reworking circuit boards for the past 30 years. After solder touch-up we remove flux residues with ordinary alcohol, then clean with soap and water. We then dry each assembly with a blower. We have never encountered issues with microprocessors.
A new quality assurance engineer insists that electronics components, especially microprocessors, should not be cleaned with water. Can you enlighten us?
Expert Panel Responses
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?
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:
- 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.
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.
- 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.
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.
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:
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
- 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.
- 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.
- 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?
- 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.
Jim Willimas is a PhD Chemist in Polymers and Materials Science. He specialize in printing, cleaning, inks, and coatings used in electronics manufacturng operations. Williams has more than 30 years experience.
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.
Vice President, Technical Director
At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification programs and provides customers with expert consultation in electronics manufacturing, including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the Assembly/Joining Process Committee.
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.
Senior Applications Chemist
Dr. Poole is a Senior Applications Chemist in Henkel Technologies, electronics assembly materials application engineering group. He is responsible for all of Henkel's assembly products including soldering products, underfills, PCB protection materials, and thermally conductive adhesives.
I would not be too thrilled with a process that cleans with ordinary soap. A special saponifier is more appropriate.
Dr. Craig D. Hillman
CEO & Managing Partner
Dr. Hillman's specialties include best practices in Design for Reliability, strategies for transitioning to Pb-free, supplier qualification, passive component technology and printed board failure mechanisms.
LOL, I loved reading all the responses. I'm thePM here in the lower west and the company has been using tap water for 20+years. The RMA cabinet is full and parts and have rust on them. Despite my veryloud concerns the owner refuses to see the light and has since installed anwater softener! Electronics, water and now just a little bit of extra salt addfor good measure.
In my past I have worked with all types of cleaning systems andstand by Filtered Tap (2 + 5 micron) wash a 1meg DI rinse. Tricloro 111 is myfavorite, but most people do not know how to correctly use it.
I loved all the comments. I learned a lot today and now have a new IPC handbook to purchase. Thank you all so much for your input.
Danielle Kindig, UQM Technologies, Inc.
I am a little confused with the cleaning process the big manufacturers used to clean their PCBs. We run a small repair shop specialized in liquid damaged device recovery.
We use distilled water as our main source for cleaning the contaminants and corrosions. We wash the boards with distilled water first to clean up the visible contaminants. Then to ultrasonic cleaner for 3 minutes each to 4 sides with electronic contact cleaner mixed at certain temperature. Rinsed out the solution with distilled water again and then 99.9% IP Alcohol. After rinsing the alcohol, air dry the boards overnight or let the fan dry run for about 30 minutes. Then we use oven (any oven with temperature control) to set temperature not to damage the board or melt the solder to 30 to 45 minutes depend on the condition. After cooled down the boards those are not seriously damaged look almost new PCBs just came out from assembly line.
The process repeats as necessary and after rework is done. We offer 1 year warranty on our repaired products and manufacturers offer 90 days max.
We had less than 1% of return rate for the same issue. The return customers are mostly with other issues not related or they caused some damage.
Water is the most powerful cleaning agent we have seen so far and it depend on how it was used also another fact. May be we do not worry so much for things that are not necessary or can be ignored.