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SMT electronics assembly manufacturing forum.

Ultrasonic washing for boards


Ultrasonic washing for boards | 23 April, 2005

Does someone use Ultrasonic washing machine to remove nc or rma flux residu from the pcb???

I have no experience with this device and I plan to use this for a very small production lot

Do you recommand this ???

How are your results ???

What kind of liquid is used to dip them ???

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Mike Konrad


Ultrasonic washing for boards | 25 April, 2005

The issue of using ultrasonic technology for post reflow de-fluxing presents challenges in two categories:

Controversial: Although there are recent studies that indicate acceptance with ultrasonic technology on populated assemblies, there remains significant concern regarding damage to wire bonds and other devices by the application of ultrasonic energy. Regardless of the accuracy of these concerns, the appearance of the concern may be enough to render ultrasonic technology unacceptable in post-reflow de-fluxing applications.

Lack of automation and SPC: Most ultrasonic cleaning systems were designed for parts cleaning (including stencils) and not post-reflow assemblies. Cleaning reflowed assemblies is generally more critical than degreasing parts or cleaning stencils. In the latter applications, there are few documented cleaning specifications that refer to ionic contamination. Although ultrasonic technology is a very good cleaning method, the machines that utilize ultrasonic technology usually lack a complete wash + rinse + cleanliness test + dry process.

Most ultrasonic cleaning systems do not provide adequate rinsing for circuit assemblies (rinsing is the most important process step in post-reflow de-fluxing). Additionally, I am not aware of any ultrasonic cleaning system that offers nearly enough process control (such as cleanliness testing) to make them a viable resource.

My recommendation is a spray-in-air de-fluxing system. As a matter of full disclosure, we manufacture both spray-in-air and ultrasonic cleaning systems so we have no axe to grind with any one technology.

Spray-in-air technology offers a fully automated process (wash + rinse + cleanliness test + dry). There are no issues of potential component damage like that of ultrasonic technology. Spray-in-air technology represents conventional wisdom.

You will find many spray-in-air systems available. Batch format for medium to low production and inline systems for higher throughput.

Here is a list of manufacturers:

Aqueous Technologies Batch and Inline

Austin American Batch and Inline

UnitDesign Batch

Speedline Batch and Inline

EMC Global Technologies Batch and Inline

I hope this helps!

Mike Konrad (909) 944-7771 ext 29

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Ultrasonic washing for boards | 25 April, 2005

Mike Conrad's "matter of full disclosure" is not quite complete. He fails to mention that he only makes spray-in-air board cleaners and only ultrasonic stencil cleaners. He does not make ultrasonic board cleaners. So, he apparently he is "grinding the Aqueous Tech axe."

There was an article in SMT magazine, October 2004 by William Kenyon:

This article sums things up.

I recommend contacting Branson, Crest or Blackstone. These companies do make ultrasonic cleaners for PCBs.


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Mike Konrad


Ultrasonic washing for boards | 25 April, 2005

Hi Carl / Bill,

I seem to miss your point regarding disclosure. As I CLEARLY stated, it is the perception of damage more than the possibility of damage. As a twenty year veteran of de-fluxing systems, I can assure you that there remains enough controversy regarding the use of ultrasonic technology on populated assemblies to prevent its wide spread use. I am not saying that it is not a good technology. What I am saying is that if a user chooses to apply ultrasonic energy to populated assemblies, they should be prepared to defend it. May I remind you of the military cleaning standard that stated �subject to review and disapproval�.

You do not address the issues of process control (or lack thereof) with regards to ultrasonic cleaning systems. Perhaps you can recommend just one ultrasonic cleaning system designed specifically for populated circuit assemblies.

I am a proponent of ultrasonic cleaning. I am also very pragmatic.

Mike Konrad

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Ultrasonic washing for boards | 27 April, 2005

It was a resonant frequency that brought down the Narrows bridge. Memorex can shatter a wine glass with resonance. Ultrasonic washers use frequency to do what they do. If anything on the pcb has a length width or mass that resonates at the washers frequency then expect trouble. Failing conections, seperation of bonds, and even internal Ic damage or moisture intrusion may result.

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Ultrasonic washing for boards | 28 April, 2005

Hello Paul,

Prior to 1980, I would say that your concerns were real regarding the resonant frequency. However, since then all major ultrasonic cleaner manufacturers use a "sweep" frequency technology. By "sweeping" or alternating the frequency between say 38 - 42 kHz, the standing resonant wave is eliminated and frequency-sensitive components have been shown to be safe. GEC Marconi has done extensive research on the subject. Contact me if you would like a copy.

However, Power Density is an issue and the research indicates that ultrasonic power should be kept below 10 watts per liter of wash solution (Total watt output of the ultrasonic generator / total volume of cleaning solution in the wash tank).

This is where the cleaning chemistry plays an important role. If the cleaning efficiency of the chemistry is weak, the ultrasonic cleaner will need to operate at a high power density to compensate for the weak or non-specific chemistry. This is like turning up the nozzle pressure on a spray-in-air machine or scrubbing harder with a stiff brush. If an efficient chemistry is used that is specific to the application, the necessary power density required will be less and components will be safe. Make sure that your ultrasonic machine or stencil cleaner operates at 10 watts / liter or less.

Bill Schreiber Smart Sonic Corporation Tel: 1(818) 610-7900 E-mail:


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Frank R.


Ultrasonic washing for boards | 3 May, 2005

We received about 5K assembly boards from china. They left flux residu on top of the board and the flux they use was different than us. RESULT ... we use a translucent cylicon to cover the board and it was not possible to dry the cylicon because of a chemical reaction between their flux and our cylicon. So, we clean 5K board with an Ultrasonic stencil cleaner with exactly the same standard product inside the tank and the result is perfect.

Do you recommand this ??? If I have this problem in the futur I will do this process again.

How are your results ??? Perfect

What kind of liquid is used to dip them ??? we use SmartSonic 440-R SMT Detergent. This product is a standard product we use to clean stencils.

I hope this help Frank R.

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Ultrasonic washing for boards | 4 May, 2005

Hello Frank,

Just a quick note regarding the use of your Smart Sonic Stencil Cleaning process for cleaning PCBs; if the boards are populated, some components my require an ultrasonic rinse with DI water as ultrasonics will deliver the wash solution under and around components where spray rinses cannot reach. Therefore, to effectively remove all of the wash solution, an ultrasonic rinse with DI water would be a good idea.

Bill Schreiber Smart Sonic Corporation Tel: 1-818-610-7900 E-mail:


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Ultrasonic washing for boards | 10 May, 2005

just want to know the pcb of ultrasonic cealner to make a one

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