In the past, there have been concerns about the possibility of ultrasonic energy damaging specific types of components such as wire-bonded IC’s and crystals.

Modern ultrasonic stencil cleaners utilize a lower power model (watt density) than older ultrasonic cleaning systems. Additionally, the sweep frequencies of modern stencil cleaning systems prevent damage to sensitive components.

One should be careful when considering spray-in-air technology for misprinted cleaning applications. Too much power and you increase the chance of directing solder paste (more specifically solder balls) into a via and under components. Too little energy, and you leave paste on the assembly.

Dr William Kenyon wrote an excellent article on this subject. It was published in SMT Magazine in October, 2004.

We use saponifier and steam to effectively clean no clean.

We use a semi-aqueous cleanser that works very well at removing "no-clean" residues when we are required to do so.

Best alternative is to use water soluable flux/paste.

Do not use Ultrasonic's. There are several methods of cleaning board assemblies on the market look at the Zestron, Austin Americas and Aqueous web sites.

You say very little about the type of component. Doe it contain wirebonds, what type of damage are you seeing? You also say that you are removing No Clean solder paste. I suspect you meant to say no clean solder flux, after reflow?

It would help if you could be more specific.

Generally a spray-in-air (like diswasher type batch cleaning process where top and bottom spray bars rotate as they spray the cleaning solution on the substrates) or alternatively a spray-under-immersion type process (where the spray bars with nozzles are completely submersed in the solution, recirculation and spraying action takes place in the cleaning solution) should be to work gently on these sensitive parts.

If there is already an ultrasonic tank, one can easily retrofit this tank with small recirculation pump anda single spray manifold with nozzles on it.

These days, the cleaning of no cleans is only surprising to the marketing people at solder companies. It is a daily occurrence to clean so called “no clean” materials and to do so in standard equipment with exceptional results.

The most common process today is an aqueous spray system using a modern cleaning agent that should be non-hazardous and designed to clean “no cleans” be they lead bearing or lead free. This can be a batch system (as your ultrasonic is) or if your throughputs are high, may be an in line system.

Another approach is to use a semi-aqueous technology. While not as popular as aqueous, this is a terrific technology option and may work in your current equipment with some minor modifications (we have experience in this area).

Again, there are many legacy technologies offered alongside newer materials that have been developed for lead free and lead bearing no clean materials. Both may be good options for you.

Using ultrasonics on assembled boards is a bit unusual in the US, though not uncommon in other parts of the world. With the process adjustment you are considering, you are moving toward the main stream.

Without knowing what you qualify as “damage” and also not knowing the type of ultrasonic cleaner and chemistry you are using, if is difficult to address the question. However, we maintain a selection of published articles on the subject on our web site: www.SmartSonic.com/article.html

Research by B.P. Richards et al at GEC Marconi and the EMPF Laboratory suggests four parameters for the safe cleaning of PCBs using ultrasonic technology:

1. The ultrasonic frequency should be 40 kHz or higher. The lower the frequency the more aggressive the ultrasonic cavitation becomes.
2. “Sweep” or “Alternating” frequency technology be used to prevent “hot spots” in the cleaning bath.
3. The “Power Density” should be 10 watts per liter or less (referred to as Low Power Density). The higher the power density the stronger the “scrubbing” action (the electrical output of the ultrasonic generator(s) divided by the total liters of cleaning solution in the bath).
4. The ultrasonic wash cycle should be 10 minutes or less.

Today, most all ultrasonic cleaning systems incorporate the first two parameters and the wash cycle time is easy to control. The “power density” is the variable that may be the cause.

Most ultrasonic cleaning systems are made to be used with generic cleaning chemistries and therefore need to incorporate the highest power density that is economically feasible.

Comparing the ultrasonic frequency and power density to a manual “scrub brush” application, the frequency is similar to the type ob brush used. 20 kHz would be equal to a wire brush and 60 kHz would be equal to a toothbrush. 40 kHz is somewhere in between.

The power density is equal to the amount of exertion placed of the brush. High power density (> 10 watts per liter) is like scrubbing hard using two hands. Low power density (< 10 watts per liter) is like scrubbing lightly using only one hand.

Therefore, a combination of low frequency and high power density provides the most aggressive ultrasonic cleaning action and high frequency and low power density provides a more gentle cleaning action.

Most ultrasonic cleaning systems incorporate a high power density because they are designed to be used with non specific cleaning chemistries. Some chemistries are less efficient than others and require a heavy duty scrubbing action.