Printed circuit board, especially those used in PDAs (personal digital assistants) such as cell phones, are vulnerable to abuse. In addition to collecting dust that can seep into the case of a phone, PCBS are also prone to soaking in or splashing out of liquids during daily use on e-book readers and similar handheld devices. As a result, a service industry has emerged that provides cleaning and repair services for contaminated PCBS, but without physical damage in PDAs and large equipment.

Cleaning printed circuit boards (PCBS) to repair high-purpose products is as delicate a process as making circuit boards. If the wrong cleaning method is used, it can damage connections, loosen components and damage materials. To avoid these defects, you need to take as much care in choosing the right cleaning method as you do in designing, specifying, and manufacturing boards.

What are these traps? How can they be avoided?

Below, we’ll explore proven PCB cleaning options and some that you may not want to use.

Different types of pollutants

All kinds of pollutants can accumulate on PCBS. Using the right response to an annoying problem will be more effective and will reduce headaches.

Dry contaminants (dust, dirt)

One of the most common conditions is that dust accumulates in or around the PCB. Gently use a small, delicate brush (such as a horsehair paint brush) to remove dust without affecting components. There is a limit to where even the smallest brush can reach, such as under the component.

Compressed air can reach many areas, but can damage important connections, so care should be taken when using it.

A specially designed vacuum cleaner for electronic components is also an option, but it is ubiquitous.

Wet contaminants (dirt, waxy oil, flux, soda)

High-temperature operations can turn certain wax-coated components into magnets for dust and dirt, resulting in sticky grime that can’t be removed with a brush or vacuum cleaner. Otherwise, the product will get sticky soda and mess up the boards. Either way, these substances should be addressed before they accumulate and affect performance.

Most stains can be removed with cleaners, such as isopropyl alcohol (IPA) and q-tips, small brushes or clean cotton cloth. Use solvents such as IPA to clean the PCB only in a well-ventilated environment, preferably in a fume hood.

You can use deionized water instead. Be sure to remove excess moisture and dry the plate properly (a few hours in a low oven will help remove any remaining moisture.)

In addition to IPA, there are many commercially available PCB cleaners, ranging from acetone to chemicals used to clean electronic equipment. Different cleaners can deal with specific types of contaminants, such as flux or wax. Keep in mind that harsh cleaners can remove marks from components or damage plastic or electrolytic capacitor jackets or other exotic components (such as humidity sensors), so make sure that the cleaner you use is not too strong. If you can, you don’t need to test cleaners on older components or connectors to make sure you don’t do too much damage.

Ultrasonic PCB cleaning

The use of high frequency ultrasonic cleaning machine causes cavitation. The violent implosion of billions of tiny bubbles in the cleaning solution contained in the ultrasonic cleaner tank. The bubbles are generated by a transducer attached to the bottom of the tank and are excited by the generator at an ultrasonic frequency. The bursting of these bubbles will be blown away by contaminants from the clean surface of the parts.

Ultrasound can be defined as sound waves whose frequencies are above the upper limit of the normal range of human hearing, i.e., about 20 kHz (20 kHz per second or 20,000 cycles). Indeed, the sound of the ultrasonic cleaner can be heard during operation due to the effect of what we call ultrasonic cavitation.

The technique loses some of its advantages as a cleaning method because it can cause component damage or loose connections as well as dust and dirt. In fact, NASA has issued a directive not to use ultrasonic cleaning because it could unintentionally cause component end caps to separate and actually damage the bonding wires inside the IC and the ultrasonic conduction of the bonding wire pad energy through the IC lead frame.

Having said that, there are still places where ultrasonic cleaning can be used. The ultrasonic cleaning process can reach the most difficult, hard-to-reach locations below the high-density assembly on most parts of the circuit board. This is not the case for SMD equipment with small gaps that are smaller than the surface tension coefficient of the cleaning fluid. However, the process is fast, and there are many high-volume machines that can handle large quantities of cleaning.

PCB ultrasonic cleaning machine

Cavitation is not a gentle process. It has been calculated that temperatures in excess of 10,000°F and pressures in excess of 10,000 PSI will be generated at the bursting site of cavitation bubbles.

Ultrasonic cleaners can produce frequencies ranging from 25 kHz to 100+ kHz, measured in cycles per second. Lower frequencies produce larger cavitation bubbles compared to higher frequencies. Larger bubbles burst more violently, for example to remove total contaminants from manufactured metal parts. Higher frequencies produce smaller bubbles, making bubble cleaning gentler but more able to penetrate cracks, crevices and blind holes. Higher frequencies are used to clean highly polished or fragile surfaces.

conclusion

There are companies specializing in PCB cleaning. Depending on your needs (such as a large number of planks, what needs to be cleaned, and how fragile the planks are), you may look for the right external source to meet your cleaning needs.

If you often have problems with boards that need cleaning, there are probably more important things to check during the design or manufacturing process.

Cleaning PCBS doesn’t have to be a daunting task. Keeping the above tips and suggestions in mind will help ensure that cleaning is done correctly.