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A Printed Circuit Board Cleaning Case Study

by: Dec 12,2013 549 Views 0 Comments Posted in Engineering Technical

Printed Circuit Board PCB Cleaning

label: printed circuit board,PCB Cleaning

A Printed Circuit Board Cleaning Case Study

Several of our blog posts on ultrasonic cleaning focus on printed circuit boards, either repair or manufacturing. As with most of our posts they provide suggested recommendations that users will refine based on their own experimentation. Here we’re pleased to share specific information on cleaning PCBs with ultrasonic cavitation as developed by IDC Technologies. While it relates to cleaning hand-assembled circuit boards using a water-soluble flux its value lies in the fact that the customer developed the optimum PCB cleaning process through experimentation.

Ultrasonic Cleaning Equipment Selection

We suggested three lines of equipment as candidates for the job: the Elmasonic S, E and P series. IDC’s Tom Schurr selected the heater-equipped P180H model with internal tank dimensions 12.9” long, 11.8”wide and 7.9”deep and a liquid capacity to 5 gallons. This is because of the three lines the P series offers adjustable ultrasonic power that can be set from 30% to 100% of the P180H unit’s 330-watt effective power, and the option of using a less aggressive ultrasonic frequency of 80 kHz in addition to the 37 kHz delivered by the E and S models. The P line as with the E and S lines provides the critical “Sweep” function to prevent harmonic vibrations that could damage delicate PCB electronics, and a degas mode to drive off cavitation-inhibiting entrapped air.

Ultrasonic Cleaning Solution Selection

Specifying ultrasonic cleaning solution chemistry is as important as the equipment. Today’s biodegradable cleaning solution concentrates are formulated for a variety of cleaning challenges. In this case the mildly alkaline concentrate elma tech clean A1 proved the best choice for cleaning electronics such as printed circuit boards. It can be reduced to 3 to 10% with water. “For our operations a 5.5% dilution was prepared by combining 13 quarts of water and 0.75 quart of A1 in the cleaning tank,” Mr. Schurr said.

The unit is started and the degas mode activated to thoroughly mix and degas the solution. This step applies to each time fresh cleaning solution is prepared.

IDC’s PCB Cleaning Steps

Boards are carefully positioned in the cleaning basket so they do not contact each other. The ultrasonic cleaner is readied by turning on the generators, activating the sweep mode, setting the thermostat to 30⁰C (86⁰F) and the power to 30%. Set and actual values are displayed on the control panel. When all is ready the basket is immersed in the solution and the timer set for 7 minutes.

“Selecting the correct power level was achieved by experimentation during operational tests,” Mr. Schurr said. “We wanted gentle but through cleaning and this is optimized by keeping the level below 10 watts per quart. And, since ultrasonic cavitation produces heat 30⁰C was specified so the boards do not get too warm and subject to thermal shock during the rinsing operation.”

Mr. Schurr commented that the 7-minute cleaning cycle may vary depending on the number of boards cleaned and their condition. “At the end of the cycle the basket is removed and the boards are rinsed using deionized water then air-dried under a fan,” he said, and cautioned that while the process in general is excellent for PCB cleaning it cannot be used when they contain sealed board-mounted relays.

Contact the ultrasonic cleaning professionals at Tovatech for recommendations on equipment, cleaning solutions and procedures that meet your requirements.


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