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Perfect PCB Cleaning: Remove Flux & Ionic Residue with Ultrasonic Cleaners
If you manufacture printed circuit boards or service/repair electronics such as PDAs, mother boards and other delicate electronic components, your best friend can be an ultrasonic cleaner.
Why is this? An ultrasonic cleaner is the perfect way to safely remove RMA-type flux and ionic contaminants for both Through-Hole & SMD PCBs.
Top 7 reasons precision electronics industry has widely accepted eco-friendly, controlled, precision, sub-micron level ultrasonic cleaning for these important reasons:
- Removes flux, solder paste, and other residues
- Zero damage to delicate electronics
- Lowers QC rejects, increases product reliability
- Uses eco-friendly chemicals
- Penetrates into tight spaces with complex geometries
- Superior to spray washing
- Maintenance cleaning of dispensing nozzles and print heads
Advances in Cleaning PCBs and Other Precision Electronics
First a Bit of History
With trichloroethylene no longer available for cleaning PCBs, earlier posted information related to cleaning, soaking and scrubbing using high purity alcohol, flux removal sprays and special biodegradable solvents.
The problem was that these manual processes were time consuming, risked damaging delicate components, were often environmentally unfriendly. Most important there was no guarantee contaminants were completely removed from complex PCB configurations.
Also in the past some PCB manufacturers resisted migrating to ultrasonic cleaning. Two reasons were concerns related to possible water damage and that single-frequency ultrasonic energy commonly used at the time created harmonic vibrations that could damage the components.
These concerns no longer apply. Water can be used when the appropriate ultrasonic cleaning solution is employed and the PCBs are thoroughly dried after the cleaning step.
As to component damage, ultrasonic cleaning equipment such as the Elma S series offered by Tovatch employs a feature called a Sweep Mode that continually shifts the ultrasonic sound field from a single harmonic wave that could cause damage. As an added benefit, the Sweep Mode optimizes the cleaning process, saving more time.
A Real-Life PCB Cleaning Application
Here's an example of 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
IDC selected the heater-equipped Elmasonic P180H model . The dual-frequency Elma P series offers adjustable ultrasonic power that can be set from 30% to 100% and the option of using either a 37 kHz or 80 kHz frequencies. It also 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 at IDC
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. At IDC a 5.5% dilution was prepared by combining 13 quarts of water and 0.75 quart of A1 in the cleaning tank.
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.
An advantage of the Elmasonic P units is that selecting the correct power level can be achieved by experimentation during operational tests. The company looked for 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.
The typical 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. A caution is that while the process in general is excellent for PCB cleaning it cannot be used when they contain sealed board-mounted relays.
Other Examples of Ultrasonic Cleaning PCBs
Dust, dirt and corrosion can impact the performance of PCBs used in electronic equipment exemplified by sophisticated hand-held devices such as iPhones and multifunctional iPods. An ultrasonic cleaner is a great tool to clean and restore this equipment
Another more general look at this topic is in our post on overall procedures for removing PCB soldering flux.
Ensure Clean Stencils and Reclaim Misprinted Circuit Boards
Process engineers estimate that a high percentage of surface mount technology defects are due to insufficient solder caused by clogged stencil apertures. Our ultrasonic cleansers ensure the efficient and complete removal of residual solder paste from your stencils. A clean stencil can be critical in preventing misprints on the circuit board.
Misprinted circuit boards are a common occurrence among assemblers. This becomes a significant part of production costs especially when dealing with misprints on side ‘B’ with ‘A’ already populated.
Rather than simply treating them as QC rejects, our ultrasonic cleaners enable you to reclaim these boards. Sweep mode ensures that none of your delicate electronics on side ‘A’ are damaged through the cleaning process and you are able to reclaim the misprinted sides.
Tovatech’s Ultrasonic Cleaners Suited for Lean Manufacturing
Designed to support lean manufacturing processes, our ultrasonic cleaning units are portable and can be quickly moved around your production lines as needed. German engineering brings high performance and industrial durability to your production floor giving you many hours of continuous operation.
Summing it Up:
Choosing the right combination for your specific situation can be challenging if this is your first time. Just call us. We’ll quickly help you identify the exact product and cleaning chemistry combo that you need.
Your PCB and Electronic devices need a specific combination of a Tovatech Ultrasonic Cleaner and a suitable chemical cleaning solution. For effective cleaning the ultrasonic cleaner must use the right cleaning chemistry, operate at the right temperature, and use the correct frequency and power level. The material being cleaned, its tolerance for ultrasonic vibrations, and the type of soil, determines this. Just call us and we’ll guide you to the right solution quickly.