We remember the wonderful meals that we cook and serve, but do we remember what happened next? Cleanup. We remember the creative works of art that our children bring home to us from school, but do you know what the teacher did after those projects were finished? Cleaned up. Cleaning up after a job is such an integral part of our lives that it is easy to dismiss its importance. But without taking the time to do it, we would quickly be in a lot of trouble. This is also true in the manufacturing of circuit boards.
You may not even have realized it, but cleaning a circuit board while it is in production is critically important. A PCBA can collect different contaminants during the manufacturing process that, if not properly taken care of, could impact its ability to function correctly. There are various industry standards PCB manufacturers may follow to ensure proper cleanliness of your board, including IPC Test Methods (TM) 650 and IPC-A-610. The important thing is that your contract manufacturer should have processes in place for inspection and cleanup of assembled boards. Let’s take a moment to talk about why that is important, and why you should expect full attention to printed circuit board assembly cleanliness specifications from your CM.
What Can Happen if Printed Circuit Board Assembly Cleanliness Specifications Aren’t Met?
A circuit board goes through many different processes while it is being manufactured, from the etching of the metals during fabrication to the application of solder during the assembly. All of these processes have the potential of leaving various residues and contaminants on the finished board. These residues can cause short-term and long-term problems with the board.
In the short term, any visible residues and contaminants on the board will be very obvious and could cause concern, even in cases in which it may not actually be a problem. No-clean flux residue is an example of this. Although there aren’t any problems with it, it will leave the board looking as if it hasn’t been properly cleaned. For cleanable fluxes that aren’t properly removed during the cleaning process, their residue could cause problems in testing. They may also cause intermittent functional problems in the board that are difficult to find or reproduce.
The long-term problems of inadequate cleaning, however, pose a much larger threat. By not thoroughly cleaning the finished PCBA, residues and contaminants can compromise the reliability of the finished board.
An example of this is ionic contamination. When ionic residues remain on a finished PCB, they contain molecules that could become conductive when exposed to moisture. This can result in accelerated corrosion or dendritic growth of conductive metal slivers that cause unintended shorts between nets.
Some of the ionic residues that can collect on a PCB during manufacturing include:
- Salts
- Flux activators
- Plating chemistries
- Acids
- Perspiration
Additional long-term problems from inadequate cleaning include poor adhesion of conformal coatings, functional problems with board mounted relays and switches, and poor contact with interconnects such as cables, edge connector fingers, and sockets. You can see why PCB cleaning is such a vital part of the entire manufacturing process.
PCB Cleaning and Testing Methods
To clean circuit boards, PCB manufacturers will use an in-line wash with heated DI (deionized) water. The water pressure will be set according to the guidelines set by the solder and equipment manufacturers. There may also be additional cleaning processes, including IPA (isopropanol alcohol) wipedowns, removal of no-clean flux residues, and ultrasonic cleaning. These specialized cleanings are typically done only when there are documented requests for them.
To ensure that they are performing adequate cleaning of PCBAs, CMs should regularly test their cleaning processes. This is usually done with the industry standard ROSE (Resistivity of Solvent Extract) test. The CM will submit a sample for regular testing, usually to an outside service provider. The CM will also visually inspect the finished PCBA to make sure that it passes their internal standard of cleanliness.
What You Should Expect of Your CM for PCB Cleanliness
To make sure that your circuit board is fully cleaned by your CM, you should get answers to the following:
- Does the CM have a facility and company culture that promotes attention to detail and cleanliness in their operation?
- Are they fully versed in PCB manufacturing cleanliness standards?
- Do they have the equipment and processes in place to adequately clean your circuit board?
- Are they able to respond to any specialized cleaning requests that you might have?
At the end of the day, your CM should put quality first, and that includes ensuring circuit boards are properly cleaned. The CM should be fully versed in cleanliness standards and have cleaning processes and equipment that are fully documented and top of the line. Asking these questions can ensure you’re working with a partner that is committed to the highest level of quality.
