Guidence for a clean PCB assembly board

Guidence for a clean PCB assembly board

Having a clean PCB assembly gives your circuit board design the best chance at success while ensuring longevity for your product. Contaminants found on PCBs can sometimes just be cosmetic but they can also cause functional issues or corrosion leading to product failure. If there are containments on your completed PCBAs, actions must be taken to eliminate them because this is a sign that there is something wrong with your CM or your own cleaning system process. This article will run through different kinds of discrepancies in the realm of circuit board assemblies.

1.Clean PCB – Flux Residues

The most commonly discussed and seen kind of contaminant on PCBs is flux. Flux is used in all kinds of assembly processes and is mainly used to prepare metal surfaces for soldering by cleaning and removing any oxides and impurities. There is however a “no-clean” process that leaves an acceptable kind of residue. To remove “no-clean” flux is also very difficult so if you plan on getting visually clean circuit boards, specify to your CM to use a “clean” process. With normal solder and “clean” process however, it is best to remove all flux from a circuit board. This can be done manually or with equipment such as an inline wash or ultrasonic cleaner.

2.Chlorides, Carbonates, and White Residues

Chlorides, Carbonates, and White Residues remaining after a PCB cleaning process can be caused by a variety of different chemicals reactions. Rosin and water-soluble fluxes, circuit board resins and epoxies, component materials and other contaminates all contribute to the complex chemistry of your circuit board. This kind of contamination can be eliminated or mitigated in several different ways. First of all it is important to clean the boards promptly after the soldering process. The longer contaminants have to sit on the board the harder it will be to clean off. More time also gives chemicals a higher chance of reacting and creating these kinds of contaminants. Avoiding excessive flux will also aid in less contaminants. Switching to a “clean” process solder will also help. No clean fluxes are usually the culprits of these kinds of contaminants and are very difficult to remove. Switching to a clean process with an inline wash or ionic cleaner will fix this issue. If these don’t work, it may be a materials issue.

3.Foreign Object Debris (FOD)

Foreign Object Debris can cause failures in PCBs. They could provide an electrical path and short circuit your board or they could become dislodged and create a problem in your final product. In either case, its important to make sure your assembly and storage processes are optimized to eliminate any potential risk of FOD.

4.Flux Residues – No Clean Process

No clean flux is widely used in the industry. Using a no clean process can be due to cost savings or because a part cannot be washed. Using this kind of flux however generally leaves some residue on the board. It should be flagged if it inhibits visual inspection, inhibits test points, or is in too much excess. Other than that, it should be fine in most cases.

Conclusion for Clean PCB Importance

Having a clean PCB is important for the functionality and longevity of your circuit board. Receiving dirty PCBs is a process indicator for you or your CM.