Common Solder Mask Issues With PCBs

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When you enlist the help of professional PCB assembly services to create circuit boards for your business, you expect everything to go smoothly. And, if you work with a reputable PCB manufacturer, that will likely be the case. However, inexperienced manufacturers may not have the know-how needed to produce superior results every time. That doesn't just apply to the actual circuitry, either. Sometimes, something as seemingly simple as the board's solder mask may be to blame. Having a state-of-the-art setup may help, as using a system that involves a solder paste applier, high-speed chip shooter, pick-and-place machine, and infrared oven can allow a manufacturer to apply, place, and solder upwards of 50,000 parts in a single hour. But even with all the latest technology, things can still go wrong. Below, we'll list some of the most common issues that occur when applying solder mask to printed circuit boards and why they happen.

Solder Bridging

While forming a bridge might sound like a positive event, that's not the case with PCB assembly. It refers to an unintentional connection that's formed between two solder joints. This connection can actually cause short-circuiting, which presents a major problem for electronic PCB prototypes. This issue could be caused by a miscalculation in design (wherein the weight of the board's largest components is distributed poorly), failure to leave ample space between the solder mask layer and the surface mount pad, or misdirection of orientation components. Any printed circuit board assembly professional should be able to identify this if and when it occurs and assess the possible reasons for this problem.

Solder Balling

The concept of solder balling is fairly straightforward. It occurs when a small piece of solder actually attaches itself to the PCB surface during some part of the soldering process. This occurrence wasn't a big deal in the past, as PCBs used to be cleaned after soldering was performed. However, that part of the process was eliminated once wave soldering (e.g., the more rapid method we mentioned earlier) came about. That's yet another reason why PCB inspection at every stage is so important. Frequently, solder balling is caused by excessive soldering temperatures or the splash-back of solder caused by excessive turbulence or gaseous release. Provided that your PCB manufacturer maintains proper working conditions and inspects boards regularly, this should not become an issue for you.

Excessive Solder

Have you ever heard the phrase, "too much of a good thing?" That definitely applies to solder mask. Although jet paste printers eliminate most errors todays, in the past if a PCB picks up too much solder while it passes through the machine, excess buildup occured. This buildup might not corrupt the electrical connections on the PCB, but the buildup of solder makes it much harder to determine this definitively. Generally, this is caused by excessively speedy conveyor belts, improper design ratios of lead length to pad, or mis-orientation of PCB components.

Solder Skips

Though it may sound like a physical expression of joy, these skips won't be a welcome find on your PCB. They occur when the solder mask literally skips over the surface mount pad, thus leaving an area totally unconnected. There are a few different reasons why solder skips occur, but they typically happen due to gassing issues that lead to improper adherence, the use of uneven pad sizes during the design phase, or the utilization of an improper height between the soldering wave and the board itself. Your PCB manufacturer should be able to determine what led to this issue and take steps to prevent it.

In order to avoid these common solder mask pitfalls, it's important that you choose a respected PCB manufacturer with ample experience and, preferably, jet paste printers. Contact us today to learn more about how our services can help you to create the highest-quality products.

Posted on Aug. 31, 2018 Copyright © 2018 Advanced Assembly