Not Just an Engineer

Board contamination can happen at any time and, as a result, reliability may suffer. Your product, regardless of where it was assembled or how well it was designed, will move down the line to its next or final destination. Which means that at any point in the process, something outside of your control can cause circuit board failure. As we all know, failure is not a desired outcome. But so many factors impact the performance of a board that the root cause can be quite elusive.

That’s why, when it comes to circuit board failure, you need an investigator, not just an engineer. You need someone who knows what to look for, and is familiar with what the medical community calls comorbidities—the presence of two or more conditions.

There are many places along the way that contamination can occur. Our team of investigators looks at each and every one of these stops.

• Design

• Fabrication

• Assembly

• Manufacturing Environment

• Storage

• Shipping

The underlying problem is usually hidden along one or more of these. That’s why it is crucial to look for clues and analyze the complete journey of a circuit board. By finding out how and when this failure began, you can avoid the issue in the future or hold the right people accountable in the present.

At Foresite, we investigate by using a tool called the C3/C.I. as well as ion chromatography. This way, we’re able to observe the chemical signature by isolating board areas and quantifying what those residues are. Our team knows residues and which ones can be problematic. In essence, we know what to look for.

Assembly residues are mostly organic acids. In some environments we find a huge range of contaminants. You’ll see high levels of phosphate, sulfate, or in some cases, you’ll see the chlorate instead of chloride, or nitrates and nitrites. These aren’t part of the normal chemical signatures.

So, we start observing and working our way backwards to see exactly where the electronic failure occurred. This isn’t a task for a pure engineering mindset. It is really a task that requires an investigative approach. Often, we have clients who believe they know why a failure occurred. Usually, they blame the later and more obvious steps of the process: storage and shipping. But upon working backwards, we discover the exact moment failure occurred was not at all what they surmised.

Sometimes, it’s in the very first stages.

Here are three examples from clients and how our team discovered the who, what, where, and how of their circuit board failure.

1. One client believed they were making all the right choices to protect their boards and prevent contamination. But after encountering failure after failure, they called us in to figure out the underlying cause. It became clear fast that fabrication and assembly were contributing to the problem.

   1. First, they had snap-fit enclosures that did not incorporate a seal. Moisture could easily work its way in, causing corrosion and carrying contamination.

   2. Second, they conformally coated their boards. Unfortunately, conformal coating is not truly hermetic, and if other aspects of the fabrication or assembly are wrong, moisture will get through conformal coating. This happens especially if there’s a strong acid in the moisture—it will eat through the coating.

   3. Lastly, the tops of the leads and the top edge of the parts were exposed (poor step coverage). So exposed metalization on components allows moisture to bridge and run right across because it is open and vulnerable.

      The poor coating and lack of true seal proved to be the root of their issues. The client reevaluated and pushed to double coat their circuit boards in the future.

2. A second client discovered a series of failures and asked for our help. This investigative process was complicated because the company outsourced everything. And when it comes to working with multiple companies, no one wants to take the blame for a failure. Especially when, on first glance, everything looks perfect. Here’s what was actually going wrong:

   1. Parasitic leakage due to the process residues—this turned out to be a great prognosis because the assemblies could be cleaned and restored to reliable functionality.

   2. The why is more complicated. We commonly encounter clients who believe a temperature cycle from -40 to 125 degrees Celsius is the ideal way to challenge a board—but that’s actually how you challenge a solder joint. The high temperatures dry out moisture which can mask parasitic leakage issues, or cause intermittent results. We directed them to test their boards in lower temperatures instead (40 degrees Celcius with 90% relative humidity). This allowed us to uncover moisture-related issues.

3. Another client had three different recalls on faulty products before they contacted our team. This client’s circuit board supplier was confident the technology was appropriate for the challenge—a transmission control module. However, we traced the problem to thermal vent implementation within the PCB. Thermal dissipation was poor, resulting in thermal overstress which corroded and compromised the solder joints of power devices. This design problem from the initial steps led to those three recalls and millions in restitution to our client.

These examples show why we call our team investigators and not engineers. They look past the obvious and most recent observations and go deeper into every step of the process.

Don’t wrestle with contamination issues that lead to product failure in the field. Get to the heart of the matter fast and keep in mind these variables are changing as often as designs innovate. The quest for reliability is a moving target. And those moving targets are our specialty.