Quest for Reliability: What’s Lurking in the Shadows?

There are two terms in the electronics industry that I feel need to be in wide use. The first is an acronym for “violates minimum electrical clearance,” which is obviously, and simply, VMEC. It has always confused me why this isn’t already in heavy use. We use TLAs for everything (TLA is an acronym for three-letter acronyms, by the way).

The second term I use on a regular basis, and the focus of this month’s column, is “contamination relocation.” I use this term mostly when I test a PCBA that has gone through some sort of localized cleaning process after a manual or selective soldering operation. In most of the cases I have seen, when a no-clean flux is used, localized cleaning is a totally useless practice intended to only improve a cosmetic issue. Cosmetic issues are usually just that and don’t have any impact at all on functionality or reliability. I’d rather have an ugly, reliable board than a sparkling clean field failure.

In some cases, there are legitimate reasons to perform localized cleaning. The number one reason is if you are using a water-soluble flux for the soldering process. As with any water-soluble flux, the activators are never rendered near benign through a thermal excursion and will always be hygroscopic, as well as corrosive. That means you don’t only have to worry about electrical leakage failures. The residues can cause corrosion without any bias differential or available atmospheric moisture. That’s one reason I really like working on PCBA failures if they were built with a water-soluble flux. If you see flux residues, that’s more than likely your root cause of failure. It’s a short day, and I can go fishing in no time.

Another valid reason to perform localized cleaning is if you are planning to use conformal coating on the PCBA. Flux residues can cause adhesion issues in some cases, and if you use parylene, a full cleaning is required. You may also need to clean the residues to access test points if you’re not using a probable flux. Sensitive RF circuits can also be affected by flux residues and need to be removed to ensure proper operation. I think that pretty much exhausts the good reasons to perform localized cleaning. It’s not a long list. Please note that cosmetic appearance did not make the list.

What is lurking in the shadow? It is most likely active flux residues spread around by the localized cleaning process. And much like a teenager standing on your porch, trying to score some candy from you by stuffing a few pens in their shirt pocket and saying they’re a nerd, you just don’t want that. And ouch, by the way, that’s just rude. This month, I want to highlight localized cleaning that is performed correctly and incorrectly and the impact on cleanliness and reliability.

I often go into a production facility for a process review and see operators using an acid brush of questionable cleanliness dipped in IPA scrubbing away after a manual soldering process and then inspecting the area of concern for residues. If none are found, they simply pass the boards down the line for subsequent processing. What I never see is that the same operator looking in the adjacent areas for residues. Those areas are the shadows I mentioned. In almost every case, you can’t inspect monolayers for residue under components with low standoff height for some time.

That same low standoff height makes them very difficult to clean under the best of circumstances. When you add IPA or other solvents to the flux residue, all that does is make it soluble. What it does not do is magically make detrimental flux residues disappear like many seem to think it does. Don’t believe me? Let’s look at some ion chromatography (IC) data from a field failure.

camden_1020_1.jpgTouch-up soldering was done to an SMT component, and according to the work instruction, this process includes a quick cleaning with IPA. The boards are already built with no-clean flux, but any touch-up requires cleaning. Figure 1 shows the SMT part that was cleaned, as well as the capacitor and PTH pins that were tested.

The IC data in Table 1 shows low levels of ionics at the SMT location, but much higher levels are now present in the other two areas. Performing localized cleanliness testing was key to shining light on those “shadows.” The chemical signature shows that the flux uses a weak organic acid, and at these levels in the PTH/capacitor, areas are at an increased risk of electrical leakage or even dendrite growth. This same board was put through an inline wash process, and the second set of IC data shows acceptable levels of ionics across the board.

camden_1020_2.jpg

A large batch of boards processed like this had to be recovery cleaned before shipping to the customer because of that increased reliability risk. It’s what we had to do to get that darn teenager off the porch. This method of localized cleaning is like running your vacuum without a bag, or you could also say contamination relocation. Please say it as a matter of fact. It’s my "Git-r-done" if you will. The similarities stop there.

camden_1020_4.jpgcamden_1020_4.jpgThe good news is there is a simple way to enhance this same basic cleaning method while reducing the spread of IPA and solubilized residues onto neighboring components. Instead of dipping the end of the acid brush into a bottle, soak a lab wipe with IPA and then place that wipe over the area that needs to be cleaned. Then, you use the brush on top of that wipe to clean as normal (Figure 2). The wipe will absorb the flux/solvent mixture (Figure 3), not allowing the solution to transfer to neighboring components and become a potential risk for electrical leakage in the field.

The wipe is then simply discarded. It’s important that a new wipe is used for each individual cleaning process. A wipe or brush will collect residue over time, so using a new wipe eliminates cross-contamination. As with any assembly process, you need to create objective evidence that the process is effective using some sort of cleanliness or environmental exposure testing.

Conclusion

It might be close to Halloween, but there isn’t any reason to be afraid of what your cleaning process is doing to reliability if you shine enough light on the process. And should teenagers try and haunt your porch this year, give them full-size candy bars instead of a hassle. Everyone likes candy.

This column originally appeared in the October 2020 issue of SMT007 Magazine.

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2020

Quest for Reliability: What’s Lurking in the Shadows?

10-05-2020

This month, Eric Camden focuses on contamination relocation—a term he mostly uses when testing a PCBA that has gone through some sort of localized cleaning process after a manual or selective soldering operation. He also highlights localized cleaning that is performed correctly and incorrectly and the impact on cleanliness and reliability.

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Quest for Reliability: Reliability Starts at the Bottom

09-02-2020

It is much cheaper to perform product-specific reliability testing before the product goes into the field. Eric Camden shares some testing recommendations based on failure analysis, as well as lessons learned from a few of our customers over the years using case studies and data on failed units.

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Quest for Reliability: Correlating COVID-19 With Reliability?

06-01-2020

I submit this month’s column from my secure bunker while safely—and smartly, if I may say so myself—practicing social distancing. The word quarantine is more “popular” than ever in that I hear it upward of 4,562 times per day. Before COVID-19, the first thing that popped into my mind when I heard the word “quarantine” was the cages in the receiving area for non-conforming products or similar spaces for built hardware that doesn’t pass some sort of inline test.

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Quest for Reliability: New Solder, Same Old Testing

05-20-2020

Solder is inarguably one of the required building blocks for electronic assemblies and, apart from a few exotics, every assembly in the world has it. When it comes to meeting the lead-free requirement, opinions and historical reliability data are not taken into consideration. Eric Camden explores testing and reliability related to solder.

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Quest for Reliability: Improving Reliability for Free

04-14-2020

Eric Camden has seen more than a few factories make the move to use more and more automation that has indeed improved production numbers but has done very little to address cleanliness and reliability. In this column, he offers up a few easy steps you can take to reduce risks.

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Quest for Reliability: Big Trouble Comes in Tiny Packages

02-03-2020

When it comes to making consumers happy and electronic assemblers miserable, nothing achieves both quite like miniaturization. With our ever-increasing demands to house a full-size movie theater with surround sound and limitless digital storage in the palm of our hands, the only way for CMs to respond is with miniaturization (and cursing—lots of cursing). In this installment, I’ll revisit the history of shrinking packaging and lessons learned.

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Quest for Reliability: Sunshine and Circuit Boards

01-02-2020

IPC APEX EXPO may be over, but this column by Eric Camden serves as a great introduction to IPC standards. If you've been thinking about getting involved with manufacturing and assembly standards but weren't sure how to go about it, this column is a must-read for you.

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2019

Quest for Reliability: Voices Carry

12-06-2019

The title of Eric Camden’s column this month is “Voices Carry,” so not only is it a great chance to revisit the wonderfully written, top-10 hit song by ‘Til Tuesday/Aimee Mann, but it is also a good opportunity to share the voices of modern electronics and electronic assembly processes.

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Quest for Reliability: Old Dogs, New Tricks

12-02-2019

I hear two phrases way too often on a production floor: “We have always done it this way,” and its first cousin, “We have been building this board for 20 years and never had a problem.” Inevitably, these phrases are always uttered by a “seasoned” engineer in the industry that probably should know better. Don’t get me wrong, these phrases are going a long way in my effort to send two kids to college, but they aren’t very helpful regarding reliability. Times change, and technology changes even faster, and if you don’t keep up, you will be left behind. This means focusing on emerging technologies and the associated risk that may be unique to that package.

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Quest for Reliability: Artificial Reliability Over Intelligence

11-26-2019

As the industry begins to shift from standard design tools to artificial intelligence (AI), reliability might be overlooked in an effort to build “smarter.” Over the last few years, the desire to manufacture anything and everything for less has included removing humans from as many positions as possible. There are a couple of viewpoints, and I can see positives in both.

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Quest for Reliability: Reliability by the Book

11-04-2019

Having been in electronics for just shy of 20 years, I can say that the next time we work on a Class I failure analysis project, it will pretty much be the first. Class I electronics serve a different purpose in life, and if they fail, it’s normally not a big deal; instead, it’s mainly a minor inconvenience. In this month’s column, I’ll speak to specifications for Class I, II, and III products per IPC definitions as well as the IPC standards process.

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Quest for Reliability: SMTAI 2019 Thoughts

10-16-2019

Before I headed to Rosemont, I was a little skeptical if it would be worth it for me, considering the lack of task groups that had become my SMTAI/IPC APEX EXPO focus. But after three days of sessions (and a somewhat impressive third-place showing at the SMTA trivia night), I was reminded of why I went to SMTAI in the first place: to learn about the newest technology and how to address age-old problems that are ever-evolving in this era of miniaturization.

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Sealing Your Fate

08-16-2019

Coating does not always prevent failures; it is just as important to look at your cleanliness levels just as you would with an assembly that is not bound for coating. If you have a dirty assembly, you might be buying a little time, but ultimately, you've sealed your own fate.

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Quest for Reliability: The F Word

07-19-2019

The word "failure" is as nasty as it gets in our world. It goes against everything we thought we knew. All contract manufacturing facilities strive to build a reliable product, or at least they all should. The problem is too many companies hope they are building reliable products without doing the work required to ensure they are.

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Quest for Reliability: These Darn Kids/Back in My Day

04-24-2019

This month’s topic is focused on youth, both in terms of humans and technologies. I think these two topics go together since they rely on each other to a large degree. The latter has more than likely shaped or even invented by the former.

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How Smart Is Your Factory?

04-03-2019

When you plan a production facility with the mindset that connectivity and optimization will be key aspects of your operation, it will pay dividends in the form of lower production cost, better traceability, and higher reliability.

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The Cost of Quality and the Higher Cost of Failure

03-13-2019

If you are shopping a new product around to multiple contract manufacturers (CMs), and if all other things in two separate CMs are equal including price and delivery times but one offers a more comprehensive ongoing quality monitoring system, why wouldn't you go with that one? You usually pay some type of premium for the CM that has an overall quality monitoring system that goes beyond just ICT or bench level testing. Definitely, most CMs will give you some sort of assurance that the product is working as it leaves the facility, but if one has a mindset that more than basic testing is required to show reliability, you will more than likely have fewer field failures.

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2018

Does Medical Device Reliability Worry You Sick?

12-06-2018

When you are manufacturing high-reliability assemblies related to medical industry, it is critical to take a very close look at the assembly process and all other processes that can influence the end-use reliability—even seemingly unrelated processes, such as post-installation cleaning—as it really could be a matter of life or death.

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Are You Connected to Reliability?

10-30-2018

The need for communication between every operator on the manufacturing floor can be a critical difference between a reliable piece of hardware and one that presents some level of unexpected performance. This column highlights a few things happening in the shop floor, such as as touch-up soldering and third shift issue, not commonly communicated, which can cause performance issues.

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Are Megatrends Putting Your Product at Megarisk?

10-03-2018

It took 38 years for radio to get 50 million users, television made it in 13 years, Internet in four, iPod in three, and Facebook in only two years. What these numbers mean to our industry is the need to create electronics at blazing speeds that we haven’t seen before. But how will it affect reliability? Read on.

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Cleaning a No-clean Flux: The Worst Decision You’ve Ever Made?

09-04-2018

There are a few reasons to choose to clean a no-clean flux, such as when the PCB assembly requires conformal coating, or when probes are required for testing. Other than that, there seems to be no need to clean a no-clean flux. This column tells you more.

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Contamination: The Enemy of Electronics

07-18-2018

Welcome to the first installation of “Quest for Reliability.” The goal behind this column is to use my experience at an independent laboratory for over 18 years to help readers understand PCBA reliability issues, and more importantly, prevent suspect conditions in the first place. The laboratory I work in has served every sector of the electronics industry, from oil and gas equipment designed to function miles below the surface of the earth, to aerospace companies and everywhere in between.

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