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Test and Inspection

David Bernard

Down the radiation rabbit hole!

Increased use of x-ray inspection throughout the component and PCBA supply chain to check the quality of optically hidden joints and features can elevate a component’s level of radiation dose during assembly. A simple and sensible question, therefore, is can this cause any issues? For example, could this increase the risk of component failure, either a complete, temporary or intermittent failure, that happens during manufacture or potentially at some later time in the field? A sensible and simple question perhaps, but, unfortunately in my experience, one that generates many further questions and uncertain answers.

In general, the industry consensus, together with the reality that x-ray inspection has been widely used for years, is that for most components there is probably not an issue with the radiation doses likely during x-ray inspection. But here we enter our rabbit hole of additional questions: What constitutes the “not most” components?

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David Bernard

What are the questions we should ask before diving in?

To deliberately misquote and mangle Shakespeare once again, I come to praise AI, not to bury it, but does the potential evil it may do live after and the good oft interred in the dataset?

I apologize, but … discussion of the benefits of AI in all manner of applications has been the flavor of the month for much of the last two years, and there seems no end in sight! It has been one of the drivers of processor manufacture and use in recent times. However, two recent articles from BBC News seemed to highlight some pros and cons regarding use of AI for x-ray inspection and test.

The first1 describes how AI has been trained to best radiologists examining for potential issues in mammograms, based on a dataset of 29,000 images. The second2 is more nuanced and suggests that after our recent “AI Summer” of heralded successes on what could be considered low-hanging fruit, we might now be entering an AI Autumn or even an AI Winter. In the future, it suggests, successes with more complex problems may be increasingly difficult to achieve, and attempts are made only due to the hype of the technology rather than the realities of the results.

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Rob Boguski

Finding our next customer, one trinket at a time.

Green is sexy. One ignores the wave – in politics, marketing, journalism, social media, commerce – at one’s peril. In 2019, The Economist published an entire edition raising the alarm about climate change and its implications. Three years ago, Pope Francis wrote an encyclical letter (Laudato Si) about the environment, emphasizing care for our neglected “common home.” Self-righteous millennials and impressionable younger people march, advocating immediate, drastic control of greenhouse gases and other toxic emissions. A Swedish teenager cuts school and uses her sudden free time to excoriate industrialized nations and big corporations at the UN General Assembly for favoring economic growth over ecological sustainability and contaminating the world, shaming magistrates and captains of industry alike for their perceived callous indifference to the effects of rising temperatures. It is a good time to be a scold.

To be green is to hate waste. Waste is anathema. Angels recycle. Daily. So say those who are woke.

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David Bernard

It’s cheaper and faster to inspect by machine over microsection.

Most of my columns have attempted to discuss the “typical,” and often more obvious, solder joint failures that can be seen using x-ray inspection. This is usually the main and most important function of this type of analysis.

Nondestructive inspection of cracks within solder joints or components is also desirous, however, but this is much more difficult to evaluate optically or by x-ray. Even for those joints that are not optically hidden, optical inspection for cracks is likely limited to the very end of the termination and requires a mostly edge-on view at a reasonable magnification (FIGURE 1) to have the best chance of seeing a crack failure. When inspecting fully populated boards, achieving this level of magnification and orientation may be difficult to do optically, and any cracks present will need to be distinct by showing a separation in the joint. If the two halves of the cracked solder are still touching, then analysis may be almost impossible to make. Furthermore, such a crack will be at the end of the termination and not necessarily extending further back into the joint – for example, into the heel fillet of a QFP, which is more crucial to joint integrity. This may mean a cosmetic issue is seen on one joint, and the actual fault may remain hidden elsewhere.

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Robert Boguski

Needed: Solder joint forensic scientist. Common sense preferred.

Wanted: X-ray engineer. A test engineer with an interest in x-ray technology will suffice. So will a skilled and teachable technician. Hell, an intelligent person with a pulse will do in this economy. We’re open-minded. Just show us. No shrinking violets here. Honesty still matters to us (like being honest about the state of the economy and its effects on available talent). You should be honest, too, if you’d like us to hire you. Bring the aptitude; we’ll give you the qualifications.

We will train you.

 

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David Bernard

IPC-STD-001 is revising criteria for voiding and fill percentage.

In my September column, I spoke with Dave Hillman about IPC committee work on voiding guidelines for QFN central pad terminations. But he also told me the J-STD-001 task group increasingly receives requests from users for additional information and clarification of x-ray usage in other areas. This is because use of x-ray technology for analyzing solder joints has resulted in significant soldering process improvements. As with all technology introductions, however, the benefits and questions that result from the new information provided must be characterized, assessed and disseminated into practical form. One such area where x-ray technology has provided a tremendous amount of new information is plated through-hole (PTH) solder joints. The “insides” of these joints were previously “hidden” from scrutiny, unless subject to destructive methods, and the standards writers will need time to carefully revise old criteria to accommodate this new information. With this in mind, IPC formed a task group (called Team Skeleton) to discuss this and other matters, with the goal to develop additional x-ray-related guidelines and requirements for inclusion in future IPC documentation. As usual, Dave says, “All are welcome to participate and provide their comments and suggestions.”

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