Features Articles

Martin WickhamCorrective measures include adjusting the solder paste chemistry and reflow profile.

Voids in solder joints are not uncommon after reflow soldering and can be easily detected using x-ray. Champagne voiding is related to hundreds of very small voids seen at the solder joint-to-surface pad interface (FIGURE 1). When they occur in reflow voiding, the cause may be related to the solder paste and profile. The voids will be seen in the bulk of the solder joint or near the top of the joint at the component pad interface.

 

 

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Nick KoopMany flex designs perform well with panel plating for countless bend-to-install applications.

When copper-plating vias and through-holes, there are several process options in the PCB manufacturer’s toolbox. Typically, they fall into three buckets: panel plating, pattern plating and button plating.

Panel plating (FIGURE 1) means the entire panel surface and all the holes will be electrolytic copper plated to the full plating thickness requirement. The etch process will etch down through the base and plated copper, leaving a pattern with features comprised of both the base and plated copper. Pattern plating is accomplished by creating a pattern of all the circuitry on the two exposed layers with a plating resist, then plating up the pattern of the outer layers. After stripping the resist, the etch process will etch away the base copper between all the plated patterns, leaving a pattern with features comprised of both the base and plated copper. Panel and pattern plating essentially result in the same end-product. For this discussion, we will compare button plating and panel plating.

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Peter BigelowNew industries outside electronics may have different products, but share a familiar approach.

Last February, at the same time and place as IPC Apex Expo, maybe you noticed the signs for something called “Traffic & Conversion 2018.” Perhaps it was my age, or perhaps just naivety, but I just assumed the event dealt with roadway equipment used to manage vehicular traffic. Boy was I wrong.

Had I focused on the attendees, I would have immediately noticed that virtually all of them were young and tethered to their iPads. Over their morning coffee at Starbucks, there was no conversation or early morning banter. Instead, everyone was in a trance, staring at their screens. At night, the same youthful attendees held court at the bar, laughing and networking. During a conversation with one, I finally learned what the group was all about. “Traffic & Conversion” was really an annual pilgrimage by data geeks to learn the latest trends, technology and methods employed in the world of “data mining.”  

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Martin WickhamDespite years of research, whiskering remains a problem.

FIGURES 1a and 1b are examples of tin whisker growth on tin-finish printed circuit boards. You must have good eyesight to spot these. These examples were found on the surface of assembled boards. We have also seen much longer whiskers on boards supplied by producers just one week after manufacture. Other assessments have shown tin whiskers on the surface of a plated through-hole PCB coated with tin. The boards were produced and shipped to a manufacturing site in Europe and, when examined prior to assembly, were found to have whisker growth. Tin has become popular on printed boards as one of the alternative coatings, and has become the finish of choice in the component manufacturing industry. However, many concerns have been shared over the formation of whiskers and the long-term solderability of tin finish and its viability for double-sided soldering with long hold times between reflow or second stage soldering.

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David BernardEveryone has an x-ray system for BGAs. Why not use it for through-hole too?

I am often asked about the use of x-ray inspection to investigate issues with surface mount components. Quite naturally, there is always a focus on BGAs, flip-chips, QFNs, etc., where the optically hidden nature of the joints lends those parts to x-ray techniques for analysis.  I am rarely asked about through-hole joints, however. Is this because no one uses them anymore? I don’t think so. Indeed, I would venture to suggest there probably are more through-hole joints made today than ever. I am surprised PTH joints do not come up in conversations more frequently because they are obviously hidden joints.

IPC-A-610 guidelines qualify the level of hole fill to be expected within these joints. How else can you nondestructively check during manufacture if these conditions have been met? Are all through-hole joints made perfectly with 100% fill, and never with any issues? Or, as I suspect, is through-hole seen as a great, but slightly less fashionable, technique, and do many not consider an x-ray system can also quickly and simply confirm the quality of these joints? In other words, you already have an x-ray system for BGAs, so why not also get the benefits of its quality control capabilities for through-hole joints?

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Peter BigelowNot everyone is. That’s a mistake.

It hit me while walking through IPC Apex Expo in February. Talking with various colleagues, the famous quote from A Tale of Two Cities kept repeating in my head: “It was the best of times, it was the worst of times.”

At every industry meeting I have been to in recent months, the mood has been quite bullish, reflecting the best of times. The HKPCA Expo in Shenzhen was well-attended, and money was being spent – lots of it! Ditto for Apex, where attendance appeared brisk and North American companies were in a buying mood. Discussions revolved around adding capacity, further incorporating higher technology capability, and exciting new customer relationships – all of which overshadowed the news that tariffs and trade restrictions could be in the offing.

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