Interview with Robert Rush, Metcal’s Product Support Engineer, discussing the evolution of hand soldering with Connection Validation.

Recently, I met with Metcal’s Product Support Engineer Robert Roush. Metcal, an OK International brand, unveiled a patented hand-soldering technology at this year’s IPC APEX EXPO, in San Diego. It sounds like a real game-changer, from a reliability and process control standpoint, and promises to bring a new level of science and control to the world of hand-soldering.

Judy Warner: Robert, why don’t you start by giving me a brief description of Metcal’s history and product focus?

Roush: Metcal’s been around for a little more than 35 years. They came to market with SmartHeat®, a new technology at the time, which used Curie point heating to really change how soldering was traditionally performed. Over the years, we’ve expanded our focus into convection rework, capital equipment, and fume extraction. Overall, our product line has evolved, and today we’re focusing on risk mitigation, process control, and automation—key industry pain points.

Those are seen to be the key tenets of the industry that everyone is focusing on—the bread and butter of hand-soldering rather than just getting a piece of iron hot, which has been traditionally the focus of industry players. There’s been an element of keeping up with the Joneses, but the core technology hasn’t advanced much in more than 30 years. It has just become more competitive, with minor changes in power and features overall. The evolution has not really moved the needle much in terms of technology and delivery on key customer needs.

SmartHeat has always been the outlier in that realm and just one of many solutions. Metcal has always done things a little differently. We’ve held several patents over the years and every one of the patents has done something differently; or, we’ve taken a different focus and tried to solve a problem with a new product, that may not have been known to the customers at large.

Warner: Sounds like Metcal has been driving hand-soldering technology, which is a great position to be in the marketplace. I understand there are some inherent challenges relative to process control and reliability. How do those impact the final product?

Roush: Many challenges are associated with hand soldering. There’s hardware, materials, and the personnel side. On the hardware end, you do a lot of things to control the type of solder, the amount of heat, the time on the joint, the flux chemistry, the solder chemistry, and the components that go into it. All those factors are controlled going into the soldering process.

Pair that up with operator training to an industry standard. Production supervisors hope that with tight process control and well-trained operators, at the end of the day, when they put the hot iron to the joint, they get a good solder joint. That’s really what happens on the production line. You strive for a good, consistent result every time. Then you inspect and move on to the next stage.

Warner: I visited a high-end EMS company that focused on NPI and prototypes recently. One thing they pointed out to me was that there was not a single soldering iron in the place—which surprised me. They had instead bought selective soldering equipment to address their own risk mitigation. Is this an effective strategy?

Roush: Selective soldering has some advantages over hand soldering, but there’s also some disadvantages that can’t be solved with a selective soldering machine. With a selective soldering machine, it’s possible to program many of the variables into the process and eliminate some of the risks that an operator may add to the mix.

Even the best solderer has a bad day from time to time. Hitting that joint 100% of the time and making sure the standard is adhered to is challenging even with the best of operators. A selective soldering machine, in that case, can just be programmed; ideally, at the end of the day, it is successful.

But the selective soldering machine has expenses too. There’s a lot of programming involved. There are still components that are either temperature sensitive, or sensitive to some of the solders. You’re trading one risk for another. You’re trading the operator’s risk versus whether the selective solder machine can accomplish the task without damaging the board.

In a prototyping house, where parts may be one-offs, or a batch of few that could cost thousands of dollars, it’s important to mitigate risk as much as possible. I’m sure they feel that eliminating the operator and going to something more automated helps mitigate that risk. What they’ve done is removed the human element, but introduced more process control and hardware risk, with the hope that they come out the other side with a product that can go into mass production.

Warner: That’s interesting. Before we move on, you mentioned standards. Are the IPC standards clear and straightforward? Has anyone at Metcal gotten involved in collaborating on those standards?

Roush: The IPC standards, especially when it comes to hand soldering, are primarily visual based, whether it’s IPC 610, or the J-STD-001. They provide reference materials for what every type of solder connection should look like.

The standards assume that if you control process variables and an operator has been properly trained, and the solder joint looks good at the end of the day, it will be a good joint. But because the standards are visual based, there’s no inherent guarantee. The standards just provide a visual to compare whether the operator has met the standard and whether the inspector or the automated inspection equipment employed afterward has met this visual standard. In that context, that’s as far as standards have gone.

Our chief technology officer is working with IPC in that regard. He discusses our future, and he’s involved in the development and reviewing the standards and participating, pushing those standards forward and making sure that we have a robust set of controls in the industry.

Warner: Regarding the challenges you mentioned and all the moving parts of processes and standards, you mentioned SmartHeat. Will you explain how Metcal, as a 35-year-old company, has looked at these challenges and how you’re currently addressing them in the marketplace and helping your customers mitigate risk?

Roush: Metcal introduced SmartHeat 35 years ago. As of today, Metcal soldering stations are all based on SmartHeat technology. With SmartHeat, we use Curie point heating, which allows very precise temperature control within 1.1 degree of accuracy and essentially eliminates any overshoot. It’s all based on power-on-demand. We only apply enough power to effectively solder a joint. Then it backs off and you can move on to the next joint.

Over the last few years, we’ve looked more closely at what a good solder joint is. We’ve developed a new technology that we introduced at IPC APEX EXPO 2017, which looks at how a solder joint is formed. The technology is called Connection Validation (CV). CV provides real-time feedback to the operator and indicates whether they’ve successfully achieved a “good” solder joint, or if there’s been some fault during the soldering process. It’s revolutionary; current systems are open loop and always have an element of risk.

Warner: Can you tell me about the features and benefits of this new technology?

Roush: In any successful soldering process, you have an intermetallic that forms as the solder bonds with the pad composition. During soldering, they form an intermetallic alloy.

We know that one of the challenges with the visual standard is that it can look good, but still be bad from an electrical or intermetallic formation standpoint. We understand that when you have too little of an intermetallic formation, you get a cold or dry solder joint. Too much, and you have embrittlement. There’s an optimum right in the middle.

What we’ve done is develop a technology that monitors, in real time, the solder joint as it forms, and calculates the intermetallic formation; it provides feedback to the operator that the intermetallic formation is formed at the ideal level. Coupled with the visual standard, not only does this result in an external joint that looks good and meets the visual requirements, but now you have an internal control mechanism that ensures the intermetallic is ideal. This provides a “belt-and-suspenders” approach to soldering where you’ve only had a “belt-and-fingers-crossed” solution in the past.

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