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40 SMT007 MAGAZINE I JUNE 2018 Feature Interview by Stephen Las Marias I-CONNECT007 During NEPCON China 2018, I met with Zen Lee, technical director, and Michael Gould- smith, sales and marketing director of Ther- maltronics, a manufacturer of soldering prod- ucts and rework equipment. We discussed the challenges of flex circuit assemblies, especially during the rework process. They highlighted the power-on-demand feature of smarter hand- soldering systems, as well as how Curie Point helps operators avoid temperature overshoots during rework. Stephen Las Marias: What are the top challenges when working with flexible circuits? Zen Lee: The most important consideration is that the parts are very small. You need to have a fixture, since you cannot hold the flex board. The tip needs to be of the correct geometry, for the application and you need address, (touch), and the joints in the correct manner – in other words – "not heavy handed". Basi - cally, you cannot fool around, when doing this kind of rework, because the real challenge is the potential for delami- nation of the flex circuit. Good solder joints are essential —you have to take away the energy from the tip and give it to the joint, but you don't want to overshoot. Otherwise, you will also have solder splash issues, on top of delaminating the flex circuit. That's the problem. Las Marias: When reworking flex circuits, what are the key issues to consider? Lee: I think it is the control issues. Because if soldering is done by hand, the operator needs training as well as the knowledge to select the right soldering tip. Michael Gouldsmith: One of the key points Zen is making is concern- ing the tips we manufacture, which feature a unique tech- nology called Curie Point. There is no overshoot in temperature; we main- tain the temperature very well. It's also a power-on- demand basis. So, if there's enough stored energy in the tip, unlike a conventional soldering iron, which is provid- ing constant power, there's less chance of delamination, less chance of solder splash, less chance of rework problem, and losing the flexible circuit.

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