Issue link: https://iconnect007.uberflip.com/i/989774
48 SMT007 MAGAZINE I JUNE 2018 Feature by Stephen Las Marias I-CONNECT007 At the recent NEPCON China 2018 event in Shanghai, I spoke with Ralf Wagenfuehr, plant manager at Rehm Thermal Systems (Dongguan) Ltd, to gain insight into flex circuit assembly, and the challenges of reflow soldering. According to Wagenfuehr, flex circuits are increasingly being used in mobile phones over the past two years as manufacturers have been rede- signing their phones with more curves and more functions and additional components inside. "The PCB is getting smaller, and modules are being built on the flex printed circuits, not only the connector. Now, it's integrated circuits in the flex boards, and sensors, which are becom- ing much smaller. As an example four years ago, the smallest chip component was 03015. Now, the 008004 chip component is also on the market. The 008004 component is 35% smaller than the 03015 component. The chal- lenge of reflow soldering is how to ensure the oxygen content in the reflow chamber and how to ensure the stability of the reflow air volume to avoid such defects as tombstone." Wagenfuehr says. "You can now bring the components in mobile phones to the position that is good for the user. More and more, these applications—mobile phones, smart devices, and other similar applications—are definitely increasing the market demand for flex circuits. But I think, in big components like in auto- motive, it is very seldom used because of the reliability of flex circuits in such applications. They should last for years, not only just for a short time., They are using other components, for instance, the flex circuits may be integrated in housings, MID's moldings—in automotive electronics. But flex circuits, definitely more and more in handheld devices." One of the biggest challenges when it comes to the reflow soldering of flexible circuit assemblies is warping. "First of all, flexible circuits are very light. While some customers are trying to process flex circuits without hold- ers or carriers, experienced manufacturers are using magnetic holders or similar things to keep the flex circuits in place. But I think soldering is not only the biggest issue. I believe, print- ing and chip mounting are definitely a chal- lenge for manufacturers when it comes to flex circuits because they are not steady." According to Wagenfuehr, mitigating this problem starts with the design. He says designers should consider not only the appli- cation but also the manufacturing. In fact, there is a clear definition of IPC-6013 with