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JUNE 2018 I SMT007 MAGAZINE 19 and use an X-ACTO knife and cut that away." Kan notes, with flex the processes are not straightforward. "It's much different than your regular rigid board. There are back-end processes to consider as well, such as rework, wave solders, selective solder, 2nd operation, forming, etc., that you have to cope with. You can easily burn a flex circuit or damage a trace without knowing it. If you're not care- ful in what you're doing, not optimizing your rework temperature for instance, you can easily damage the flex itself before you even damage the components." Moisture is a big factor with flex circuits as well, as they absorb moisture at least 30% faster than the traditional rigid PCBs. Which is why prebaking before assembly is essential. According to Kan, they bake two to three hours prior the assembly process. He notes that planning correctly will avoid impacting cycle time. "If you bake, use dry cabinets. Sometimes, things don't always go according to plan. Back when we started, we just kept rebaking them. Over time, we started using dry cabinets. After baking, we seal them and throw them in the cabinets. Sometimes, you don't even have to seal them, you just throw them in the dry cabi- net. We find that it works very well, and you don't have to keep rebaking them," says Kan. A Growing Market The flex printed circuit market continues to be one of the fastest growing segments in the PCB industry. According to a new report by industry analyst firm Transparency Market Research, the global market for flexible printed circuits, which was worth $14.51 billion in 2017, is anticipated to expand at a CAGR of 11.8% over the period from 2018 to 2026 and reach a value of $38.27 billion by the end of the forecast period. In particular, multilayer flex circuits are enjoying a greater demand among the products in this sector, and this trend is projected to remain so over the next few years, according to the report. Mainly driving this growth is the signifi- cant rise in the consumer electronics industry, led by the growing demand for smartphones, tablets, and LCD displays, according to the report. Moody sees the wearables market as one of the key sectors driving the flex circuit indus- try. "The wearables market sees a lot of things conforming to your body, or going around your wrist, going around your ankle, strapped to your back or your chest or your forehead. The conforming of that circuit to meet the environ- ment that the circuit is going to live in, let's just say if it's something that's going to be around your wrist, there's going to be a flat portion of it that needs to be there so that you can have your components, and then there's got to be an aspect of that circuit that's going to be able to conform around your wrist. We want to keep components out of the areas where the circuit is bending or folding or conforming." It's a fascinating field, according to Moody, wherein you get challenged with something new almost every day. "That's actually the fun aspect of this industry. Every day, some- body's coming in with a new application and you think, 'Wow, haven't thought of that. Let's try to figure that one out.'" SMT007

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