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SMT-Oct2017

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44 SMT Magazine • October 2017 Next is the customer's temperature ranges for the components in PCBs. There's a wide range of applications. Some cannot have nitrogen, some need nitrogen. The solder paste is very im- portant, but connecting the components to the board is a process that influences the long-term reliability of the parts themselves. Las Marias: It's important that the paste suppli- er, the assembler, equipment supplier, and cus- tomer are all working together. Wagenfuehr: Yes, that's very important. If you choose the wrong surface finish, then you will have defects built in from the beginning. That will cause defects on a long-term view. Of course, most people are already considering this. But I think it's very important to have the right paste. Las Marias: Ralf, what are the other soldering issues from your perspective? Wagenfuehr: Wrong profiling is one. We still see people doing wrong profiling. Wrong de- signs and wrong storages are the other issues. Design has a big influence. We have a lot of en- gineers working together, we have a lot of com- ponents, solder paste, solder pads, so the design (of the board) has a really big impact. Wrong storage (of solder paste) is also one of the big- gest culprits. Las Marias: Why is voiding a big issue right now? Wagenfuehr: Things are getting more compact, and the power usage is getting higher. We have more applications running on a smaller surface. That means everything is consuming more pow- er, even on the PCB. Of course, in applications such as automotive, medical, and other critical industries, it can cost lives. You don't want a PCB to break down on the airplane when you're in it. Your mobile phone breaks down, it's a quality issue; you can make a decision in the future. But for other things, you only have one chance to make it right. As things become small- er, more compact, with more built-in functions into the circuits, and into the components, it is important to have less soldering voids. Las Marias: How do you help customers address their voiding problem? Wagenfuehr: We have the main systems, includ- ing our condensation soldering, our vacuum soldering, and vacuum reflow. But we also have a whole process chain that we can support. Our customers call us not only for voiding but main- ly also for this, and how we can support them is through our process chain. Here, the design is one of the main factors for the voiding. The design often is the wrong choice. Things can- not escape, and air cannot escape. The soldier joint is the wrong size, or has the wrong pad. We have to design it with some holes so air can escape from the solder pad. Of course, the print- ing process is very important. How we pressur- ize the components on the solder pad itself is very important. We have done studies, and we figured that with an improved process, you can nearly achieve around 20% or less in higher ap- plications, but of course, if you can control all your factors with our systems, you can go down to 2% voiding. Las Marias: What are the key considerations to achieve this? Wagenfuehr: Atmosphere is one of the factors that have an impact on the process. For in- stance, you have less oxygen when the solder melts. It's important to have the right surround- ing atmosphere. The process must be seen as a whole process chain to avoid voiding. We have trained process engineers at all locations, and we can support on the process chain as well. This is why Rehm is very strong—not only for making machines, but by being able to support the process chain as well. Las Marias: Finally, Ralf, what are some of the latest innovations from Rehm that will help ad- dress this voiding challenge? Wagenfuehr: We have the condensation sol- dering system for very high-reliability appli- cations. We have four different kinds of series for each market, so two condensation soldering machines with vacuum. For industries that do not have the possibilities for condensation sol- CHOOSING SOLDER PROCESSES: GETTING IT RIGHT

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