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42 SMT Magazine • October 2017 by Stephen Las Marias I-CONNECT007 To find out more about achieving the per- fect solder joint, I interviewed Ralf Wagenfuehr, plant manager at Rehm Thermal Systems, dur- ing the recent NEPCON South China exhibition in Shenzhen to get his insights on this issue from the perspective of a reflow oven supplier. Stephen Las Marias: Ralf, why do you think sol- der joints are among the key factors in PCB de- fects? Ralf Wagenfuehr: It all comes down to the sol- der joint. It's getting (the components) connect- ed to the board. The other factors are based on the suppliers, the components, the PCBs, etc. I think the solder joint is the main purpose of the whole SMT industry. Everything else is easy to control, but bringing them together, it is im- portant to have the correct parameters in there. Las Marias: How would you define or character- ize a perfect solder joint? Wagenfuehr: A perfect solder joint, we believe, can be only achieved in the nitrogen atmo- sphere. You don't look only at when it's con- nected, you have to look at the next 10 years, where the end-user is using the product contin- uously. The perfect solder joint is reliable, and I think the important thing is it has a clear sur- face, that it's not impacted, and that there are no corrosions, among other things. While a good connection on the surface is very impor- tant, you also must make sure the joints are sta- ble. Las Marias: Why do you need a nitrogen envi- ronment? Wagenfuehr: In a nitrogen environment, you can exclude oxygen already, so mostly, you would achieve better wetting. Sure, it depends on the paste, but I believe reliable solder joints can be achieved under a nitrogen atmosphere. That's why we designed nitrogen ovens. Las Marias: What are the parameters to consid- er for achieving the perfect solder joint? Wagenfuehr: The main ingredient is the solder paste, and it is important for material surfaces. You have different components and different surfaces for different customer requests. That's why choosing the right paste for the right com- ponents is one of the most important things. FEATURE

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