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90 SMT Magazine • April 2016 ity analysis using dedicated tools that are com- mercially available on the market. For select wave soldering with a small noz- zle, it is possible to measure the wave height continuously using a camera. For this process, a board warpage measurement might be neces- sary when the boards tend to warp frequently. The robot should be capable of compensating for warpage and correct the position if fiducial recognition is used. The robot position is monitored as part of the PLC control. This is very accurate as shown in the machine capability analysis. Any excep- tion will trigger an alarm. Conclusion Many parameters must be controlled to es- tablish a robust and consistent selective solder- ing process. Some important process param- eters (dry flux amount per square inch, top side board temperature and contact time) are hard to monitor continuously. Modern selective soldering machines are delivered with a machine capability analysis al- ready performed that proves that the machine is able to maintain consistency and achieve high yields. Statistical process control can be applied on critical process parameters. Data is logged in files and traceability is part of the software. This paper recommends how to control the process. The recommendations are only a guide to set-up a process. Also critical but not dis- cussed in this paper are the issues of the board design and material quality. Many soldering defects can be avoided when materials are selected that are high qual- ity and products have designs that meet se- lective soldering requirements. The machine supplier is happy to support users with design guidelines to make their products even more dedicated to selective soldering. Design for manufacturing often means a better design for selective soldering. SMT consisTEnT conTrol ovEr ThE sElEcTivE soldErinG ProducTion ProcEss Figure 17: Contact times measured during machine capability analysis.