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82 SMT Magazine • April 2016 consisTEnT conTrol ovEr ThE sElEcTivE soldErinG ProducTion ProcEss many engineers run a board at the start of a new production session or at random to verify temperatures. Similar data is shown for a forced convec- tion preheater tested in a machine capability analysis. This data proves the consistency of the ma- chine. The process however is run with boards that have different thermal builds. On one board there are Cu-rich areas as well as other areas with less thermal mass. It is not only a challenge to maintain a constant temperature, but also to achieve small ΔT's across the board. Otherwise some parts may be out of the flux specification limits that define the acceptable preheating temperatures. Many engineers run a golden board during production. This board contains thermocouples on cold and hot areas of the assembly to verify process conditions. Some selective soldering machines are equipped with closed loop controlled systems in the last preheat zone. A pyrometer measures the topside board temperature when the board enters the IR lamp heater. The machine calcu- lates the time before soldering and modifies the Figure 6: Accuracy of the fluxer robot in y-direction. Table 2: Recommended methods to control position of flux.