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84 SMT Magazine • April 2016 power of the heaters in such way that the final end temperature is always the same. Another method to verify if the complete as- sembly is heated correctly is to take a thermal image with a thermal camera. The advantage of such an image is that one is able to analyze the complete assembly in detail. However, it is only one shot at the end of the preheating—a one- moment temperature picture. Soldering process Just before soldering, the assembly is clamped onto the conveyor or in a robot. Then the assembly is positioned above the sol- der device. In the next study the accuracy of the robot, the repeatability of the clamping system, and consistency of the fiducials are monitored. A fiducial is mounted on the robot. The ro- bot itself including the assembly is moved to a camera that records the x, and y position of the fiducial of the robot as well as the fiducial of the assembly. The test is repeated with the same as- sembly and with different assemblies introduc- ing the noise of poor fiducials. The machine capability proofs the accuracy of the robot. All x and y position are repeatable and Cp values are well above the requirements. The graph shows that for a process accuracy of ±0.10 mm, the data is not consistent enough. For a select wave process (point to point solder- ing) a fiducial recognition system corrects the Figure 7: Ishikawa diagram of flux amount per square inch. Figure 8: An organic no clean flux applied on the test board. consisTEnT conTrol ovEr ThE sElEcTivE soldErinG ProducTion ProcEss Table 3: recommended board temperature control.