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52 SMT Magazine • April 2015 • Topside heaters to reduce temperature drop and keep the board at temperature • Cooling devices to avoid overheating of components • Vacuum or other devices to keep the board flat and avoid warpage • Tooling to prevent components from moving or lifting due to the heat of the solder • Tooling to keep the component in place and achieve accurate placement (up to flatness of -0 to +0.1mm) Conclusions Selective soldering is a robust soldering pro- cess when the process parameters are addressed and under control. In the different process steps we identified critical parameters: Flux process: In this first process there are no elevated temperatures and accuracy is estab- lished by the following: pOSiTiON aCCuraCy MaCHiNES FOr SElECTivE SOlDEriNG OF FiNE-piTCH COMpONENTS continues FeAture 1. Accurate x and y position of the robot. 2. Flux flow measurement. 3. Verification of the flux flow direction. Preheat process: No special requirements for board handling or placement accuracy. The temperature of the print is measured with a py- rometer to guarantee flux activation and pre- vent overheating. Dip soldering process: Several requirements need to be fulfilled to have a consistent dip process: 1. Position of the PCB in the gripper has to be defined via either mechanical fix or fiducial recognition. 2. Position of the nozzle plate must be defined via machine point verification with fiducials or mechanical fix of PCB/ gripper with nozzle plate. figure 5: The variation in wave height as a function of the pump speed.