Issue link: https://iconnect007.uberflip.com/i/488725
48 SMT Magazine • April 2015 pOSiTiON aCCuraCy MaCHiNES FOr SElECTivE SOlDEriNG OF FiNE-piTCH COMpONENTS continues FeAture flux is going in the right direction, perpendicu- lar to the print. For a given flux type, machine settings and solder mask the software will de- fine the spread of the flux on the board ensur- ing there is no excess flux on the assembly. Flux Robot Accuracy Test: To define ma- chine capability (accuracy of the flux robot) laser sensors were installed to measure the distance of the robot to a pre-defined point. Repeatability is required without influence by environmental noise, like temperature and hu- midity changes. For the flux robot, an accuracy of ±0.15 mm is defined in the specification. As shown in the graph the robot is capable and has a standard deviation of only 0.014 mm. The robot moved 120 times to this position over a time period of two hours. No drift was visible in the raw data. The robot was even more accurate in the y-di- rection where the standard deviation was only 0.007 mm. Gripper Robot Accuracy Test: The robot gripper that picks up the board after preheating and moves the PCB exactly above the nozzles in the solder pot has to be more accurate than the flux robot. The specification of this unit is defined ±0.10 mm. This is more accurate than systems that move a solder pot underneath the printed circuit board. Using an identical mea- surement device as in the previous test the x, y and z-direction of the gripper robot are tested for consistency. Despite the higher specified ac- curacy the x, and y-direction positioning of the gripper robot proved to be consistent. For both directions the standard deviation is approxi- mately 0.008 mm resulting in Cp values of ap- proximately 4. When the pins on the board are dipped into the solder the height (z-direction) of the robot gripper should be placed at the correct height. The board may warp due to the higher tempera- tures. To make sure that the board is not touch- figure 4: probability plot of the y-direction robot gripper. consistency of placement is measured toward laser sensor.