Hi, I have a PS4 Mainboard to repair and the APU needs to be raballed. I desoldered the APU already and placed new balls several times. Tried to solder the Balls by Heat gun and IR infrared soldering station at 180-200C. I tried several ball sizes 0.5 0.55 0.60 but everytime when I apply heat the balls dont "jump" or stick to the belonging places like some pros on YT do they just melt together and produce shorts and long lines along the pins. What am I doing wrong? Is it my flux absorbing the heat and melt those balls together. Without the use of flux I dont think to get good results as well.

 

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... one possibility is that there is a layer of oxidation on the pad surfaces. As an example, the lead terminals on car batteries will develop a noticeable dull coloring after a few minutes of direct exposure to air. A wire battery brush will remove the oxidation and produce a bright conductive surface on the terminals. ... can't say precisely how to proceed with cleaning the solder pads. You would have to be wary about displacing the pads and causing additional problems. Some type of mild abrasive should do the job, but can't say for sure what that would be.