Touch the PCB board by handNot familiar with the machine/ processConfuse the uncleaned board with the cleaned onesBlocked nozzleSmall water containerSmall compress air filterUnstable DI water pressureSurface oxidationAbnormal thicknessUneven thicknesssurface scratchcomponent oxidationcomponent oxidationHigh density componentPCB exposed to air too longWashing TemperatureWashing TimeDrying TemperatureDrying TimeDust in the airHigh humidity