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If the pin count is low, I can do it with a heat gun. You must mark the PCB with an outline so that you can center the part. Touch a soldering iron to each PCB pad with a little solder and then remove it with solder wick so that each pad is tinned. Place the part on the board and then heat it with the heatgun. I use a wooden toothpick to gently push the part down to hold it in place when the solder reflows. It would be nice to have a paste stencil but sometimes you cannot afford one. This won't work if you have already removed the part and the balls are damaged.