Originally Posted by
Mechanic688
Easyrecycle; One of the first rules of electronic repair is you suck the old solder off the board because you never want to reuse contaminated solder. It makes for a terrible solder joint, not smooth looking. Makes what they call in the business, cold solder joints! Just my opinion,,,
Another reason to fully flow the old solder and remove it is to prevent the barrel of the through hole from shearing internal layer connections when pulling out the component. The boards you are dealing with are most likely multi layer.
Mechanic688 
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