Unless your board fabricator put an unusual amount of solder during there hasl process I cant see how just applying flux can give you a reliable solder joint. This is certainly not the norm. Normally you apply solder paste that has flux in it, place the parts and then reflow. And you said there were cold solder joints on the sockets. Was that the sockets only. If it was the sockets only then your cold solder joints were probobly due to something else like maybe reflow temperature or board handling after reflow. [log in to unmask]