I have some fine pitch QFP's to rework with our smt rework system (forced air). There are no intitial concerns in removing the component (we havent actually begun the rework process) however, installing a new chip presents a problem.
The QFP has a ground plane on the bottom of the chip that must be soldered to the pad of the PCB
. After removal of the component, we would clean the pads to remove excess solder and wick the excess solder from the ground pad on the PCB. A new component would be used for installation and prior to placement, a dab of solder paste must be placed on the ground pad of the PCB. After placement of the QFP, reflow would begin.
The problem that I foresee is with reflow. If the solder paste melts underneath the package prior to the leads, wouldn't it cause the component to drift hence, get the leads out of alignment? Do I need to modify my profile such that leads reflow first, followed by the ground pad (the idea is that the surface tension of the leads would keep the component from drifting)? Any thoughts as to how I may rework this component?