What's a reflow

kmlaport, here is an excellent paper on solder reflow. Basically what you are trying to accomplish is to reflow the solder around the contacts of the components, whatever they may be, or like in your case the GPU. The GPU is a BGA "The Ball Grid Array or BGA, is a very different package to those using pins, such as the quad flat pack. The pins of the BGA package are arranged in a grid pattern and this gives rise to the name. In addition to this, rather than having the more traditional wire pins for the connections, pads with balls of solder are used instead. On the printed circuit board, PCB, onto which the BGA components are to be fitted there is a matching set of copper pads to provide the required connectivity." from here. A search on Youtube.com about reball may yield some better visual answers to your question. Reball in principle is the same for any BGA component. Hope this helps, good luck.