To all of you so called repair experts quit telling people that putting heat to the board will fix it! It will only make it worse! Here is some tech data.I just can't take it anymore with all the crap that has been placed all over the net! Key Points: BGA Solder Balls
[/color]Reliable solder joints
High quality, low defect soldering requires identifying and repeating the optimum reflow process: every solder joint on every board needs to be treated in exactly the same way. How the heat is applied does not matter as long as it is in a controlled manner. Heating and cooling ramp rates must be compatible with both solder paste and the assembly, and the time of exposure to high temperatures must be defined and maintained. Suppliers of solder paste will recommend different process conditions for their products to obtain optimum performance, particularly with low residue pastes.
The aim is to raise the temperature of the board and component terminations sufficiently far above the reflow temperature of the solder paste for the right length of time to create reliable solder joints. The process has to be hot enough to enable the solder to wet the board and components yet
cool enough not to damage the items being soldered and have
a controlled cooling phase to ensure the joints are sound.
If the reflow temperature of a paste is not achieved, the paste will not become a liquid; if the paste is not at reflow temperature for a sufficient time, full wetting will not take place.
We also need to ensure that both component and board reach the reflow temperature at almost the same time in order to get satisfactory joints.
The temperature profile
As an assembly moves through a soldering system, it is exposed to a controlled rise and fall in temperature. A plot of temperature against time is called a temperature profile.
Double-sided reflow
The key issues with double-sided reflow are that:
The first side is reflowed twice, which ages the joints. That is, the joints are moving towards the point where they may start dewetting
Components on the underside during the second reflow operation are supported only by the surface tension of the solder and are vulnerable to any form of mechanical disturbance, especially where parts are heavy in relation to their pad size/solder volume
During the second reflow, the previously wetted joints are being reflowed without the benefit of any protective flux. Oxidation reduces the surface tension of the solder, and hence reduces the uplift on the components
Microsoft recommends that its ICs and PCBs be reflowed or reworked to a maximum of 3 three times.
If after reflowing 3 times, the problem is not resloved then reballing is the only solution.
Read and reread all of this and then since you people like the internet some much look up how to rework BGA's maybe then you will get the picture. MS is reballing most of the boards not reflowing. It takes expensive machines to do this work with X-ray monitors to aligne the CPU's and GPU's to the board. So do your self a favor and leave the heat gun where it belongs in the tool box collecting dust. SEND IT IN FOR A REAL REPAIR! BY A SHOP THAT HAS THE RIGHT EQUIPMENT!