This paper discusses how to successfully profile a printed circuit board when reworking Ball Grid Array and Chip Scale Packages.
Board Profiling for Production vs. Rework
If we consider profiling a PCB for reflow in production, we are generally concerned with achieving an even Delta T (DT) across all of the joints being soldered. This is accomplished by evenly heating both the top and bottomside of the whole board, generally through a multi-zoned convection reflow oven. The capacity of the oven would be appropriate to the size or thermal mass of the PCB and the production throughput requirements.
When we consider reworking an array package such as a BGA or CSP, it is recognised that process control is of paramount importance to achieve a successful result. The normal way to approach the rework is to try and emulate the production reflow profile for the individual component being removed or replaced. The nature of the operation dictates that we only wish to reflow the component being reworked and therefore we have to heat a specific area of the circuit board. Selective heating of an area of board can inadvertently cause process failure even when all the parameters appear to be correct. This note discusses the influential factors and the potential pitfalls to be avoided....
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