Thermal dynamics and BGA ball reflow

Reflow technology has undergone some major changes in recent times. This is largely due to the requirements in the industry to improve process control. Three major factors contribute to achieve this: temperature, time and atmosphere. Not only must each segment be controlled, but it must all be done simultaneously, as each interacts with the other. It is no longer tolerable for one of the ingredients to be held to specifications while the other is not. Current furnaces are therefore drastically different from the common convection furnace designed for the SMT circuit industry. They must be compact and must be environmentally friendly, i.e. use less electricity, and less nitrogen or forming gas. For the processing of plastic BGAs, for example, a cycle rate of 10 seconds or less must be achieved and this should be accomplished in single file. The furnace must be less than 5 feet long. This paper discusses how to achieve these aims.