| A three stage heat transfer is employed to eliminate the tin ball-up problem. A void nucleation problem is encountered in stage I and it can be reduced by minimizing time at stage I. Therefore, T(,d), the tin depletion time, is important in order to minimize time at stage I. Experiments on stage I heat treatment in three geometrical conditions, planar, internal tin and external tin, are studied in order to determine T(,d) values. The depletion of tin layer is proportional to the square root of time for the planar and external tin cases. A finite-difference numerical analysis is applied to study these three geometrical conditions. The numerical model predicts T(,d) values slightly less than the experimental results. Possible causes of disagreement have been discussed. The results show that the planar geometry is the upper bound solution of the external tin wire condition and the internal tin wire condition is the lower bound solution of the external tin wire condition. |
