Rheological characterization of solder pastes for surface mount applications

Accurate rheological measurements are needed in order to correlate the rheological behavior of solder pastes to their performance in the surface mount technology (SMT) process. In this paper, we summarize our efforts to measure the rheological properties of solder pastes, and outline the difficulties in obtaining their true rheological properties. In particular, we show that the rheological measurements of solder pastes are affected by "slip" at the test-apparatus surfaces and by shear fracture within the sample which have not been taken into consideration heretofore.