Rheological Measurements of Solder Pastes in Heating Processes

In production of printed circuit boards, the solder pastes are deposited on the boards by screen printing and the conductive lines are formed by melting the solder particles at high temperatures. For formation of precise patterns and sufficient adhesion, the solder pastes are required to hold their shapes until the solder particles begin to melt. An evaluation method of practical processability of solder pastes is examined through dynamic viscoelastic measurements in heating process. However, the difficulties arise in cleaning the sensors (parallel-plate geometry in the present study) because the sensor surfaces are covered with the solidified solder after the measurements. By the use of disposable aluminum sensors, the measuring procedure is established at temperatures above the melting points of solder. The temperature dependence of dynamic viscoelasticity would be useful to design the binder resins and to control of reflow processes.