Microstructural dependence of constitutive properties of eutectic SnAg and SnAgCu solders

The paper presents constitutive models for eutectic SnAg and SnAgCu solders. Experimental investigations were carried out on specimens of different microstructures. The three specimen types have been flip chip solder joints, pin trough hole solder joints and standard bulk solder specimens. The bulk solder specimen was a dog-bone type specimen (diameter = 3 mm, length = 117 mm). The pin trough hole solder joint consisted on a copper wire that was soldered into a hole of a double sided printed circuit board (thickness 1.5 mm, solder gap 0.1 mm). The flip chip solder joint specimen consisted of two silicon chips which were connected by 4 flip chip joints (one on each corner). Flip chip bumps (footprint 200 mum x 200 mum, joint height 165...200 mum) were created by printing solder paste. Constant-load creep tests were carried out on all three specimen types at temperatures between 5 degreesC and 70 degreesC. Creep data was taken for strain rates between 10(-10) s(-1) and 10(-3) s(-1). The specimens were tested in "as cast" condition and after thermal storage. Beside the creep behaviour of the solders, the time independent elastic plastic behaviour was determined. Strain-stress-curves were recorded from the "flip chip solder joint" specimens, using a micro shear tester. The microstructural properties of the bulk specimens and real solder joints were examined using metallographic sectioning, optical microscopy techniques, and SEM-microprobe analysis. The results of the microstructural analysis were related to the investigated mechanical properties of the solders. Models of SnAg3.5 and SnAg4Cu0.5, that can be used with the ANSYS(TM) FEM software package, will be presented.