the thickness of the above mentioned layers were investigated with an optical light microscope the reliability of solder joints was examined by placing a solder ball indium sac305 balls having a diameter of 450 u03bcm onto contact pads having a tin surface and a diameter of 400 u03bcm and a printed flux alpha ws9160 m7 the specimens were reflowed under nitrogen atmosphere in a typical lead free solder profile the solder joint reliability was then determined by shearing off the solder bumps before and after ageing the resulting average shear forces are given in gram definition of failure modes obtained from a solder joint reliability test as described above failure mode 1 u2192 less than 5 fracture in the solder joint interface and most desirable failure mode 2 u2192 5 to 25 fracture in the solder joint interface and less desirable the contact pads of a substrate were immersion tin plated after cleaning and etching the thickness of the tin layer was 4 94 u03bcm the loss of copper from the contact pad was 3 8 u03bcm i e 77 in respect to the thickness of the plated tin layer after cleaning and etching the surface of the contact pads a layer of copper was deposited from an electroless plating bath followed by activation of the electroless plated copper surface and immersion plating of tin the thickness of the copper layer deposited from an electroless plating bath was 2 71 u03bcm and that of the tin layer 3 46 u03bcm approx 0 65 u03bcm of the.