solder paste 52 was formed and applied on a test leadframe 51 in the form of a pad having a diameter of 1 57 mm and a height of 0 15 mm the employed solder paste was sn u2014 ag u2014 cu based solder paste m705 221cm5 42 11 manufactured by senju metal industry co ltd the thus applied solder paste was heated for one minute at 230 u00b0 c to thus reflow the diameter of the reflow in an arbitrary direction was measured an average of five sets of data was determined solder wettability and spreadability was computed as a ratio of a diameter achieved before reflow to a mean radius achieved after reflow similar tests were conducted through use of the test leadframe sample heated for 30 seconds at 400 u00b0 c before application of paste in the sample where the sn layer sandwiched between the pd layer and the au layer has a thickness of 0 1 u03bcm the diameter was reduced when the leadframe was coated with a paste after having been heated at 400 u00b0 c and deterioration of solder wettability and spreadability was exhibited from these results the desirable thickness of the sn layer is found to preferably range from 0 001 to 0 05 u03bcm noble metal au pd ag used as an exterior material of a leadframe is known to have poor adhesion.