Flip-chip solder bumps are formed on the area array electrodes of high-speed computer LSI chips. A high-density spring probe (600 probes/9 mm*9 mm) was developed for testing these LSIs by vertical insertion into the solder bumps. Solder with an extremely high lead content is used to lengthen the life for the soldered joint. This oxidized lead with high resistivity causes poor contact. Probing tests are conducted to find a suitable probe tip shape and processing conditions for 97 Pb/3 Sn solder bumps. Probe tips with adequately small opening angles easily break through the oxide film covering the solder surface and obtain sufficient contact area with the new surface of the solder bump. By using a probe with a tip opening angle of 30 degrees , contact resistance remains stable when a probe is inserted into a solder bump before melting into a spherical shape.
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