Shear Resistance Of The Tin-silver Solder Joints Under Creep Strain Characteristics

Creep behavior characteristic of Pb-free solder joints is a hotspot in the reliability issues. The dissertation performs systemic study on the electronic-resistance strains of Sn-3.5Ag solder joints shear creep with an in-situ micro electronic-resistance measurement, including four sections of modeling the mathematic relationship between equivalent cracks in solder joints and electronic-resistance strains, implementations of shear creep testing system, shear creep tests, and discussing the theory about electronic-resistance strains of solder joints creep, with some effective improvements. A mathematic model on the basic relationship between equivalent crack and electronic-resistance strains of solder joints is set up to settles the base of theory, which is in view of the metal electric classical theory and Griffith's theory of fracture. A software system based on Delphi and a hardware system based on MCS-51 series singlechip have been separately developed, with in-situ micro electronic-resistance measurement using four-probe techniques. The shear creep testing system consists of a software system and a hardware system. A lot of solder specimens' testing results have been processed using Origin software. The correlative tables and graphs show that l)the relationship between longest life and maximal electronic-resistance of solder joint is complex in the extreme, and it is necessary to study it further; 2) the great mass of "electronic-resistance strains - time" graphs can show the continual development of crack/damage and fracture mechanisms which are consistent with results reported by literatures, and their stages of creep are shown clearly; 3) however, a specialphenomena——falls firstly and climbs up lately——can be found in some"electronic-resistance strains - time" graphs of Sn-3.5Ag solder joints which have small scale. At last, the discussing about the basic theory on electronic-resistance strains of solder joints shows that the micro crack development in solder joint was a long course and its electronic-resistance was being changed slowly during the initial creep. So, a long and smoothed linear stage is formed in "electronic-resistance strains - time" graph. When the main cracks develop or join each other and the equivalent damage in solder joint grows up quickly, the electronic-resistance increases abruptly and "electronic-resistance strains - time" graph hoiks. Because vacancies translate into dislocations and the consistency of point defect decreases, some"electronic-resistance strains - time" graphs present a special phenomena——falls firstly and climbs up lately.