Stabilisation of Cu_6Sn_5 by Ni in Sn-0.7Cu-0.05Ni lead-free solder alloys

摘要

Cu_6Sn_5 exists at least in two crystal structures with an allotropic transformation from monoclinic eta'-Cu_6Sn_5 at temperatures lower than 186 deg C to hexagonal eta-Cu_6Sn_5. We recently discovered that the hexagonal structure of Cu_6Sn_5 in lead-free solder alloys with trace Ni additions is stable down to room temperature using high resolution TEM/ED/EDS. This report further confirm the phase stabilising effect of Ni by analysing samples of Cu_6Sn_5 extracted from a Sn-0.7wt percentCu-0.05wt percentNi lead-free solder alloy. Techniques used include X-ray diffraction, transmission electron microscopy and differential scanning calorimetry.