The process of SnPb immersion in Ag/Cu coated light emitting diode lead frames (LED LFs) (alloy 42) was investigated. SnPb solder was found to cause dewetting of the LF substrate after 6 s of immersion. We believed that the dewetting of the SnPb solder could be attributed to spalling of the interfacial compound grains. The addition of a small amount of Ni to the molten SnPb solder (0.1 wt.%) retarded that spalling and helped to prevent dewetting. The mechanisms for spalling retardation by the addition of Ni additives are as follows: (1) the Ni additives slow down the reaction rate between the molten SnPb solder and the Ag/Cu plating layer; (2) the Ni additives participate in interfacial reactions to form (Cu,Ni) 6Sn 5 ternary compounds, which are more stable than binary compounds and have a slower ripening process.
- Light emitting diode lead frames (LED LFs)