The Pb-free solder which Fujitsu developed consists of “stannum zinc and aluminium” and has following features. (1)low melting point: This solder succeeded in realizing melting point of 199? similar to melting point of solder consisting of “stannum and lead” such as 183? although conventional solder consisting of “stannum silver and copper” was high melting point. (2) good wettability: Added aluminum suppresses oxidation of Zn to ensure good wettability. (3)corrosion resistance under high-temperature and high-humidity environment: Aluminium inhibits oxidation process by forming passivation film on the surface of the solder. (4)high bonding reliability to copper substrate: Gold plating processing which is necessary to solder consisting of stannum zinc and bismuth is unnecessary to this solder. In case lead is added to electrode device lead –bismuth intermetallic compound layer is formed on copper substrate interface and boundary separation occurs to the copper substrate by warping stress. As the Pb-free solder which Fujitsu developed does not contain bismuth at all no lead –bismuth intermetallic compound layer is formed. As a result it is possible to maintain high bonding reliability.
Significant change of the soldering machines was necessary to bring in the conventional solder consisting of “stannum silver and copper” to the existing leaded soldering method which is designed supposing the melting point is 183? because the conventional solder’s melting point is about 220? and the heat load to the parts in conjugation is high. In addition it is high-cost because the solder itself contains silver. As this solder’s melting point is low and similar to that of existing leaded solder there is almost no necessity to change the existing soldering method. This Pb-free solder can be low in cost by adopting “stannum zinc and aluminium” used generally.; nondisclosure