Strong Zn concentration effect on the soldering reactions between Sn-based solders and Cu

摘要

The acute Zn concentration sensitivity of the reaction between Sn-based solders and Cu substrate is reported and explained in this article. Three Sn-xZn solders (x = 0.5, 0.7, and 2 wt percent) were reacted with Cu substrates at 250 deg C for 2-10 min. A slight variation in the Zn concentration changed the reaction product formed at the interface. When the Zn concentration was low (x = 0.5 wt percent), the reaction product was Cu_6Sn_5. When the Zn concentration was slightly increased to 2 wt percent, the reaction product became Cu_5Zn_8. When Zn concentration was in-between (x = 0.7 wt percent), Cu_6Sn_5 and CuZn co-existed. The above findings are explained using the Cu-Sn-Zn phase diagram. The implication is that the type of compound forms at the interface can be controlled by adjusting the Zn concentration of the Sn-based solders.