OSAKA, JAPAN — Copper and nickel are "essential" elements in forming a stable intermetallic compound layer in lead-free soldering, a joint industry-academia study has found.

Nihon Superior and the University of Queensland compared IMC layers at the interface between various lead-free solders and a copper substrate. Fluxed copper/OSP test boards were exposed to the solders for five seconds in a mini-wave machine with a pot temperature of 255°C. It was found that after 528 hr. at 150°C, the IMC on the board soldered with SnCu0.7Ni0.05 was smoother with slower growth of CuSn3 and no cracking.

By contrast, the IMC layer in SnCu0.7CuAg0.3 and SnCu0.7CuAg0.3B0.1 with additions of 0.3 Ag and 0.3 Ag+0.1Bi was uneven with growth of CuSn3 and cracking, Nihon said in a press statement.

SnCu0.7Ni0.05 is the basis for Nihon's SN100C solder.