Tin-Lead solder has been widely used in microelectronic packaging for its beneficial electrical and mechanical properties. But, the motions of banning Pb which is toxic for human health and environment are expanded in a worldwide and specially for electronic products. So, increased environmental and health concerns regarding the toxicity of lead have stimulated research and development of alternative, lead-free solders. Lead-free solders have to satisfy varied requirements, ranging from safety, economy, material availability, and manufacturability to long-term reliability
A problem with Sn-rich lead-free solders might be the allotropic transformation of β-tin(bct) into α-tin(diamond cubic). This transformation product, termed tin pest, occurs at temperatures below 286K. The allotropic change is accompanied by a 26percent increase in volume, which could have serious repercussions when considering a solder joint life time.
In the present work, Creep properties of Sn & Sn-0.7Cu based alloy which contained Bi, Sb, Zn or Bi were studied by single lapshear creep test. Creep tests were performed under constant loads for stress levels lower than 10MPa at 373K. Solder balls with 8 different compositions of Sn-x & Sn-0.7Cu-x (x=0.5Bi, 0.5Sb, 0.5Zn and 0.5In) were reflowed on Ni-P pad. The $Ni_3Sn_4$ intermetallic compound(IMC) formed between Sn-x solders and Ni-P substrate, while the $Cu_6Sn_5$ IMC formed between Sn-0.7Cu-x and Ni-P. Sn-0.7Cu-x alloys showed better creep resistance than Sn-x alloys because $Cu_6Sn_5$ particles were dispersed in the solder matrix.
본 연구에서는 Lap Shear 크리프 방법을 이용하여 거의 순수한 Sn계 솔더의 크리프 특성을 연구하였다. 솔더 합금은 Sn과 Sn-0.75Cu에 고용도가 있는 금속(Bi, Sb, Zn, In)을 소량 첨가시킨 합금을 사용하였으며, 패드는 Cu pad위에 무전해 도금을 이용하여 Ni-P를 plating하여 사용하였다. Sn-x 솔더합금의 경우 Ni-P위에서 리플로우 솔더링을 하였을 경우 Ni3Sn4 intermetallic compund(IMC)가 생성되었으며, IMC가 spalling되는 현상이 나타났다. 반면에 Sn-0.75Cu-x의 경우에는 Cu6Sn5 IMC가 spalling 현상없이 발생되었다. 이는 솔더 내부의 Cu가 spalling 발생을 억제 했기 때문이다. 이러한 Cu의 spalling 발생 억제 효과로 인하여 Sn-0.75Cu-x 솔더합금이 Sn-x 솔더 합금보다 더 좋은 크리프 특성을 보여준다.
