Liquid/solid and solid/solid reactions between SnAgCu lead-free solders and Ni surface finish
Journal
4th International Symposium on Electronic Materials and Packaging 2002
Pages
330-334
ISBN
078037682X
9780780376823
Date Issued
2002
Author(s)
Luo W.-C.
Abstract
The SnAgCu series of solders are the most promising lead-free candidates to replace the Pb-Sn solders. The Ni metallization is one of the most common surface finishes for the electronic packages. During soldering (a liquid/solid reaction), the reaction between SnAgCu solders and Ni strongly depended on the Cu concentration. When the Cu concentration /spl les/ 0.2wt.%, only a continuous (Ni/sub 1-x/Cu/sub x/)/sub 3/Sn/sub 4/ layer formed at the interface. When the Cu concentration's 0.6 wt.%, (Ni/sub 1-x/Cu/sub x/)/sub 3/Sn/sub 4/ disappeared, and only (Cu/sub 1-y/Ni/sub y/)/sub 6/Sn/sub 5/ was present. After soldering, samples were subjected to several different temperatures isothermal aging (a solid/solid reaction) for time as long as 1000 hours. When the reaction time was 200 hours at 180/spl deg/C, it was surprising found that a discontinuous (Cu/sub 1-y/Ni/sub y/)/sub 6/Sn/sub 5/ intermetallic particles formed over the (Ni/sub 1-x/Cu/sub x/)/sub 3/Sn/sub 4/ layer in the solid/solid reaction between Sn3.9Ag0.2Cu and Ni. At higher Cu concentration (/spl ges/0.6 wt.%), (Ni/sub 1-x/Cu/sub x/)/sub 3/Sn/sub 4/ disappeared, and only (Cu/sub 1-y/Ni/sub y/)/sub 6/Sn/sub 5/ was present. It showed that the initial difference in the intermetallic compounds right after reflow can be aged out at high temperatures.
Publisher
Institute of Electrical and Electronics Engineers Inc.
Type
conference paper