A new review paper from Nanjing University, China and the China Electronics Technology Group Corporation will collate some of the very recent data on effect of alloying additions on properties and microstructures of SnAgCu solders. It is of particular interest because it discusses some of the extensive work done in China on addition of RE elements.

Rare earth (RE) elements such as Ce and La are abundant in China and new applications are strongly encouraged. They are known to improve properties of metals and indeed this has been demonstrated in lead-free solders.

Research on RE addition has now started to be published in Europe and the US. There is still some doubt as to whether they can alone give sufficient improvement to properties for all applications and a recent paper from Beijing University has suggested that they may cause tin whiskers.

The paper also discusses Zn addition and its ability to reduce undercooling and suppress Ag3n platelet formation.

Improvement to wettability by addition of Bi and Ga, as well as Ni, are discussed.

The roles of Co, Fe and Ge are described.

The paper will be published in the Microelectronic Engineering journal and is available online on the reference link below.