Least lead addition to mitigate tin whisker for ambient storage

• Published in: Journal of materials science. Materials in electronics Vol. 24; no. 8; pp. 3108 - 3115
• Main Authors: Jo, Jung-Lae, Kim, Keun-Soo, Sugahara, Tohru, Nagao, Shijo, Hamasaki, Kyoko, Tsujimoto, Masanobu, Suganuma, Katsuaki
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01.08.2013; Springer; Springer Nature B.V
• Subjects: Applied sciences; Characterization and Evaluation of Materials; Chemistry and Materials Science; Columnar structure; Cross-disciplinary physics: materials science; rheology; Electrical engineering. Electrical power engineering; Electrodeposition, electroplating; Electronics; Electroplating; Exact sciences and technology; Grain boundaries; Grains; Lead (metal); Materials; Materials Science; Methods of deposition of films and coatings; film growth and epitaxy; Optical and Electronic Materials; Other heat and thermomechanical treatments; Physics; Surface layer; Texture; Tin; Treatment of materials and its effects on microstructure and properties; Lead Addition; Hillock Growth; Room Temperature Storage; Hillock Formation; Whisker Growth; Lead addition; Doped materials; Equiaxed structure; Grain boundary migration; Precipitate; Long term; Texture; Composite material; Columnar structure; Whisker; Grain boundary; Microelectronic fabrication; Stress relaxation; Internal stress; Plating; Electrodeposition; Room temperature
• ISSN: 0957-4522; 1573-482X
• DOI: 10.1007/s10854-013-1218-y

Long term surface evolution of matte tin electroplating has been investigated under room temperature to understand the tin whisker mitigation by a trace amount of lead addition. No whisker growth has been observed on all the Sn– x Pb samples (1 ≤  x  ≤ 10 wt%), while at least 3 wt% of Pb addition is required to alter the columnar grain structure of pure Sn plating to equiaxed grains. The mitigation mechanism by such a trace amount of Pb is not caused by the grain texture control, but is due to the less inter-metallic composite (IMC) growth; the segregated Pb at the columnar grain boundaries disrupts the IMC growth, and releases Sn grain boundary migrations to relax the internal stress. This mechanism of stress relaxation and whisker growth suppression suggests that lead-free Sn plating without whisker growth can be realized by co-plating Sn with a Pb-like metal element that precipitates at the grain boundary to interfere with the IMC growth.