Heat and mass transfer effects of laser soldering on growth behavior of interfacial intermetallic compounds in Sn/Cu and Sn-3.5Ag0.5/Cu joints. (January 2018)

• Record Type: Journal Article
• Authors: Kunwar, Anil; Shang, Shengyan; Råback, Peter; Wang, Yunpeng; Givernaud, Julien; Chen, Jun; Ma, Haitao; Song, Xueguan; Zhao, Ning
• Is Part Of: Microelectronics and reliability. Volume 80(2018)
• Page Start: 55
• Page End: 67
• Publication Date: 2018-01
• Subjects: Enthalpy -- Finite element method -- Intermetallic compound -- Laser soldering -- Diffusion -- Scan speed; Electronic apparatus and appliances -- Reliability -- Periodicals; Miniature electronic equipment -- Periodicals; Appareils électroniques -- Fiabilité -- Périodiques; Équipement électronique miniaturisé -- Périodiques; Electronic apparatus and appliances -- Reliability; Miniature electronic equipment; Periodicals; 621.3815
• DOI: 10.1016/j.microrel.2017.11.016
• Languages: English
• ISSNs: 0026-2714

Abstract

Abstract: The magnitudes of input power and scan speed of laser heat source can affect the morphology and size of interfacial Cu6 Sn5 intermetallic compound (IMC) formed or grown in Sn/Cu and Sn-3.5Ag-0.5Cu/Cu (SAC/Cu) joints. Experimentally, it has been observed that greater power and smaller scan speed can create temperature field of higher magnitude, thereby enhancing the interfacial reaction. The occurrence of conglomerated, prismatic (faceted) and scalloped IMC morphologies in the specimens corresponding to designated laser processing parameters, has been explained with the help of Jackson parameter. The heat and mass transfer phenomena during laser soldering, is modeled using finite element analysis. Enthalpy method is applied in the FEM based computational model to describe the phase change based heat transfer at the melting regime of the solder. With an attainment of transient temperature profiles at several scan speeds through the numerical analysis, the values of interfacial reaction temperature at solder/substrate interface and diffusion phenomenon based mass transfer of Cu into solder are then utilized to explain the experimental results of IMC size. In comparison to pure Sn solder, SAC solder type is characterized with the formation of thicker IMC at laser power of 50 W and scan speeds below 180 mm/min. Graphical Abstract: Highlights: Laser soldering is performed for Sn-3.5Ag-0.5Cu/ Cu and Sn/Cu joints at varying scan speeds and laser input power. Interfacial Cu6 Sn5 intermetallic compounds (IMC) is characterized by prismatic, scalloped and conglomerated morphologies for both solder types. The thickness of IMC decreases with increase in scan speed and lowering the power. At input power of 50 W, the IMC corresponding to SAC alloy is thicker than that of Sn solder for all values of scan speed below 180 mm/min. Enthalpy method based numerical model has been implemented in FEM to compute the transient temperature in solder.