Degradation of Sn-Ag-Cu heat-sink attachment during thermal shock cycling

• Published in: Soldering & surface mount technology Vol. 17; no. 4; pp. 10 - 16
• Main Authors: Chang, Junling, Janz, Dirk, Kempe, W, Xie, Xiaoming
• Format: Journal Article
• Language: English
• Published: Bradford Emerald Group Publishing Limited 01.01.2005; Emerald
• Subjects: Acoustics; Applied sciences; Crack propagation; Design. Technologies. Operation analysis. Testing; Electronics; Exact sciences and technology; Experiments; Fatigue failure; Heat; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Integrated circuits; Interfaces; Intermetallic compounds; Investigations; Lead content; Metal fatigue; Physics; Product reliability; Propagation; Scanning electron microscopy; Scanning probe microscopes, components and techniques; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Soldering; Solder; Fatigue; Failure (mechanical); Soldering; Product reliability; Scanning electron microscopy; Thermal management (packaging); X ray microscopy; Intermetallic compound; Thermal cycle; Durability; Solder metal; Integrated circuit bonding; Scanning microscope; Energy dispersion; Acoustic microscopy; Thermal shock; Soldered joint; Cooling system; Lead free soldering; Void; Reliability; Scanning mode; Delamination; Heat sink; Damaging
• DOI: 10.1108/09540910510630386
• ISSN: 0954-0911

Purpose - To investigate the degradation of lead free solder heat-sink attachment by thermal shock. Samples with high voiding percentages were selected for the investigation in order to get information on the significance of voids on the reliability of Sn-Ag-Cu heat-sink attachment.Design methodology approach - Through the use of X-ray, C-mode scanning acoustic microscopy, dye penetration, cross section and scanning electron microscopy energy-dispersive X-ray tests, the degradation of Sn-Ag-Cu heat-sink attachment during thermal shock cycling was evaluated.Findings - The results showed that the Sn-Ag-Cu heat-sink attachment where the area of voiding was 33-48 per cent survived 3,000 thermal shock cycles, although degraded. The main degradation mechanism for the solder attachment was not solder fatigue but interface delamination due to Kirkendall voids at the Cu Cu3Sn interface. It was found that the large voids in the Sn-Ag-Cu heat-sink attachment were not significantly affecting the solder joint lifetime. Big differences of intermetallic compound growth behaviour and Kirkendall voids at device solder and solder Cu pad interfaces are found and the reasons for this are discussed.Originality value - This work has clarified the general perception that large voids affect the thermo-mechanical lifetime of solder joint substantially and also provides further understanding of the Sn-Ag-Cu heat-sink attachment degradation mechanism.