Effect of the loop forming process on the lifetime of aluminum heavy wire bonds under accelerated mechanical testing

• Published in: Microelectronics and reliability 2024-03, Vol.154, p.115337, Article 115337
• Main Authors: Felke, Florens, Groth, Anne, Hempel, Martin, Czerny, Bernhard, Khatibi, Golta, Döhler, Torsten, Geissler, Ute
• Format: Article
• Language: English
• Subjects: Aluminum heavy wire bonding; Heel crack; Loop forming process; Mechanical accelerated lifetime testing method; Wrinkling
• ISSN: 0026-2714; 1872-941X
• DOI: 10.1016/j.microrel.2024.115337

Heavy wire bonding is one of the most common interconnection technologies in manufacturing of high-power electronics. For industrial applications, the long-term reliability of these connections is crucial. Besides the selection of the wire material and the loop geometry itself, the loop forming process parameters also have an influence on the reliability of the wire bond. In this work, the influence of the backward bond head movement during wire bonding process on the quality of wire bond connections was systematically investigated and qualified by cyclic mechanical lifetime tests, surface roughness measurements of the heel area by laser confocal microscopy and static pull tests. The wire bond loops were fabricated with 300 μm aluminum H11 and H14CR wires with different hardness values. The lifetime at low frequency cycle and high frequency cycle regime was determined by means of two different mechanical cyclic test methods operating at 5 Hz and at 60 kHz respectively. The results have shown, that the surface topology of the heel region caused by the initial plastic deformation during the loop forming process has a significant effect on the wire bond failure due to heel cracking. The number of loading cycles to failure shows an inverse correlation with the degree of surface roughness in a so called wrinkling analysis in the low and high frequency cycle regime. The soft wire exhibits different lifetimes compared to the hard ones depending on the testing conditions, while a significant decrease of the lifetime is observed with >30 % reverse movement during bonding in all cases. [Display omitted] •Wrinkling in the heel of the wire bonds allows statements to be made on the lifetime.•A slight reverse movement in the loop forming process should not be exceeded.•BAMFIT and cycle test work in a fundamentally different way.•Quantification of the heel damage of wire bonds with surface roughness measurements•Softer wires achieve higher lifetime values in BAMFIT.