Joint reliability of Al wire bonding on OSP and ENIG surface-finished substrates under complex stress induced with current and temperature

• Published in: Journal of materials science. Materials in electronics 2022-09, Vol.33 (26), p.21127-21136
• Main Authors: Ahn, Byeongjin, Kim, Jahyeon, Cheon, Gyeong-Yeong, Lee, Tae-Ik, Park, Young-Bae, Kim, Jungsoo, Ko, Yong-Ho
• Format: Article
• Language: English
• Subjects: Aluminum; Bonded joints; Characterization and Evaluation of Materials; Chemistry and Materials Science; Circuit reliability; Copper; Electric currents; Electron probe microanalysis; Finishing; High temperature; Intermetallic compounds; Materials Science; Optical and Electronic Materials; Preservatives; Solderability; Substrates; Wire
• ISSN: 0957-4522; 1573-482X
• DOI: 10.1007/s10854-022-08917-z

In this study, we investigated the joint reliability of Al wires bonded on an Al-based metal printed circuit board with Cu pads that are finished using two finishing processes, i.e., organic solderability preservative (OSP) and electroless nickel/immersion gold (ENIG), during a complex stress test, which was performed by the simultaneous application of an electrical current density of 4 × 10 4  A/cm 2 and an elevated temperature of 175 °C. During the complex stress test, we evaluated the changes in electrical resistance at the wire joints to define the joint properties and lifetime of the wire bonding joints, such as the formation of intermetallic compounds (IMCs) and voids, which were also analyzed using scanning electron microscopy, energy-dispersive spectrometry, and electron probe microanalysis. Under the complex stress test, the joint lifetime of Al wires bonded on the ENIG-finished substrates was approximately three times higher than that on the OSP-finished substrates. Furthermore, Al 2 Cu IMCs, voids, and cracks, which cause degradation of joints, were observed on the OSP-finished substrate after only 100 h in the complex stress test; conversely, no such defects were observed on ENIG-finished substrates up to approximately 300 h. Therefore, we suggest that ENIG finishing is superior to OSP finishing for Al wire bonding joints that are exposed to complex stress in environments with both electrical currents and elevated temperatures.