{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,30]],"date-time":"2026-07-30T17:48:04Z","timestamp":1785433684162,"version":"3.56.0"},"reference-count":26,"publisher":"MDPI AG","issue":"14","license":[{"start":{"date-parts":[[2026,7,22]],"date-time":"2026-07-22T00:00:00Z","timestamp":1784678400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100003052","name":"Ministry of Trade, Industry and Energy","doi-asserted-by":"publisher","award":["RS-2025-22812972"],"award-info":[{"award-number":["RS-2025-22812972"]}],"id":[{"id":"10.13039\/501100003052","id-type":"DOI","asserted-by":"publisher"}]},{"award":["RS-2025-22812972"],"award-info":[{"award-number":["RS-2025-22812972"]}],"id":[{"id":"https:\/\/ror.org\/008nkqk13","id-type":"ROR","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Materials"],"abstract":"<jats:p>The interfacial microstructure evolution and high-speed ball shear reliability of SAC305 (Sn-3.0Ag-0.5Cu)\/Cu-20wt%Zn solder joints were systematically investigated after isothermal aging at 180 \u00b0C for up to 250 h. SAC305\/electroless nickel immersion gold (ENIG) joints were used as a comparative reference. Unlike prior studies that benchmarked Cu-Zn against bare Cu, this work directly compares the two systems, establishing ENIG as the industrially relevant reference. Cu6(Sn,Zn)5 was identified as the dominant intermetallic compound (IMC) phase at the SAC305\/Cu-Zn interface by SEM\/EDS analysis. At the SAC305\/ENIG interface, (Cu,Ni)6Sn5 formed as the dominant IMC phase, accompanied by a P-rich layer at the (Cu,Ni)6Sn5\/Ni(P) boundary. The IMC thickness of SAC305\/Cu-Zn joints increased from approximately 2.50 \u03bcm in the as-reflowed condition to 3.41 \u03bcm at 250 h, consistently exceeding that of SAC305\/ENIG joints (1.94\u20132.25 \u03bcm) throughout aging. Despite this, the high-speed ball shear strength of SAC305\/Cu-Zn joints was equivalent or superior to that of SAC305\/ENIG joints at all aging durations. Fractographic analysis confirmed that the P-rich layer in ENIG joints acted as a preferential crack propagation path under impact loading, driving the brittle fracture ratio to approximately 75% at 250 h\u2014compared to approximately 47% in SAC305\/Cu-Zn joints. These results demonstrate that Cu-Zn electroplated from a neutral pyrophosphate-based bath constitutes a highly reliable wetting layer, offering impact reliability equivalent or superior to that of the conventional ENIG surface finish.<\/jats:p>","DOI":"10.3390\/ma19143138","type":"journal-article","created":{"date-parts":[[2026,7,22]],"date-time":"2026-07-22T09:20:39Z","timestamp":1784712039000},"page":"3138","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Interfacial Microstructure Evolution and High-Speed Ball Shear Fracture of SAC305\/Cu-20wt%Zn Solder Joints Under Isothermal Aging"],"prefix":"10.3390","volume":"19","author":[{"given":"Jae-Yong","family":"Park","sequence":"first","affiliation":[{"name":"Division of Materials Science & Engineering, Hanyang University, Seoul 133-791, Republic of Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7036-6188","authenticated-orcid":false,"given":"Sehoon","family":"Yoo","sequence":"additional","affiliation":[{"name":"Advanced Packaging Integration Center (APIC), Korea Institute of Industrial Technology, Incheon 406-840, Republic of Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,7,22]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"4724","DOI":"10.1007\/s10854-017-8426-9","article-title":"Comparative Study of ENEPIG and Thin ENEPIG as Surface Finishes for SAC305 Solder Joints","volume":"29","author":"Yoon","year":"2018","journal-title":"J. Mater. Sci. Mater. Electron."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"4457","DOI":"10.1007\/s11664-014-3395-8","article-title":"Effect of Bath Life of Ni(P) on the Brittle-Fracture Behavior of Sn-3.0Ag-0.5Cu\/ENIG","volume":"43","author":"Seo","year":"2014","journal-title":"J. Electron. Mater."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"119","DOI":"10.4071\/1551-4897-6.2.119","article-title":"IMC Growth Mechanisms of SAC305 Lead-Free Solder on Different Surface Finishes and Their Effects on Solder Joint Reliability of FCBGA Packages","volume":"6","author":"Kim","year":"2009","journal-title":"J. Microelectron. Electron. Packag."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"129","DOI":"10.1007\/s10854-022-09510-0","article-title":"Interfacial Microstructure and Brittle Fracture Behavior of Sn-Based Solder on Novel Nickel-Less DEG and EPIG Surface Finishes","volume":"34","author":"Lee","year":"2023","journal-title":"J. Mater. Sci. Mater. Electron."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"527","DOI":"10.1007\/s11664-007-0360-9","article-title":"Origin of Surface Defects in PCB Final Finishes by the Electroless Nickel Immersion Gold Process","volume":"37","author":"Kim","year":"2008","journal-title":"J. Electron. Mater."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"1262","DOI":"10.1007\/s11664-001-0159-z","article-title":"Electroless Ni\/Immersion Au Interconnects: Investigation of Black Pad in Wire Bonds and Solder Joints","volume":"30","author":"Snugovsky","year":"2001","journal-title":"J. Electron. Mater."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"182","DOI":"10.1109\/TADVP.2007.914962","article-title":"Surface Finish Effects on High-Speed Signal Degradation","volume":"31","author":"Wu","year":"2008","journal-title":"IEEE Trans. Adv. Packag."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"121","DOI":"10.4071\/imaps.1227802","article-title":"Reliable Nickel-Free Surface Finish Solution for High-Frequency, HDI PCB Applications","volume":"17","author":"Shah","year":"2020","journal-title":"J. Microelectron. Electron. Packag."},{"key":"ref_9","doi-asserted-by":"crossref","unstructured":"Kim, Y.M., Oh, C.Y., Roh, H.R., and Kim, Y.H. (2009, January 26\u201329). A New Cu-Zn Solder Wetting Layer for Improved Impact Reliability. Proceedings of the 2009 59th Electronic Components and Technology Conference, San Diego, CA, USA.","DOI":"10.1109\/ECTC.2009.5074135"},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Kim, Y.M., and Kim, Y.H. (2008, January 22\u201324). Drop Impact Reliability of Cu-Zn\/Sn-Ag-Cu\/Cu-Zn Solder Joints. Proceedings of the 2008 10th International Conference on Electronic Materials and Packaging, EMAP, Taipei, Taiwan.","DOI":"10.1109\/EMAP.2008.4784272"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"2627","DOI":"10.1007\/s11664-010-1349-3","article-title":"Microstructural Variation and Phase Evolution in the Reaction of Sn-XAg-Cu Solders and Cu-YZn Substrates during Reflow","volume":"39","author":"Yu","year":"2010","journal-title":"J. Electron. Mater."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"176","DOI":"10.1016\/j.jallcom.2011.09.024","article-title":"Intermetallic Compound Growth Suppression at High Temperature in SAC Solders with Zn Addition on Cu and Ni-P Substrates","volume":"511","author":"Kotadia","year":"2012","journal-title":"J. Alloys Compd."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"5916","DOI":"10.1007\/s10854-016-4510-9","article-title":"Effect of Zn Concentration on the Interfacial Reactions between Sn\u20133.0Ag\u20130.5Cu Solder and Electroplated Cu\u2013XZn Wetting Layers (x = 0\u201343 wt%)","volume":"27","author":"Park","year":"2016","journal-title":"J. Mater. Sci. Mater. Electron."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"778","DOI":"10.1007\/s10854-024-12558-9","article-title":"Exploring Mechanism of Suppressing Void Formation at Interface of Sn\u20139Zn and Cu","volume":"35","author":"Shen","year":"2024","journal-title":"J. Mater. Sci. Mater. Electron."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"2504","DOI":"10.1007\/s11664-010-1379-x","article-title":"Kinetics of Intermetallic Compound Formation at the Interface Between Sn-3.0Ag-0.5Cu Solder and Cu-Zn Alloy Substrates","volume":"39","author":"Kim","year":"2010","journal-title":"J. Electron. Mater."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"230","DOI":"10.1007\/s11664-009-0992-z","article-title":"Interfacial Reaction of Sn and Cu-xZn Substrates After Reflow and Thermal Aging","volume":"39","author":"Yu","year":"2010","journal-title":"J. Electron. Mater."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"5852","DOI":"10.1007\/s10854-015-3153-6","article-title":"Improved Drop Reliability of Sn\u2013Ag\u2013Cu Solder Joints by Zn Addition to a Cu Wetting Layer","volume":"26","author":"Park","year":"2015","journal-title":"J. Mater. Sci. Mater. Electron."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"134659","DOI":"10.1016\/j.matlet.2023.134659","article-title":"Cu Aggregation Behavior on Interfacial Reaction of Sn-3.0Ag-0.5Cu\/ENIG Solder Joints","volume":"348","author":"Sun","year":"2023","journal-title":"Mater. Lett."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"122","DOI":"10.1016\/j.jallcom.2004.12.009","article-title":"Interfacial Reactions between Sn-0.4Cu Solder and Cu Substrate with or without ENIG Plating Layer during Reflow Reaction","volume":"396","author":"Yoon","year":"2005","journal-title":"J. Alloys Compd."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"6467","DOI":"10.1007\/s10853-012-6581-1","article-title":"Growth Mechanisms of Interfacial Intermetallic Compounds in Sn\/Cu\u2014Zn Solder Joints during Aging","volume":"47","author":"Yu","year":"2012","journal-title":"J. Mater. Sci."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"9741","DOI":"10.1007\/s10853-020-05702-3","article-title":"A First-Principles Computation-Driven Mechanism Study on the Solders Dilute Doping Effects to g\u2019-Cu6Sn5 Growth Kinetics","volume":"56","author":"Wang","year":"2021","journal-title":"J. Mater. Sci."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"502","DOI":"10.1007\/s11663-018-1456-8","article-title":"Experimental Determination of the Sn-Cu-Ni Phase Diagram for Pb-Free Solder Applications","volume":"50","author":"Henao","year":"2019","journal-title":"Metall. Mater. Trans. B Process Metall. Mater. Process. Sci."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"343","DOI":"10.1007\/BF02692455","article-title":"Phase Distribution and Phase Analysis in Cu6Sn5, Ni3Sn4, and the Sn-Rich Corner in the Ternary Sn-Cu-Ni Isotherm at 240 \u00b0C","volume":"35","author":"Li","year":"2006","journal-title":"J. Electron. Mater."},{"key":"ref_24","unstructured":"Tee, T.Y., Luan, J.E., Pek, E., Lim, C.T., and Zhong, Z. (2004, January 4). Advanced Experimental and Simulation Techniques for Analysis of Dynamic Responses during Drop Impact. Proceedings of the 54th Electronic Components and Technology Conference, Las Vegas, NV, USA."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"449","DOI":"10.1109\/TCAPT.2006.880455","article-title":"Advanced Numerical and Experimental Techniques for Analysis of Dynamic Responses and Solder Joint Reliability during Drop Impact","volume":"29","author":"Luan","year":"2006","journal-title":"IEEE Trans. Compon. Packag. Technol."},{"key":"ref_26","unstructured":"Zeng, K., Stierman, R., Abbott, D., and Murtuza, M. (June, January 30). Root Cause of Black Pad Failure of Solder Joints with Electroless Nickel\/Immersion Gold Plating. Proceedings of the Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITHERM), San Diego, CA, USA."}],"container-title":["Materials"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1996-1944\/19\/14\/3138\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,7,22]],"date-time":"2026-07-22T09:26:39Z","timestamp":1784712399000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1996-1944\/19\/14\/3138"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,7,22]]},"references-count":26,"journal-issue":{"issue":"14","published-online":{"date-parts":[[2026,7]]}},"alternative-id":["ma19143138"],"URL":"https:\/\/doi.org\/10.3390\/ma19143138","relation":{},"ISSN":["1996-1944"],"issn-type":[{"value":"1996-1944","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,7,22]]}}}