{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,6]],"date-time":"2026-10-06T04:52:59Z","timestamp":1791262379228,"version":"4.1.0"},"reference-count":23,"publisher":"MDPI AG","issue":"19","license":[{"start":{"date-parts":[[2026,10,3]],"date-time":"2026-10-03T00:00:00Z","timestamp":1790985600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"National Science and Technology Council of Taiwan","award":["114-2221-E-194-001"],"award-info":[{"award-number":["114-2221-E-194-001"]}],"id":[{"id":"https:\/\/ror.org\/02kv4zf79","id-type":"ROR","asserted-by":"crossref"}]},{"award":["114-2221-E-194-001"],"award-info":[{"award-number":["114-2221-E-194-001"]}],"id":[{"id":"https:\/\/ror.org\/02kv4zf79","id-type":"ROR","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Materials"],"abstract":"<jats:p>Ag is widely used as a surface-finish material in electronic packaging, while Sn\u2013Zn is a representative lead-free solder system. This study investigates the interfacial reactions and microstructural evolution in Sn\u2013Zn\/Ag\/Cu couples during solid-state aging at 170 \u00b0C. Unlike the conventional approach, in which Ag is electroplated onto Cu substrates followed by reflow soldering, Ag (~2.0 \u03bcm) and Cu (~50 \u03bcm) layers were sequentially electroplated onto three Sn\u2013Zn solders containing 1, 3, and 9 wt.%Zn. By eliminating the reflow process, the Ag layer remained at the interface, allowing the reactions to proceed in the Sn\u2013Zn\/Ag\/Cu couples and preserving the sequential interactions among these elements. The effects of Zn concentration on interfacial phase evolution, elemental diffusion, and reaction mechanisms were systematically investigated. For the Sn\u20131Zn and Sn\u20133Zn couples, Ag3Sn preferentially formed near the solder\/Ag interface during the early stage, accompanied by Ag5Zn8 in the inner reaction region. With prolonged aging, the Ag\u2013Zn phases were progressively redistributed into the solder, while the reaction at the Cu side evolved from Cu5Zn8 to CuZn, and eventually to Cu6Sn5 as Zn was progressively depleted. In contrast, the Sn\u20139Zn couple exhibited a distinct reaction pathway, initially dominated by Ag5Zn8, AgZn3, and Cu5Zn8, with no continuous Ag3Sn layer detected. The higher initial Zn content provided a greater supply of Zn for interfacial reactions, leading to substantial Zn consumption and accelerating the transition from Cu\u2013Zn to Cu\u2013Sn reactions, with localized Cu consumption and subsequent Cu6Sn5 formation. Comparison with the Sn\u2013Zn\/Ag couples, in which AgZn was formed, further demonstrated that the limited Ag supply from the thin Ag layer in the Ag\/Cu couples favored Ag5Zn8 formation and promoted the continuous redistribution of Ag into the solder.<\/jats:p>","DOI":"10.3390\/ma19194217","type":"journal-article","created":{"date-parts":[[2026,10,5]],"date-time":"2026-10-05T10:02:27Z","timestamp":1791194547000},"page":"4217","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Microstructural Evolution in Solid-State Sn\u2013Zn\/Ag\/Cu Interfacial Reactions at 170 \u00b0C"],"prefix":"10.3390","volume":"19","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-4137-5584","authenticated-orcid":false,"given":"Chao-Hong","family":"Wang","sequence":"first","affiliation":[{"name":"Department of Chemical Engineering, National Chung Cheng University, Chiayi 621301, Taiwan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Chu-An","family":"Li","sequence":"additional","affiliation":[{"name":"Department of Chemical Engineering, National Chung Cheng University, Chiayi 621301, Taiwan"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,10,3]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"6400","DOI":"10.1016\/j.jmrt.2023.11.123","article-title":"Effect of Ag addition on the microstructure and corrosion properties of Sn\u20139Zn lead-free solder","volume":"27","author":"Pu","year":"2023","journal-title":"J. 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Perform."}],"container-title":["Materials"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1996-1944\/19\/19\/4217\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,10,6]],"date-time":"2026-10-06T04:17:51Z","timestamp":1791260271000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1996-1944\/19\/19\/4217"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,10,3]]},"references-count":23,"journal-issue":{"issue":"19","published-online":{"date-parts":[[2026,10]]}},"alternative-id":["ma19194217"],"URL":"https:\/\/doi.org\/10.3390\/ma19194217","relation":{},"ISSN":["1996-1944"],"issn-type":[{"value":"1996-1944","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,10,3]]}}}