Purpose　This　study　aims　to　analyze　the　shear　strength　and　fracture　mechanism　of　full　Cu-Sn　IMCs　joints　with　different　Cu3Sn　proportion　and　joints　with　the　conventional　interfacial　structure　in　electronic　packaging.　Design/methodology/approach　The　Cu-Sn　IMCs　joints　with　different　Cu3Sn　proportion　were　fabricated　through　soldering　Cu-6　mu　m　Sn-Cu　sandwich　structure　under　the　extended　soldering　time　and　suitable　pressure.　The　joints　of　conventional　interfacial　structure　were　fabricated　through　soldering　Cu-100　mu　m　Sn-Cu　sandwich　structure.　After　the　shear　test　was　conducted,　the　fracture　mechanism　of　different　joints　was　studied　through　observing　the　cross-sectional　fracture　morphology　and　top-view　fracture　morphology　of　sheared　joints.　Findings　The　strength　of　joints　with　the　conventional　interfacial　structure　was　26.6　MPa,　while　the　strength　of　full　Cu-Sn　IMCs　joints　with　46.7,　60.6,　76.7　and　100　per　cent　Cu3Sn　was,　respectively,　33.5,　39.7,　45.7　and　57.9　MPa.　The　detailed　reason　for　the　strength　of　joints　showing　such　regularity　was　proposed.　For　the　joint　of　conventional　interfacial　structure,　the　microvoids　accumulation　fracture　happened　within　the　Sn　solder.　However,　for　the　full　Cu-Sn　IMCs　joint　with　46.7　per　cent　Cu3Sn,　the　cleavage　fracture　happened　within　the　Cu6Sn5.　As　the　Cu3Sn　proportion　increased　to　60.6　per　cent,　the　inter-granular　fracture,　which　resulted　in　the　interfacial　delamination　of　Cu3Sn　and　Cu6Sn5,　occurred　along　the　Cu3Sn/Cu6Sn5　interface,　while　the　cleavage　fracture　happened　within　the　Cu6Sn5.　Then,　with　the　Cu3Sn　proportion　increasing　to　76.7　per　cent,　the　cleavage　fracture　happened　within　the　Cu6Sn5,　while　the　transgranular　fracture　happened　within　the　Cu3Sn.　The　inter-granular　fracture,　which　led　to　the　interfacial　delamination　of　Cu3Sn　and　Cu,　happened　along　the　Cu/Cu3Sn　interface.　For　the　full　Cu3Sn　joint,　the　cleavage　fracture　happened　within　the　Cu3Sn.　Originality/value　The　shear　strength　and　fracture　mechanism　of　full　Cu-Sn　IMCs　joints　was　systematically　studied.　A　direct　comparison　regarding　the　shear　strength　and　fracture　mechanism　between　the　full　Cu-Sn　IMCs　joints　and　joints　with　the　conventional　interfacial　structure　was　conducted.