Purpose　This　study　aims　to　analyse　the　changes　in　the　microstructure　and　grain　orientation　of　the　full　Cu3Sn　solder　joint　(Cu/Cu3Sn/Cu)　during　isothermal　aging　at　420　degrees　C.　Design/methodology/approach　The　Cu3Sn　solder　joint　was　fabricated　through　soldering　Cu/Sn/Cu　structure　and　then　aged　at　420　degrees　C.　The　microstructure　evolution　and　grain　orientation　were　studied　by　observing　the　cross-section　and　top-view　surfaces　of　solder　joints.　Findings　Original　Cu3Sn　solder　joint　initially　transformed　into　the　full　Cu(41)Sn(11)solder　joint　(Cu/Cu41Sn11/Cu)　at　10　h　and　finally　into　the　full　alpha(Cu)　solder　joint　(Cu/alpha(Cu)/Cu)　at　150　h　during　aging.　Micro-voids　formed　in　the　center　of　the　solder　joint　interface　during　the　conversion　of　Cu(41)Sn(11)to　alpha(Cu),　resulting　in　lower　reliability　of　the　solder　joint.　Cu3Sn　and　Cu41Sn11　grains　presented　a　column-like　shape,　while　alpha(Cu)　presented　an　irregular　shape.　The　average　grain　sizes　of　interfacial　phases　first　increased　and　then　decreased　during　aging.　Original　Cu3Sn　solder　joint　exhibited　two　main　textures:　[100]//TD　and　[203]//TD.　For　Cu41Sn11,　the　preferred　orientation　of　[111]//TD　was　found　in　the　early　nucleation　stage,　while　the　orientation　of　the　formed　full　Cu41Sn11　solder　joint　was　dispersed.　Furthermore,　alpha(Cu)　grains　exhibited　{100}　preferred　orientation.　Originality/value　Few　researchers　focused　on　the　process　of　microstructure　and　grain　orientation　changes　during　high-temperature　(＞　300　degrees　C)　aging　of　Cu3Sn　solder　joint.　To　bridge　the　research　gap,　a　high-temperature　aging　experiment　was　conducted　on　Cu3Sn　solder　joints.