The　void　defect　in　intermetallic　compounds　(IMCs)　layer　at　the　joints　caused　by　inhomogeneous　atomic　diffusion　is　one　of　the　most　important　factors　limiting　the　further　development　of　Sn-based　solders.　In　this　work,　the　thermodynamic　stability　of　IMCs　(high-temperature　η-Cu6Sn5　and　o-Cu3Sn　phases)　was　improved　by　adding　small　amounts　of　indium　(In),　and　the　IMCs　layers　with　moderate　thickness,　low　defect　concentrations　and　stable　interface　bonding　were　successfully　obtained.　The　formation　order　of　compounds　and　the　interfacial　orientation　relationships　in　IMCs　layers,　the　atomic　diffusion　mechanism,　and　the　growth　tuning　mechanism　of　In　on　η-Cu6Sn5　and　Cu3Sn,　after　In　adding,　were　discussed　comprehensively　by　combining　calculations　and　experiments.　It　is　the　first　time　that　the　classic　heterogeneous　nucleation　theory　and　CALPHAD　data　were　used　to　obtain　the　critical　nucleus　radius　of　η-Cu6Sn5　and　Cu3Sn,　and　to　explain　in　detail　the　main　factors　affecting　the　formation　order　and　location　of　IMCs　at　joints　during　the　welding　process.　A　novel　and　systematic　growth　model　about　IMCs　layers　in　the　case　of　doping　with　alloying　elements　was　proposed.　The　growth　tuning　mechanism　of　In　doping　on　η-Cu6Sn5　and　Cu3Sn　was　further　clarified　based　on　the　proposed　model　using　first-principles　calculations.　The　growth　model　used　in　this　study　can　provide　insights　into　the　development　and　design　of　multielement　Sn-based　solders.　©　2023