Taking　the　most　promising　substitute　of　the　Sn-3.8Ag-0.7Cu　solder　as　the　research　base,　investigations　were　made　to　explore　the　effect　of　rare　earths　(REs)　on　the　creep　performance　of　the　Sn-3.8Ag-0.7Cu　solder　joints.　The　SnAgCu-0.1RE　solder　with　the　longest　creep-rupture　life　was　selected　for　subsequent　research.　Creep　strain　tests　were　conducted　on　Sn-3.8Ag-0.7Cu　and　SnAgCu-0.1RE　solder　joints　in　the　intermediate　temperature　range　from　298　K　to　398　K,　corresponding　to　the　homologous　temperatures　eta　=　0.606,　0.687,　0.748,　and　0.809　and　eta　=　0.602,　0.683,　0.743,　and　0.804,　respectively,　to　acquire　the　relevant　creep　parameters,　such　as　stress　exponent　and　activation　energy,　which　characterize　the　creep　mechanisms.　The　final　creep　constitutive　equations　for　Sn-3.8Ag-0.7Cu　and　SnAgCu-0.1RE　solder　joints　were　established,　demonstrating　the　dependence　of　steady-state　creep　rate　on　stress　and　temperature.　By　correcting　the　apparent　creep-activation　energy　of　Sn-3.8Ag-0.7Cu　and　SnAgCu-0.1RE　solder　joints　from　the　experiments,　the　true　creep-activation　energy　is　obtained.　Results　indicated　that　at　low　stress,　the　true　creep-activation　energy　of　Sn-3.8g-0.7Cu　and　SnAgCu-0.1RE　solder　joints　is　close　to　the　lattice　self-diffusion　activation　energy,　so　the　steady-state　creep　rates　of　these　two　solder　joints　are　both　dominated　by　the　rate　of　lattice　self-diffusion.　While　at　high　stress,　the　true　creep-activation　energy　of　Sn-3.8Ag-0.7Cu　and　SnAgCu-0.1RE　solder　joints　is　close　to　the　dislocation-pipe　diffusion　activation　energy,　so　the　steady-state　creep　rates　are　dominated　by　the　rate　of　dislocation-pipe　diffusion.　At　low　stress,　the　best-fit　stress　exponents　n　of　Sn-3.8Ag-0.7Cu　and　SnAgCu-0.1RE　solder　joints　are　6.9　and　8.2,　respectively,　and　the　true　creep-activation　energy　of　them　both　is　close　to　that　of　lattice　self-diffusion.　At　high　stress,　it　equals　11.6　and　14.6　for　Sn-3.8Ag-0.7Cu　and　SnAgCu-0.1RE　solder　joints,　respectively,　and　the　true　creep-activation　energy　for　both　is　close　to　that　of　the　dislocation-pipe　diffusion.　Thus,　under　the　condition　of　the　experimental　temperatures　and　stresses,　the　dislocation　climbing　mechanism　serves　as　the　controlling　mechanism　for　creep　deformation　of　Sn-3.8Ag-0.7Cu　and　SnAgCu-0.1RE　solder　joints.　The　creep　values　of　Sn-3.8Ag-0.7Cu　and　SnAgCu-0.1RE　solder　joints　are　both　controlled　by　dislocation　climbing.　Dislocation　glide　and　climb　both　contribute　to　creep　deformation,　but　the　controlling　mechanism　is　dislocation　climb.　At　low　stress,　dislocation　climbing　is　dominated　by　the　lattice　self-diffusion　process　in　the　Sn　matrix　and　dominated　by　the　dislocation-pipe　diffusion　process　at　high　stress.