Lightweight　carbon　fibers　with　high　mechanical　performance　are　referred　to　as　an　ideal　reinforcement　for　an　extensive　variety　of　composite　materials.　However,　the　addition　of　carbon　fibers　into　electronic　interconnection　solders　is　extremely　limited　so　that　the　expected　reinforcement　in　the　mechanical　properties　of　the　composite　solder　joints　has　not　been　completely　realized.　Here,　we　used　magnetic　fields　to　align　Ni-coated　carbon　fibers　in　the　Sn-3.0Ag-0.5Cu　solder　vertically　with　the　Cu　substrate　and　prepared　the　oriented　composite　solder　joints.　We　achieved　a　further　improvement　in　the　shear　performance　of　composite　solder　joints　(∼58　MPa)　with　a　small　addition　of　Ni-coated　carbon　fibers　(0.5　wt%),　which　is　25%　higher　than　that　of　pristine　joints.　It　is　found　that　these　vertically　oriented　carbon　fibers　changed　the　propagation　path　of　shear　cracks　and　thus　increased　the　shear　resistance.　Ni-coated　carbon　fibers　also　promoted　nucleation　of　interfacial　Cu6Sn5　in　the　solder　joints　during　reflow,　but　prevented　the　formation　of　brittle　Cu3Sn　phase　during　isothermal　aging,　thus　ensuring　the　high　shear　strength　of　composite　solder　joints　after　isothermal　aging.　This　success　provides　a　new　pathway　to　fabricate　a　strong　composite　solder　joint　with　a　limited　addition　of　reinforcements　by　aligning　their　orientation.　©　2024　Elsevier　B.V.