Since　Pb-containing　electronic　products　were　banned　in　2006,　the　predominant　substitute　for　Sn-Pb　solder　was　hypoeutectic　Sn3.0Ag0.5Cu　(SAC305),　which　has　been　extensively　utilized　in　contemporary.　In　recent　years,　there　has　been　a　surge　in　interest　towards　Sn-based　lead-free　composite　solder　because　of　their　exceptional　mechanical　properties　and　service　performance.　Carbon-based　particles,　as　a　reinforcing　material,　exhibit　commendable　mechanical　and　chemical　stability,　high　strength,　temperature　resistance,　and　other　superior　properties.　Numerous　researchers　have　utilized　nickel　as　a　coating　agent　to　enhance　the　interfacial　compatibility　between　carbon-based　materials　and　Sn　matrix.　In　this　work,　we　examined　the　impact　of　nickel-coated　graphite　(GR@Ni)　and　nickel-coated　carbon　fiber　(CF@Ni)　on　the　microstructure　and　properties　of　SAC305　solder.　The　findings　revealed　that　the　GR@Ni　tended　to　rise　to　the　surface　of　the　solder　owing　to　a　density　mismatch　with　the　Sn　matrix,　thereby　leading　to　a　heterogeneous　microstructure.　The　microstructure　of　the　micro-bump　was　found　to　contain　Ni-Sn　intermetallic　compounds　(IMC),　which　led　to　an　enhancement　in　the　hardness　of　the　Sn　matrix　by　refining　the　eutectic　Ag3Sn　network.　In　contrast,　CF@Ni　was　uniformly　distributed　within　the　micro-bump,　resulting　in　a　reduction　of　similar　to　30%　in　the　interfacial　IMC　thickness　and　an　increase　in　hardness　in　the　CF@Ni　composite　solder.　However,　it　was　observed　that　the　incorporation　of　CF@Ni　exceeding　4　wt.%　resulted　in　an　increase　in　the　thickness　of　interfacial　IMC　and　a　sharp　decrease　in　hardness　due　to　the　presence　of　residual　flux-induced　pores.　Therefore,　it　is　recommended　to　limit　the　additional　amount　of　CF@Ni　to　within　the　range　of　0　similar　to　3　wt.%.