In　this　work,　a　novel　composite　solder　was　fabricated　by　mechanically　incorporating　Ni-coated　carbon　fiber　(NiCF)　into　the　Sn-3.5Ag　solder　paste　in　an　effort　to　improve　the　overall　service　capability,　where　the　intermetallic　compound　(IMC)　formation　and　growth　is　a　fundamental　issue　for　consideration.　General　findings　indicated　that　the　addition　of　Ni-CF　did　not　significantly　impact　the　processing　properties　of　the　base　alloy,　such　as　melting　temperature　and　wettability,　when　the　reinforcement　fraction　was　less　than　2　wt%.　Isothermal　aging　tests　were　carried　out　to　study　the　formation　and　growth　of　interfacial　IMC　layers　between　the　composite　solder　and　Cu　substrate.　The　addition　of　Ni-CF　into　Sn-3.5Ag　solder　could　effectively　promote　the　formation　of　interfacial　(Cu,　Ni)(6)Sn-5　phase　during　reflow　but　retard　its　growth　in　the　solid-state　aging.　The　addition　of　1　wt%　Ni-CF　was　believed　to　be　more　effective　to　restrict　and　reduce　the　subsequent　growth　rate　of　the　IMCs　during　solid-state　aging　due　to　the　initial　formation　of　a　thicker　(Cu,　Ni)(6)Sn-5　layer　after　reflow.