The　voids　induced　by　electromigration　(EM)　can　trigger　serious　failure　across　the　entire　cathode　interface　of　solder　joints.　In　this　study,　alloying　and　composite　approaches　showed　great　potential　for　inhibiting　EM　in　lead-free　solder　joints.　Microsized　Ni,　Co,　and　Sb　particles　were　added　to　the　solder　matrix.　Cu　and　Sn　particles　were　added　to　the　melting　solder　to　form　in　situ　Cu6Sn5,　which　formed　a　barrier　layer　in　the　underbump　metallization　of　flip-chip　solder　joints.　The　polarity　effect　induced　by　EM　was　observed　to　be　significantly　inhibited　in　the　alloyed　and　composite　solder　joints.　This　indicates　that　the　Sn-Ni,　Sn-Co,　Sn-Sb,　and　Cu6Sn5　intermetallic　compounds　may　act　as　barriers　to　obstruct　the　movement　of　the　dominant　diffusion　species　along　phase　boundaries,　which　in　turn　improves　the　resistance　to　EM.　However,　Sb　particles　could　induce　crack　formation　and　propagation　that　might　lead　to　joint　fracture.