Composite　solders　were　prepared　by　mechanically　dispersing　different　volumes　of　nano-sized　Ag　particles　into　the　Sn-0.7Cu　eutectic　solder.　The　effects　of　Ag　particle　addition　on　the　microstructure　of　Sn-0.7Cu　solder　joints　were　investigated.　Besides,　the　effects　of　isothermal　aging　on　the　microstructural　evolution　in　the　interfacial　intermetallic　compound　(IMC)　layer　of　the　Sn-0.7Cu　solder　and　the　composite　solder　reinforced　with　1vol%　Ag　particles　were　analyzed,　respectively.　Experimental　results　indicate　that　the　growth　rate　of　the　interfacial　IMC　layer　in　the　Ag　particles　reinforced　composite　solder　joint　is　much　lower　than　that　in　the　Sn-0.7Cu　solder　joint　during　isothermal　aging.　The　Ag　particles　reinforced　composite　solder　joint　exhibits　much　lower　layer-growth　coefficient　for　the　growth　of　the　IMC　layer　than　the　corresponding　solder　joint.