More　extensive　application　of　electronic　products　lead　electronic　packaging　trend　to　be　miniaturization　and　multi-functional.　With　prohibiting　of　solder　containing　SnPb,　lead-free　solder　now　has　been　widely　utilized.　However,　there　are　still　a　plenty　of　reliability　issues　exist　in　it　such　as　high　melting　point,　poor　wettability,　more　apparent　electromigration　effect　and　heat　transfer　effect.　Thus,　it　is　necessary　to　find　comprehensive　approach　to　improve　the　overall　performance　of　lead-free　solders.　Besides,　the　volumes　of　solders　at　the　electrical　interconnects　have　been　limited　to　be　microscopic　level　due　to　the　miniaturisation　of　circuitry　proportionally　while　the　volume　fraction　of　intermetallic　compounds　(IMCs)　was　increased　in　the　microstructure　of　solder　joints.　Such　as,　the　proportion　of　IMCs　in　a　solder　continually　increases　while　the　electronic　packaging　size　decreased,　which　could　deteriorate　the　solder　reliability.　Adding　reinforced　particle　is　one　of　effective　ways　to　improve　the　performance　of　solder　joints.　POSS,　a　kind　of　reinforced　particles　with　Si-O　cage　structure,　could　be　a　good　connection　with　metal　atoms,　highly　dispersed　distribution　in　the　solder,　effectively　hinder　dislocation　motion.　However,　the　influence　of　POSS　on　IMCs　structure　was　rarely　considered.　In　this　paper,　the　effects　of　POSS　reinforcing　particles　on　IMCs　microstructure　and　crystal　orientation　evolution　were　inversitgated　during　the　interfacial　reactions　between　Sn-3.5Ag　solders　and　Cu　substrates.　The　growth　and　solidification　are　considered　during　the　experiment　by　blocking　the　melting　solder　from　natural　cooling　or　controlling　the　melting　parameters　to　distinguish　the　enhancment　effect　of　POSS.　To　explore　the　true　effect　of　POSS,　no　addition　solder　group　is　set　with　respective　melting　condition　all　the　same　but　not　adding　reinforcing　particles.　As　the　result　shows,　adding　reinforcing　particle　like　POSS　into　Sn3.5Ag　makes　scalloped　Cu6Sn5　achieve　planarization,　which　results　from　that　the　average　thickness　of　the　intermetallic　compounds　was　significantly　suppressed　by　the　reinforcing　particles.　During　the　growth　behavior,　as　soldering　takes　longer　time,　Cu　diffuses　more　inside　of　solder　and　reacted　more　entirely　with　Sn,　resulting　in　interfacial　IMC　size　becomes　larger.　POSS　reinforcing　particles　inhibit　Ag　from　diffusing,　resulting　in　the　inhibition　of　Ag3Sn　formulation.　POSS　inhibits　Cu　from　diffusing　inside　of　solder,　blocking　Cu6Sn5　growing　into　solder,　and　POSS　makes　scalloped　Cu　more　level　and　smooth,　decreasing　interfacial　energy　of　Cu6Sn5.　Cu6Sn5　is　growing　in　the　process　of　solidification,　and　once　solder　added　POSS　its　Cu6Sn5　will　be　limited　from　growing　into　the　insider　of　solder,　which　decreases　the　interfacial　surface　energy　of　Cu6Sn5.　Besides,　POSS　makes　interfacial　IMC　more　level　and　smooth,　which　increases　the　strength　of　solder　and　Cu　connections　and　reduce　the　possibility　of　crack　at　interfacial　surface　in　solder,　improving　the　performance　of　solder.