This　paper　made　a　review　of　the　kinds,　morphology　and　distribution　of　intermetallic　compound(IMC)　formed　in　the　bulk　solder　and　at　the　solder-pad　interface　during　reflow　soldering　of　components　and　printed　circuit　boards,　and　then　the　formation　or　evolution　of　them　was　investigated　after　aging.　The　effect　of　IMC　on　the　mechanical　properties　and　fracture　mechanism　of　the　joint　was　also　discussed　in　this　paper.　The　results　show　that　during　the　soldering,　the　kinds　of　IMCs　are　controlled　by　the　diffusion　rate　of　metals,　which　correspond　to　the　of　saturation　solubility　of　the　metals　in　the　eutectic　solder　alloys　and　thermodynamics　(Gibbs　energy　change)　and　diffusion　kinetics　of　the　new　formed　IMCs,　the　amount　of　Cu　in　SnAgCu　could　affect　the　compositions　of　IMCs　when　Ni　is　used　as　substrate;　the　morphology　of　IMC　is　related　to　the　heating　and　cooling　speed　during　reflow　soldering　and　the　temperature　gradient　at　the　solder　joint　interface,　also　related　to　the　content　of　Ag　for　Sn3.5Ag　or　SnAgCu　eutectic　solder,　large　plate　Ag3Sn　formed　easily　with　more　than　3.5%Ag;　the　distribution　of　IMC　depends　on　the　composition　of　solder　alloys　and　the　diffusion　rate　of　metallic　elements　in　the　solder　joint.　The　evolution　of　IMCs　or　the　formation　of　new　IMCs　during　aging　is　related　to　the　composition　of　the　solder　alloys　and　the　touch　pad,　welding　technique,　aging　temperature　and　time.　The　microstructures　of　solder　and　the　IMCs　formed　during　reflowing　trend　to　coarsen　commonly.　New　IMCs　will　be　formed　or　the　compositions　of　the　original　IMCs　will　change　with　the　diffusion　of　the　metallic　elements　such　as　Au,　Ag,　Cu,　Ni.　The　study　of　mechanical　properties　and　fracture　mechanism　of　the　solder　joint　shows　that　fracture　pattern　of　the　Pb-free　solders　is　mainly　the　interfacial　fracture.　The　high　Ag　low　Cu　solder　are　bad　for　the　mechanical　properties　of　soldering　joint,　and　high　reflow　temperature　and　slow　cooling　rate　is　also　bad　for　the　mechanical　properties　of　soldering　joint.　©2005　IEEE.