Sn　grain　orientation　in　solder　matrix　has　recently　been　considered　as　one　of　the　principal　failure　contributions　in　lead-free　solder　joints.　Since　beta-Sn　exhibits　high　anisotropy,　the　differences　of　electromigration　behavior　of　solder　joints　with　various　grain　orientations　are　dramatic.　With　different　angle　(theta)　between　the　c-axis　of　Sn　grain　and　the　direction　of　electron　flow,　the　solder　joints　often　demonstrate　varying　degrees　of　electromigration-induced　damage.　The　present　investigation　illustrated　significant　differences　in　microstructural　features　on　the　surface　of　Cu　reinforced　composite　solder　joints,　even　with　similar　angle　theta.　Two　Cu　particles　reinforced　Sn3.5Ag　composite　solder　joints　with　the　similar　angle　theta　of　35A　degrees　and　40A　degrees　were　selected　to　investigate　the　effects　of　Sn　grain　c-axis　on　electromigration　under　high　current　stressing　for　528　h.　A　large　number　of　Cu6Sn5　compounds　were　observed　and　occupied　nearly　the　whole　surface　with　clear　polarization　effect　in　one　sample.　In　contrast,　very　few　Cu6Sn5　were　found　on　the　surface　of　the　solder　matrix　in　the　other　sample　after　current　stressing,　and　the　Cu6Sn5　which　was　formed　after　reflow　disappeared　with　subsequent　current　stressing.　Even　though　polarization　effect　was　not　obvious,　and　the　cathode　interfacial　dissolution　was　observed　on　such　sample.　Systematic　study　revealed　that　the　angle　theta　alone　was　not　a　sole　factor　to　determine　the　electromigration　damage.　It　has　to　be　considered　along　with　the　coordinate　system　containing　the　orientation　of　the　c-axis　of　the　Sn　grain,　a　more　dominative　factor　for　the　diffusing　species.