With　a　body-centered　tetragonal　crystal　structure,　Sn　grains　were　demonstrated　to　have　highly　anisotropic　behaviors　in　various　properties.　The　electromigration　behavior　of　lead-free　solder　was　impacted　by　the　grain　orientations.　In　this　paper,　the　angle　between　the　c-axis　and　the　electron　flow　direction　in　composite　solder　joints　(angle　theta)　was　proven　to　be　an　important　factor　during　electromigration.　The　effects　of　angle　theta　on　the　electromigration　of　composite　solder　joints　were　investigated　in　this　paper.　Cu　particle-reinforced　Sn3.5Ag　solder　joints　were　stressed　under　a　current　density　of　10(4)　A/cm(2)　at　room　temperature.　After　336　h　current　stressing　time,　different　electromigration　phenomena　occurred　at　the　two　sides　of　the　grain　boundary　in　the　composite　solder　joint　which　contained　two　Sn　grains　with　different　angle　theta.　The　Sn　grains　with　the　larger　angle　theta　had　a　smaller　growth　rate　of　Cu6Sn5.　In　addition,　a　composite　solder　joint　with　a　single　Sn　grain　was　set　as　the　contrast　and　its　angle　theta　was　smaller　than　that　of　the　composite　solder　joint　with　two　Sn　grains.　The　growth　rate　of　Cu6Sn5　in　the　composite　solder　joint　with　a　single　grain　was　faster　than　that　of　the　composite　solder　joint　with　two　Sn　grains.