Through-Silicon-Vias　(TSV)　for　3D　integration　are　susceptible　to　mechanical　failures　such　as　TSV　extrusion,　chip　cracking,　and　carrier　mobility　change,　mainly　due　to　significant　thermal　mismatch　between　electroplating　copper　and　silicon　wafer.　Assessing　TSV　reliability　requires　accurate　mechanical　properties　of　electroplating　Cu,　which　may　not　be　achieved　by　traditional　testing　methods　for　large-size　samples.　Alternatively,　nanoindentation　can　be　used　as　a　versatile　and　non-destructive　technique　to　obtain　material　properties　at　micro-scale　or　nan-scale.　The　technique,　however,　is　sensitive　to　experimental　data　variation　and　may　yield　non-unique　properties,　which　is　not　yet　fully　understood　for　TSV-Cu　and　other　packaging　materials.　This　paper　reports　the　results　and　analysis　of　in-situ　nanoindentation　for　TSV-Cu　specimens.　Each　specimen　has　a　diameter　of　20　um　and　a　depth　of　180　um,　fabricated　on　a　200-mm　silicon　wafer.　The　relationship　of　power-law　hardening　was　used　to　characterize　the　mechanical　behaviors　of　TSV-Cu　with　Young＇s　modulus　(E),　yielding　strength　(Y),　and　strain　hardening　exponent　(n).　To　extract　these　properties,　two　methods　of　so-called　reverse　analysis　were　applied　to　experimental　test　data.　Finite　element　models　were　also　built　to　reproduce　the　displacementloading　curve　based　on　the　extracted　material　properties.　The　following　results　were　observed:　1)　with　very　different　yield　strength　and　hardening　coefficient,　identical　load-displacement　curves　were　produced.　This　indicates　that　single　indentation　testing　cannot　provide　unique　material　properties　for　TSV-Cu;　2)　the　loading-displacement　curves　vary　with　the　locations　of　the　specimens,　possibly　due　to　the　effect　of　grain　size　on　nanoindentation,　or　experimental　＂errors＂;　3)　the　plastic　properties　can　vary　dramatically　with　a　slight　change　in　the　loading-displacement　curve.　This　implies　the　sensitivity　of　extracted　properties　on　experimental　data　variations.　Generally,　the　non-uniqueness　and　sensitivity　due　to　experimental　data　variations　of　nanoindentation　testing　are　not　independent.　This　study　concludes　that　single　nanoindentation　testing　itself　may　not　be　able　to　adequately　and　uniquely　determine　the　material　properties　of　TSV-Cu.　To　make　the　best　use　of　the　nanoindentation　technique,　a　robust　methodology　is　needed　to　minimize　the　sensitivity　to　experimental　errors　and　analysis.