Design and optimization of redistribution layer (RDL) on TSV interposer for high frequency applications

The fabrication of redistribution layer (RDL) for TSV 3D integration and its optimization are presented in this paper. BCB is selected as the passivation layer and the electroplated Cu is used as the metal layer. CYCLOTENE 3024-46 is utilized and it is deposited by spin-coating and soft cure at 210 °C in annealing oven for 40 minutes with N₂ protection. Sputtered Ti/W/Cu and electron beam evaporated Ti/Cu on BCB have shown good adhesion. Daisy chain of the two metal layers and double layer of CPW are fabricated. The RDL of MSL and CPW are simulated by Ansoft HFSS. In condition of folded shape of RDL, multilayer of folded RDL gives the better performance than that of single layer and even has lower attenuation than straight line by optimization. Multilayer of RDL can also offset the insertion loss brought by TSV and has lower return loss. Multilayer of RDL with increasing width of metal line gradually from bottom to top is good for signal transmission and system reliability.