High Speed SerDes Design on FOCoS with Thick RDL

Because copper thickness of redistribution layer (RDL) is thinner than normal substrate, the signal loss of fan out chip on substrate (FOCoS) is worse than flip chip ball grid array (FCBGA) for the same trace length. In this paper, FOCoS with different RDL thickness is studied. Will show RDL combines thick and thin copper thickness can effectively reduce RDL transmission loss. We also compare the high speed SerDes eye diagram of different RDL copper thickness. High speed SerDes signals with thicker RDL and thoughtful design can have better eye diagram performance than traditional design.