Study on the electrical performance of Au bump in FC ceramic package

In traditional FC ceramic package, we mostly use the solder bump. But in high speed signal transmission FC package, the solder bump doesn't have good electrical performance as the signal frequency higher and higher, so we advise to use the Au bump instead of the solder bump, because of the Au bump has better electrical performance compared to the solder bump. For the same size of Au bump and solder bump, the Au bump has less resistance than the solder bump, so the Au bump has little parasitic effect in high speed signal transmission. In the signal transmission loss, the Au bump not only has low insertion loss but also has good ductility which is easy to be molded for transmission line impedance match, thus reduce the return loss in high speed signal transmission. In this paper, we built the Au bump model in package design software firstly, and then simulated the parasitic parameters, return loss and insertion loss respectively of the Au bump in EM simulation software. Lastly, we compared the return loss and insertion loss of the Au bump with the solder bump. From the simulation results, we can see that the insertion loss and return loss of Au bump and solder bump have no distinct difference when the signal frequency is below 5GHz. But when the signal frequency is above 5GHz, the solder bump has a distinct deteriorated on electrical performance, then the Au bump is still well. From this study, we can give a beneficial suggestion for the package design of high speed signal FC package device.