Study on the electrical performance of one differential pair bonding fingers on different layers in wire bonding package

Traditional, the bonding fingers of one differential pair should be on the same bonding layer for bonding wire package. But in practical design, the engineer of chip design has to put a differential pair pads separately on the inner edge and outer edge of the die because kinds of difficulties. In this case, the bonding fingers of the differential pair have to be put on different bonding layers. So it is necessary to study on if the differential pair can meet the electrical performance need when the signal transmission. In this paper, we built the differential pair model in package design software firstly, and then simulated the parasitic parameters, return loss and insertion loss respectively of the differential pair in EM simulation software. Lastly, we compared the return loss and insertion loss of the differential pair bonding fingers on different bonding layers with that on the same layer. From the results, we can find that they have the same well electrical performance below the 2GHz frequency. But when the signal frequency is above 2GHz, the differential pair bonding finger on different layers has a distinct deteriorated on electrical performance and can't meet the signal transport need. However, the differential bonding fingers on the same layer is still well in the whole analysis frequency band. From this study, we can get an obvious design rule about the differential pair routing. Meanwhile, it also has very good meaning for the chip design engineers when they design the differential signal pads.