Design, Fabrication and Measurement of Micro-Bumps Array for RF Application

In recent years, radio frequency (RF) systems have been moving towards miniaturization. Traditional wire-bonding technology used in RF systems have significant disadvantages in terms of parametric inductance and package size scaling-down. Therefore, people pay more attention to the high-performance and small-size interconnection schemes of RF systems. In this regard, we designed a series of micro bumps arrays for RF application, including arrays with diameters of 15 μm / 30 μm / 40 μm and a pitch of 30 μm / 60 μm / 80 μm. To study RF property of micro bumps array, Cu / Sn micro bumps arrays jointed double-layer coplanar waveguide (CPW) structures were prepared and tested. By subtracting the insertion loss of CPW line from the test structure's insertion loss, the insertion loss of the micro bumps array can be obtained. Comparing the insertion loss of micro bumps arrays with different diameters, the insertion loss of the micro-bumps array with a diameter of 15 μm is the smallest, and the micro bumps with multiple rows have lower insertion loss than a single micro bump. Among them, the insertion loss of a 3 × 6 micro bumps array with a diameter of 15 μm after bonding is 0.15 dB@40GHz.