PERFORMANCE EVALUATION OF GOLD (Au) WIRE AND RIBBON INTERCONNECTS IN HIGH FREQUENCY CIRCUITS

Abstract

Abstract Gold (Au) wires and ribbons are widely being used in military and space applications of high frequency RF/microwave circuits. The purpose of this study is to examine the RF performance of different dimensions of Au wires & ribbons, which are typically bonded in cascade and parallel forms in the circuits operating microwave frequencies within 0–50 GHz. The second goal of this study is to establish a performance chart/handbook of Au wires, ribbons for high frequency circuit designers in order to show them which type of wire or ribbon as well as which type of interconnect form is suitable for their intended design. First, the test circuit board is manufactured by using chip & wire, epoxy attach method. The substrate material of used RF circuit materials is chosen as Alumina to minimize losses and the material of wires, ribbons are chosen as %99.99 pure Gold (Au). Au plated copper traces are used as conductive layers for optimal reliability and conductivity in the test circuit board. Automated thermosonic ball bonders are used for Au round wire bonds to reduce process errors. Manual parallel gap resistance welders and manual thermosonic wedge bonders are used for Au ribbons and always pay great attention to form the same length by using high magnification microscopes. The experiment conducted with the help of 0.7 mil, 1 mil round wires and 3×0.5 mil, 3×1 mil, 5×0.5 mil, 7×1 mil and 10×1 mil ribbons. Single bonds, parallel double bonds as well as V-type bonds, stitch over ball bonds are performed onto the circuit pads as interconnect types and forms. The RF tests (S11 return losses and S21 insertion loss) we performed showed that 0.7 mil and 1 mil round wires can be used in the frequency range of 0–20 GHz circuits. A better RF test result can be achieved if double parallel bonding method is used. For higher frequency range, 20 to 50 GHz, 3×0.5 mil, 3×1 mil, 7×1 mil and 10×1 mil ribbons should be used. On the other hand, the bare chip bonding pads and dimensions of transmission line conductive layer bond pads are limiting the usage of desired ribbon. Last but not least, a performance chart of RF wire/ribbon interconnects including a suggestion of bonding method with sustainable current load and shape is generated for design and application engineers who are dealing with high performance circuit efficiency.