Transmission characteristics in GHz region at the conductive adhesive joints

Interconnection technology using conductive adhesives is generally used in place of solder interconnection. However, it is not clarified whether or not the conductive adhesive joints are adequate to high-speed signal transmission and power supply with large current, because there are not suitable methods for measuring and evaluating performance of the intended electrical function of an electronic system. In this study, to elucidate the feasibility of the conductive adhesive joint for high-speed signal transmission, transmission characteristics at the conductive adhesive joint were experimentally evaluated using a specially designed interconnection model which consists of a high-speed LSI, a BGA package, and a circuit board. In this model, there is eight conductive adhesive joints in daisy chain configuration, and the signal passes through repeatedly between the BGA package and the circuit board. Experimental results show that pulse signals can be transmitted without degradation at the pulse rate of 12 Gbps through eight conductive adhesive joints in daisy chain configuration, and that this joint has an ability to supply power in the condition of current switching rate, di/dt, of 24 mA/60 ps although the direct current resistance of the conductive adhesive joint is approximately 10 times higher than that of the conventional solder joints. This is considered to be probably caused by the compensation effect of capacitive coupling interference for higher DC resistance.