Glass based IDC sensor element for flex loads on MLCCs in PCB manufacturing chain

This paper presents a new in situ monitoring method of mechanical flex loads, which are acting on MLCC (multi-layer ceramic capacitors) devices in a PCB (printed circuit board) manufacturing chain. This method allows also considering solder joint properties as well. For this purpose a S³MD (stress sensitive surface mounted device) was designed as glass based package equivalent with strain sensitive pattern for a 0805 SMD chip device. Here, an interdigital capacitor was used as strain sensitive element. A solderable termination was created to enable the solder mounting. To obtain the load limits for different MLCC termination types, several bending tests were done in accordance to AEC Q200 Board Flex standard. In this case a suitable active measurement circuit was used with an overall accuracy of 4 fF and a noise level of 15 aF. Finally the characteristics of the sensor response, related to the AEC Q200 standard bending experiment, were determined. The use of such a S³MD instead of MLCC allows to record loads at several device locations during specific processes. This sensor can further be used as assessment criteria for process validation in the PCB manufacturing chain.