Adhesion and Reliability Studies Of The Heterogeneous Integration of Conductive LSR And Other Components On SiP For Bio-Sensing Applications

Healthcare with continuous bio-signal monitoring is one of the leading applications of wearable technology. More and more functions, such as Electrocardiography(ECG) and blood chemicals, are to trigger next waves of blooming demand in the wearable device market. We introduced world's first ECG biosensor in ear-tip in 2022 ECTC conference [1] by using conductive liquid silicone rubber (LSR) as molding material to form 3D flexible SiP structure as well as ECG sensor electrode. Conductive LSR(CLSR) is a promising material for such a purpose. However, ways to improve adhesion among heterogeneous parts and the reliability to the level of wearable usage are critical. In this paper, material properties of the LSR are explored, and it is found that the silicon based primer, when applied to the interface properly, can be a way to greatly improve adhesion between conductive LSR and several other materials commonly used in the system-in-package integration. In order to quantify the adhesion between silicone elastomers and other parts, ASTM D3330 pull-off test is proposed, performed, and result shown in this paper. In combination with reliability test, very positive results are obtained by using the primer for wearable user scenario. The insights to the material properties are keys to the selection and use of the primer. It is concluded the conductive LSR(CLSR) meet these needs of heterogeneous integration of SiP for bio-sensing applications of wearable devices