Evaluation of the use of a rubber buffer layer to protect embedded SIP devices from high mechanical forces

Smart objects - objects that can sense and communicate - are the underpinning components of smart environments and the emerging Internet of Things. Smart objects demand the permanent embedding of electronic systems in the objects. An example might be the embedding of a stress sensing system in a structural beam. Such embedding typically requires a system-in-a-package (SIP) approach to capture maximum functionality in a minimum volume. Such embedded systems may often be exposed to high mechanical stresses and impacts. In this paper, we present the use of a rubber buffer layer to protect embedded SIP devices from high mechanical forces. The approach is to, first, encapsulate the SIP using standard epoxy encapsulant, then to further encapsulate with a rubber buffer material and to, finally, encapsulate for a third time using standard epoxy encapsulant. The buffer material examined in this paper is a medium-stiffness rubber that absorbs stress imposed on the external epoxy layer encapsulant so that the stress transmitted to the embedded SIP is significantly reduced, particularly after optimizing the layer dimensions and buffer rubber material properties. Using both simulations and measurements, it is demonstrated that the strain on the core SIP can be reduced by as much as 84% with a relatively thin layer of buffer material.