Low-Temperature Assembly of Surface-Mount Device on Flexible Substrate Using Additive Printing Process

Flexible substrates with printed electronics and surface-mount devices are being increasingly explored for various applications. For the assembly of surface-mount devices, conductive adhesives and films are being thought of as suitable alternatives to solder reflow assembly. However, such assemblies face many performance limitations particularly at high frequencies, and process limitations when the surface-mount devices are thin. This paper presents an innovative, low-temperature ink-to-ink fully-additive sintering process for surface-mount device assembly on a liquid crystal polymer (LCP) substrate with printed Ag pads. The printed ink is characterized using tape peel and button shear tests. Upon assembly of a surface-mount device, the strength of the device-to-substrate joint is assessed through a die shear test, and it is seen that the joint is stronger than the adhesion of the printed conductor to the flexible substrate. Thus, the proposed fully-additive assembly process appears to be a viable assembly method for attaching surface-mount devices on flexible substrates.