Low Temperature Solder Interconnection of Surface Mount Devices with Additively Printed Pads on Flexible Substrate

Printed electronics are rapidly increasing and competing against the traditional way of manufacturing electronics. Different aspects of the processes are already being taken over that avoids material wastage, reduces cost and lead times. For example, printing technologies are very popular in depositing reliable and very fine conductive traces as opposed to conventional etching. Previously, authors have developed process studies by utilizing Aerosol Jet Printing technology in realizing multi-layer metallization with successive metal and dielectric layers and additively printing a donut micro-via. However, the merits of printing technologies do not stop here. Recently, assembly of Surface Mount Devices (SMD) on a flexible substrate has been of interest that requires low processing temperatures. Conventionally, this is done by components mounted on a solder paste and reflowing to about 220 °C. This temperature is extremely high and induces many reliability concerns. With the use of printing technologies, this can be avoided. A viable method would be to utilize low temperature solder for which the peak reflow temperature could be much lower than 220 °C. Nevertheless, with new methods, there comes new complications. For example, reliability concerns involving the interconnection joints between SMD and substrate. Since this is to be done additively, another concern comes about the printer's capability to dispense the solder paste as well as the metal conductive pad simultaneously. Having to additively print conductive pad, and screen print the solder brings about much manual work and just not feasible. In this work, authors have utilized state-of-art micro-dispense additive printer to dispense the metal conductive ink and the Low Temperature Solder (LTS) for SMD attachment. Process studies are done that addresses the physical profile of the low temperature solder for various print parameters. Multiple SMDs such as resistors, capacitors, and Inductors are mounted with semi-automatic pick-and-place machine. The reflow will still be done but at a lower temperature. Process development of additive part of the assembly will be done, along with the characterization of physical, electrical and mechanical properties.