Optimizing solder joints on biodegradable PCBs with vapour phase soldering

The paper focuses on biodegradable Printed Circuit Boards (PCB) from the aspect of PCB fabrication technology and soldering. Different biodegradable Cellulose Acetate (CA) PCBs were used during the tests (one sided and two sided), and the possible application of pre-preg was also taken into account to improve pad adhesion on the base material. The surfaces of the boards were evaluated in order to obtain information about copper adhesion. FR4 test boards were also investigated as a reference, both for soldering and surface analyses. The soldering profile setup was focused on minimizing high temperatures on the heat-sensitive biopolymer substrates. The soldering profiles were created with a custom vapour phase soldering (VPS) device. The customized solder profile setting is conducted with an adaptive temperature-tracker sample holder. The boards and the solder joints were investigated with non-destructive optical microscopy, X-ray microscopy (deformation and joint analysis), and destructive shear tests. The results are promising for future application of biodegradable PCBs.