Thermal Cycle Testing of Printed Circuit Board Vias (Barrel Plates)

Printed circuit board (PCB) reliability is a very important factor from the point of total quality of output products. The ambient environment has influence on the reliability of PCBs and various issues can appear during its lifetime, even if the PCB properly passes the quality control before and after its assembly. This article deals with reliability test - monitoring of resistance behavior of the printed circuit board vias (barrel plates) during thermal stress (shock test). Appropriate printed circuit boards have been designed for this purpose. PCB sample was double-sided, vias were connected serially and PCB design allowed the use of four wire measurement method for measuring of all vias at once. The temperature sensor Pt100 was attached onto the PCB for better temperature monitoring of PCB during shock test. The shock test cycle took 20 minutes, the temperature of hot zone was set to 160°C and the temperature of cool zone was -60°C. The experiments help in understanding the barrel plate behavior during thermal stress, when the thermal expansion of composite substrate (glass-epoxy laminate) cause force (Young's modules), which stretches the barrel plate from the middle outwards. The identification of faulty vias is not easy during ambient temperature, it is easier when a measurement is conducted during thermal cycling or when the PCB is heated.