Impact of Laser Welding on Assembly of Printed Circuit Boards in Medical Devices

Reusable medical devices play a crucial role in healthcare, but their reliability hinges on robust assembly processes. Their failure during usage can be catastrophic. These devices face aggressive sterilization procedures, exposure to harsh chemicals, and extreme temperature fluctuations. Assembling printed circuit boards (PCBs) into mechanical subsystems introduces subtle failure mechanisms that often elude traditional manufacturing quality control processes. Unfortunately, these latent defects become more pronounced during device usage or storage, exacerbated by thermal variations, vibrations, and mechanical shocks. The need to seal, hermetically or otherwise, for medical devices stems from their use in repeated surgeries. Biohazard safety requires that the medical instruments are capable of being functionally connected to the surgical system to perform its primary purpose, while at the same time remain internally isolated from the environment that they are operating in. This becomes particularly relevant due to the need for sterilization and cleaning procedures to allow their use in multiple surgeries. When an electronic assembly in a medical device like an edge card or connector, which is needed to be available and accessible outside the sealed region to contact the rest of the surgical system, it faces the issue of defining and controlling an ‘exposed’ area which contains the edge card fingers', while isolating the rest of the electronics in a hermetic or sealed zone. The interface region for such a transition is often sealed with a combination of soldering, epoxy sealing and welding. When applying welding as a sealing approach in combination with the other approaches, the relative movements, and expansions of the dissimilar materials lead to unexpected failure modes and effects. This paper aims to address the challenges associated with laser welding during PCB assembly in medical devices. We investigate process variations in laser welding and discuss how these factors exacerbate underlying defects. By analyzing failure modes and conducting thorough failure analysis, we provide insights into mitigating these vulnerabilities. The findings are particularly relevant for industries where the robustness of printed circuit assemblies (PCAs) directly influences device performance and patient safety.