Selecting Impedance Pin Connector Class for Medical-Grade Printed Circuit Boards
In the world of electronics, the International Printed Circuits Association (IPC) sets the standards for printed circuit board (PCB) manufacturing quality. For medical devices, where reliability is paramount, the choice between IPC Class 2 and Class 3 PCBs becomes crucial.
IPC establishes PCB classes, with higher classes indicating higher quality standards. The IPC Class 3 PCBs are used in high-reliability electronic parts, including medical applications. On the other hand, Class 2 PCBs are more commonly found in general electronic products such as cameras and smartphones.
When it comes to medical device flexible PCBs, the specific IPC standards for copper plating and surface finish coating voids are primarily covered under IPC-6012 and IPC-2220 series.
IPC-6012 specifies quality requirements including minimum copper plating thickness, annular ring width, and dielectric thickness. It mandates strict control for defects such as voids, cracks, and plating thicknesses to avoid reliability issues like shorts or opens.
IPC-2220 series pertains to design rules including test coupons for cross-sectioning which is used to inspect plating quality and voids.
Class 3 boards demand the highest quality and reliability. Imperfections such as voids, cracks, or plating defects are not acceptable. Even small visual defects or voids in plating can cause failure in inspection. In contrast, Class 2 boards allow minor visual defects and small voids that do not affect electrical or mechanical performance.
Plating thickness and quality must comply with IPC requirements to ensure sufficient copper coverage and no voids inside vias or through-holes, critical for durability in high-reliability medical flex PCBs. Via aspect ratios should conform to guidelines (e.g., 10:1 for through holes) to prevent plating defects.
While the documentation does not provide explicit IPC limits on voids for surface finish coatings, it does imply that voids or cracks in surface finish coatings that compromise barrier functions or solderability would be unacceptable, especially in Class 3.
Flex PCB surface finish guidelines for class 3 boards prohibit more than one void per hole, 5% of holes having voids, and voids not exceeding 5% of the hole length. For Class 2 boards, three voids per hole are acceptable, but all other requirements remain the same.
In summary, for medical device flexible PCBs, Class 3 standards per IPC-6012 and IPC-2220 series require that copper plating and surface finishes be free of voids or defects to ensure reliability and pass inspections, while Class 2 may allow minor voids that do not impact functionality.
For more detailed information, the IPC Class 3 Design Guide and the Flex PCB Design Guide provide valuable resources for manufacturers and designers. The IPC Class 3 Design Guide covers IPC guidelines for manufacturing defects, IPC standards for assembly processes, common differences between the classes, and IPC documents to set the level of acceptance criteria. The Flex PCB Design Guide includes topics such as calculating the bend radius, annular ring and via specifications, building a flex stack-up, controlled impedance for flex, fab and drawing requirements, and more.
In the realm of medical device flexible PCBs, the IPC-6012 and IPC-2220 series set stringent standards for copper plating and surface finishes, particularly for Class 3 boards, where voids or defects are strictly prohibited to maintain reliability and pass inspections. On the other hand, Class 2 boards may tolerate minor voids that do not impair functionality.
