Selecting Dielectric Substrates for High Speed Multilayer Stackup Design
Selecting dielectric substrates requires balancing dissipation factor, glass weave uniformity, foil roughness, and panel yields to meet high-speed impedance targets.
IPC-2221B Coupons
Test Geometry
Standardized copper patterns located on the edge of a production panel provide a way to verify the quality of the manufacturing process. The ipc-2221b coupons represent the features found on the actual circuit boards and undergo the same chemical treatments. These small sections are removed after fabrication.
They undergo destructive testing to ensure the batch meets the required specifications.
Design Compliance
Layout requirements include these patterns to meet international quality standards for rigid printed boards. An ipc-2221b coupons set includes specific shapes for checking trace width, hole registration, pad alignment and dielectric thickness. They act as a proxy for the internal structures of the board that cannot be inspected without damaging the finished product.
Confirming the quality of the coupon allows the laboratory to verify the entire panel. Detailed drawings specify the location of these patterns in the waste area of the production sheet.
Quality Verification
Certification of a production lot often depends on the successful passing of the tests performed on these representative samples. The ipc-2221b coupons are cross sectioned and examined under a microscope to measure the plating thickness inside the holes. They also provide a location for electrical testing to check for open circuits or shorts.
Systemic failure in the etching or drilling equipment is often identified this way. Results must be documented before the boards are released for assembly.