Printed Circuit Design & Fab Online Magazine

Designer’s Notebook

John Burkhert, Jr. Effective PCB testing depends on balancing electrical validation with manufacturable design practices throughout product development.

“Don’t get testy with me.” People might say those words when they’re annoyed by a challenging statement. The point of testing is to challenge assumptions. It’s the “find out” phase of product development. Printed circuit boards benefit from testing at multiple stages of production. Let’s dive into the deep end.

Read more: Printed Circuit Board Design for Test

John Burkhert, Jr. Connector selection and footprint design require careful DfM consideration, as tolerances, spacing and assembly constraints directly impact manufacturability and performance.

When it comes to interconnects for printed circuit boards, I found one vendor with 25,217 options. A specialty vendor offered only about 9,000 different connector SKUs. Luckily, connector selection can typically be narrowed by pin count, pitch and other key parameters.

Read more: A Guide to PCB Connectors: Selection, Design and DfM Tips

John Burkhert, Jr. In PCB fabrication drawings, the nominal value gets the spotlight, but the tolerances decide what actually ships.

When it comes to coloring in the fabrication drawing, the way we provide the data creates the space the fabricator must fill. For each datapoint, there is a least material condition (LMC), a maximum material condition (MMC) and a nominal. Process variation is permitted between the two extremes and rejected when it is outside the envelope.

Read more: Tolerances and Dimensions for PCB Fabrication

John Burkhert, Jr. As PCB designs grow more complex, partitioning and teamwork become part of the layout strategy.

Printed circuit board design grows in complexity with each passing year. Many protocols must be implemented. An ASIC (application-specific integrated circuit) or an FPGA (field-programmable gate array) may be the center of attention, but there will likely be a memory bus along with other architectures, such as ethernet or USB, to move data around. Interacting with the world around us requires some sort of sensor to read the room, while other circuits are used to feed this processed data back to the user.

Read more: Splitting a PCB for Concurrent Design