PCB Fiducial Design Guide A pcb fiducial is a small mark on the board that exists purely so that a camera can find it. The placement machine measures the mark, compares its position with the programmed position, and shifts the whole placement program to match. Without the mark, the machine…

Moisture Sensitivity Level Management In Assembly Plastic packages absorb water from the air. Once that water is inside the moulding compound and the reflow oven brings the whole package above the boiling point of water in a few seconds, the vapour has nowhere to go and the package can crack…

Test Point Design Guide A test point is a piece of copper that exists only so that a machine or a person can touch the circuit. It takes no part in the function of the product, it costs area on every layer it passes through, and it is the difference…

Crosstalk Measurement and Eye Diagram Testing Methods Two traces running side by side are coupled, whether the designer intended it or not. Energy from one appears on the other, and at high data rates that coupling closes the eye, adds jitter and eventually causes errors. Crosstalk and eye diagram measurements…

Popcorning during Reflow: Causes and Prevention A board that looks perfect after reflow can still be internally damaged. Trapped moisture turns to steam during the thermal excursion, and the resulting pressure separates layers or cracks a plastic package from the inside. Popcorning during reflow is one of the few defects…

Analog Digital Partitioning and Ground Strategy on Mixed Boards Analog and digital circuits share a board happily as long as they are not allowed to share return currents. Most mixed signal problems are not caused by the analog signal itself but by the reference it is measured against, which has…

Development Board Layout for Application Processor Modules A development board exists to make a processor usable before the final product exists. It must expose interfaces, tolerate mistakes and stay flexible enough to support experiments that were not planned when it was designed. That brief is different from a production board,…

Multicore Processor Board Layout for Embedded Systems A multicore processor board looks like a single core board with more pins, and that assumption is what makes the first prototypes misbehave. Several cores running at once change the current profile, the thermal load and the way peripherals contend for memory, so…

RF Board Fabrication Control for Repeatable Performance A microwave board can pass every electrical check in the design office and still miss its performance target after fabrication. The difference between a simulation and a finished board comes from tolerances that matter little at low frequency but dominate at gigahertz: line…

Pcb Panelization: Design Rules and Process Limits PCB panelization is the step where a single board becomes a production panel. The panel is what the pick and place machine handles, what the printer clamps and what the assembly line moves from station to station. A panel that is designed only…