Impedance Matching in PCB Design: Why It Matters Impedance is easy to ignore on a slow board and impossible to ignore on a fast one. When the rise time of a signal becomes comparable with the time it takes to travel along a trace, the trace stops behaving like a…

Board Level Vibration Testing: Fixture Design and Failure Modes Vibration testing of a populated board is where mechanical design, material choice and soldering quality meet. A test can be run in a few hours, yet the result depends almost entirely on how the board was held, how the excitation was…

EMC Pre-Compliance Testing Before the Accredited Lab The accredited test house reports whether the product passes. The pre-compliance work in the company’s own facility is what determines whether it passes on the first visit, and it costs a fraction of a repeat test. What Pre-Compliance Achieves It finds the large…

Radiated Emission Troubleshooting: Finding the Source A product that fails a radiated emission limit has one or more current loops that are acting as antennas. Finding which loop is the work, and the tools for it are cheap. Start With the Cables In most products that fail, the emission comes…

Humidity Sensor: Design Rules and Process Limits Humidity is one of the harder environmental quantities to measure, because the sensing element is in direct contact with the air and therefore with everything the air carries. Dust, chemical vapours and condensation all affect the reading, and a sensor that is accurate…

Thermal Simulation: Copper, Airflow and Junction Temperature A thermal simulation predicts the temperature of a component from its dissipation and its surroundings. Where the prediction is wrong, the usual cause is one of three inputs: the copper, the airflow or the interface. What the Simulation Needs The dissipation of each…

Battery Charging and Management on a Board A battery charger is a power converter with a measurement problem attached. It must deliver current safely, measure the battery’s condition accurately and stop at the right moment, and each of those depends on the layout. The Charge Profile The profile is usually…

Spray Fluxing in Wave Soldering: Nozzle, Volume and Coverage Spray fluxing is the step that decides whether a wave soldered joint can form at all, and it is also the step most often left on default settings. The flux has to be applied in the right amount, in the right…

PCB Laminate Selection for Mixed Circuits A product that contains a radio, a processor and a sensor front end on one board puts three different electrical requirements on the same laminate. Selecting the material is a compromise between the loss the radio can tolerate, the impedance the digital interfaces need…

Plasma Treatment for PCB Surface Activation Before Coating Conformal coating and adhesive bonding both depend on a surface that the material can wet. A board that has passed through soldering, cleaning and handling carries an invisible layer of contamination that prevents that wetting, and the coating that looks continuous may…