Chip on Board Assembly Design Guide Chip on board places a bare semiconductor die directly on the printed circuit board, connects it with fine wires and protects it with a blob of encapsulant. It removes the package from the assembly, which saves space and cost in high volume products, and…

Multilayer PCB Production Process Explained A multilayer board is built by repeating two operations: printing a pattern of copper and bonding a stack of layers together. Everything else, from drilling to surface finish, exists to connect those layers and to protect the result, and understanding the sequence makes the tolerances…

PCB Footprint Design: Pads, Silk and Mask Two engineers can open the same component and find that the recommended land pattern differs between their libraries. The differences are small, but they decide whether a part self aligns or shifts, whether a connector survives a drop, and whether an inspector can…

Aging and Long Term Storage of Assemblies An assembly that has been in a warehouse for two years is not the same assembly that was packed. The solder joints have aged, the finishes have oxidised, the plastic parts have absorbed moisture and the electrolytic capacitors have lost part of their…

Closing the Gap Between Simulation and Measurement A simulation that disagrees with a measurement is a common and useful situation. The disagreement contains information about the model, and the work is to find which assumption is responsible rather than to adjust parameters until the curves match. Why They Disagree The…

Heat Pipe and Fan Cooling Design Guide When a device dissipates more heat than a small copper area can spread, the answer is usually to move the heat somewhere else rather than to make the board bigger. A heat pipe does that without moving parts, and a fan does it…

Castellation: Preparation, Placement and Process Control A castellation is a plated half hole cut into the edge of a board so that the module can be soldered onto a carrier like a surface mount component, and it is the standard way to build a small sub assembly that has to…

Plane Capacitance and Embedded Capacitance Materials A pair of copper planes separated by a thin dielectric is a capacitor distributed across the whole board. It is not a substitute for discrete capacitors, and it does something the discrete parts cannot: it works at the frequencies where their inductance makes them…

Differential Pair Routing in Practice: Skew, Coupling and Length A differential pair is not two single ended traces that happen to be adjacent. It is a transmission line whose properties depend on the coupling between the two conductors, and the rules that follow from that are frequently misunderstood. What a…

LED Matrix Driver and Multiplexing Design An LED matrix replaces a wire per pixel with a grid of rows and columns, which reduces the number of connections from hundreds to a handful. The saving comes at a price: each LED is only lit for a fraction of the time, so…