Lead-Free Solder and Tin-Lead Assembly: What Changes Assembly with tin-lead solder and assembly with lead-free solder look like the same process with a different alloy, and they are not. The alloy melts at a different temperature, which changes the entire thermal profile; the joints that form behave differently under stress;…

Laminate Selection for High-Speed Designs: Performance Against Cost The material a board is built on stops being a background choice once the data rates rise. Above roughly ten gigabits per second, a conventional laminate absorbs enough of the signal to consume the link budget on its own, and laminate selection…

Calculating Trace Width for Current and Temperature Rise Trace width is decided by two questions that pull in opposite directions. The trace has to carry its current without getting too hot and without dropping too much voltage, which pushes the width up; and the routing has to fit into the…

Through-Hole Pad and Hole Size Design Through-hole parts are easier to justify than to design. The decisions that matter are small numbers — the hole diameter, the land around it and the distance between two holes — and each of them is a compromise between making the part easy to…

Reducing RF Effects in PCB Interconnect Design Once the signals on a board reach the gigahertz range, the interconnect stops behaving like a connection and starts behaving like a circuit. Corners reflect, surfaces resist more than their cross section suggests, finishes add loss where they were meant only to protect,…

Impedance Design on a Six-Layer Stack-Up A six-layer board is the point at which controlled impedance stops being optional and starts being structural. There are enough layers to give fast signals a proper reference, and enough density that the trace geometry which produces a given impedance has to be designed…

Power Plane Inset and the 20H Rule Open a well-designed multilayer board and the power plane is often slightly smaller than the plane above or below it. The difference is deliberate. It exists because the field between a plane pair is not entirely contained inside the board: at the cut…

Black Hole Process and Electroless Copper Compared A drilled hole is not yet a connection. The wall of the hole is laminate, and laminate does not conduct, so before any copper can be electroplated onto it the surface has to be made conductive by some means. Two families of process…

Via Design Rules: Sizes, Spacing and Fanout Vias are the cheapest way to add a layer’s worth of routing, and they are also one of the largest single contributors to the cost of a board: the drilling and plating operations behind them account for a large share of what a…

PCB Layout Workflow: From Schematic Review to Release A layout does not become good because it was drawn carefully. It becomes good because the sequence of decisions was taken in an order that leaves each later decision with room to be made. The practical layout workflow below follows that order:…