Flexure Life and Bend Fatigue in Flex Circuits A flexible circuit that is bent once during assembly and a flexible circuit that bends twice a day for ten years are entirely different design problems. The first can be treated almost like a rigid board; the second is a fatigue structure,…

HDI Blind and Buried Via Process Chain Explained High density interconnect design solves the problem of routing a dense board in limited space. The blind and buried via structures that make it possible are produced by a process chain in which each step has a narrow window, and a deviation…

Board Strain Measurement During Assembly A board that flexes by a fraction of a millimetre during assembly can crack a multilayer ceramic capacitor or lift a solder joint, and the damage may not appear until months later in the field. Because the cause is mechanical and the effect is electrical,…

Metallizing Aluminium Nitride Substrates Aluminium nitride occupies a specific niche among substrate materials. It is a ceramic that is electrically insulating and thermally conductive, and it is chosen when a circuit has to move a large amount of heat through an insulating layer rather than around it. The material itself…

Layer Stack: Manufacturable Design: Decisions That Belong Up Front Casting a design in the language of a manufacturing process forces a level of precision that a schematic review does not, and the exercise usually finds something. The items below are the ones that most often turn out to be decided…

Microvia: Design Rules and Process Limits Microvias are the feature that makes high density interconnect possible, and they are also the feature with the least tolerance for process variation. Understanding how they are made explains why the design rules around them are stricter than for a conventional through hole. How…

Copper Pour and Via Connection Rules for PCB Layout Copper pour is one of the last steps in a layout and one of the easiest places to introduce a defect, because the connection between the pour and every via, pad and plane is controlled by rules rather than by the…

Four Layer Flex and Rigid Flex Boards Flexible circuits are used because they bend, and bending is exactly what limits how many layers they can carry. A four layer flex is routine in modern designs, but it is a different construction from a two layer flex with extra copper, and…

Reactance And Impedance Explained For Board Design Resistance, capacitance and inductance are the three properties that describe how a circuit responds to a signal, and impedance is the term that combines them. On a board the distinction matters because a component that looks like a small capacitance on a schematic…

Reflow Profile: Reflow Profiling: Measuring What the Solder Sees Thermal profiling is the measurement that connects a reflow oven’s settings to what the solder actually experiences, and it is the only way to know whether a profile is suitable for a particular assembly. The oven’s display shows the air temperature,…