RTD Excitation Current and Measurement Circuit A platinum resistance thermometer is the default choice when temperature has to be measured accurately and repeatably over a wide range. Its resistance is nearly linear with temperature, it is stable over years, and the accuracy of the measurement then depends almost entirely on…

PIR Sensor Motion Detector Circuit Design A passive infrared detector responds to a change in the infrared radiation reaching it, and that single sentence explains most of its behaviour: it detects movement, it ignores a stationary person, and it can be triggered by anything that changes the temperature of what…

OSP Surface Finish In PCB Assembly An organic solderability preservative, usually shortened to OSP, is not a metal. It is a thin organic film that is applied to the copper surface and that protects it from oxidation until the board is soldered. Because there is no metal layer, the pad…

Designing Boards for High Performance IC Devices A high performance IC asks more of its board than any other part on the assembly. Its core current steps in nanoseconds, its memory interface runs on a parallel bus with hundreds of synchronous lines, and its supply rails have impedance requirements that…

Building a High Quality PCB: Design Priorities Almost everything that makes a high quality PCB is decided before the board is ordered. The stackup, the copper weight, the surface finish, the tolerances and the test coverage are all choices, and the ones that are made by default are the ones…

Embedded Capacitance In PCB Laminates A power and ground plane pair separated by a dielectric is a capacitor, because two conductors with an insulator between them always are. In an ordinary board the separation is large and the capacitance is small, so the planes are treated as a low impedance…

Impedance Test Coupon Design and Verification Methods Controlled impedance is a promise about a physical dimension that nobody can see. The trace width, the dielectric thickness and the material properties all determine whether a signal sees fifty ohms or sixty, and none of them can be confirmed by looking at…

Placement Force and Paste Displacement Control A placement machine has to press the component into the paste hard enough to make it stick and softly enough to leave the deposit in place. The window is narrow, and it changes with the nozzle, the paste and the pad size. What the…

Microvia Reliability: Stacked, Staggered and Filled A microvia is a small hole with a thin wall, and its reliability depends on the shape of the wall rather than only on its thickness. The copper that plates a blind hole tapers, and the taper is where the cracks begin. Why Microvias…

PCB Annular Ring Design And Tolerance The annular ring is the width of copper that remains around a drilled hole after the barrel has been plated. It is the feature that connects the barrel to the trace, and it is consumed by every tolerance in the process, from the drill…