Connector Reliability Under Thermal Cycling A connector is a mechanical assembly made of several materials, and it is mounted to a board that expands at a different rate. The joints at its ends carry the resulting load, and they are the first to fail. Where the Stress Comes From The…

RoHS: Material Compliance Documentation for Assemblies Every product sold into a regulated market carries a documentation obligation. The materials have to be declared, the exemptions recorded and the evidence kept, and none of it is visible on the board. What Has to Be Declared The restricted substance requirements set limits…

Segment LCD Driver Circuit Design A segment liquid crystal display is one of the most durable and readable ways to show a few digits, and it works by chemistry rather than by light emission. The driver has to present the right waveform to each segment, and a direct current across…

Desmear and Hole Wall Preparation Before Copper Plating Drilling a hole through a multilayer board melts a thin layer of resin onto the copper inner layers. That layer is called smear, and it is the enemy of a reliable connection. Left in place, it sits between the copper barrel and…

Black Oxide Treatment and Inner Layer Bonding Control Copper does not bond to resin on its own. The surface has to be prepared so that the laminate can grip it mechanically and chemically, and the traditional way of doing that is to grow a controlled oxide layer on the inner…

Sampling Plans for Inspection and Test Inspection is a sample of what was built, and a sample is only useful if it is large enough and taken in the right place. A sampling plan that is chosen by habit gives a figure that looks like control and is not. What…

Etch Factor Control and Sidewall Angle in PCB Etching Etching removes copper, but it does not remove it in a straight line. The etchant attacks sideways as well as downward, so a trace emerges with a trapezoidal cross-section narrower at the top than at the base. The relationship between that…

LED Constant Current Driver Circuit Design An LED converts current into light, and the voltage across it is a consequence rather than a control. A constant current driver is therefore the normal way to power one, and the design questions are about where the current is measured, how much voltage…

Battery Charger Constant Current Constant Voltage Design A rechargeable lithium cell charges in two phases, and the circuit that does it has to switch between them without overshooting. The transition, the accuracy of the two set points and the way the charge is terminated are what separate a charger that…

Wave Solder Flux Application and Control In wave soldering the flux has to do its work in seconds, on a surface that is partly oxidised by the preheat. How much flux is applied and how it is applied decides whether the joint fills and what residue is left behind. What…