Conformal Coating Masking: Keeping Critical Areas Bare Conformal coating protects a finished assembly from moisture, contamination and the ions that would otherwise corrode a joint. It also causes damage if it reaches the wrong places: a coated connector cannot make a reliable contact, a coated test pad cannot be probed,…

Stencil Cleaning and Solder Paste Life on the Line Paste printing is a chemical process as much as a mechanical one. The material on the stencil changes through a shift: it loses solvent, it picks up contamination and it dries in the apertures. Most of the defects that appear an…

PCB Panelisation and Breakaway Design for Assembly The panel is what the assembly line actually handles. Boards are built in groups because a machine that places components efficiently needs a surface with enough area, and because handling one small board at a time wastes more time in transport than it…

Common Mode Choke: Design Rules and Process Limits A common mode choke has two windings on one core, arranged so that the current flowing out on one conductor and back on the other produces no net flux. It presents a high impedance to the current that flows on both conductors…

Fiducial: Design Rules and Process Limits A fiducial is a small mark on the board that exists only to be seen by a camera. It is a patch of copper with a clear area around it, and the vision system of a stencil printer or a placement machine uses its…

TVS Diode: Design Rules and Process Limits A transient voltage suppressor is a diode that conducts when the voltage across it exceeds a threshold and absorbs the energy of the event. Choosing one is a matter of three numbers, and getting any of them wrong produces a circuit that either…

Digital Signage Board Design for Multi Display Players A media player that drives one or two screens around the clock has to be simple, quiet and reliable. Digital signage board design is mostly about the display interfaces and the thermal path, because those two decide whether the product survives its…

Thermal Fuse Protection Circuit Design A thermal fuse is a one time device that opens when its temperature exceeds a set value, and it is the last line of defence in a product that can overheat. Used well, it converts a dangerous failure into a product that stops working; used…

Thermal Pad Soldering and Void Control in QFN Assembly A QFN package connects to the board through terminals around its perimeter and through a large exposed pad in the centre. The perimeter joints are visible before reflow and inspectable after, but the thermal pad sits underneath the body where nothing…

How SMT Line Automation Works in PCB Assembly A modern assembly line turns a bare panel into a tested board with very few people involved. Understanding how an smt line is automated explains which layout decisions help the process and which ones cause stoppages. What Automation Means on the Line…