Conformal Coating Rework Practice for PCB Assemblies A conformal coating protects a circuit from moisture, contamination and mechanical damage, and it also makes any subsequent repair more difficult. The coating has to be removed locally before the joint can be reworked, and then the protection has to be restored so…

Fiducial Design and Placement for Placement Machines A fiducial is a reference mark that the placement machine locates optically so that it can align the board to the stencil and to the component image. Without one the machine relies on the board edge, and the board edge is the least…

Conformal Coating Masking and Keep Out Control Conformal coating protects a board only where it is present, and the areas where it must not be present are as important as the areas where it must. Masking is the step that keeps the two apart. Areas That Must Stay Clear Connectors,…

Board Level Shielding Effectiveness and Can Mounting A metal can over a circuit is a simple idea with a complicated set of consequences. It blocks the coupling between the circuit and the outside world, but it also adds a resonant cavity, changes the thermal path and introduces a soldering and…

Board Packaging and Shipping Requirements A finished assembly is at its most vulnerable between the end of test and the moment the customer opens the box. Every handling step in that interval can introduce damage that no inspection will find, and the cost of the protection is trivial compared with…

Via Stub and Back Drilling for High Speed Boards A via that passes through a board leaves a stub below the layer where the signal turns, and at high frequency that stub behaves as a transmission line with an open end. It reflects energy back into the signal, and the…

Nitrogen Atmosphere Effects in Reflow Nitrogen in a reflow oven is not a soldering process, it is an atmosphere that slows oxidation so that the flux has more time to do its work. The benefit is real and it is often overstated, because nitrogen changes the process window without removing…

PCB Antenna Design and the Effect of the Ground Plane A PCB antenna is a tuned structure that happens to be made of copper on a board, and its performance depends on everything around it. The ground plane, the enclosure, the battery, the hand of the user and the components…

Press Fit Connector: Preparation, Placement and Process Control A press fit connector makes its connection by deforming a compliant pin inside a plated hole. There is no solder, so the quality of the joint rests entirely on the geometry of the hole and the pin and on the plating inside…

Board Thickness Selection and Stack Up Tolerance Board thickness is usually quoted as a single number, but that number is the sum of several layers each with its own tolerance. Understanding where the figure comes from decides whether the specification can be met and at what price. How the Nominal…