Connector Pinout Design for PCBs A connector pinout is a small piece of design work with a disproportionate effect on how well a board performs. The same set of signals can be assigned to the same connector in several ways, and the choices determine how much crosstalk the cable carries,…

Differential Via: Key Checks Before Release A differential pair that runs cleanly on one layer and then changes layer through a via is no longer a differential pair at that point. The transition introduces an impedance discontinuity, an opportunity for the two halves of the pair to become slightly different,…

Moisture Sensitivity Levels and Bake Requirements for SMT Plastic packages absorb water from the air, and that water turns to steam when the package passes through a reflow oven. The pressure has to go somewhere: it either escapes slowly through the moulding compound or it lifts the die attach, cracks…

Inner Layer Registration In Multilayer Boards Layer registration is the alignment of the copper patterns on the different layers of a multilayer board, one to another. It is not the same as the alignment of the artwork to the drill, although the two are related: registration describes how the inner…

Power Sequencing Design for PCB Boards Power sequencing is the question of which supply rail comes up first, how fast it rises and how the rest of the board behaves while it does. On a simple board with a single rail the question does not arise, and on a board…

Clock Distribution Design for PCB Layouts A clock is the signal that every synchronous part of the board depends on, and it is also the one most easily degraded by the layout. Clock distribution covers the choice of source, the way the clock is routed to the devices that need…

Teardrop Pad Design At Trace Entries A teardrop is a short flare of copper added where a trace meets a pad, so that the junction widens gradually instead of meeting at a sharp step. It is a small feature, it costs a little routing space, and it protects the most…

Solder Paste Viscosity and Rheology in Stencil Printing Solder paste is a suspension of metal powder in flux, and its flow behaviour decides how it fills a stencil aperture, how it releases onto the pad and how long the deposit holds its shape. Two pastes with the same alloy and…

PCB Panel Coupon Design And Placement A panel coupon is a small pattern placed on the panel, outside the product boards, that is used to measure a property of the process. Because it travels through every step with the product, it is the only way to obtain a measurement that…

Signal Integrity Budget for PCB Designs A signal integrity budget is an allowance made before layout begins, in which the total margin available in a design is divided between the effects that will consume it. The alternative, which is what most projects actually do, is to lay out the board…