Via Tenting: Key Checks Before Release A via that passes through a solderable area has to be dealt with. The two standard answers are tenting, where solder mask is printed over the hole, and plugging, where the hole is filled with a material before the mask is applied. The names…

Copper Thickness Measurement Methods on PCB Copper thickness is specified for the current it carries and for the impedance it produces, and the figure that matters is the finished thickness rather than the foil that was purchased. Measuring it correctly means knowing which of the two is being reported. Foil…

Solder Mask Plugging Versus Tenting: Which Vias Need It Solder mask plugging and via tenting are often treated as interchangeable ways to keep solder out of a via, but they belong to different process families and leave different surfaces behind. Tenting is a mask-only operation in which the imaged film…

Stackup Dielectric Thickness A stackup is usually specified by the number of layers and by the finished board thickness, and both of those numbers can be met while the dielectric thicknesses inside the board are wrong. The inner layer spacing is what sets the impedance, the crosstalk and the coupling,…

Wicking: Preparation, Placement and Process Control Solder wicking is the movement of molten alloy along a metal surface under capillary action. In a barrel it is what fills the joint, and on a stranded wire or a pad it is what carries alloy where it was never meant to go.…

Washable Versus No Clean Flux Selection for Assembly Flux choice is often made at the same time as the solder alloy and then left alone for years, even though it decides whether the assembly needs a cleaning line, what the residue will do in service and how much process control…

Solder Mask Damage and Its Disposition Solder mask is a polymer coating and it is damaged by the same things that damage a coating: an edge, a tool, a chemical and a temperature. The damage is usually cosmetic and it becomes functional when it exposes copper or when it opens…

Drill Registration and Machine Calibration in the Drill Room Registration in the drill room decides whether a board has enough annular ring to survive thermal cycling, and it is one of the few process errors that cannot be corrected after the fact. The drill must place a hole inside a…

Press Fit Connector Assembly A press fit connector is held by friction rather than by solder. A compliant pin is pushed into a plated through hole that is deliberately smaller than the pin, and the elastic deflection of the pin presses against the barrel wall for the life of the…

PCB Baking and Moisture Sensitivity Plastic packages absorb moisture from the air. During reflow that moisture turns to steam, and the steam has nowhere to go until it finds a path, usually by cracking the package from the inside. Baking is the remedy, but a bake is a process step…