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…

Coating Cure Verification Methods A conformal coating that has not fully cured does not protect the assembly, and it looks the same as one that has. Cure verification is the measurement that separates the two, and it is the check that is most often replaced by a touch test. Why…

First Article Inspection and Its Record A first article is the first board of a run inspected completely, and its purpose is to confirm that the process, the documentation and the design agree. It is the cheapest point at which a setup error can be found, and it is only…

Via Tenting: Preparation, Placement and Process Control 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…

Copper Balance: Design Rules and Process Limits Inner layer copper is rarely uniform, and that is a design decision as much as a manufacturing one. Where one area of a layer is solid copper and the next is bare laminate, the board behaves differently under heat, under lamination pressure and…

Obsolescence: Preparation, Placement and Process Control Every component on a board has a life that is decided by its maker rather than by the product it sits in. A part that is perfectly good in service can be discontinued because the wafer fab moved on, the package fell out of…

Wave Solder Pallet: Design Rules and Process Limits Wave soldering a board with parts on the solder side usually means a pallet. The pallet holds the assembly, masks the areas that must stay dry and carries the board through preheat, the wave and cooling as a rigid unit. Because it…