Squeegee Pressure And Solder Paste Printing The squeegee is the moving blade that rolls the solder paste across the stencil and presses it into the apertures. Three settings describe it: the pressure that holds it against the stencil, the speed at which it travels and the angle at which the…

Statistical Process Control PCB Guide Statistical process control is the practice of measuring a process while it runs and reacting to the result before the product is out of specification. It is not a report, and it is not a one off study, both of which are common misunderstandings. The…

PCB Fuse Trace Design And Current Limiting A fuse trace is a deliberately narrow section of copper that is meant to melt and open the circuit when the current exceeds a limit. It is used instead of a fuse where a component would add cost or where the space does…

Process Capability Cpk PCB Guide Process capability is a statistical description of how well a process holds a dimension relative to its tolerance. The index that is usually quoted is Cpk, and it is a ratio between the distance from the process centre to the nearest limit and three standard…

Plated Hole Copper Thickness Specification The copper in the wall of a plated hole is the only connection between the layers that the hole serves, and its thickness is specified in every fabrication drawing, usually as a minimum in microns or in thousandths of an inch. The figure seems simple…

PCB Shelf Life Management Guide PCB shelf life is the period during which a finished board remains solderable under defined storage conditions. It is not a single number, because it depends on the finish, the packaging and the environment, and it is not a property of the laminate alone. Managing…

Poka Yoke: Design Rules and Process Limits A mistake proofing feature is one that makes an error impossible or immediately obvious rather than relying on the operator to notice it. In electronics assembly the errors that matter most are the ones that produce a working product at the factory and…

Legend Printing and Silkscreen Quality Control on PCBs The legend is the printed information on the surface of a board: reference designators, polarity marks, pin one indicators, part outlines and sometimes the board name and revision. It carries no electrical function, which is why it is often treated as an…

Manufacturing DFM Review Checklist Guide A DFM review is the point at which the design meets the process that will build it. The review is a checklist because the questions are known, repetitive and easy to forget under schedule pressure. A board that passes the review is not necessarily a…

Popcorning and Moisture Induced Defects During Reflow A plastic package that has absorbed moisture behaves like a sealed pressure vessel when it passes through a reflow oven. The water turns to steam, the vapour cannot escape quickly enough, and the internal stress cracks the mould compound or separates it from…