Cavity Board Design Guide A cavity board carries a recess in the laminate so that a component can sit below the surface, either to keep the overall height within a limit or to bring a sensor or an optical part closer to the outside face. The cavity is produced by…

Blind Via Filling Guide A blind via connects an outer layer to an inner layer and stops without passing through the board. When another via has to be placed directly above it, or when the via lies in a pad that must be printed flat, the hole has to be…

Fiducial Mark: Practical Checks for Production A fiducial mark is a small copper feature that the placement machine uses to find the board. The machine photographs the marks, calculates their position, and offsets its program so that components land on the pads regardless of small errors in the position of…

Embedded Resistor: Design Rules and Process Limits An embedded resistor is a resistive layer inside the board, patterned into individual elements and connected to the rest of the circuit by vias. It replaces a discrete part with a structure that has no solder joint and no placement, and it is…

Copper Balance Design For Multilayer Panels Copper balance is the extent to which the amount and the distribution of copper on each layer of a board match the layers around it. An unbalanced design distorts during lamination and produces boards that are warped, that vary in thickness, or that fail…

Solder Joint Corrosion in Humid and Polluted Environments A solder joint is a piece of metal in a chemical environment, and that environment contains water, oxygen, flux residue and whatever the atmosphere brings with it. Corrosion is the result, and it appears as a change in resistance, a growing leakage…

Fine Line Etching Uniformity Control on Inner Layers Etching is a subtractive process, which means that every variation in the way the etchant reaches the copper becomes a variation in the conductor that remains. On a fine line board the conductor width is a controlled parameter, because it sets the…

Embedded Capacitor Design Guide An embedded capacitor is a layer of dielectric placed between two copper planes inside the board, so that the planes and the material between them form a large distributed capacitor. It is not a replacement for every discrete capacitor on the board, and it is not…

Drill Smear And Desmear Control In Multilayer Boards Drilling a multilayer board generates heat at the cutting edge, and that heat is enough to soften the resin and smear it across the inner layer copper. The smear is an insulating film, and if it is not removed the plated barrel…

Print Head Technology in SMT Printing The print head is the part of a stencil printer that turns paste into a deposit. It carries the squeegee, applies the force and moves across the stencil, and the way it does those three things sets the fill of the aperture and the…