Dry Film: 5 Rules for Lamination Control A dry film is a photosensitive resist supplied as a thin layer on a carrier sheet, and it is laminated onto the copper surface before imaging. Compared with a liquid resist it gives a uniform thickness across the panel, which is why it…

Tented Via: 5 Rules for Mask Coverage A tented via is a via whose opening is covered by solder mask, so the hole and its annular ring are sealed under the coating instead of being left open. The purpose is simple. An open via next to a pad can wick…

Step Board: 5 Rules for Cavity Depth Control A step board is a printed circuit board with a pocket milled into it so that a tall component can sit below the surface of the panel. The pocket, usually called a cavity, is created by controlled routing depth, and it lets…

Stacked Via: 5 Rules for HDI Reliability A stacked via is a microvia placed directly on top of another microvia, so the connection passes through two or more HDI layers without a landing pad between them. The arrangement saves the space that an offset or staggered build would need, which…

Solder Fountain: 5 Rules for Selective Soldering A solder fountain is the small, localised wave that a selective soldering machine raises under a single through hole component, and its height decides how much of the barrel the alloy touches. Setting that height is more delicate than it looks, because the…

Nanocoating: 5 Rules for Stencil Paste Release Stencil nanocoating is a thin film applied to the aperture walls of a laser cut stencil so that solder paste releases cleanly rather than smearing down the side of the opening. On a stainless steel stencil that has no coating, the striated edge…

Outgassing: 5 Causes in Lamination and Assembly Outgassing is the release of trapped gas from inside a board when it is heated. The gas comes from moisture absorbed by the laminate, from volatiles left in the resin and from air trapped in a via or under a plane, and it…

Entry Material: 5 Rules for Hole Quality Entry material is the sheet that sits on top of the panel when it is drilled. It looks like a consumable detail, and it decides a surprising amount about the quality of the hole: it cushions the drill as it enters, it holds…

Solder Skip: 5 Causes on a Wave Solder Line A solder skip is a pad or a lead that passes over the wave without being soldered, leaving the metal bright and bare. It is different from a cold joint, because no alloy was ever applied, and different from a missing…

Metal Squeegee: 5 Rules for a Clean Wipe A metal squeegee is the steel blade that pushes solder paste across the stencil. It is chosen because it keeps a sharp edge for a very long time, which makes the print repeatable from the first board of a campaign to the…