Spray Fluxing Control: Density, Coverage and Preheat Balance Flux has to be present in the right amount at the right place when the wave arrives, and spray fluxing is the method that places it without touching the board. The controls are the density of the liquid, the pattern the nozzle…

Cosmetic Acceptance Criteria: Scratches, Dents and Laminate Defects Cosmetic acceptance is decided by a person looking at a board, and it becomes repeatable only when the criteria are written as measurements rather than as adjectives. A scratch is accepted or rejected according to where it is, how deep it is…

Squeegee Blade Selection: Durometer, Edge Condition and Paste Release The blade that pushes solder paste across a stencil decides how much of the aperture is filled and how cleanly the stencil is wiped afterwards. Its hardness, its edge condition and the pressure behind it form one system, and changing any…

Conformal Coating Coverage: Masking, Thickness and Inspection A coating protects a circuit only where it is present and bonded, and the places where it is absent are usually the ones that matter most: the edge of a connector, the side of a component and the inside of a via. Coverage…

Reflow Profiles for Mixed Thermal Mass: Soak, Peak and Measurement A board with a heavy connector at one end and 0402 chip parts at the other does not have one reflow temperature; it has a range, and the range is set by the difference in thermal mass. The profile has…

Ionic Contamination Testing: ROSE Method and Extraction Control Ionic contamination is the residue that carries current when it becomes wet, and it is measured by extracting the board in a solvent and watching the conductivity of the liquid. The test is simple, cheap and often misunderstood, because it reports one…

Fiducial Teaching: Vision Alignment and Board Stretch Compensation A placement machine does not know where the board is until it looks at a fiducial, and the measurement it makes there is applied to every component it places afterwards. The fiducial design, the teaching of the threshold and the compensation for…

Hole Wall Quality: Drill Burrs, Desmear and Plating Adhesion Plating only adheres to a surface it can reach, and the surface inside a drilled hole is created by a rotating cutter that tears fibres, smears resin and leaves debris. The drilling and desmear steps decide whether the copper that follows…

V-Score: Design Rules and Process Limits A panel is separated into boards by breaking or cutting, and both methods leave a mark that the board carries for the rest of its life. The choice between scoring and routing is made from the board outline, the components that sit near it…

Solder Mask Dams at Fine Pitch: Registration, Width and Bridging The strip of solder mask between two pads is a structural feature, not a cosmetic one. It keeps molten alloy from running between the pads, and at fine pitch it becomes the narrowest feature on the board, which means the…