Tip Temperature: Design Rules and Process Limits A soldering iron has a setpoint on its display and a temperature at its tip, and the two are not the same. The display reads a thermocouple inside the heater or the tip, and what the joint experiences is the temperature of the…

Edge Plating and Castellations: Design and Process Limits Edge plating turns the side wall of a board into a conductor, and castellations turn a row of plated barrels into a soldering interface for a module. Both are mechanical features that behave like electrical ones, which is why they have to…

Blind Via and Buried Via Fabrication Limits and Reliability Blind and buried vias buy routing area on the layers below them, and they charge for it in fabrication stages, registration risk and inspection difficulty. The structures are buildable, but only inside aspect ratio limits that depend on the drilling method…

Exhaust System: Reflow Oven Exhaust and Flux Condensation Control A reflow oven produces more than heat. The paste releases flux vapour and solvent, the laminate releases moisture, and the conveyor carries dust, and all of it has to leave the tunnel without condensing on the surfaces inside it. The exhaust…

Placement Nozzle Contact Force and Height Control The placement nozzle is the last thing to touch a component before it is put on the board, and it is the only part of the machine that contacts the part directly. It picks the component from the tape by vacuum, holds it…

Stencil Aperture Wall Quality and Paste Release The aperture in a stencil is a hole with walls, and the paste has to slide down those walls as the stencil lifts away from the board. A smooth wall with a slight taper releases the deposit cleanly; a rough wall with a…

Squeegee Pressure and Angle in Solder Paste Printing The squeegee is the part of the printing process that turns a stencil into a measured deposit, and it is usually the last thing to be adjusted and the first thing to be blamed. Pressure, blade angle, print speed and separation speed…

Aqueous Cleaning: Bath Concentration and Rinse Control Cleaning is the step that decides whether the flux residue on a board is a harmless cosmetic film or a future leakage path. It is also the step that is most often run on a schedule rather than on a measurement, which is…

PCB Stack-Up: Layer Assignment and Reference Planes A stack-up fixes dielectric thickness, copper weight, layer order and the distance between each signal layer and its reference plane. Those choices set the impedance of every controlled net, the coupling that produces crosstalk, and the mechanical balance of the board before a…

Solder Paste Working Life and Replenishment Solder paste is a mixture of alloy powder, flux and solvent, and it changes from the moment the container is opened. Solvent evaporates, the flux absorbs moisture, the powder oxidises and the viscosity rises. Working life is the period over which those changes stay…