DC-DC Layout and Routing Points for Switching Converters A switching converter is a small circuit with large currents, and the board around it is part of the circuit. The loop that carries the switching current has inductance that the schematic does not show, and every millimetre of it contributes to…

PCB Layout: Placement and Routing Practice PCB layout is where a schematic becomes a piece of hardware, and most of the problems that appear during bring up were decided on the screen rather than in the fabrication shop. Placement sets the shape of every current path on the board, the…

Solder Void Formation and Vacuum Reflow Voids in a solder joint come from gas that cannot escape before the solder solidifies. The gas can come from the paste, from the plating or from the surfaces, and the way to remove it is to make it easier to leave. Where the…

Load Cell Amplifier Gain Selection A load cell converts a force into a small differential voltage, and the amplifier that follows decides how much of that voltage the system can actually use. Gain selection is not a single number: it depends on the full scale output of the bridge, the…

Drill Registration and Layer-to-Layer Alignment Control Holes rarely land exactly where the artwork intended them to. Every layer is imaged, etched, laminated and drilled with its own small errors, and the hole must still land inside the pad on every layer it passes through. Registration is the discipline of keeping…

Engineering Change Orders in PCB Production A change order is a small document with a large effect. It invalidates drawings, programs, fixtures, test limits and stock, and it does so in several places at once. The cost of a change is rarely in the change itself. What a Change Order…

ENIG Process Control: Electroless Nickel Immersion Gold Electroless nickel immersion gold is the finish of choice for fine pitch, for wire bonding and for boards that will be stored for a long time before assembly. It is also the finish with the narrowest process window, because the nickel layer is…

Via in Pad for BGA Fanout: Process and Design Points A via in pad places the connection directly in the centre of a surface mount land instead of beside it. On a fine pitch ball grid array the pads are already close together and the escape routing between them is…

Placement Nozzle: Design Rules and Process Limits The only part of a placement machine that touches the component is the nozzle, and the entire accuracy of the machine passes through it. A nozzle that is the wrong size for the part produces a pick up that is off centre, a…

Reflow of Assemblies With Mixed Thermal Mass A board that carries a heavy connector, a thick copper plane and a small chip component on the same side does not heat evenly. The profile that satisfies one of them will not satisfy the other, and the compromise decides the yield. Why…