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…

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…

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…

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…

Blind and Buried Vias: Density Without Dead Layers Blind and buried vias exist because a through hole occupies every layer it crosses. On a dense board the through holes themselves become the limiting factor: they block routing channels on inner layers, they force the escape pattern of every large device,…

Flying Probe and Fixture Test Cost Comparison for New Builds Electrical test is the last gate before a board leaves the shop, and the method used to open it has a cost structure that changes completely with volume. A flying probe needs no tooling and is ready as soon as…

Flux Residue and Board Cleanliness Requirements in Assembly Every soldering operation leaves something behind. Flux is essential for wetting, but the residue it leaves on the board is a chemical film with its own electrical behaviour, and whether that film is harmless or damaging depends on its chemistry, its quantity…