Wireless Charging: Design Rules and Process Limits Wireless charging transfers power through a pair of coils that are only loosely coupled, and the circuit design is mostly about compensating for that looseness. The coil geometry, the resonant capacitor and the shielding together determine how much power reaches the receiver and…

Microvia Reliability And Failure Modes A microvia is a small hole, usually no more than a hundred and fifty micrometres across, that connects two adjacent layers in a high density board. It is formed by a laser rather than by a drill, and its geometry is measured in tenths of…

Solder Ball Contamination on Assembled Circuit Boards Small spheres of solder sitting on the surface of an assembled board are one of the most common cosmetic defects in SMT. They are also one of the most misdiagnosed, because the mechanism that produced them determines whether they are harmless or represent…

High Power LED Thermal Design A high power LED converts a large fraction of its input into heat, and that heat leaves through the back of the package. The optical design is what most people notice, and the thermal path is what determines whether the light output and the colour…

Conformal Coating Thickness And Coverage Verification A conformal coating is a thin polymer film that is applied after assembly to protect the board from moisture, ionic contamination, and the occasional mechanical insult. It is not a paint, and its performance depends on three properties that can each be measured: the…

Solder Paste Inspection And Print Quality Control Solder paste printing is the step that determines most of the defects in a surface mount line, and the deposit is the one thing that can be measured before the components are placed. Solder paste inspection does exactly that: it scans the board…

MOSFET Gate Charge Drive Circuit Design The gate of a power MOSFET looks like a capacitor, and the datasheet figure that matters is not that capacitance but the charge that has to be moved to take the device from off to on. Sizing the driver from the gate charge and…

Panel Rails, Tooling Holes And Breakaway Tabs A panel exists because most assembly equipment cannot handle a small, irregular board. The individual circuits are laid out on a frame that carries them through the printer, the placement machine, the reflow oven, and the test fixtures, and the frame is made…

Wave Solder Pallet: Key Checks Before Release A wave solder pallet is the fixture that carries a printed board across the solder wave while shielding the parts that must not be soldered. It looks like a simple carrier, but it decides which joints the wave reaches, how hot the assembly…

PCB Circuit Types Classification for Mixed Signal Layout Before a mixed signal board can be laid out it has to be classified. Separating the circuit types on the drawing, and then deciding what interferes with what, is what turns a general set of layout rules into decisions for one board.…