Assembly Documentation And Work Instructions A board is built from documents. The assembly drawing says what goes where, the fabrication drawing says what the bare board is, the work instruction says how each operation is performed and what the result should look like, and the traveler records that it was…

Digital Isolator Circuit Design A digital isolator passes logic levels across an isolation barrier, and it has replaced the optocoupler in most new designs. The advantages are a shorter and more consistent delay, a longer life and a lower power consumption, and the layout rules are stricter than they look.…

BGA Solder Quality: Design Rules and Process Limits Ball grid array packages hide their solder joints, so quality has to be built into the process rather than inspected at the end. A board that leaves the line with a cold joint, an unreflowed ball or a large void may pass…

Low Power SoC Board Design for Battery and IoT Products Low power processors are marketed on their sleep current, but the board around them decides whether that number survives contact with a real product. A low power SoC board design has to deliver clean power to a fine-pitch package, hold…

Surface Finish Selection for PCB Assembly The surface finish on a bare board is a compromise between three requirements that pull in different directions. It has to protect the copper before assembly, it has to allow the solder to wet during it, and it has to do both at a…

Isolation Amplifier Circuit Design An isolation amplifier measures a signal that is referenced to a potential the measuring circuit cannot share. It is used to read a current in a motor phase, a voltage on a high side switch or a signal from a sensor at the end of a…

Aluminum Substrate PCB Thermal Design for Power Boards When a board has to carry several amperes and has nowhere to put a heatsink, designers reach for an aluminum substrate. A metal base spreads heat far better than any amount of copper on a standard laminate, but the same structure changes…

FPC Resin Plug Via Process for Dense Flexible Circuits Flexible circuits pack dense routing into a thin, bendable structure, and the vias inside them are the weak point of the whole assembly. A resin plug via process fills the hole with an insulating compound so the surface can be planarized,…

Camera SoC Power Design and Clock Planning for IP Cameras An IP camera board looks simple from the outside: one system on chip, one image sensor, one Ethernet transformer and a handful of passives. In practice the power tree and the clocking scheme decide whether the product streams reliably for…

High Frequency Material Selection for RF Loss Budgets Above a few gigahertz, the laminate stops being a passive substrate and becomes part of the circuit. Loss, phase shift and impedance all depend on material properties that change with frequency, temperature and humidity. High frequency material selection is therefore an engineering…