Surge and ESD Protection Layout Two Different Threats Electrostatic discharge and surge are different events with different energies and different timescales, and a protection design has to account for both. An electrostatic discharge is a short, fast event with a rise time measured in hundreds of picoseconds and a current…

EMC Filters on the Board: Layout and Return What a Filter Has To Do A filter on a board is there to keep noise from leaving through a cable, or to keep noise from entering a circuit from outside. It works by presenting a high impedance to the noise while…

Ceramic Substrates for Thermal Designs Why Ceramic A ceramic substrate is used where the electrical and thermal requirements exceed what a polymer laminate can deliver. Ceramics are dimensionally stable, they tolerate high temperatures, they have a high dielectric strength and a low loss at high frequency, and some of them…

PTFE Laminates: Processing and Design Why PTFE Is Used PTFE-based laminates are chosen for their electrical properties: a low and stable dielectric constant and a very low loss tangent, which keeps insertion loss down at high frequency. They are also used where the dielectric constant has to be predictable across…

Metal Core PCB: Design and Thermal Path What a Metal Core Board Is A metal core board uses a metal plate, usually aluminium and sometimes copper, as the base instead of the usual FR4 laminate. The circuit is built on a thin dielectric layer bonded to the metal, and the…

Convection Versus Vapour Phase Reflow Two Ways to Heat Every reflow oven has to deliver heat to a board and its joints, and there are only two mechanisms available: convection, where the heat is carried by a moving gas, and condensation, where the heat is released when a vapour turns…

Wave Soldering: Setup and Defects What the Wave Does Wave soldering passes the board over a standing wave of molten solder, so that every exposed joint is soldered in a single pass. It is fast, it suits through-hole assemblies and mixed boards with the surface mount side already reflowed, and…

Refurbishing Assemblies and Re-Balling Packages What Refurbishing Covers Refurbishment is the restoration of an existing assembly to a usable condition. It covers replacing a failed component, re-balling a package whose solder balls were removed, replacing a worn connector, cleaning contamination from a board that has been in service, restoring a…

Process Capability for PCB Features: Using CpK What CpK Measures CpK compares the spread of a process with the tolerance it has to meet, and it also takes account of how far the process mean sits from the centre of that tolerance. A process with a small spread but a…

Stencil Cleaning Cycles and Underside Paste Why the Underside Matters The underside of a stencil is the surface that touches the board, and it is the surface that decides whether the print is clean. Paste accumulates there through aperture fill, through squeeze-out at the aperture edge and through the transfer…