Copper Thickness and Current Capacity Planning for PCBs Two boards can carry the same circuit and behave completely differently under load, because the copper is not the same thickness. Copper thickness determines how much current a trace can carry before it gets too hot, how much voltage it drops along…

Component Storage, Floor Life and Solderability A component that has been in a store for two years is not the component that was qualified. The terminations oxidise, the moisture content changes, and the packaging that protected it has been opened and resealed more than once. Why Components Age The termination…

Hole Wall Roughness and Its Effect on Plating Adhesion The wall of a drilled hole is the surface that the plating has to grip, and its condition decides whether the copper stays attached through assembly and through the life of the product. A wall that is too smooth gives the…

Solder Bath Composition and Alloy Contamination Control The solder in a wave or selective soldering machine is not a fixed material. It picks up copper from the boards, it loses the more reactive elements to oxidation, and it accumulates whatever the process drags into it. The result is an alloy…

Ionic Contamination And Cleanliness Testing A flux that is described as no clean leaves a residue on the board, and the description means that the residue is designed to be harmless rather than that no residue is present. Whether it is actually harmless depends on the chemistry, the process and…

Current Derating: Design Rules and Process Limits A connector datasheet lists a current per contact, and it is tempting to read that figure as the current the contact can carry. It is not. The rating is established under defined test conditions, and a real application differs from those conditions in…

Heatsink Mounting and Thermal Interface Materials A heatsink solves one problem and creates three. It removes heat from the device, and it adds a mechanical load, a thermal interface that can degrade, and a set of mounting tolerances that must be compatible with the board. The Thermal Path in Series…

Digital Potentiometer Circuit Design A digital potentiometer is an array of switchable resistors with a tap that a serial command can move. It replaces a trimming screw with something a processor can set, and it brings a set of limitations that a mechanical part does not have: voltage range, current…

Panel Utilisation and Copper Balance Planning Rules Panel layout is where the board design meets the cost of making it. A panel that leaves large unused areas wastes laminate, a panel that balances copper badly produces plating and etching variation, and a panel that ignores the handling and tooling requirements…

Immersion Silver Finish In Assembly An immersion silver finish deposits a thin layer of silver on the copper pads, which protects them from oxidation and provides a solderable surface. It is flat enough for fine pitch components, it is cheaper than a gold finish, and it avoids the nickel layer…