Hold Time Between Steps: 5 Rules That Protect Yield Hold time is the interval a panel spends waiting between one process step and the next, and on a PCB line it is a process parameter even though it is not written on any machine. A panel that waits an hour…

Coating Thickness: 6 Rules for Conformal Film Coating thickness is the number that decides whether a conformal coating does its job, because the film has to be thick enough to be continuous and thin enough to cure without trapping solvent. A specification that names a material and a process but…

Electromigration: 5 Design Rules for Long Life Electromigration is the movement of metal atoms in a conductor that carries current. The electrons push atoms along the trace, slowly thinning the metal upstream and piling it up downstream. The process is slow, but it never stops, and a trace that is…

Rectifier Ripple: 5 Checks for Even Plating Rectifier ripple is the variation that remains in a direct current output after rectification, and it changes the deposit that a plating tank produces even when the average current is exactly right. The plating reaction responds to the instantaneous current at the cathode,…

Artwork Film Control: 5 Checks Before Imaging Artwork film is the transparent master from which a panel is imaged, and it remains in use for outer layers, solder mask and legend on lines that have not moved to direct imaging. Because the film is a physical object, it changes with…

Exposed Pad Soldering: 6 Rules for a Flat Joint An exposed pad is the metal land on the underside of a package that carries heat out of the die and into the board. It is soldered at the same time as the pins around it, yet it behaves like a…

Hole Aspect Ratio: 6 Rules for Plating Hole aspect ratio is the board thickness divided by the drilled hole diameter, and it is the single number that best predicts whether a plated through hole will be reliable. A 1.6 mm board drilled with a 0.3 mm hole has a ratio…

Legend Print: 6 Rules for Board Marking Quality Legend print is the silkscreen layer that identifies components, pin one positions, connectors and orientation, and it is the only part of the board a human reads directly. It does not carry current and it does not affect impedance, which is exactly…

HAST Test Setup: 5 Rules for PCB Reliability A HAST test puts a board or an assembly under high temperature and high humidity while it is electrically biased, and it is used to find humidity driven failure modes in days rather than in the months a steady state humidity test…

Panel Edge Control: 5 Checks Before Lamination Panel edge control is the set of checks applied to the outside of a panel before it enters the press, and it decides both how the panel presses and how it behaves afterwards. A burr, a chipped corner or a film of resin…