Best Practices for More Reliable PCB Assemblies

What actually makes a PCB assembly reliable, not just functional?

Printed circuit board assemblies (PCBAs), also called PWBs (Printed Wiring Boards) or CCAs (Circuit Card Assemblies), end up everywhere from remote controls to hospital equipment to aircraft systems. The cost of a failure is easy to predict: lost money, lost function, and lost time. Building a board that passes inspection on day one is one thing; building a board that keeps working reliably for years is another. This article covers what actually goes into that second, harder goal.

Quality vs. Reliability: Two Different Things

Quality is measured at the moment a board leaves the manufacturer, checked against a fixed set of requirements and workmanship standards. Reliability is measured over the board’s entire service life, and it’s a much harder thing to quantify. A board can pass every quality check on day one and still fail after a year, five years, or ten. Good quality is necessary for reliability, but it isn’t the same thing, and it isn’t sufficient on its own.

Understanding IPC Reliability Classes

The IPC classification system (defined primarily under IPC-A-610) sorts boards into three tiers based on how critical their reliability needs to be. Class 1 covers general consumer electronics, remote controls, toys, short-lifespan products where occasional failure is an acceptable cost tradeoff, and where minor cosmetic defects that don’t affect function are tolerated. Class 2 covers dedicated, longer-service products like laptops and commercial equipment, where reliability matters more, and defect tolerance is tighter. Class 3 covers mission-critical electronics, aerospace, defense, and medical life-support systems, where failure isn’t an option and inspection standards are the strictest of the three. Knowing which class a design needs to meet, before manufacturing starts, shapes nearly every other decision in this article.

Maintaining Connectivity Under Stress

A highly reliable board (Class 3-level) keeps every connection intact for its entire service life, whether those connections are formed by soldering, vias, or bonding wires, and whatever conductive material they use. Good design and good workmanship both increase the odds that connections stay intact under the vibration, thermal cycling, and mechanical stress a board experiences over years of real use, not just during initial testing.

Matching Coefficient of Thermal Expansion (CTE)

Every material on a board (the laminate, the copper, the components) expands and contracts at its own rate as temperature changes. That rate is the material’s Coefficient of Thermal Expansion (CTE). When materials with significantly different CTEs are paired on the same board, repeated thermal cycling can pull them apart at the boundary, leading to cracking or delamination over time, even if the board worked perfectly when it was new. Selecting materials with closely matched CTEs where possible reduces this long-term risk.

Getting the Thermal Profile Right

Whether a board is built with reflow or wave soldering, the temperature profile used during that process matters for long-term reliability, not just for getting a clean solder joint on day one. Lead-free solder requires higher peak temperatures than leaded solder, though for a shorter duration, and every component on the board needs to be rated to survive that profile without damage. An incorrectly tuned thermal profile can leave joints that look fine at inspection but are more prone to fatigue and failure over the board’s service life.

Conformal Coating for Environmental Protection

For boards that will face humidity, dust, vibration, or chemical exposure in the field, a conformal coating adds a protective layer that standard PCB finishing doesn’t provide. Acrylic coatings are easy to rework and offer good general protection; silicone coatings hold up well under high humidity and vibration; polyurethane and epoxy coatings resist chemicals and solvents better than most alternatives. The right choice depends on the environment the board will actually operate in, and it’s a design decision worth making early, since it can affect component selection and layout spacing.