Both my physics and engineering college professors expressed a mentality of “do it right or do it twice” to instill course material and problem-solving methods into their student’s heads. They thought anyone in those courses could pass one of their notoriously difficult exams. However, there would be little information retained beyond that, a dangerous proposition when subject topics continually build on one another. Instead, studying according to their rigorous methods, with an eye towards quality reviews instead of cramming, helped maintain the subject matter throughout the course and later classes.
Abstractly, the secrets of long-lasting PCB lifespans are similar to long-term study habits. The maximum effort attributed to each should be spread out over long periods to encourage long-term effectiveness. Most designers are familiar with a design that promotes reliability over absolute performance, although design intent must still be met within that stipulation.
Design Considerations to Extend PCB Lifespan
Like many focuses, PCB lifespan must be embraced early in the development process to engage all facets of design. Designers interpret the engineer’s schematic within the manufacturer’s constraints. Juggling these tasks is a give-and-take, and particular points of emphasis will vary across designs. However, ideal starting points for a design will maximize lifespan:
- Heat: Heat ages material of all kinds; some of the most popular reliability tests simulate the effects of long-term installations or boards subjected to extensive thermal loading. Therefore, boards that can effectively mitigate heat buildup, whether through active, passive, or a combination of features, are less likely to experience thermomechanical failure modes.
- Component stability: Choosing devices involves more than finding the first part in a manufacturer’s catalog that fits the technical requirements. Certain materials, package technology, etc., yield many steady and predictable results over time — usually reflected in the tight tolerances of those components. Per unit, prices are likely to increase over less stable parts, but this demonstrates the lifetime performance and longevity of the device.
- Electrical overstress (EOS): EOS is a condition that occurs when components are subjected to voltage, current, or power greater than maximum tolerances. This event usually results from transients during on-off cycles of power systems; a driver for a particular device may be operating towards the extreme of its operating range, and the transient can push it past its intended limit. In extreme cases, grid surges or lightning can travel through and over-energize components that lack sufficient protection. Overvoltage and current limiting devices clamp the voltage at some maximum value or reduce the current flowing through a circuit branch.
How Design for Reliability Impacts Continuous Usage Devices
It’s useful to define reliability from a design perspective. After all, extended uptimes and reliability go hand-in-hand when a product is intended for continuous, uninterrupted usage for any appreciable length of time. Reliability can be accounted for across the following criteria:
- A product functions within a certain range of tolerable conditions.
- A defined length of useful life (at the very least, a minimum length of life).
- The performance reliability depends on usage, including operational stresses and environmental considerations.
While any board features extensive planning and testing to curtail failure in the finished product, this becomes the central focus for a design tabbed for continuous usage. As failure exists in many forms, designers should note that wear out, instead of overstressing, occupies the majority of design for reliability concerns. The former deals with cases of repeat or extended usage leading to failure of the two failure modes. The latter is associated with catastrophic failure due to exceeding certain material properties or product ratings.
Wearout can occur across various board features depending on decisions made during the manufacturing process. Therefore, it’s important to review processes to determine the root causes where failures may be occurring:
- Fabrication. Substrates possess a different coefficient of thermal expansion values in the plane and are normal to the plane as the reinforcing glass fiber weave does not extend appreciably in the z-axis. Due to this, uneven expansion can occur between the normal direction and the plane, resulting in significant stress on vias structures. Common FR4 has a glass transition temperature of 130-140℃, making via barrel cracks extremely plausible without proper thermal management.
- Assembly. While components may experience early failure due to misapplication or poor operating conditions, it is far more likely to encounter issues in the solder interface between bare board and assembly. Both creep and fatigue can set into solder bonds, causing bond deformation and leading to intermediate or complete disconnects between the component and pad. Stress in the solder bonds can also develop from inadequate vibration resolution due to drops, bends, etc., that lead to cracks and also disrupt continuity.
Your Contract Manufacturer Can Prioritize Uptime for Your Profitability
PCB lifespan depends on sound decision-making throughout the design and manufacturing process to develop a product that can run without interruption. While this is not a “high reliability” product in terms of PCB classification, end users will be happy to benefit from design choices that improve uptime with minimal maintenance and repair. Ideally, the product should run without issue in the timeframe until the components associated with the board become obsolete. Suppose your design is suffering from earlier-than-acceptable wear or frequent maintenance and downtime. In that case, a study can peer into the different stages of development and determine the best layout, fabrication, and assembly steps to ensure a synergistic product. At VSE, our engineers can evaluate your current build for optimization opportunities or design from the ground up with NPIs. Alongside our professional and experienced manufacturing partners, we strive to deliver a PCB that exceeds all expectations.