Preparing for aerospace PCB assembly requires a greater understanding of reliability and its impact on electronic devices. No one wants their electronic device to fail, but the cost and safety concerns of electronic failure with aerospace systems are unacceptable. Complicating this additional requirement is the greater range and extremes of environments that aerospace electronics must contend with.
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How Temperature Affects Reliability
PCB manufacturing is repetitive, and for good reason – the less things change, the easier it is to identify and control output variance. Succinctly: if it ain’t broke, don’t fix it. Aerospace PCB assembly takes this concern to heart by actively avoiding design strategies that could potentially compromise reliability. This avoidance could mean eschewing the latest or standard manufacturing strategies in favor of ones that bolster device reliability.
Take the Restriction of Hazardous Substances (RoHS) initiative as an example: while most electronics applications strictly forbid lead and other harmful board materials due to electronic waste concerns, aerospace applications permit lead-based solders due to their exemplary reliability characteristics over non-leaded solder alloys. Leaded alloys also have a significantly lower eutectic point, which means less thermal stress for the components during solder reflow and, thus, a lower chance of spontaneous failure. Additional areas for reducing temperature wear include:
- Surface finishes – Hot air solder leveling (HASL) is a common surface finish technique due to its well-known material properties, cost, and general applicability. However, electroless nickel immersion gold (ENIG) provides better reliability (at a higher cost) without exposing the board to further thermal excursion.
- Copper weight – Power distribution for aerospace applications may require thicker copper weights than standard due to the lack of sufficient atmosphere for air circulation. However, thicker copper weights affect the ability of the fabricated board to sink heat during the thermal soaking stage of reflow soldering. The greater heat capacity of the copper can affect the final assembly quality.
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Similarly, environmental ruggedness is also a concern for aerospace electronics. From take-off to altitude, electronic components may experience temperature swings over 100 degrees F – these changes can be a one-time experience during deployment or a regular part of operations. Aerospace electronics that repeatedly experience these changes may also have to navigate different humidity, pressure, and airborne debris. Encapsulation of otherwise exposed electronics is one method for limiting debris ingress and maintaining a relatively static operating environment. Designers will want to ensure their component choices – beyond meeting electrical requirements – are suitable for the strenuous environment of aerospace applications.
Aerospace PCB Assembly Certifications
When working towards an aerospace PCB assembly, designers can improve performance outcomes by keeping a few critical design philosophies in mind:
- IPC Class 3 – IPC designates Class 3 electronic products where failure during operation is unacceptable. This stringent requirement elevates quality control necessary during manufacturing, reducing the instance and severity of manufacturing defects before they develop or exit the shop. Overall, IPC Class 3 requirements significantly increase per-board manufacturing costs due to greater yield losses and heightened manufacturing constraints.
- AS9100 – An aerospace-specific extension of ISO9001, AS9100 establishes a basis for continual improvement and refinement of manufacturing outcomes to meet customer needs and remain competitive.
Your Contract Manufacturer
Aerospace PCB assembly is a complicated process – but it is not so different from standard PCB assembly. The lower tolerance for risk creates a greater demand for reliability, but an experienced PCB contract manufacturer will be able to navigate the process deftly and assist designers throughout the manufacturing process. Here at VSE, our engineers are committed to building electronics for our customers. With our valued manufacturing partners, we’ve been realizing life-changing and life-saving devices for over forty years.
