Introduction

In automated test environments, PXI systems often operate 24/7 and experience frequent power cycles, heating from dense chassis, and environmental exposure. Over time, repeated thermal cycling can lead to mechanical stress on components — especially on solder joints. These stresses cause microscopic cracks that can result in intermittent or permanent failures, particularly in high-pin-count PXI modules.

What Is Thermal Cycling?

Thermal cycling refers to the process of continuously heating and cooling a system. In test setups, this often occurs during:

• Daily power-up/power-down sequences
• Fan-induced thermal gradients in the PXI chassis
• External temperature fluctuations (e.g., in production floors or environmental chambers)

This results in expansion and contraction of PCB materials and solder, which have different coefficients of thermal expansion (CTE). Repeated mismatch leads to fatigue and eventual solder joint cracking.

Why PXI Modules Are Vulnerable

PXI modules, especially those with high-density connectors or BGA components, are particularly sensitive due to:

• Compact form factor: High component density increases localized heating
• Frequent re-insertion: Mechanical stress during hot swaps contributes to microcracks
• Edge connectors: Wear on gold fingers and flex during seating adds stress to soldered areas
• Chassis airflow variation: Some modules may heat unevenly compared to neighbors

To learn more about PXI hardware structure, visit the PXI Platform overview.

Symptoms of Solder Joint Fatigue

• Intermittent signal loss or digital channel dropout
• Unstable self-test results in NI MAX or LabVIEW
• Excessive temperature variation reported by module sensors
• Soft failures — module passes diagnostics but fails in actual measurement

Prevention Strategies

1. Control Environmental Cycling

Maintain consistent ambient temperature in your rack or chamber. Avoid sudden power shutdowns during peak load.

2. Use PXI Modules with High-Reliability Solder Alloys

Some vendors offer options with improved SAC305 or leaded solder for thermal durability. Always ask for thermal cycling endurance specs.

3. Implement Thermal Profiling

Log temperatures at key components over time. Ensure no module exceeds its thermal spec under typical workloads. See more in PXI Modules.

4. Avoid Frequent Insertion/Removal

Unless modules are hot-swappable and rated for cycling, avoid moving them during temperature transitions.

5. Use Conformal Coating in Harsh Environments

Some manufacturers offer optional coating to minimize moisture absorption and extend PCB lifespan.

Thermal Testing Standards

Several standards define how electronics should be tested under thermal cycling conditions:

• JEDEC JESD22-A104: Defines temperature cycling between −55°C and +125°C
• IEC 60068-2-14: Common for telecom and industrial modules
• IPC-9701: For solder joint reliability under thermal-mechanical stress

Ask vendors if their PXI modules were qualified to these standards.

FAQs: PXI Thermal Fatigue

What’s the typical failure mode of thermal fatigue?

Cracks in solder joints under BGA packages or at connectors, leading to signal loss or contact resistance variation.

Can thermal cycling affect analog performance?

Yes. Thermal stress can impact gain stability, reference voltages, and offset drift.

Can LabVIEW detect signs of fatigue?

Not directly, but logging unexpected self-test failures or repeated channel faults may indicate emerging fatigue.

Conclusion

Thermal cycling is a major factor in long-term PXI module degradation. By adopting preventive design and usage practices — including temperature monitoring, gentle cycling, and using thermally qualified modules — engineers can significantly reduce solder joint failures and downtime. To find robust PXI hardware rated for industrial thermal conditions, visit the PXI Platform or Instrumentation sections of our catalog.