Environmental Assessment
Reliability evaluation procedures subject printed circuit board assemblies to extremely rapid transitions between temperature extremes to expose latent manufacturing weaknesses. Included in this class is high acceleration thermal shock, which utilizes fluid baths or dual-zone chambers to achieve temperature transfer rates exceeding sixty degrees per minute. The testing method evaluates the structural strength of solder joints, internal vias, and laminate interfaces by forcing rapid volumetric expansion and contraction.
This environmental evaluation does not apply to assemblies that are only rated for benign, controlled office environments.
Testing Mechanism
Specimens move rapidly from a hot chamber to a cold chamber using a motorized transfer basket, which minimizes the transition time to under ten seconds. The rapid temperature change creates severe transient temperature gradients between the component bodies, solder joints, and the substrate. These gradients produce localized mechanical stresses that cause defective plated holes to fail or weak solder joints to fracture.
Real-time resistance logging during the cycle monitors for intermittent open circuits that might close again when the temperature stabilizes.
Qualification Threshold
Failure occurs when the resistance of a daisy chain circuit rises above a predefined limit, usually ten ohms. This identifies early wear-out mechanisms before the assembly is sent to the field.
