Reliability Standard
Environmental stress test designed to determine the effect of long-term exposure to elevated temperatures on the mechanical and electrical integrity of an electronic assembly. High temperature storage life testing subjects components or boards to a constant thermal load without electrical bias. This procedure accelerates the growth of intermetallic compounds and the degradation of polymer materials in the substrate.
It establishes the shelf life and operational durability of the product in harsh environments.
Intermetallic Growth
Thermal energy during the storage period drives the diffusion of atoms between the solder and the conductive pads. While a thin intermetallic layer is necessary for a good bond, high temperature storage life often results in excessive thickening of these brittle phases. This thickening can lead to the formation of Kirkendall voids, which are microscopic holes that weaken the joint.
As these voids coalesce, the mechanical strength of the interconnect decreases, making it prone to failure under vibration. Structural degradation occurs silently until a stress event triggers a fracture.
Data Analysis
Testing durations often span hundreds or thousands of hours at temperatures such as 125 or 150 degrees Celsius. Evaluation of high temperature storage life involves periodic cross-sectioning or electrical testing to monitor the progression of degradation. If the resistance of a daisy-chain circuit increases beyond a specified limit, the test indicates a failure in the metallization or the interface.
Results from this study guide the selection of materials that can withstand the thermal demands of automotive or aerospace applications. Thermal stability defines the long-term utility of the hardware.
