Plating Bath Metallic Dopant Dosing for Kirkendall Void Suppression
Dosing electroplating copper baths with controlled nickel or manganese trace dopants suppresses Kirkendall void accumulation and preserves joint shear strength.
High Temperature Storage Aging
Meaning
Reliability testing procedures for electronic components involve exposing devices to elevated temperatures for an extended period without electrical bias to evaluate their long-term stability. High temperature storage aging measures the physical and chemical degradation of materials, such as the growth of intermetallic compounds or the oxidation of interfaces. This test simulates the effects of years of storage or operation in a harsh environment within a few weeks.
It applies to semiconductors, automotive electronics and industrial sensors that must withstand extreme conditions. The procedure stops once the specified duration, often 1000 hours, is reached or a catastrophic failure occurs.
Test Conditions
The samples are placed in a calibrated thermal chamber where the temperature is maintained at a constant level, typically between 125 and 150 degrees Celsius. These temperatures are high enough to accelerate the diffusion of atoms but low enough to avoid melting the solder or damaging the plastic packaging. The chamber must have a uniform temperature distribution to ensure that all samples experience the same stress.
Air circulation is required to prevent localized hotspots and maintain a stable environment. The humidity is usually kept low to isolate the effects of temperature from those of moisture. Technicians monitor the chamber temperature using high-precision thermocouples and digital loggers.
These records are necessary for verifying that the test was conducted according to the applicable industrial standards like JEDEC or MIL-STD.
Degradation Mechanism
The primary focus of the aging process is the study of the solid-state reactions that occur at the junctions of different materials. In copper-aluminum wire bonds, the heat causes the formation of brittle intermetallic layers that eventually lead to electrical failure or mechanical separation. This phenomenon is often called the Kirkendall effect, where the different diffusion rates of the metals create voids at the interface.
The aging also accelerates the degradation of polymers and the outgassing of volatile compounds from adhesives and coatings. These chemical changes can increase the contact resistance of connectors and degrade the insulation properties of the circuit board. By examining the parts after the test, engineers can identify the weakest points in the design.
The data is used to select better materials and improve the manufacturing process.
Reliability Assessment
After the storage period is complete, the components undergo a series of electrical and mechanical tests to determine if they still meet the original specifications. Any shift in parameters like leakage current, gain or switching speed is recorded and analyzed. Failure is defined as a change that exceeds a pre-defined threshold or a complete loss of functionality.
Visual inspection and cross-sectioning are used to observe the physical changes inside the package. The results of high temperature storage aging help manufacturers estimate the shelf life and the warranty period of their products. This information is required for the qualification of new products in the automotive and aerospace industries.
Robust performance in this test gives customers confidence in the durability of the devices. The findings also provide a baseline for comparing the quality of different suppliers.
Modeling Vacancy Flux Kinetics and Kirkendall Void Nucleation in High Temperature Electronic Packaging Solder Joints
Electroplated copper bath impurities drive vacancy supersaturation and Kirkendall voiding, requiring dynamic SIMS screening and high-speed shear verification.