Highly Accelerated Life Test for reliability assessment of solder joints-Shenzhen Fitech
2023-03-27
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Highly Accelerated Life Test for reliability assessment of solder joints
Highly Accelerated Life Test is the process of accelerating the damage factors that occur in the actual use of an electronic product, triggering failure in a shorter period of time than in actual use, in order to determine whether the product meets the design requirements, as well as to analyse the failure mode and suggest improvement options.
Basic principle of High Accelerated Life Test
The basic principle of High Accelerated Life Test is that accelerated stress accelerates the failure mechanism of the test piece, causing it to exhibit the same failure modes and failure distributions in a shorter period of time than under normal stress levels. With reasonable engineering and statistical assumptions, and statistical models relating to physical failure patterns, the results of accelerated life testing can be converted into reliability information at normal stress levels.
Highly Accelerated Life Test has a wide range of applications in the field of electronic packaging, particularly for the reliability assessment of solder joints.
Causes of fatigue failure of solder joint
Solder joints are key components in electronic packaging that connect different materials and structures such as chips and substrates, substrates and external pins, and their reliability has a direct impact on the performance and lifetime of electronic products. Solder joints are subject to repeated mechanical and thermal stresses, resulting in microscopic cracking and gradual expansion, which eventually leads to fracture, i.e. fatigue failure of the solder joint.
In fatigue failure, there are two basic theories for the final cracking of solder joints, one is the overgrowth of grains and the other is the Kirkendall effect during IMC growth.
Overgrowth of grains means that the grains in the solder will become larger and larger under high temperature or long thermal cycles, the gap between the grains will also gradually increase, the grains become less dense and brittle, and eventually the abrupt grains collapse and break.
The Kirkendall effect during IMC growth refers to the diffusion process of the intermetallic compound (IMC) in the solder joint, which, due to the different diffusion rates of different metal atoms, can create voids or vacancies within the IMC or at the interface, leading to brittle IMC and easy cracking. Currently identified Kirkendall effect metals are e.g. Ag-Au, Ag-Cu, Au-Ni, Cu-Al, Cu-Sn.
Test items of High Accelerated Life Test
In order to assess the reliability of solder joints, the Highly Accelerated Life Test consists of thermal cycling tests (functional thermal cycling, temperature cycling, temperature shock), mechanical cycling (temperature + mechanical stress), vibration tests (random, vibration, fixed source vibration, sine vibration), creep fracture tests, mechanical shock tests, through a series of tests that can be compared to each other to assist in the determination, accelerated fatigue failure of solder joints to achieve the test The purpose of the test is to accelerate the fatigue failure of the welded joint.
In summary, the Highly Accelerated Life Test is an effective method of assessing the reliability of solder joints, it accelerates the damage factors that can occur in actual use, analyses the failure modes of solder joints and proposes improvement solutions to provide reliability assurance for the design and optimisation of electronic packaging products.
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