Creep-Fatigue Behaviours of Sn-Ag-Cu Solder Joints in Microelectronics Applications

Electronic manufacturing is one of the dynamic industries in the world in terms of leading technological advancements. Electronic assembly’s heart lies the ‘soldering technology’ and the ‘solder joints’ between electronic components and substrate. During the operation of electronic products, solder joints experience harsh environmental conditions in terms of cyclic change of temperature and vibration and exposure to moisture and chemicals. Due to the cyclic application of loads and higher operational temperature, solder joints fail primarily through creep and fatigue failures. This paper presents the creep-fatigue behaviours of solder joints in a ball grid array (BGA) soldered on a printed circuit board (PCB). Using finite element (FE) simulation, the solder joints were subjected to thermal cycling and isothermal ageing. Accelerated thermal cycling (ATC) was carried out using a temperate range from 40°C to 150°C, and isothermal ageing was done at −40, 25, 75 and 150°C temperatures for 45 days (64,800 mins). The solders studied are lead-based eutectic Sn63Pb37 and lead-free SAC305, SAC387, SAC396 and SAC405. The results were analysed using the failure criterion of equivalent stress, strain rate, deformation rate, and the solders’ strain energy density. The SAC405 and SAC396 have the least stress magnitude, strain rate, deformation rate, and strain energy density damage than the lead-based eutectic Sn63Pb37 solder; they have the highest fatigue lives based on the damage mechanisms. This research provides a technique for determining the preventive maintenance time of BGA components in mission-critical systems. Furthermore, it proposes developing a new life prediction model based on a combination of the damage parameters for improved prediction.

Microstructure and Damage Evolution During Thermal Cycling of Sn-Ag-Cu Solders Containing Antimony

Antimony is attracting interest as an addition to Pb-free solders to improve thermal cycling performance in harsher conditions. Here, we investigate microstructure evolution and failure in harsh accelerated thermal cycling (ATC) of a Sn-3.8Ag-0.9Cu solder with 5.5 wt.% antimony as the major addition in two ball grid array (BGA) packages. SbSn particles are shown to precipitate on both Cu6Sn5 and as cuboids in β-Sn, with reproducible orientation relationships and a good lattice match. Similar to Sn-Ag-Cu solders, the microstructure and damage evolution were generally localised in the β-Sn near the component side where localised β-Sn misorientations and subgrains, accelerated SbSn and Ag3Sn particle coarsening, and β-Sn recrystallisation occurred. Cracks grew along the network of recrystallised grain boundaries to failure. The improved ATC performance is mostly attributed to SbSn solid-state precipitation within β-Sn dendrites, which supplements the Ag3Sn that formed in a eutectic reaction between β-Sn dendrites, providing populations of strengthening particles in both the dendritic and eutectic β-Sn.

Performance of Photovoltaic Modules After an Accelerated Thermal Cycling Degradation Test

Typically, datasheets of photovoltaic (PV) modules state that the guaranteed power production remains constant for a certain period of time and after this point, a linear reduction begins reaching an estimated 80% of the original rated power. Moreover, literature reports that the degradation of PV modules reaches less than 1% per year. In this regard, after 20 years of operation a typical PV module will deliver approximately 20% less energy than a the beginning of its life. In this article, the results of an accelerated thermal cycling degradation test are compared to its brand new conditions. These results demonstrate that although the performance among the PV modules is variable when new, after the cycling test the performance of the degraded PV modules is similar. In this case, the power reduction of the degraded module varies from 1.4% up o 7.6% when compared to the initial condition. Furthermore, an Electrochemical Impedance Spectroscopy (EIS) analysis demonstrates that at high frequencies the results are practically the same regardless if the panel is new or degraded, but at low frequencies the variation of the impedance is notorious.

Experimental analysis of steel joints bonded with automotive grade hot setting structural adhesives

Recent trends in car body manufacturing indicate that the use of a consistent mix of lightweight materials in conjunction with adhesive bonding, not only allows substantial weight reduction, but can also drive down costs and potentially enables more intelligent designs. Yet, presently, it is highly desirable that the introduction of structural adhesives is made with minimum impact on the automotive body framing systems. Adhesives commonly deployed in car body production (i.e. body-in-white) are applied without any prior surface preparation and final curing is carried out during the baking process that follows the electrophoretic coating. Several structural adhesives have been tailored to the conditions dictated by the automotive production process. The aim of this work is to assess the mechanical properties of adhesive joints bonded with automotive grade hot setting epoxy adhesives employed for the assembly of frame and panels. Single-lap and T-joints were fabricated and adhesive hardening was carried out following the typical curing cycle employed in the process chain of automobile production. The resulting mechanical properties were assessed before and after exposure to a standard accelerated thermal cycling under controlled humidity. The evaluation of the mechanical behavior was done through a combination of testing and analysis, which included the assessment of fracture surfaces using optical microscopy to resolve the locus of failure.

Predictive Failure Analysis of Solder Joints with Simultaneous High Speed EBSD and EDS

The results presented here show how high-speed simultaneous EBSD and EDS can be used to characterize the essential microstructural parameters in SnPb solder joints with high resolution and precision. Analyses of both intact and failed solder joints have been carried out. Regions of strain localization that are not apparent from the Sn and Pb phase distribution are identified in the intact bond, providing key insights into the mechanism of potential bond failure. In addition, EBSD provides a wealth of quantitative detail such as the relationship between parent Sn grain orientations and Pb coarsening, the morphology and distribution of IMCs on a sub-micron scale and accurate grain size information for all phases within the joint. Such analyses enable a better understanding of the microstructural developments leading up to failure, opening up the possibility of improved accelerated thermal cycling (ATC) testing and better quality control.