Effects of load and thermal conditions on Pb-free solder joint reliability (original) (raw)
Related papers
Effects of Board Design Variations on the Reliability of Lead-Free Solder Joints
IEEE Transactions on Components, Packaging and Manufacturing Technology, 2013
Sn-Ag-Cu (SAC) solder alloys, such as Sn-3.0Ag-0.5 Cu (SAC305) are the popular choices of lead-free solders replacing SnPb solders. However, SAC solders are more brittle in nature due to stiffness and excessive intermetallic compounds growth at the solder joint to pad interface. This leads to higher risk of solder joints failures. Memory module-type smaller lead-free ball grid array (BGA) packages are constantly under dynamic stresses during handling and thermal stresses during operations. It is important to understand the dynamic performance and long-term reliability of memory module lead-free BGAs. It is believed that the printed circuit board (PCB) design variations cause dynamic and long-term failure discrepancies in the fields. In this paper, different pad and trace designs are introduced to evaluate the effects of PCB design variations on the bend and accelerated thermal cycling (ATC) performance of lead-free solder joints. Pad designs with nonsolder mask defined, solder mask defined (SMD), and a unique web design are assembled and tested. Different solder alloys, including SAC305, Sn-1.0Ag-0.5Cu (SAC105) SAC105, and SnPb solders, have been evaluated in this paper. Different PCB materials have also been evaluated in the test. Four-point monotonic bend tests are performed to characterize the bending performance variations with different PCB designs and compared with conventional Sn-Pb solder. The SMD pad is shown to have the best bend performance among all other types of designs in this paper. In addition, this design also shows improvement in mitigation of PCB pad cratering with lead-free solders. Wide trace width seems to degrade the strength and is not preferred. Just as it shows superior shock resistance when compared with SAC305, the SAC105 solder alloy also shows better bend performance. There is no significant improvement in bend performance with web design. After aging treatment, bend performance of both SAC305 and SAC105 degraded by up to 34% and 29%, respectively. However, the bend performance of eutectic SnPb is actually improved after aging. ATC tests are performed to investigate the effects of design variations on the long-term reliability of lead-free solder joints; SMD design shows less reliability life than others. The implications of these results for the reliability of lead-free solder joints are discussed in this paper.
2017
This study treats the reliability of solder joints of electronic assemblies, in terms of methodology of evaluation, applicable stress tests and analyses. This study is focused on lead-free solder alloys and describes the solder joint microstructure and its changes caused by thermal stresses, ATC (Accelerated Thermal Cycling) and thermal shock, which cause thermomechanical stresses to the solder joints. In particular, this study compares the different stresses caused by the fast and slow thermal swings. Another topic is a revision of the criteria to evaluate the solder joints on the base of the link between the stress tests and the conditions of the product life. Finally, a proposal for the stress tests and the evaluation criteria is described.
Thermal Fatigue-Life Prediction of Lead-Free Solder Joints
Electronic and Photonic Packaging, Electrical Systems Design and Photonics, and Nanotechnology, 2004
Reliability of lead-free solder joints is investigated. Emphasis is placed on the design for reliability (DFR) of lead-free solder joints. In particular, the thermal-fatigue life of the lead-free solder joints of a plastic ball grid array (PBGA) package assembly is predicted and discussed.
Pb-free Solder Joint Reliability in a Mildly Accelerated Test Condition
2011
Two different temperature cycling profiles were used to compare the thermal fatigue reliability of Pb free and SnPb solder joints in 16 different, high strain surface mount (SMT) packages. In some applications, high strain Pb free (SnAgCu) components are expected to fail earlier than the equivalent SnPb version. In this program, test results were compared for a 0100°C thermal cycle used often for evaluating high reliability applications to those of a comparatively mild accelerated thermal cycle condition of 20-80°C. A total of 6957 cycles was completed in the 0-100°C testing and a total of 9792 cycles was completed in the 20-80°C thermal cycling. The program was completed after over more than two years of elapsed test time. Weibull analysis, acceleration factors between the tests and failure analysis are included. The results indicate that the SnAgCu (SAC) components that create a high strain in thermal cycling tend to perform worse in 0-100°C testing than identical SnPb soldered co...
Reliability of Lead-Free Solder Joints Under a Wide Range of Thermal Cycling Conditions
2011
In this paper, we report a comprehensive set of accelerated thermal cycling (ATC) tests that were performed on test vehicles with different package types, sizes, pitches, and solder joint alloy metallurgies using four different thermal cycling profiles: 0 to 100, -40 to 125, -55 to 125, and -60 to 150°C. Samples from the tests were analyzed for their failure modes, and failure rates were calculated by using Weibull statistics. The characterized life for each test condition was determined and analyzed. The impact of solder alloy metallurgies, package types, sizes, and pitches on acceleration factors of the ATC tests to fatigue life was also analyzed and discussed. The quantified discrepancies among several acceleration factors from different studies compared to the experimental data presented in this paper are illustrated. The results provide valuable guidance on the effects of package types, size, pitches, and solder joints alloy metallurgies on various ATC test conditions. In addition, failure analysis was performed at different stages of the tests for each thermal cycling condition. Dramatic failure mode shifts at extreme ATC conditions were observed. The significance and the long-term impact of the failure modes and failure mechanism shift between various ATC test conditions to the life prediction of lead-free solders are extensively discussed.
High temperature reliability of lead-free solder joints in a flip chip assembly
Journal of Materials Processing Technology, 2012
The visco-plastic behaviour of solder joints of two models of a flip chip FC48D6.3C457DC mounted on a printed circuit board (PCB) via SnAgCu solder is investigated using Anand's model. While the bumps of one of the models are realistic with 6 m thickness of intermetallic compound (IMC) at interconnects of solder and bond pads, the other are made up of conventional bumps without IMC at these interconnects. The solder bump profiles were created using a combination of analytical method and construction geometry. The assembled package on PCB was accelerated thermally cycled (ATC) using IEC standard 60749-25. It was found in the result of the simulation that IMC does not only impact solder joint reliability but also is a key factor of fatigue failure of solder joints. The IMC sandwiched between bond pad at chip side and solder bulk is the most critical and its interface with solder bulk is the most vulnerable site of damage. With reference to our results, it is proposed that non inclusion of IMC in solder joint models composed of Sn-based solder and metalized copper substrate is one of the major causes of the discrepancy on solder joint fatigue life predicted using finite element modelling and the one obtained through experimental investigation.
Thermal Fatigue Evaluation of Pb-Free Solder Joints: Results, Lessons Learned, and Future Trends
JOM, 2015
Thermal fatigue is a major source of failure of solder joints in surface mount electronic components and it is critically important in high reliability applications such as telecommunication, military, and aeronautics. The electronic packaging industry has seen an increase in the number of Pb-free solder alloy choices beyond the common near-eutectic SnAg -Cu alloys first established as replacements for eutectic SnPb. This paper discusses the results from Pb-free solder joint reliability programs sponsored by two industry consortia. The characteristic life in accelerated thermal cycling is reported for 12 different Pb-free solder alloys and a SnPb control in 9 different accelerated thermal cycling test profiles in terms of the effects of component type, accelerated thermal cycling profile and dwell time. Microstructural analysis on assembled and failed samples was performed to investigate the effect of initial microstructure and its evolution during accelerated thermal cycling test. A significant finding from the study is that the beneficial effect of Ag on accelerated thermal cycling reliability (measured by characteristic lifetime) diminishes as the severity of the accelerated thermal cycling, defined by greater DT, higher peak temperature, and longer dwell time increases. The results also indicate that all the Pb-free solders are more reliable in accelerated thermal cycling than the SnPb alloy they have replaced. Suggestions are made for future work, particularly with respect to the continued evolution of alloy development for emerging application requirements and the value of using advanced analytical methods to provide a better understanding of the effect of microstructure and its evolution on accelerated thermal cycling performance.
Reliability of solder joints assembled with lead-free solder
2002
To protect the natural environment, we will introduce the use of lead-free solder instead of the current tin-lead solder in the assembly of printed circuit boards in electronics equipment. During the transition to lead-free soldering, these two types of solders will be used in combination in joints. After the transition, a new element, bismuth, from components will contaminate the lead-free solder joints. We investigated the two types of solder through dynamic mechanical examination and concluded that lead-free solder can be used in combination with the current tin-lead solder and on its own to form sufficiently reliable joints.
Microelectronics Reliability, 2007
Aging and accelerated thermal cycling (ATC) have been performed on 2512 chip resistors assembled with Sn3.8Ag0.7Cu (wt.%) solder. The boards were finished with immersion Ag (IAg), electroless nickel/immersion gold (ENIG), and hot air solder leveling Sn-Pb eutectic solder (HASL), and the components' terminations were finished with 100% Sn and Sn8.0Pb (wt.%). The boards were reflowed with an average cooling rate of 1.6°C/s. It was found that the microstructure and reliability of the solder joints depended on the board surface finish. The boards containing small amounts of Pb (from board/component terminations) were the most reliable. Solder joints to copper showed a significantly higher number of cycles to first failure than the joints on nickel. Better reliability of the Sn3.8Ag0.7Cu/Cu joints was attributed to an increased copper content in the bulk due to substrate dissolution.
Welding Journal, 2017
Whether structural or electronic, all solder joints must provide the necessary level of reliability for the application. The Part 1 report examined the effects of filler metal prop erties and the soldering process on joint reliability. Filler metal solderability and mechan ical properties, as well as the extent of base material dissolution and interface reactions that occur during the soldering process, were shown to affect reliability performance. The continuation of this discussion is presented in this Part 2 report, which highlights those factors that directly affect solder joint reliability. There is the growth of an intermetallic compound (IMC) reaction layer at the solder/base material interface by means of solidstate diffusion processes. In terms of mechanical response by the solder joint, fatigue remains the foremost concern for longterm performance. Thermal mechanical fatigue (TMF), a form of lowcycle fatigue (LCF), occurs when temperature cy cling is combined with mi...