Study of Lead Free Solder Joints Subjected to Isothermal Mechanical Shear Cycling

2020 ◽  
Author(s):  
Mohd Aminul Hoque ◽  
Mohammad Ashraful Haq ◽  
Jeffrey C. Suhling ◽  
Pradeep Lall
Keyword(s):  
Printed Circuit Boards ◽  
Solder Joints ◽  
Polarized Light ◽  
Lead Free ◽  
Lead Free Solder ◽  
Circuit Boards ◽  
Sac305 Solder ◽  
Mechanical Cycling ◽  
Before And After ◽  
Free Solder

Abstract Electronic packages are usually subjected to varying temperature conditions, thus subjecting the package to thermal cyclic loadings. As the different components of the package are made up of materials of different Coefficients of Thermal Expansion (CTE), the thermal cyclic loading brings about fluctuating shear stress to arise within the package, ultimately leading to its failure. It has been seen in previous literature that the recrystallization assisted cracking is a major factor that leads to the failure of solder joints when subjected to thermomechanical cycles. In this study, the authors have tried to determine whether the mechanical shear cycling of aged and non-aged samples of SAC305 lead free solder joints undergo a recrystallization phase before its ultimate failure. Arrays (3 × 3) of SAC305 solder joints of roughly 750μm in diameter were reflowed in between two FR-4 printed circuit boards to create a sandwiched structural sample. The samples were then polished to expose the solder joints. A polarized light microscope was utilized to capture the images of the joints before and after the mechanical cycling and analyzed to observe any changes in the microstructure in the form of recrystallization of the tin grains.

Effect of Aging on the Properties of Intermetallic Layers in SAC+Bi Solder Joints

2021 ◽  
Author(s):  
Mohammad Ashraful Haq ◽  
Mohd Aminul Hoque ◽  
Jeffrey C. Suhling ◽  
Pradeep Lall
Keyword(s):  
Solder Joints ◽  
Lead Free ◽  
Lead Free Solder ◽  
Aging Condition ◽  
Sac305 Solder ◽  
The Poor ◽  
Free Solder ◽  
Lead Free Solders ◽  
Overall Reliability ◽  
Intermetallic Layers

Abstract A major problem faced by electronic packaging industries is the poor reliability of lead free solder joints. One of the most common methods utilized to tackle this problem is by doping the alloy with other elements, especially bismuth. Researches have shown Bismuth doped solder joints to mostly fail near the Intermetallic (IMC) layer rather than the bulk of the solder joint as commonly observed in traditional SAC305 solder joints. An understanding of the properties of this IMC layer would thus provide better solutions on improving the reliability of bismuth doped solder joints. In this study, the authors have used three different lead free solders doped with 1%, 2% and 3% bismuth. Joints of these alloys were created on copper substrates. The joints were then polished to clearly expose the IMC layers. These joints were then aged at 125 °C for 0, 1, 2, 5 and 10 days. For each aging condition, the elastic modulus and the hardness of the IMC layers were evaluated using a nanoindenter. The IMC layer thickness and the chemical composition of the IMC layers were also determined for each alloy at every aging condition using Scanning Electron Microscopy (SEM) and EDS. The results from this study will give a better idea on how the percentage of bismuth content in lead free solder affects the IMC layer properties and the overall reliability of the solder joints.

Damage Evolution in Lead Free Solder Joints in Isothermal Fatigue

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Awni Qasaimeh ◽  
Sa’d Hamasha ◽  
Younis Jaradat ◽  
Peter Borgesen
Keyword(s):  
Crack Initiation ◽  
Mechanical Response ◽  
Solder Joints ◽  
Fatigue Testing ◽  
Hysteresis Loops ◽  
Damage Function ◽  
Lead Free ◽  
Lead Free Solder ◽  
Sac305 Solder ◽  
Free Solder

The extrapolation and generalization of accelerated test results for lead free solder joints require the identification of a damage function that can be counted on to apply beyond the region of the test. Individual ball grid array (BGA) scale Sn3Ag0.5Cu (SAC305) solder joints were subjected to isothermal shear fatigue testing at room temperature and 65 °C. The resulting mechanical response degradation and crack behavior, including strain hardening, crack initiation, and propagation, were correlated with the inelastic work and effective stiffness derived from load–displacement hysteresis loops. Crack initiation was found to scale with the accumulated work, independently of cycling amplitude and strain rate. The subsequent damage rate varied slightly with amplitude.

Effects of Shear Cycling on the Mechanical Properties of SAC and SAC+X Lead Free Solder Joints

2019 ◽  
Author(s):  
Mohd Aminul Hoque ◽  
Md Mahmudur Chowdhury ◽  
Sa’d Hamasha ◽  
Jeffrey C. Suhling ◽  
Pradeep Lall
Keyword(s):  
Mechanical Properties ◽  
Solder Joints ◽  
Coefficient Of Thermal Expansion ◽  
Real Life ◽  
Material Behavior ◽  
Lead Free ◽  
Lead Free Solder ◽  
Cyclic Shear ◽  
Mechanical Cycling ◽  
Free Solder

Abstract Solder joint reliability is a chief concern in electronic assemblies. Electronic packages consist of various materials, each having their own Coefficient of Thermal Expansion (CTE). When assembled packages experience high temperature gradients and thermal cycles, a mismatch in the CTE values brings about cyclic shear strains in the solder joints, which can ultimately lead to failure. Thus, it is important to understand the effects of shear cycling on the damage accumulated in solder joints. Previous studies conducted on the effect of mechanical cycling on the material behavior of lead free solders have been performed on bulk samples subjected to tension and compression. Our goal in this study was to determine the evolution of the mechanical properties of doped lead free solder joints when subjected to mechanical shear cycling. Experiments conducted on actual solder joints would help us gain a better understanding on the real life effects of shear cycling. The test specimens consisted of a 3 × 3 array of nine solder joints of approximately 0.75 mm diameter. With the aid of specially designed test fixtures, the specimens were gripped and then subjected to mechanical cycling in the shear using an Instron Micromechanical tester. Testing was performed on both SAC305 and SACX (SAC+Bi) solder joints. The joints were cycled for certain durations, and a nanoindentation system was used to measure the evolution of the mechanical properties (elastic modulus, hardness, creep rate) as a function of the number of shear cycles.

Investigation of the Effects of High Temperature Aging on Mechanical Behavior and Microstructural Changes in Lead Free Solders

2019 ◽  
Author(s):  
Jing Wu ◽  
Mohammad S. Alam ◽  
Jeffrey C. Suhling ◽  
Pradeep Lall
Keyword(s):  
Ostwald Ripening ◽  
Solder Joints ◽  
Particle Diameter ◽  
Lead Free ◽  
Average Particle ◽  
Lead Free Solder ◽  
Aging Effects ◽  
Sac305 Solder ◽  
Free Solder

Abstract Aging effects are common in lead free solder joints within electronic assemblies that are exposed to isothermal environments for extended periods. Such exposures lead to evolution of the solder microstructure, which results in changes in the mechanical properties and creep behavior of the solder joints. In our recent investigations, we have been utilizing Scanning Electron Microscopy (SEM) to better understand aging induced degradations. The microstructural evolutions were observed in SAC305 and SAC_Q (SAC+Bi) alloys exposed to isothermal conditions at T = 125 °C for several different regions from several different joints. The microstructures in several fixed regions of interest were recorded after predetermined time intervals of aging, which were 1 hour (up to 24 hours) and 10 hours (up to 150 hours) for the short term aging samples; and 250 hours (up to 2500 hours) for the long term aging samples. Using the recorded images and imaging processing software, the area and diameter of each IMC particle was tracked during the aging process. As expected, the quantitative analysis of the evolving SAC_Q microstructure showed that the particles coalesced during aging leading to a decrease in the number of particles. This caused an increase in the average diameter of the particles of slightly more than 100% for long term aging of 2500 hours. For SAC305, the average particle diameter was found to increase at three times the rate (increase of 200% after 2500 hours of aging). Thus, coarsening of IMC particles was greatly mitigated in the SAC_Q alloy relative to that observed in SAC305. Immediately after reflow solidification, Bismuth rich phases were present in the SAC_Q joints. During aging at T = 125 °C, the bismuth was observed to quickly go into solution both within the beta-Sn dendrites and in the intermetallic rich regions between dendrites. This resulted in solid solution strengthening of the lead free solder. It was also found that the aging-induced presence of bismuth in solution within the beta-Sn matrix provided an increased resistance to the Ostwald ripening diffusion process that coarsens the Ag3Sn IMC particles. The combination of these two effects in the SAC+Bi alloy lead to greatly improved resistance to aging induced effects relative to the SAC305 solder alloy. Finally, we have compared the time dependent evolution of microstructure with the degradation in strength during aging for of the two solder alloys, and good correlations were observed.

Reliability of an 1657CCGA (Ceramic Column Grid Array) Package With 95.5Sn3.9Ag0.6Cu Lead-Free Solder Paste on PCBs (Printed Circuit Boards)

2003 ◽  
Author(s):  
John Lau ◽  
Walter Dauksher
Keyword(s):  
Fatigue Life ◽  
Thermal Fatigue ◽  
Printed Circuit Boards ◽  
Lead Free ◽  
Lead Free Solder ◽  
Solder Paste ◽  
Circuit Boards ◽  
Printed Circuit ◽  
Thermal Fatigue Life ◽  
Free Solder

In many applications such as computers and telecommunications, the IC chip sizes are very big, the on-chip frequency and power dissipation are very high, and the number of chip I/Os is very large. The CCGA (ceramic column grid array) package developed by IBM is one of the best candidates for housing these kinds of chips [1–7]. There are two parts in this study. One is to show that the 2-parameter Weibull life distribution is adequate for modeling the thermal-fatigue life of lead-free solder joints. This is demonstrated by comparing the 2-parameter and 3-parameter Weibull distributions with life test data of an 1657-pin CCGA package with the 95.5wt%Sn3.9wt%Ag0.6wt%Cu lead-free solder paste on lead-free PCBs (printed circuit boards) under thermal cycling conditions. The other part of this study is to determine the time-history creep strain energy density of the 1657-pin CCGA solder column with two different solder paste materials, namely, 95.5wt%Sn3.9wt%Ag0.6wt%Cu and 63wt%Sn37wt%Pb and under three different thermal cycling profiles, namely, 25 ↔ 75°C, 0 ↔ 100°C, and −25 ↔ 125°C. The effects of these solder pastes and temperature conditions on the thermal-fatigue life of the high-lead (10wt%Sn90wt%Pb) solder columns of the CCGA package are provided and discussed.

A Study on Evaluation Technique for the Fatigue Life Scatter of Lead-Free Solder Joints

2007 ◽  
Author(s):  
Hiroki Miyauchi ◽  
Qiang Yu ◽  
Tadahiro Shibutani ◽  
Masaki Shiratori
Keyword(s):  
Fatigue Life ◽  
Printed Circuit Boards ◽  
Solder Joints ◽  
Electronic Device ◽  
Electronic Devices ◽  
Lead Free ◽  
Sensitivity Analyses ◽  
Lead Free Solder ◽  
Free Solder ◽  
Design Factors

The electronic device equipments using a lot of semiconductors are widespread to all industrial fields. Solder joints are used to mount the electronic chips, such as ceramic resistors and capacitors, on the printed-circuit boards in almost all electronic devices. However, since in many cases the thermal expansion coefficients of electronic parts and PCBs have mismatch, cyclic thermal stress and strain causes solder fatigue. Especially in the power electronic module and car electric module, the evaluation of thermal fatigue life for the chip components is important. It is understood that the fatigue lives of some electronic devices show large scatter in the thermal cycle test, even if their design is the same. The dispersion of main design factors of solder joints is thought as one of these reasons. Moreover, the influence of the dispersion grows when the lead-free solder materials are used in the devices. Therefore, it cannot be bypassed as the main issue for the reliability evaluation in the solder joints. In this study, how the dispersion of design factors influences the fatigue life in lead-free solder joint was investigated by the analytical approach. At first, sensitivity analyses were carried out to study the main effect of the dispersion of each factor on solder joints. And then, the interacting effects between the factors on the reliability were studied by considering the structural asymmetry due to the unbalanced solder joints. FEM analyses were carried out, and the fatigue life in solder joints was calculated from the inelastic strain range. As a result, practical evaluating approach for the fatigue life scatter of solder joints was proposed.

Reliability of an 1657CCGA (Ceramic Column Grid Array) Package With 95.5SN3.9AG0.6CU Lead-Free Solder Paste on PCBS (Printed Circuit Boards)

2005 ◽  
Vol 127 (2) ◽  
pp. 96-105 ◽  
Author(s):  
John Lau ◽  
Walter Dauksher
Keyword(s):  
Fatigue Life ◽  
Printed Circuit Boards ◽  
Lead Free ◽  
Lead Free Solder ◽  
Solder Paste ◽  
Circuit Boards ◽  
Printed Circuit ◽  
Thermal Fatigue Life ◽  
Free Solder ◽  
Two Parameter

In many applications such as computers and telecommunications, the IC chip sizes are very big, the on-chip frequency and power dissipation are very high, and the number of chip I/Os is very large. The CCGA (ceramic column grid array) package developed by IBM is one of the best candidates for housing these kinds of chips. There are two parts in this study. One is to show that the two-parameter Weibull life distribution is adequate for modeling the thermal-fatigue life of lead-free solder joints. This is demonstrated by comparing the two-parameter and three-parameter Weibull distributions with life test data of an 1657-pin CCGA package with the 95.5 wt %Sn3.9 wt %Ag0.6 wt %Cu lead-free solder paste on lead-free printed circuit boards under thermal cycling conditions. The other part of this study is to determine the time-history creep strain energy density of the 1657-pin CCGA solder column with two different solder paste materials, namely, 95.5 wt %Sn3.9 wt %Ag0.6 wt %Cu and 63 wt %Sn37 wt %Pb and under three different thermal cycling profiles, namely, 25↔75°C, 0↔100°C, and −25↔125°C. The effects of these solder pastes and temperature conditions on the thermal-fatigue life of the high-lead (10 wt %Sn90 wt %Pb) solder columns of the CCGA package are provided and discussed.

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