Mechanical Characterization of SAC305 Lead Free Solder at High Temperatures (original) (raw)
Related papers
High temperature tensile and creep behavior of lead free solders
The mechanical behavior of lead free solders is highly dependent on the testing temperature. Previous investigations on mechanical characterization of conventional and doped lead free SAC solders have mainly emphasized stress-strain and creep testing at temperatures from 25 to 125 °C. However, solders are exposed to very high temperatures from 125-200 °C in several harsh environment applications including well boring, geothermal energy, and aerospace engines. In the current work, we have extended our previous studies to explore mechanical properties for SAC305, SAC_Q, SAC_R, and Innolot solders at temperatures from 125-200 °C at a strain rate of 0.001 (sec-1). The Anand constitutive model with parameters measured previously using test data from 25-125 has been shown to fit the high temperature stress-strain curves reasonably well. In addition, high temperature creep behavior of SAC305 was explored. Finally, the high temperature tensile properties of the abovementioned solders have been compared. Our results show a significant degradation of mechanical properties of lead-free solders at higher temperatures. Also, a noteworthy increase in the secondary creep strain rate has been observed. Comparison of the results for different solders has shown that the addition of dopants (e.g. Bi, Ni, and Sb) in the traditional SAC alloys improve their properties significantly.
A Comparative Study of the High Temperature Mechanical Behavior of Lead Free Solders
Lead free solders are renowned as interconnects in electronic packaging due to their relatively high melting point, attractive mechanical properties, thermal cycling reliability, and environment friendly chemical property. The mechanical behavior of lead free solders is highly dependent on the operating temperature. Previous investigations on mechanical characterization of lead free solders have mainly emphasized stress-strain and creep testing at temperatures up to 125 o C. However, electronic devices, sometimes, experience harsh environment applications including well drilling, geothermal energy, and aerospace engines where solders are exposed to very high temperatures from 125-200 o C. Mechanical properties of lead free solders at elevated temperatures are limited. In this work, we have compared the mechanical properties of two popular Solder alloys, such as SAC305, and SAC_Q at extremely high temperatures up to 200 o C. For each elevated temperature, stress-strain tests were performed at three strain rates (0.001, 0.0001, and 0.00001 1/sec). The experimental results have been compared with the prediction of Anand constitutive model. In addition, high temperature tensile properties of the solders as mentioned above have been compared. Our results show a significant degradation of mechanical properties of lead-free solders at higher temperatures. Comparison of the results between SAC305 and SAC_Q solders has shown that the addition of dopants (e.g. Bi) in SAC_Q solder improves the properties significantly. Good correlations were obtained between the Anand model predicted results and the experimental data over a wide range of temperatures and strain rates.
Lead free solders are renowned as interconnects in electronic packaging due to their relatively high melting point, attractive mechanical properties, thermal cycling reliability, and environment friendly chemical properties. The mechanical behavior of lead free solders is highly dependent on the operating temperature. Previous investigations on mechanical characterization of lead free solders have mainly emphasized stress-strain and creep testing at temperatures up to 125 °C. However, electronic devices, sometimes, experience harsh environment applications including well drilling, geothermal energy, automotive power electronics, and aerospace engines where solders are exposed to very high temperatures from 125-200 °C. Mechanical properties of lead free solders at elevated temperatures are limited. In this work, we have investigated the mechanical behavior of several SAC and SAC+X lead free solder alloys including SAC305 (96.5Sn-3.0Ag-0.5Cu) and SAC_Q at extreme high temperatures up to 200 °C. Stress-strain tests were performed on as reflowed alloys at four elevated temperatures (T = 125, 150, 175, and 200 °C). In addition, changes of the mechanical behavior of these alloys due to long-term aging have been studied. Extreme care has been taken during specimen preparation so that the fabricated solder uniaxial test specimens accurately reflect the solder material microstructures present in actual lead free solder joints High temperature tensile properties of the solders including initial modulus, yield stress, and ultimate tensile strength have been compared. As expected, our results show substantial degradations of the mechanical properties of lead-free solders at higher temperatures and with aging. The degradations are even more significant when the samples are stored in a high temperature environment for a particular span of time. Furthermore, Comparison of the results for different solders has shown that the addition of dopants (e.g. Bi, Ni, and Sb) in the traditional SAC alloys improve their high temperature properties significantly.
High Temperature Mechanical Behavior of SAC and SAC+X Lead Free Solders
—In this work, we have investigated the mechanical behavior of several SAC and SAC+X lead free solder alloys at extreme high temperatures up to 200 o C. The studied alloys included SAC305 (96.5Sn-3.0Ag-0.5Cu), SAC_Q (92.8Sn-3.4Ag-0.5Cu-3.3Bi), and Innolot (90.95Sn-3.8Ag-0.7Cu-3.0Bi-0.15Ni-1.4Sb). The solder uniaxial test specimens were formed in high precision rectangular cross-section glass tubes using a vacuum suction process. The samples were initially cooled in a water bath and were later reflowed. The reflow profile was chosen to closely mimic profiles used for BGA assemblies, so that the obtained microstructures were similar to those found in typical solder joints. For each of 4 elevated temperatures (T = 125, 150, 175, and 200 o C), tensile stress-strain tests were performed at three strain rates (SR = 0.001, 0.0001, and 0.00001 sec-1). For each alloy and testing temperature, the stress-strain curve shape and high temperature tensile properties (initial modulus, yield stress, and ultimate tensile strength) of the solders were measured and compared. As expected, the results have shown significant degradations of the mechanical properties of lead-free solders at higher temperatures. However, it was found that the addition of dopants (e.g. Bi, Ni, and Sb) in the SAC+X alloys improved their high temperature properties significantly. The measured data have been used to determine the Anand model parameters for each alloy. Good correlations were obtained between the Anand model predictions and the experimental data over a wide range of strain levels, temperatures, and strain rates.
Mechanical Behavior Evolution of SAC+Bi Lead Free Solder Exposed to Thermal Cycling
IEEE ITherm Conference, 2020
Lead free electronic assemblies are often subjected to thermal cycling during qualification testing or during actual use. During the dwells at the constant high temperature extreme, the lead free solders joints will experience thermal aging phenomena, resulting in microstructural evolution and material property degradation. Additional aging effects can also occur in the ramp periods from low to high temperature. In this study, we have investigated the evolution of the mechanical behavior of SAC+Bi (SAC_Q) lead free solder material under different thermal cycling loadings. The nominal chemical composition of the SAC+Bi solder in this work is 92.5% Sn, 4.0% Ag, 0.5% Cu, and 3.0% Bi. A controlled reflow profile was used to prepare rectangular solder samples for uniaxial tensile testing. Then, all the samples were preconditioned by thermal cycling from-40 C to +125 o C inside an environmental chamber under no load condition (stress-free). Several thermal cycling profiles were examined including: (1) 150 minute cycles with 45 minutes ramps and 30 minutes dwells (slow thermal cycling), (2) air-to-air thermal shock exposures with 30 minutes dwells and near instantaneous ramps (thermal shock), (3) 90 minute cycles with 45 minutes ramps and 0 minutes dwells (thermal ramping), and (4) no cycling with simple aging at high temperature extreme (aging). For each profile, sets of samples were cycled for various durations (e.g. 48, 96, and 240 cycles), which resulted in various aging times at the high temperature extreme of T = 125 o C. The cycled samples were then subjected to stress-strain or creep testing to measure the mechanical properties including effective elastic modulus, Ultimate Tensile Strength (UTS), yield stress, and the creep strain rate. This paper will report on the observed changes in the stress-strain curves, effective modulus, and UTS. The evolutions of the stress-strain curves and associated mechanical properties for each cycling profile were characterized as a function of the cycling duration, as well as the total dwell time at high temperature extreme. For the various thermal cycling profiles, only small changes in the mechanical properties were observed for the SAC+Bi solder. Also, the results for the mechanical property evolutions of SAC+Bi (SAC_Q) were compared to those for SAC305 measured in our previous studies [1-2]. Significantly higher changes were observed in the SAC305 solder relative to the SAC+Bi alloy.
High Temperature Creep Response of Lead Free Solders
Lead free solder materials are susceptible to significant creep deformations in harsh high temperature environments including automotive, avionics, military, and oil exploration applications. In addition, dramatic degradations will occur in the creep responses of lead free solder alloys when they are exposed to long term isothermal aging during product applications at high temperatures. Such degradations in the creep compliance of the solder material are universally detrimental to reliability of solder joints in electronic assemblies. In this work, we have characterized the high temperature creep behavior of SAC405 (95.5Sn4.0Ag0.5Cu) lead free solder, which is the most creep resistant of the standard SACN05 alloys. In addition, we have studied the creep behaviors of two doped SAC solders, SAC_Q and Innolot, which have been previously shown to out-perform SAC405 in simple mechanical stress-strain tests at room temperature. Tensile specimens were formed in rectangular cross-section glass tubes using a vacuum suction process, and a water quenched (WQ) solidification profile was utilized to yield fine microstructures and the upper limits of the mechanical properties for each alloy. The samples were then aged for 10 days at room temperature to stabilize their microstructures. After aging, creep testing was performed at two different stress levels (10, 15 MPa) and several different extreme/high testing temperatures (T = 100, 125, 150, 175, and 200 o C). For each set of conditions, the creep performances of the three alloys were compared. The results showed that the doped SAC alloys were more resistant to creep at high temperatures. The creep rates of SAC_Q are roughly 50% of those for SAC405, while the creep rates of Innolot are roughly 33% of those for SAC405. It is likely that the dopants can significantly block the movement of dislocations and thus increase the creep resistance of these solders. INTRODUCTION Creep becomes a dominant deformation mode in a solder material when it's homologous temperature, T H = T/T Melt > 0.5. For SnAg -Cu (SAC) lead free solders, this condition occurs at relatively low temperatures (e.g. room temperature, T = 25 o C, T H ≈ 0.6). Lead free electronics are often exposed to more severe high temperature environments including automotive, avionics, military, and oil exploration applications, where service temperatures can approach T =
The influence of aging on the stress-strain and creep behavior of sac solder alloys
2010
The microstructure, mechanical response, and failure behavior of lead free solder joints in electronic assemblies are constantly evolving when exposed to isothermal aging and/or thermal cycling environments. In our prior work on aging effects, we have demonstrated that the observed material behavior variations of Sn-Ag-Cu (SAC) lead free solders during room temperature aging (25 o C) and elevated temperature aging (125 o C) were unexpectedly large and universally detrimental to reliability. Such effects for lead free solder materials are especially important for the harsh applications environments present in high performance computing and in automotive, aerospace, and defense applications. However, there has been little work in the literature, and the work that has been done has concentrated on the degradation of solder ball shear strength (e.g. Dage Shear Tester). Current finite element models for solder joint reliability during thermal cycling accelerated life testing are based on traditional solder constitutive and failure models that do not evolve with material aging. Thus, there will be significant errors in the calculations with the new lead free SAC alloys that illustrate dramatic aging phenomena.
Mechanical Characterization of Doped SAC Solder Materials at High Temperature
Reliable lead free solders are needed for products exposed to extreme environments such as those used in the automotive, avionics, and oil-exploration industries, as well as in military applications. In this study, stress-strain curves have been measured for several doped SnAg -Cu (SAC) solder materials at high temperatures up to 200 o C, and their performances have been compared to those for standard SAC alloys. The doped lead free solder materials are referred to as SAC_R (Ecolloy), SAC_Q (CYCLOMAX), and Innolot by their vendors. SAC_R and SAC_Q are formulated with Sn, Ag, Cu, and Bi (SAC+Bi), while Innolot includes an engineered combination of six elements. Tensile specimens were formed in rectangular cross-section glass tubes using a vacuum suction process, and a water quenched (WQ) solidification profile was utilized. This profile resulted in extremely fine microstructures, and mechanical properties near the upper limit possible for each alloy. Uniaxial tensile testing was performed on the three doped alloys at temperatures of 25, 50, 75, 100, 125, 150, 175, and 200 o C, and a strain rate of 0.001 sec-1. For the SAC_Q alloy, testing was also performed at strain rates of 0.0001 and 0.00001 sec-1 , and the Anand constitutive parameters were calculated. The results for the doped solders were compared to standard SAC105 and SAC405 lead free alloys. The mechanical properties of SAC_R were found to exceed those for SAC105 at all temperatures, even though SAC_R does not contain any silver. In addition, the mechanical properties of SAC_Q and Innolot were found to match or exceed those of SAC405 at all temperatures. The new alloys show great promise for use in extremely harsh environments.
Performance of SAC305 and SAC305-0.4La lead free electronic solders at high temperature
Soldering & Surface Mount Technology
Purpose Tin-Silver-Copper is widely accepted as the best alternative to replace Tin-Lead solders in microelectronics packaging due to their acceptable properties. However, to overcome some of the shortcomings related to its microstructure and in turn, its mechanical properties at high temperature, the addition of different elements into Tin-Silver-Copper is important for investigations. The purpose of this paper is to analyse the effect of lanthanum doping on the microstructure, microhardness and tensile properties of Tin-Silver-Copper as a function of thermal aging time for 60, 120 and 180 h at a high temperature of 150°C and at high strain rates of 25, 35 and 45/s. Design/methodology/approach The microstructure of un-doped and Lanthanum-doped Tin-Silver-Copper after different thermal aging time is examined using scanning electron microscopy followed by digital image analyses using ImageJ. Brinell hardness is used to find out the microhardness properties. The tensile tests are perf...
High strain rate mechanical properties of SAC105 leadfree alloy at high operating temperatures
Fourteenth Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm), 2014
Industry migration to lead free solders has resulted in a proliferation of a wide variety of solder alloy compositions. The most popular amongst these are the Sn-Ag-Cu family of alloys like SAC 105 and SAC305. Electronics subjected to shock and vibration may experience strain rates of 1-100 per sec. Electronic product may often be exposed to high temperature during storage, operation and handling in addition to high strain rate transient dynamic loads during drop-impact, shock and vibration. Properties of leadfree solder alloys at high strain rates at low and high temperatures experienced by the solder joint during typical mechanical shock events are scarce. Previous studies have showed the effect of high strain rates and thermal aging on the mechanical properties of leadfree alloys including elastic modulus and the ultimate tensile strength. The ANAND viscoplastic constitutive model has been widely used to describe the inelastic deformation behavior of solders in electronic components. In this study, SAC 105 leadfree alloys have been tested at strain rates of 10, 35, 50 and 75 per sec at various operating temperatures of 50°C, 75°C, 100°C and 125°C. Full-field strain in the specimen have been measured using high speed imaging at frame rates up to 75,000 fps in combination with digital image correlation. The cross-head velocity has been measured prior to, during, and after deformation to ensure the constancy of cross-head velocity. Stress-Strain curves have been plotted over a wide range of strain rates and temperatures. Experimental data for the pristine specimen has been fit to the ANAND's viscoplastic model.