Effect of Dwell Times and Ramp Rates on the Thermal Cycling Reliability of Pb-Free Wafer-Level Chip Scale Packages: Experiments and Modeling

2006 ◽  
Author(s):  
S. Chaparala ◽  
J. M. Pitarresi ◽  
M. Meilunas
Keyword(s):  
Finite Element ◽  
Thermal Cycling ◽  
Thermal Shock ◽  
Dwell Time ◽  
Experimental Testing ◽  
Lead Free ◽  
Temperature Extremes ◽  
Wafer Level ◽  
Ramp Rate ◽  
Free Solder

Lead-free (Pb-free) solder has seen increasing use in interconnect systems for electronic packages due to legislative and marketing pressures. The NEMI selected eutectic Sn3.9Ag0.6Cu alloy (or a close variation near eutectic Sn3.5Ag1.0Cu used in this study) is a leading Pb-free substitute for the Sn/Pb solder candidate. The reliability of this Pb-free solder alloy under accelerated thermal cycling and thermal shock testing as a function of testing parameters such as dwell time and ramp rate is critical in qualifying the performance of these Pb-free alternatives with the traditionally used Sn37Pb solder This paper presents the reliability of Pb-free solder joints in wafer level chip scale packages (WLCSPs), which are extensions of flip-chip packaging technology to standard surface mount technology, with external dimensions equal to that of the silicon device [1]. The reliability of these packages under both liquid-to-liquid thermal shock (LLTS) testing and accelerated air-to-air thermal cycling (AATC) conditions, as a function of dwell times and ramp rates is evaluated using extensive experimental testing in combination with finite element analysis. Besides, two asymmetric cycles in which the cold and hot dwell times differ at two temperature extremes were studied. Along with the Pb-free solder, some test vehicles were built using eutectic Sn-Pb solder and evaluated for comparison purposes. Experimental results show that an increase in ramp rate does not adversely affect the solder joint reliability in the case of Pb-free solder. The reliability of lead-free WLCSPs was highly dependent upon the dwell time at the temperature extremes, with this dependency being considerably greater for the lead-free allow than for Sn/Pb at 0°C and 100°C. Accelerated test results show that increasing the dwell time from 280 to 900 seconds reduced the N63.2 of the Sn/Pb samples by 12% and the Pb-free samples by 65%. Reliability during asymmetric cycles resulted in a trend that is similar in two cases studied. A predictive equation was developed to evaluate the characteristic life of the package with respect to the dwell time. Non-linear, finite element (FE) modeling was conducted using temperature dependent creep constitutive relations for the Pb-free solder to understand the experimental trends observed. The FE results predicted the same trend of the package reliability as observed experimentally, with respect to the changing dwell and ramp times. The finite element predictions demonstrated reasonable correlation with the experimental observations.

FEA Based Reliability Predictions for PBGA Packages Subjected to Isothermal Aging Prior to Thermal Cycling

2015 ◽  
Author(s):  
Munshi Basit ◽  
Mohammad Motalab ◽  
Jeffrey C. Suhling ◽  
John L. Evans ◽  
Pradeep Lall
Keyword(s):  
Finite Element ◽  
Solder Joint ◽  
Thermal Cycling ◽  
Isothermal Aging ◽  
Material Behavior ◽  
Lead Free ◽  
Stress Strain ◽  
Solder Material ◽  
Free Solder ◽  
Temperature Aging

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 degradations of Sn-Ag-Cu (SAC) lead free solders during room temperature aging (25 C) and elevated temperature aging (50, 75, 100, 125, and 150 C) were unexpectedly large. The measured stress-strain data demonstrated large reductions in stiffness, yield stress, ultimate strength, and strain to failure (up to 50%) during the first 6 months after reflow solidification. In this study, we have used both accelerated life testing and finite element modeling to explore how prior isothermal aging affects the overall reliability of PBGA packages subjected to thermal cycling. In the experimental work, an extensive test matrix of thermal cycling reliability testing has been performed using a test vehicle incorporating several sizes (5, 10, 15, 19 mm) of BGA daisy chain components with 0.4 and 0.8 mm solder joint pitches (SAC305). PCB test boards with 3 different surface finishes (ImAg, ENIG and ENEPIG) were utilized. In this paper, we concentrate on the reporting the results for a PBGA component with 15 mm body size. Before thermal cycling began, the assembled test boards were divided up into test groups that were subjected to several sets of aging conditions (preconditioning) including 0, 6, and 12 months aging at T = 125 °C. After aging, the assemblies were subjected to thermal cycling (−40 to +125 °C) until failure occurred. The Weibull data failure plots have demonstrated that the thermal cycling reliabilities of pre-aged assemblies were significantly less than those of non-aged assemblies. A three-dimensional finite element model of the tested 15 mm PBGA packages was also developed. The cross-sectional details of the solder ball and the internal structure of the BGA were examined by scanning electron microscopy (SEM) to capture the real geometry of the package. Simulations of thermal cycling from −40 to 125 C were performed. To include the effects of aging in the calculations, we have used a revised set of Anand viscoplastic stress-strain relations for the SAC305 Pb-free solder material that includes material parameters that evolve with the thermal history of the solder material. The accumulated plastic work (energy density dissipation) was used is the failure variable; and the Darveaux approach to predict crack initiation and crack growth was applied with aging dependent parameters to estimate the fatigue lives of the studied packages. We have obtained good correlation between our new reliability modeling procedure that includes aging and the measured solder joint reliability data. As expected from our prior studies on degradation of SAC material properties with aging, the reliability reductions were more severe for higher aging temperature and longer aging times.

Thermal Cycling Reliability Predictions for PBGA Assemblies That Include Aging Effects

2013 ◽  
Author(s):  
Mohammad Motalab ◽  
Muhannad Mustafa ◽  
Jeffrey C. Suhling ◽  
Jiawei Zhang ◽  
John Evans ◽  
...  
Keyword(s):  
Finite Element ◽  
Solder Joint ◽  
Thermal Cycling ◽  
Failure Criteria ◽  
Lead Free ◽  
Aging Effects ◽  
Solder Joint Reliability ◽  
Reliability Models ◽  
Joint Reliability ◽  
Free Solder

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. Traditional finite element based predictions for solder joint reliability during thermal cycling accelerated life testing are based on solder constitutive equations (e.g. Anand viscoplastic model) and failure models (e.g. energy dissipation per cycle model) that do not evolve with material aging. Thus, there will be significant errors in the calculations with lead free SAC alloys that illustrate dramatic aging phenomena. In this research, we have developed a new reliability prediction procedure that utilizes constitutive relations and failure criteria that incorporate aging effects, and then validated the new approach through correlation with thermal cycling accelerated life testing experimental data. As a part of this work, a revised set off Anand viscoplastic stress-strain relations for solder have been developed that included material parameters that evolve with the thermal history of the solder material. The effects of aging on the nine Anand model parameters have been determined as a function of aging temperature and aging time, and the revised Anand constitutive equations with evolving material parameters have been implemented in commercial finite element codes. In addition, new aging aware failure criteria have been developed based on fatigue data for lead free solder uniaxial specimens that were aged at elevated temperature for various durations prior to mechanical cycling. Using the measured fatigue data, mathematical expressions have been developed for the evolution of the solder fatigue failure criterion constants with aging, both for Coffin-Manson (strain-based) and Morrow-Darveaux (dissipated energy based) type fatigue criteria. Similar to the findings for mechanical/constitutive behavior, our results show that the failure data and associated fatigue models for solder joints are affected significantly by isothermal aging prior to cycling. After development of the tools needed to include aging effects in solder joint reliability models, we have then applied these approaches to predict reliability of PBGA components attached to FR-4 printed circuit boards that were subjected to thermal cycling. Finite element modeling was performed to predict the stress-strain histories during thermal cycling of both non-aged and aged PBGA assemblies, where the aging at constant temperature occurred before the assemblies were subjected to thermal cycling. The results from the finite element calculations were then combined with the aging aware fatigue models to estimate the reliability (cycles to failure) for the aged and non-aged assemblies. As expected, the predictions show significant degradations in the solder joint life for assemblies that had been pre-aged before thermal cycling. To validate our new reliability models, an extensive test matrix of thermal cycling reliability testing has been performed using a test vehicle incorporating several sizes of fine pitch PBGA daisy chain components. Before thermal cycling began, the assembled test boards were divided up into test groups that were subjected to several sets of aging conditions (preconditioning) including different aging temperatures (T = 25, 55, 85 and 125 C) and different aging times (no aging, and 6 and 12 months). After aging, the assemblies were subjected to thermal cycling (−40 to +125 C) until failure occurred. As with the finite element predictions, the Weibull data failure plots have demonstrated that the thermal cycling reliabilities of pre-aged assemblies were significantly less than those of non-aged assemblies. Good correlation was obtained between our new reliability modeling procedure that includes aging and the measured solder joint reliability data.

Thermal Shock Testing as a Reliability Qualification Test for Lead-Free Solder

2006 ◽  
Author(s):  
Kunal Goray ◽  
Saketh Mahalingam ◽  
Amit Shah ◽  
Abhijit Dasgupta
Keyword(s):  
Thermal Cycling ◽  
Thermal Shock ◽  
Lead Free ◽  
Lead Free Solder ◽  
Shock Testing ◽  
Solder Interconnects ◽  
Thermal Cycling Testing ◽  
Accelerated Thermal Cycling ◽  
Free Solder ◽  
Sac Solder

Accelerated thermal cycling tests are used to ascertain the reliability of solder interconnects in electronics assemblies. These tests typically last a few months and therefore, are highly resource intensive. Thermal shock tests on the other hand are faster but have been found to be ineffective in accelerating thermal cycling failures for eutectic tin lead solder. In this paper, thermal shock testing is proposed as an alternative to conventional thermal cycling testing for lead-free solder interconnects using Sn, Ag and Cu (SAC) solder. Results from the thermal shock and thermal cycling testing of Ball-Grid-Array (BGA) components are presented. Failure analyses of the solder joints reveal the failure mode for thermal shock in comparison to thermal cycling testing. Numerical modeling results for the thermal cycling and thermal shock testing for lead free and eutectic lead solder are then presented and discussed. The simulation results agree with the experiments and theory is proposed to account for the similar trends between thermal cycling and thermal shock testing for lead free solder.

scholarly journals Reliability Evaluation of Fan-Out Type 3D Packaging-On-Packaging

Micromachines ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 295
Author(s):  
Pao-Hsiung Wang ◽  
Yu-Wei Huang ◽  
Kuo-Ning Chiang
Keyword(s):  
Finite Element ◽  
Thermal Cycling ◽  
Glass Substrate ◽  
High Speed ◽  
Coefficient Of Thermal Expansion ◽  
Three Dimensional ◽  
Design Parameters ◽  
Time To Failure ◽  
Wafer Level ◽  
Fine Pitch

The development of fan-out packaging technology for fine-pitch and high-pin-count applications is a hot topic in semiconductor research. To reduce the package footprint and improve system performance, many applications have adopted packaging-on-packaging (PoP) architecture. Given its inherent characteristics, glass is a good material for high-speed transmission applications. Therefore, this study proposes a fan-out wafer-level packaging (FO-WLP) with glass substrate-type PoP. The reliability life of the proposed FO-WLP was evaluated under thermal cycling conditions through finite element simulations and empirical calculations. Considering the simulation processing time and consistency with the experimentally obtained mean time to failure (MTTF) of the packaging, both two- and three-dimensional finite element models were developed with appropriate mechanical theories, and were verified to have similar MTTFs. Next, the FO-WLP structure was optimized by simulating various design parameters. The coefficient of thermal expansion of the glass substrate exerted the strongest effect on the reliability life under thermal cycling loading. In addition, the upper and lower pad thicknesses and the buffer layer thickness significantly affected the reliability life of both the FO-WLP and the FO-WLP-type PoP.

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