Solder fatigue
Solder fatigue is the mechanical degradation of
Overview
Solder is a
Historically, tin-lead solders were common alloys used in the
Much work has been done to characterize the creep-fatigue behavior of various solder alloys and develop predictive life damage models using a
Thermomechanical solder fatigue
During a product's operational lifetime it undergoes temperature fluctuations from application specific temperature excursions and self-heating due to component
The deformation characteristics of various solder alloys can be described at the microscale due to the differences in composition and resulting microstructure. Compositional differences lead to variations in
The resulting bulk behavior of solder is described as
Fatigue models
Solder damage models take a physics-of-failure based approach by relating a physical parameter that is a critical measure of the damage mechanism process (i.e. inelastic strain range or dissipated strain energy density) to cycles to failure. The relationship between the physical parameter and cycles to failure typically takes on a power law or modified power law relationship with material dependent model constants. These model constants are fit from experimental testing and simulation for different solder alloys. For complex loading schemes, Miner's linear superposition damage law[10] is employed to calculate accumulated damage.
Coffin–Manson model
The generalized Coffin–Manson[11][12][13][14] model considers the elastic and plastic strain range by incorporating Basquin's equation[15] and takes the form:
Here ∆ε ⁄ 2 represents the elastic-plastic cyclic strain range, E represents elastic modulus, σm represents means stress, and Nf represents cycles to failure. The remaining variables, namely σf,ε'f,b,and c are fatigue coefficients and exponents representing material model constants. The generalized Coffin–Manson model accounts for the effects of high cycle fatigue (HCF) primarily due to elastic deformation and
Engelmaier model
In the 1980s Engelmaier proposed a model,[16] in conjunction with the work of Wild,[17] that accounted for some of the limitations of the Coffin–Manson model, such as the effects of the frequency and temperature. His model takes a similar power law form:
Engelmaier relates the total shear strain (∆γ) to cycles to failure (Nf). ε'f and c are model constants where c is a function of mean temperature during thermal cycling (Ts) and thermal cycling frequency (f).
∆γ can be calculated as function of the distance from the neutral point (LD) solder joint height (hs), coefficient of thermal expansion (∆α), and change in temperature (ΔT). In this case C is empirical model constant.
This model was initially proposed for leadless devices with tin-lead solder. The model has since been modified by Engelmaier and others[who?] to account for other phenomena such as leaded components, thermal cycling dwell times, and lead-free solders. While initially a substantial improvement over other techniques to predict solder fatigue, such as testing and simple acceleration transforms, it is now generally acknowledged [citation needed] that Engelmaier and other models that are based on strain range do not provide a sufficient degree of accuracy.
Darveaux model
Darveaux[18][19] proposed a model relating the quantity of volume weighted average inelastic work density, the number of cycles to crack initiation, and the crack propagation rate to the characteristic cycles to failure.
In the first equation N0 represents the number of cycles to crack initiation, ∆W represents inelastic work density, K1 and K2 are material model constants. In the second equation, da/dN represents the crack prorogation rate, ∆W represents inelastic work density, K3 and K4 are material model constants. In this case the crack propagation rate is approximated to be constant. Nf represents the characteristic cycles to failure and a represents the characteristic crack length. Model constants can be fit for different solder alloys using a combination of experimental testing and
The Darveaux model has been found to be relatively accurate by several authors.[20][21] However, due to the expertise, complexity, and simulation resources required, its use has been primarily limited to component manufacturers evaluating component packaging. The model has not received acceptance in regards to modeling solder fatigue across an entire printed circuit assembly and has been found to be inaccurate in predicting system-level effects (triaxiality) on solder fatigue.[22]
Blattau model
The current solder joint fatigue model preferred by the majority of electronic
Here α is the CTE, T is temperature, LD is the distance to the neutral point, E is elastic modulus, A is the area, h is the thickness, G is shear modulus, ν is Poisson's ratio, and a is the edge length of the copper bond pad. The subscripts 1 refer to the component, 2 and b refer to the board, and s refer to the solder joint. The shear stress (∆τ) is then calculated by dividing this calculated force by the effective solder joint area. Strain energy is computed using the shear strain range and shear stress from the following relationship:
This approximates the hysteresis loop to be roughly equilateral in shape. Blattau uses this strain energy value in conjunction with models developed by Syed[24] to relate dissipated strain energy to cycles to failure.
Other fatigue models
The Norris–Landzberg model is a modified Coffin–Manson model.[25][26]
Additional strain range and strain energy based models have been proposed by several others.[24][27][28]
Vibration and cyclic mechanical fatigue
While not as prevalent as thermomechanical solder fatigue,
Additionally, low-temperature isothermal mechanical cycling is typically modeled with a combination of LCF and HCF strain range or strain energy models. The solder alloy, assembly geometry and materials, boundary conditions, and loading conditions will affect whether fatigue damage is dominated by elastic (HCF) or plastic (LCF) damage. At lower temperatures and faster strain rates the creep can approximated to be minimal and any inelastic damage will be dominated by plasticity. Several strain range and strain energy models have been employed in this type of a case, such as the Generalized Coffin–Manson model. In this case, much work has been done to characterize the model constants of various damage models for different alloys.
See also
- Cold solder joint
- Creep (deformation)
- Fatigue (material)
- Plasticity (physics)
- Potting (electronics)
- Vibration fatigue
References
- ^ Serebreni, M., Blattau, N., Sharon, G., Hillman, C., Mccluskey, P. "Semi-analytical fatigue life model for reliability assessment of solder joints in qfn packages under thermal cycling". SMTA ICSR, 2017. Toronto, ON, https://www.researchgate.net/publication/317569529_SEMI-ANALYTICAL_FATIGUE_LIFE_MODEL_FOR_RELIABILITY_ASSESSMENT_OF_SOLDER_JOINTS_IN_QFN_PACKAGES_UNDER_THERMAL_CYCLING
- ^ G. Sharon, "Temperature Cycling and Electronics", https://www.dfrsolutions.com/hubfs/Resources/services/Temperature-Cycling-and-Fatigue-in-Electronics-White-Paper.pdf
- ^ Wunderle, B.; B. Michel, "Progress in Reliability Research in Micro and Nano Region", Microelectronics and Reliability, V46, Issue 9-11, 2006.
- ^ https://www.dfrsolutions.com/hubfs/Resources/System_Level_Effects_on_Solder_Joint_Reliability.pdf [bare URL PDF]
- ^ Crina Rauta, Abhijit Dasgupta, Craig Hillman, "Solder Phase Coarsening, Fundamentals, Preparation, Measurement and Prediction", https://www.dfrsolutions.com/hubfs/Resources/services/Solder-Phase-Coarsening-Fundamentals-Preparation-Measurement-and-Prediction.pdf?t=1514473946162
- CiteSeerX 10.1.1.115.7354.
- ^ Garofalo, F., 1965, "Fundamentals of Creep and Creep-Rupture in Metals", Macmillan, New York.
- ^ Anand, L., 1985, "Constitutive Equations for Hot Working of Metals", J. Plasticity, 1(3), pp. 213–231
- ^ Brown, S. B.; Kim, K. H.; Anand, L., 1989, "An Internal Variable Constitutive Model for Hot Working of Metals," Int. J. Plasticity, 5(2), pp. 95–130
- ^ M. A. Miner, "Cumulative damage in fatigue", Journal of applied mechanics, vol. 12, pp. 159-164, 1945
- ^ L. F. Coffin, "The Problem of Thermal Stress Fatigue in Austenitic Steels", Special Technical Publication 165, ASTM, 1954, p. 31
- ^ L. F. Coffin, "A study of the Effects of Cyclic Thermal Stresses on a Ductile Metal", Trans. ASME, 76, 931–950 (August 1954).
- ^ S. S. Manson, "Behavior of materials under conditions of thermal stress", Proceedings of the Heat Transfer Symposium, University of Michigan Engineering Research Institute, Ann Arbor, Mich, pp. 9-75, 1953
- ^ Dowling, N. E., "Mechanical Behavior of Materials", 2nd Edition, Upper Saddle River, New Jersey, 1999.
- ^ Basquin, O. H. (1910). "The exponential law of endurance test". Proceedings of the American Society for Testing and Materials. 10: 625–630.
- ^ Engelmaier, W., "Fatigue Life of Leadless Chip Carrier Solder Joints During Power Cycling", Components, Hybrids, and Manufacturing Technology, IEEE Transactions on, vol.6, no.3, pp. 232-237, September 1983
- ^ Wild, R. N., "Some Fatigue Properties of Solders and Solder Joints", IBM Tech. Rep. 73Z000421, January 1973.
- ^ Darveaux, R., 1997, "Solder Joint Fatigue Life Model", in Design & Reliability of Solder and Solder Interconnections, Proceedings of the TMS, The Minerals, Metals & Materials Society, Orlando, Florida, February 1997.
- ^ Darveaux, R. (2000) Effect of simulation methodology on solder joint crack growth correlation. Electronic Components and Technology Conference, 2000 IEEE, pp 158–169
- ^ Ye, Yuming, et al. "Assessment on reliability of BGA package double-sided assembled". High Density Packaging and Microsystem Integration, 2007. HDP'07. International Symposium on. IEEE, 2007
- ^ Meifunas, M., et al. "Measurement and prediction of reliability for double-sided area array assemblies". Electronic Components and Technology Conference, 2003. Proceedings. 53rd. IEEE, 2003
- ^ https://www.dfrsolutions.com/hubfs/Developing%20Damage%20Models%20for%20Solder%20Joints%20Exposed%20to%20Complex%20Stress%20States.pdf, Hillman, C., "Developing Damage Models for Solder Joints Exposed to Complex Stress States: Influence of Potting, Coating, BGA Mirroring, and Housing on Solder Joint Fatigue", Proceedings of the EMPC, Warsaw, Poland, September, 2017
- ^ https://www.dfrsolutions.com/hubfs/DfR_Solutions_Website/Resources-Archived/Publications/2005-2007/2006_Blattau_IPC_working.pdf [bare URL PDF]
- ^ a b Syed, A., "Accumulated Creep Strain and Energy Density Based Thermal Fatigue Life Prediction Models for SnAgCu Solder Joints", ECTC 2004, pp. 737-746 - corrected.
- ^ Norris, K C, and AH Landzberg. "Reliability of Controlled Collapse Interconnections" IBM Journal of Research and Development 13, no. 3 (1969): 266-271
- ^ "Enabling More than Moore: Accelerated Reliability Testing and Risk Analysis for Advanced Electronics Packaging" (PDF). 2014.
- ^ S. Knecht; L. Fox, "Integrated matrix creep: Application to accelerated testing and lifetime prediction", in Solder Joint Reliability Theory and Applications, J. H. Lau, Ed. New York: Van Nostrand Reinhold, 1991, ch. 16.
- ^ Lee, W. W.; Nguyen, L. T.; Selvaduray, G. S., "Solder joint fatigue models: review and applicability to chip scale packages". Microelectronics Reliability 40 (2000) 231-244, 1999.
- ^ Steinberg, D. S. "Vibration analysis for electronic equipment". John Wiley & Sons, 2000.
- ^ https://www.dfrsolutions.com/hubfs/Resources/Guarantee-Reliability-with-Vibration-Simulation-and-Testing.pdf [bare URL PDF]
Further reading
- https://code541.gsfc.nasa.gov/publications Materials TIPs (Technical Information Papers) (on hold as-of July 2020)
- https://web.archive.org/web/20161227021306/https://code541.gsfc.nasa.gov/Uploads_materials_tips_PDFs/TIP%20090R.pdf Materials Engineering Branch TIP* No. 090 Fatigue Cracks in Solder Joints, Carl L. Haehner, 1987, 2003. (archived copy)