Finite element based solder joint fatigue life predictions. Design and material parameter effects on bga solderjoint. Unifed model parameter estimation through illustrative example. Now, the whole thing needs to be inspected andor replaced. Experimental and micromechanics analysis on fatigue crack. Cracking of a solder joint on a plated through joint is uncommon. The characteristics of crack propagation were correlated with the observed crack path in the solder joints.
Fracture mechanics study of fatigue crack growth in solder joints. The failure mechanism is crack propagation in the bulk of the solder joint and occurs earlier. Under vibrationinduced aging, the microstructure changes towards smaller grain sizes and also microcracks are initiated. Could selective soldering provide more consistent solder joints and thus reduce or eliminate the cracking. Solder fatigue for power modules in electric traction drive vehicles preprint. A study of crack propagation in pbfree solder joints.
Fatigue crack propagation tests were performed at room temperature in a servohydraulic fatigue machine mts810 under load control. The solder joints are subjected to thermal cycling and their crack lengths at different thermal cycles are measured. In this paper, crack propagation in solder joints made of two solder alloys, 62sn36pb2ag by weight, a commonly used solder paste for smt reflow applications, and 96. The model of thermoelasticity with a phase field approach is well suited to simulate behavior and mechanism of crack propagation in the solder material. Understand a designs breaking point with simple crack. The joint has failed due to expansion and contraction of the lead in the joint. The higher stiffness of pbfree sac solders makes pbfree assemblies more sensitive to drop impact. It was observed that a characteristic crack path is formed.
A primary crack at the packagesolder interface and a secondary crack at the solderboard interface are known to form in ballgrid array bga joints 4. Solder joint crack propagation analysis of waferlevel chip scale. Crack growth and propagation may occur in the intermetallic phase, or at the interfaces, which form the bonded joint. This leads to cracks through the whole solder joint and finally to failure of the assembly. This paper investigates a strain based crack propagation model, and discusses the application of fracture mechanics approach in the reliability validation of leadless solder joints. Differential expansion induced creepfatigue resulting from temperature cycling is an important cause of solder joint failure. The fatigue crack is expressed in terms of crack length %, which is the length of the crack observed in a sectional view though the centre of the joint expressed as a.
A crack initiation and propagation simulation and the fatigue. R red is the resistance of an interfacial imc, r bulk black is the resistance of a solder bulk, and r crack blue is the resistance of a crack. Study of fracture mechanics in testing interfacial. Fatigue cracks are also known to form underneath surface. Effect of voids on thermomechanical reliability of solder. Some of these voids are related to solder paste andor alloy and, as such, can be reduced or.
Often crosssection identified multiple cracks within a joint. The fatigue damage propagation is simulated with the. A study of solder joint failure criteria jianbiao pan, ph. Fatigue crack propagation analysis for micro solder joints. Also, the stress intensity factors at the crack tip of. Ball grid array bga solder joint intermittency detection. Techniques to evaluate solder fatigue behavior include finite element analysis and semianalytical closed form equations.
At high operating frequencies, the signal propagation is concentrated at the surface of interconnects. The equivalent strain rate for the simulation was 100s1 yield strength of solder 106mpa 25 figure 8. The benefits from a physically based description of crack propagation in solder joints include an accurate representation of the damage produced by cyclic loading and, therefore, a superior basis to evaluate. The propagation of cracks in the solder joints were monitored through electrical resistance measurement, and the rates of propagation were correlated with the observed crack paths in the solder. In this paper, crack propagation in solder joints made of two solder alloys, 62sn 36pb2ag by weight, a commonly used solder paste for smt reflow applications. Solder joint fatigue study under low temperature martian. This may be due to minor electrical noise in the test setup, cables, and environments, which happens often when an event.
Analysis of crack growth in solder joints emerald insight. Move the flame away from the joint and feed about 12 in. Expert panel responses that solder joint appears to have been defective from the getgo. Fatigue crack propagation life analysis of solder joints under thermal cyclic loadings was investigated by the strain energy release rate method using finite. A crack initiation and propagation simulation and the fatigue characteristics of solder joints considering the material property changes.
Chip resistors were soldered onto printed circuit boards and exposed to constant sinusoidal vibration at room temperature. An empirical crack propagation model and its applications. The investigation was focused on the interaction between surface morphology and microstructure of the solder joint. In both does, samples were removed from the chambers at. The present study investigates the crack propagation in one snpb and two pbfree solder joint systems. The solder will flow into all areas of a properly cleaned and fluxed joint. Dynamic crack propagation prediction of solder joints. W in3 or psi is the cyclic inelastic strain energy per unit volume obtained as the sum of strain energies due to global and local cte mismatches see. The faster ramp rate does impose more damage on solder joint than a slow ramp rate. Fatigue crack propagation analysis for microsolder joints. When the copper is hot enough, the solder will melt like butter. This means that the au dendrites within the solder joint would have a greater chance of serving as a catalyst for the propagation of cracks within the solder joint. This was achieved through the microstructural examination of fractured surfaces of the joints.
Detection of solder joint degradation using rf impedance. Fatigue crack propagation in mode 1 loading was studied utilizing a solderjoint plate specimen. Pdf a study of crack propagation in pbfree solder joints. After critical crack length is reached, the crack propagation accelerates.
Microstructural changes and crack propagation in solder. Crack growth rate measurements in surfacemount solder. However, in less than ideal conditions there could be additional factors leading voids to contribute to crack initiation and growth. In order to be able to optimise the drop test performance, it is necessary to have better insight into the crack propagation in the pbfree solder joints. The effects of vibration on the microstructure of the solder alloy sac305 96. In our model, the fatigue life of a solder joint is evaluated based on damage that is accumulated during crack propagation, and. The studies of crack growth in the solder joints of a pcb. Processing and reliability assessment of solder joint. Test the joint by touching the solder to the seam on the side opposite the flame.
Fatigue crack propagation life analysis of solder joints under thermal. However, assessing these cracks can take a long time because making a mesh to simulate crack propagation can take days even weeks. Pdf solderjoint quantitative crack analysisohmic resistance. Current engineering approaches for solder joint reliability assessment include the methodologies of the life prediction, computer modeling, and accelerated testing of solder joints. A in2 is the solder crack area for fully cracked, electrically open solder joints also the minimum solder joint load bearing area. Solder fatigue is the mechanical degradation of solder due to deformation under cyclic loading. Most solder joint fatigue models, and the supporting experimental data, do not treat the crack propagation processes that lead to failure.
Cracked joint on a printed circuit board wave soldering. In our model, the fatigue life of a solder joint is evaluated based on damage that is accumulated during crack propagation, and crack paths are automatically calculated. A numerical modelling method for the analysis of solder joint damage and crack propagation has been described in this paper. Cyclestofailure per unit area on the vertical axis serve as a scaled measure of cyclic life. Experimental data suggested that shape is the dominant factor affecting crack initiation time while standoff height is the major factor influencing crack propagation time. This study combines online resistance measurements of a solder joint during drop testing and high speed bend testing. W inc given by the multiplication of w in obtained from an arbitrarysized square region surrounding the crack tip by the side length of the square region did not depend. A phase field approach to fatigue crack propagation in. Analysis of crack growth in solder joints deepdyve. Crack propagation path an overview sciencedirect topics.
The fatigue lifetime of high standoff hourglassshaped solder joint is improved mainly by prolonged crack propagation time, with slight improvement in crack initiation time. Figures 3 and 4 show correlations of solder joint characteristic lives scaled for solder joint crack or load bearing areas, a, for snpb and sac387405 assemblies, respectively, versus cyclic strain energy. In this study, evaluation of fatigue crack properties in the sn5. In contrast to temperature shock tests the crack is initiated at the surface of the solder joint meniscus instead of.
In addition, a robust solder joint design was proposed and validated. Utilizing eutectic pbsncu as a reference system and assuming the presence of a prede. Solder joint reliability a unified thermomechanical model approach a thesis submitted to the graduate faculty of the north dakota state university of agriculture and applied science. Nrelcp54045957 solder fatigue for power modules in. This failure mode is predominant under impact conditions and is captured. Shear testing is a proven method 2 for evaluating not only the degree of crack propagation and damage to the solder joint, but also. Failure predictive modeling based on cohesive constitutive relation is used to study the effect of solderjoint array geometry on the integrity of live solder joints. Understanding the reliability of solder joints used in. However, the methodology is sensitive to the finite. The using of adaptive finite element technique greatly assist the process of simulation and also to minimization of computing time. In addition, results also showed that the leadfree solder joint during thermal shock fails faster than thermal cycling. Chapter iii solder joint reliability assessment vtechworks. The deterioration of solder joint integrity typically involves a sequential development of local stressing, microcracks, crack initiation and crack propagation, ultimately resulting in electrical opencircuiting by total joint separation from the pwb footprint.
Fatigue crack propagation behavior of leadfree solder. A diagram from a typical solder fatigue26 is shown in figure 8 with the crosssection of the failed r5 solder joint. The model includes the creep effect at different temperatures and hold times, and correlates well the thermal cycling test of 90 pb10 sn joints. The fatigue crack is expressed in terms of crack length %, which is the length of the crack observed in a sectional view though the centre of the joint expressed as a percentage of. To be presented at the 2009 ieee vehicle power and propulsion systems conference. After the thermal cycling test, microstructure analysis was performed to confirm the crack pattern.
In every integration point of the mesh the consumed lifetime cycles of the material is calculated using the stress state and a damage evolution law. Fatiguecreep crack propagation path in solder joints. Based on the crack propagation path and the phase coarsening observed around the crack path, it was concluded that the solder joint cracking was due to low cycle fatigue. The dynamic overstress state and crack propagation of the interface between the solder and the pad results in complete interface separation. A tmf crack propagated in the solder, beginning at the joint edge under the package and propagating through the gap and then through the fillet blue arrows. The crack could propagate and lead to part failure. Wave soldering defects cracked joint on a printed circuit board.