Analysis of crack growth in solder joints emerald insight. In addition, results also showed that the leadfree solder joint during thermal shock fails faster than thermal cycling. It was observed that a characteristic crack path is formed. The crack could propagate and lead to part failure. Pendulum test 10 and 4point bending tests 67 8 9were performed to study the crack propagation in pbfree solder joints.
Often crosssection identified multiple cracks within a joint. 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. Study of fracture mechanics in testing interfacial. After the thermal cycling test, microstructure analysis was performed to confirm the crack pattern. Fatigue crack propagation behavior of leadfree solder.
A crack initiation and propagation simulation and the fatigue. Fatiguecreep crack propagation path in solder joints. A phase field approach to fatigue crack propagation in. Shear testing is a proven method 2 for evaluating not only the degree of crack propagation and damage to the solder joint, but also. 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. 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. Crack growth rate measurements in surfacemount solder.
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. The model includes the creep effect at different temperatures and hold times, and correlates well the thermal cycling test of 90 pb10 sn joints. A study of solder joint failure criteria jianbiao pan, ph. Solder fatigue is the mechanical degradation of solder due to deformation under cyclic loading. The fatigue lifetime of high standoff hourglassshaped solder joint is improved mainly by prolonged crack propagation time, with slight improvement in crack initiation time. Crack growth and propagation may occur in the intermetallic phase, or at the interfaces, which form the bonded joint. Fatigue crack propagation in mode 1 loading was studied utilizing a solderjoint plate specimen. We investigated crack propagation in the microsolder joints of a semiconductor and developed a new crack propagation model.
Fracture mechanics study of fatigue crack growth in solder joints. A diagram from a typical solder fatigue26 is shown in figure 8 with the crosssection of the failed r5 solder joint. 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. Solder joint fatigue study under low temperature martian. Cracked joint on a printed circuit board wave soldering. To be presented at the 2009 ieee vehicle power and propulsion systems conference. Experimental data suggested that shape is the dominant factor affecting crack initiation time while standoff height is the major factor influencing crack propagation time. Understanding crack growth in solder joints is important for predicting the fatigue life of solder interconnects. The faster ramp rate does impose more damage on solder joint than a slow ramp rate. Solder fatigue for power modules in electric traction drive vehicles preprint. Utilizing eutectic pbsncu as a reference system and assuming the presence of a prede. After critical crack length is reached, the crack propagation accelerates. Expert panel responses that solder joint appears to have been defective from the getgo. 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.
Finite element based solder joint fatigue life predictions. In this study, evaluation of fatigue crack properties in the sn5. 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. Also, the stress intensity factors at the crack tip of. Fatigue crack propagation life analysis of solder joints under thermal. Under vibrationinduced aging, the microstructure changes towards smaller grain sizes and also microcracks are initiated. An empirical crack propagation model and its applications. Wave soldering defects cracked joint on a printed circuit board. Analysis of crack growth in solder joints deepdyve. 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.
Fatigue crack propagation tests were performed at room temperature in a servohydraulic fatigue machine mts810 under load control. 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. Unifed model parameter estimation through illustrative example. The higher stiffness of pbfree sac solders makes pbfree assemblies more sensitive to drop impact. Detection of solder joint degradation using rf impedance. 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 numerical modelling method for the analysis of solder joint damage and crack propagation has been described in this paper. Nrelcp54045957 solder fatigue for power modules in. This can often occur at stress levels below the yield stress of solder as a result of repeated temperature fluctuations, mechanical vibrations, or mechanical loads. Some of these voids are related to solder paste andor alloy and, as such, can be reduced or. Microstructural changes and crack propagation in solder. 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. However, assessing these cracks can take a long time because making a mesh to simulate crack propagation can take days even weeks. Chapter iii solder joint reliability assessment vtechworks. Now, the whole thing needs to be inspected andor replaced.
At high operating frequencies, the signal propagation is concentrated at the surface of interconnects. Move the flame away from the joint and feed about 12 in. This may be due to minor electrical noise in the test setup, cables, and environments, which happens often when an event. The characteristics of crack propagation were correlated with the observed crack path in the solder joints. Chip resistors were soldered onto printed circuit boards and exposed to constant sinusoidal vibration at room temperature. Most solder joint fatigue models, and the supporting experimental data, do not treat the crack propagation processes that lead to failure. A in2 is the solder crack area for fully cracked, electrically open solder joints also the minimum solder joint load bearing area.
Cyclestofailure per unit area on the vertical axis serve as a scaled measure of cyclic life. The equivalent strain rate for the simulation was 100s1 yield strength of solder 106mpa 25 figure 8. Techniques to evaluate solder fatigue behavior include finite element analysis and semianalytical closed form equations. A study of crack propagation in pbfree solder joints. In addition, a robust solder joint design was proposed and validated. The studies of crack growth in the solder joints of a pcb. In both does, samples were removed from the chambers at.
Design and material parameter effects on bga solderjoint. 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. 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. Experimental and micromechanics analysis on fatigue crack. Crack propagation path an overview sciencedirect topics. 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. This failure mode is predominant under impact conditions and is captured. The ability of the gold to dissolve in that molten solder paste does increase the amount of gold per given volume of solder paste. Could selective soldering provide more consistent solder joints and thus reduce or eliminate the cracking. The solder will flow into all areas of a properly cleaned and fluxed joint.
Pdf solderjoint quantitative crack analysisohmic resistance. In contrast to temperature shock tests the crack is initiated at the surface of the solder joint meniscus instead of. Processing and reliability assessment of solder joint. Understand a designs breaking point with simple crack. Fatigue crack propagation analysis for microsolder joints.
Current engineering approaches for solder joint reliability assessment include the methodologies of the life prediction, computer modeling, and accelerated testing of solder joints. The fatigue damage propagation is simulated with the. Differential expansion induced creepfatigue resulting from temperature cycling is an important cause of solder joint failure. Effect of voids on thermomechanical reliability of solder. Fatigue crack propagation life analysis of solder joints under thermal cyclic loadings was investigated by the strain energy release rate method using finite. This was achieved through the microstructural examination of fractured surfaces of the joints. The investigation was focused on the interaction between surface morphology and microstructure of the solder joint.
The failure mechanism is crack propagation in the bulk of the solder joint and occurs earlier. 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. The joint has failed due to expansion and contraction of the lead in the joint. A crack initiation and propagation simulation and the fatigue characteristics of solder joints considering the material property changes. 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. Dynamic crack propagation prediction of solder joints. 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.
However, in less than ideal conditions there could be additional factors leading voids to contribute to crack initiation and growth. The dynamic overstress state and crack propagation of the interface between the solder and the pad results in complete interface separation. Cracking of a solder joint on a plated through joint is uncommon. This study combines online resistance measurements of a solder joint during drop testing and high speed bend testing. Fatigue crack propagation analysis for micro solder joints.
Understanding the reliability of solder joints used in. Solder joint crack propagation analysis of waferlevel chip scale. Ball grid array bga solder joint intermittency detection. You probably had just a small whisker of solder making the connection and after a year of vibration in the dashboard, that whisker finally broke. Fatigue cracks are also known to form underneath surface. The present study investigates the crack propagation in one snpb and two pbfree solder joint systems. When the copper is hot enough, the solder will melt like butter.