A model of bga thermal fatigue life prediction considering. Modeling of intergranular thermal fatigue cracking of a leadfree solder joint in a power electronic module. With increased thermal cycles these cracks grew by grain boundary decohesion. The cracks were found to originate on the free surface of the solder joint. The resistance to thermal fatigue crack could be weakened due to the hightemperature induced microstructural degradation in a solder joint during thermal cycling 7 9. Note approaches to technology of thermal fatigue life.
Effect of encapsulation materials on tensile stress during thermomechanical cycling of pbfree solder joints. Thermal fatigue lives of different chips under different thermal cycles are obtained by thermal fatigue tests, and the stress and strain intensity factors and singular orders at the soldersubstrate interface are computed at the same conditions, to determine the material constants in the established models. Modeling of intergranular thermal fatigue cracking of a leadfree. It is well known that strain and temperature, in conjunction with the coefficient of thermal expansion cte mismatch, drive thermal fatigue failures in solder joints. Expert panel responses that solder joint appears to have been defective from the getgo. Approaches to technology of thermal fatigue life prediction of solder joints like this, the life of solder joints can be predicted from the strain amplitude calculated by simulating each part and fatigue life of the solder from the test. The fatigue life of a solder joint depends on several factors including.
The authors have found if snznbi is used with another pbfree solder material, a kind of composite structure can be built during the reflowing processes. This inelastic strain accumulates with repeated cycling and ultimately causes solder joint cracking and interconnect failure 3. A systems approach to solder joint fatigue in spacecraft. Failure mechanisms of sacfeni solder joints during. Sac alloys are the solder joint strain generated during thermal cycling and the higher temperature extreme used in the cycle. For a solder joint, thermal fatigue is one of the main failure modes because of the large thermal stress between the silicon and pcb substrate in microelectronic packaging. Thermal fatigue evaluation of pbfree solder joints. Modeling thermal fatigue in nonlinear materials comsol blog. Usually the deformation of the solder in the joints is rather large, of the order of 1%, and the movements are slow, with typical cycle times measured in hours. Techniques to evaluate solder fatigue behavior include finite element analysis and semianalytical closed form equations.
This study shows that the fatigue fracture of leadfree solder joint under thermal cycling test is creep fracture, and the crack initiation always occurs at the interface of solder and cu pad. Thermomechanical analysis and fatigue life prediction for. And the fatigue life of solder joint without void is about 1600 cycles. Solder joint cracks caused by overloading are often the result of an accident or harsh treatment. The life of a part can be predicted according to its shape and temperature range where it is used. Solder joint fatigue failures published online september 8, 2015 thermal fatigue evaluation of pbfree solder joints. This paper presents the experimental results on the effects of reflow profile and thermal shock on shear force of both snpb and snagcu solder joints. The observed failure mode was solder joint fatigue cracks initiating from the solder joint corner and propagating through the bulk solder close to the solderimc interface at the. In this work, the combination of vibration loading and thermal cycle effects on the fatigue properties of a solder joint in a metaloxidesemiconductor fieldeffect transistor.
Thermal fatigue strength estimation of solder joints of surface. Assessment of fatigue induced pad cratering with a. The requirements of each model, its approach crack growth or damage. This paper reports how the solder joint fatigue lives of three types of lead free plastic bga components were affected by cracks formed in the printed pcb laminate during a. Surface roughening and grain boundary cracking were evident even in samples thermally cycled for 250 times.
The statistical method of latin hypercube sampling was employed to investigate the sensitivity of simulated damage to each input variable. Read modeling of intergranular thermal fatigue cracking of a leadfree solder joint in a power electronic module, international journal of solids and structures on deepdyve, the largest online rental service for scholarly research with thousands of academic publications available at your fingertips. Effect of pcb cracks on thermal cycling reliability of. Hard solder is goldbased eutectic solder such as ausn20, ausi3 and auge12. Comparison of thermal fatigue performance of sac105, sn3. A damaged or faulty solder joint can cause an open circuit failure that in turn can causes the complete electrical failure of the lamp or luminaire. Combination of thermal cycling and vibration loading. Thermal fatigue in solder joints pdf free download. If this happens during accelerated thermal cycling it may result in overestimating the lifetime of solder joints in field conditions. Heat resistant alloys all have high coefficients of thermal expansion.
In this study, the mechanical fatigue strength of this kind of snznbi solder joint was studied. Random vibration rsed random vibration accelerates fatigue cracking of the solder joints around voids where stress concentration is higher. Fatigue reliability analysis of snagcu solder joints. Failure mechanisms of sacfeni solder joints during thermal cycling. Among them, the technology that enables parts to be mounted on all sides was developed from 1997 to 2000. In 2004, leadfree solder was adopted for environmental conservation. The imc is the region where the copper pad and solder combine to form cu 3 sn or cu 6 sn 5. Because of their complex nature and large number of variables, fatigue failures in solder joints have historically been. When the solder joint is formed at high temperature, it is in a stressfree state.
Accelerated thermal cycling and failure mechanisms for. 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. In those years, technological changes that affect fatigue life of solder joints occurred. Both challenges require a thorough material knowledge. Solder fatigue is the mechanical degradation of solder due to deformation under cyclic loading.
L is the maximum distance to neutral point dnp max from the neutral axis of the assembly to the outermost solder joints. Could selective soldering provide more consistent solder joints and thus reduce or eliminate the cracking. Failure behavior of flip chip solder joint under coupling. A criterion is then presented to estimate the fatigue. Finite element model fem simulations have been performed to elucidate the effect of flat plate photovoltaic pv module materials and design on pbsn eutectic solder joint thermal fatigue durability. T is the temperature change between the cold and hot sides of the temperature cycle. Thermal fatigue endurance of lead free composite solder. When plastic and creep strain is the cause for solder joints fatigue crack. The second technique, cross sectioning, was used to establish failure within the solder by thermal. Thermal fatigue cracking is the cracking that happens after a metal is repeatedly heated and cooled rapidly. A pad crater is a cratershaped crack in the laminate layer beneath the copper pad of a solder joint. Jet propulsion laboratory california institute of technology pasadena, ca 91109 differential expansion induced fatigue resulting from temperature cycling is a leading cause of solder joint failures in spacecraft. In particular, more accurate prediction of thermal fatigue life is required for large thermal stress induced by power and temperature cycling.
A substrate or lead frame with an exposed heat sink is used for heat dissipation and as the dieattach pad, and soft solder generally is used as the joint because of its high thermal and electrical conductivity. The failure mode of 60sn40pb solder joints in thermal and isothermal fatigue is similar. Transgranular crack propagation in thermal cycling of. The solder joint standoff heights after assembly typically ranged from approximately.
Thermomechanical fatigue behavior of snag solder joints. The thermal fatigue endurance of two leadfree solder plasticcore solder ball pcsb composite joint structures in lowtemperature cofired ceramic ltcc modules was investigated using a thermal. Repeated loading is an important reason to cause pad cratering fatigue failure in ball grid array bga device in printed circuit board pcb assembly. Referred to as low cycle fatigue, cracking from this type of deformation may be observed in all kinds.
A fivefactor factorial design with mixed levels and three replications was selected in the experiment. As shown in figure 6 a, when the void was formed on crack propagation route, the fatigue life of solder joint is about 1100 cycles and decrease by about 32% from 1600 cycles. Comparison of thermal fatigue performance of sac105 sn1. The purpose of this project is to experimentally validate the thermal fatigue life of solder. However, fatigue failure of the solder joint, caused by thermal expansion mismatch between the device and pcb, is the most critical issue with surface mounted. In this paper we will present the solder fatigue failure mechanism and the pth fatigue failure. Top 5 reasons for solder joint failure dfr solutions. Alloys with more than 47% bi expand upon cooling, which may be used to offset thermal expansion mismatch stresses.
A test plan was created with a focus on two solder joint attributes. 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. Corrosion is an important consideration in the design of a solder joint. Solder fatigue in thermal cycling is caused by grain growth. Smt electrolytic capacitor solder joint criteria and. C are the board and component inplane coefficients of thermal expansion ctes, h s is the solder joint height or component standoff, and. The nasa thermal cycling requirements are stringent and are specified in various revisions of nasa handbooks. A prediction of the thermal fatigue life of solder joints.
Thermal fatigue is a major source of failure of surface mount smt components and it is critically important in many high reliability applications. A systems approach to solder joint fatigue in spacecraft electronic packaging r. In contrast, such behavior was not observed in the isothermal fatigue of 5sn95pb solder joints. Typically, the main reliability issue is solder joint fatigue which accounts for a large amount of failures in electronic components. Each part of the solder joint is affected by the thermomechanical loads in a different way. 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. Thermal shock testing has a much more rapid ramp rate than thermal cycling, thus inflicting much more damage to solder joints. The excessive difference in coefficients of thermal expansion between the components and the board cause a large enough strain in solder and embedded copper structures to induce a fatigue failure mode. Simulations demonstrate how fatigue cracking occurs and propagates at grain boundaries in the solder joint. A diagram from a typical solder fatigue26 is shown in figure 8 with the crosssection of the failed r5 solder joint. Both pbrich and snrich phases coarsen, and cracks form within these coarsened regions. With respect to package type, the most obvious trend in.
In literature, the fatigue life of power devices is usually evaluated by applying thermal and power cycles. Thermal fatigue evaluation model of a microelectronic chip. With high performance and high density of computer and other electronic circuits, it becomes very important to assure the reliability of smaller and smaller solder joints. The electronic packaging industry has seen an increase in the number of pbfree solder alloy choices beyond the common neareutectic snag. For electronic components, cyclic plastic strain makes it easier to accumulate fatigue damage than elastic strain. Today, we will address these challenges when modeling thermal fatigue in nonlinear materials. You must correctly represent the material behavior with a constitutive relation and find a fatigue model that captures the lifecontrolling mechanism. Investigation of the leadfree solder joint shear performance. Predicting fatigue of solder joints subjected to high number of power cycles. The latter mode, which causes the solder layer to experience crack growth with cycle number, remains one of the most critical concern for the integrity of the whole package. Delamination of the solder joint after 43,000 thermal cycles perpina et al.
Thermal mechanical stress causes fracture of the solder joint around the voids where local stress concentration is high thermal faitgue. Pdf for electronic components, cyclic plastic strain makes it easier to accumulate fatigue damage than elastic strain. Modeling of intergranular thermal fatigue cracking of a. It must be addressed with respect to the service environment or, as in the case of soldered conduit, as the nature of the medium being transported within piping or tubing. Climate specific thermomechanical fatigue of flat plate. Thermal fatigue results on 60sn40pb solder cycled between 55sup 0c and 125sup 0c show that a coarsened region develops in the center of the joint. Corrosion issues in solder joint design and service. Under thermal cyclic loading, the module exhibits several modes of fracture such as wire bonding fatigue, substrate delamination, chip metallization degradation, or solder joint fatigue benabou et al. One of the primary reasons for having solder joint geometry and wetting criteria is to ensure the creation of a consistent, repeatable solder joint that can withstand. Solder joint overstress failure typically manifests as a pad crater or a joint fracture along the intermetallic connection imc. Copper improves resistance to thermal cycle fatigue, and improves wetting properties of the molten solder. This may lead to cracking of the pcb laminate close to the solder joints, which could increase the pcb flexibility, alleviate strain on the solder joints, and thereby enhance the solder fatigue life.
For example, when using too much force to mount a soldered assembly in position in an enclosure, or when dropping a mobile phone. Solder is a metal alloy used to form electrical, thermal, and mechanical. Predicting fatigue of solder joints subjected to high. This eventually leads to crack initiation and propagation which can be. Thermal fatigue is a major source of failure of solder joints in surface mount electronic components and it is critically important in high reliability applications such as telecommunication, military, and aeronautics. Ansys act extension solder joint fatigue life version 2.
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