Solder thickness and strain rate were also found to have a significant. The reliability of 0603sized resistors solder joints formed with ir and vp soldering was investigated. The embrittlement is the result of a large volume fraction of hard ausn imc platelets in the ductile. Figure 5 shows that the shear force increases with the size of the component. What are intermetallics and how can we overcome the failures associated with them. The crack introducing mechanism and crack free bonding condition are discussed. The imc layer is essential to the mechanical strength of. Investigation of the leadfree solder joint shear performance. The improved method takes into account intermetallic dissolution during heating and intermetallic precipitation during cooling and requires as input 1 the temperaturetime profile for the soldering process, 2 the.
Cracking of the intermetallic compound layer in solder joints. Mar 21, 2019 imc layer growth over time in the solder joints. It is known that, imc grew at the interface between. There is one factor from the smt process need to be taken care of that is the voids in the solder joints deleteriously impact solder joint reliability. The total thickness of the intermetallic compounds produced at 150 oc for 500 hours and the activation energies for the total intermetallic layer in the four coppersolder systems were. Results show that the thickness of intermetallic compound imc and cu. To capture clear picture of the soldercu interface, the polished interface samples were etched by a solution containing 5% hcl and 95% c 2 h 5 oh. Nickel alloy films for reduced intermetallic formation in. An improved numerical method for predicting intermetallic. Kinetics parameters of intermetallic growth imcs layer preexponential constant a mm,s time exponent n sec. Pdf effect of intermetallic compound layer thickness on.
One of the most important factors which are known to solder joint reliability is affect the thickness of intermetallic compound imc layer formed between the solder and the substrate. For the 288 h aged solder joint, the thickness of the imc layer increased, but the roughness decreased greatly, indicating the solder imc interface became more planar than that in the 72 h aged solder joint, and thus the stress concentration caused by the rough solder imc interface was reduced greatly. Method to measure intermetallic layer thickness and its application to develop a new equation to predict its growth. Joint size, however, affected the thickness of imc layers. Reliability studies spl mubga solder jointseffect of nisn. Finite element modelling of thin intermetallic compound. If the stress is too high then rupture can occur and a crack initiates, as the stress exceeds the bond energy. Formation of intermetallic reaction layer and joining. The fracture mechanism of the imc layer is complex due to the effect of imc thickness, crack length, solder thickness and youngs modulus. Fracture mechanics analysis of cracks in solder joint. While the imc layer is necessary for achieving a reliable solder joint, it is usually hard and brittle. Ductile fracture in the bulk solder plays dominant role at the low strain rate.
Solder joint failures are a common failure mode observed in electronic packages 2. Influence of interfacial intermetallic growth on the. Therefore, there is a higher reliability risk that too large a fraction of solder joints will transform into intermetallic compounds imcs at the solder interface. What is imc intermetallic compound in the electronic. Past research has looked to solve the issue of crack propagation in solder joints using a polymer underfill system. I will say the best thickness of imc layer shall be um but the 15um is the regular acceptable thickness for the intermetallic compound of coppertin cusn and coppernickel cuni. Fracture mechanics analysis of cracks in solder joint intermetallic. Effects of the intermetallic compound microstructure on. What are intermetallics and how can we overcome the. The trend towards miniaturization of electronic products leads to the need for very small sized solder joints. The kinetics of imc layer formation is diffusioncontrolled, depending on sn and cu diffusion at the sncu substrate interface as a function of time and temperature 26. Comparing the reliability and intermetallic layer of. Finite element based solder joint fatigue life predictions.
Reliability studies spl mubga solder jointseffect of nisn intermetallic compound. Intergranular cracking simulation of the intermetallic. Solder joint from pin to surfacemount circuit board pad exhibited a crack 100x. Influence of bonded area size on cracking in reacted nial. Even if the whole solder layer is replaced by the imc in the solder joint, the fracture propaga tion possibility is greatly reduced. Statistical aspect on the measuring of intermetallic compound. Layer growth in aupbin solder joints technical report. In every solder joint, between the solder and the substrate, a layer is present containing one or more intermetallic compounds 1,2,3. Design and material parameter effects on bga solderjoint.
This damage relieves the stress in the intermetallic compound layer and reduces the crack driving force in it and consequently alleviates the risk of the intermetallic compound layer fracturing. The imc layer typically does not have an explicit role in this mode of deformation. To observe the imc layer, the aged solder joints were packaged in epoxy resin, followed by grinding and polishing with 1. Effect of intermetallic compound layer thickness on the shear strength of 1206 chip resistor solder joint article pdf available in soldering and surface mount technology 271 september 2015. Recently, underfill bonding mechanisms have become particularly common in ball grid array bga chip solder joints. Experimental methods figure 2 shows a schematic of reactive solder joint specimen. Pdf effect of intermetallic compound layer thickness on the. Contrary to intuition, it is revealed that a thicker imc layer in fact increases the reliability of solder joint for a cracked imc. The conclusion was drawn that cracking between the.
There are several other possible intermetallic phases that can form in this system including ausn, au 5 sn, au 2 pb, aupb 2, and aupb 3 4. Impact of intermetallic growth on the mechanical strength of. There is a desire to correlate imc thickness to various surface mount processes and to characterize. Effect of ni nanoparticles on intermetallic compounds. What are intermetallics and how can we overcome the failures. Influence of intermetallic compounds on rf resistance of. The effect of thermal shock on the solder joint shear strength has also been presented webster et al. This is expected because the shear force equals to the shear strength of solder alloy times the solder joint wetting area and larger components have a larger. The composition, structure, and brittleness of the imc layer are affected by the. Statistical aspect on the measuring of intermetallic.
Aug 26, 2014 purpose the purpose of this paper is to compare the reliability and intermetallic layer iml of solder joints prepared with infrared ir and vapour phase vp soldering. The solder joint is usually fabricated by the reflow process, in which a liquid solder alloy reacts with a solid metal substrate, such as a cu pad, to form a thin layer of intermetallic compounds imcs at the bonding interface. Detecting and measuring imc thickness requires crosssectioning and is difficult, time consuming and destroys the sample. While the effects of reflow conditions on intermetallic compound imc formation at the solder joint such as the. There is the growth of an intermetallic compound imc reaction layer at. The imc roughness and tensile strength of solder joint has a positive correlation.
Effect of intermetallic compounds on the shear fatigue of cu. Ki and kii, at the predefined crack in the imc layer of solder butt joint tensile. The results indicate that both the thickness and roughness of the imc layer have. Impact of intermetallic growth on the mechanical strength. The brittle fracture takes place in the layer of intermetallic compound imc that is formed at the solder metal interface during soldering. Fracture behaviour of intermetallic compound imc of solder joints. Linear elastic fracture mechanics lefm approach is used for parametric study of the stress intensity factors sif, ki and kii, at the predefined crack in the imc layer of solder butt joint tensile sample. Nickel alloy films for reduced intermetallic formation in solder. Cracking of the intermetallic compound layer in solder. Oct 10, 2000 an intermetallic layer between the solder and the alloy layer, the intermetallic layer including nickel, the alloying element and tin, the intermetallic layer being formed by the solder wetting the alloy layer.
The microstructure of cusncu solder joint consists of two imc layers at both sides. Reliability studies spl mubga solder jointseffect of ni. Effect of reflow profile on intermetallic compound formation. To prove the correlation between the data given by this new method with the intermetallic layer, it was compare with. The formation of a reliable solder joint depends on several factors such as the ability of the molten solder to rapidly and uniformly wet the surface finish and interact with it to form a consistent intermetallic layer at the interface 3. Intermetallic compound layer growth kinetics in nonlead.
Effect of solder joint thickness on intermetallic compound growth. The total thickness of the intermetallic compounds produced at 150 oc for 500 hours and the activation energies for the total intermetallic layer in the four copper solder systems were. Effects of the intermetallic compound microstructure on the. Nov, 2019 i will say the best thickness of imc layer shall be um but the 15um is the regular acceptable thickness for the intermetallic compound of coppertin cusn and coppernickel cuni. A thin intermetallic compound imc of solder ball joint induces strong stress concentration between the pad and solder where a crack propagated near the imc layer. Creation of imc is explained on the example of snpb alloy and cu substrate. Also, bulk ausolder samples were aged at 150sup 0c for metallographic analysis. Intermetallic layer growth in solder joint between sn and cu at various temperature.
Should intermetallic thickness measurements be needed to. The brittle fracture takes place in the layer of intermetallic compound imc that is formed at the soldermetal interface during soldering. Processing and reliability issues for eutectic ausn solder. This layer formed at the moment the joint was made, and was responsible for the resulting strong bond. Jul 10, 2012 in this study, the effects of ceo2 nanoparticle addition on tensile strength and formation of interfacial intermetallic compound layer for leadfree sn3. Study of intermetallic compound layer formation, growth and. The improved method takes into account intermetallic dissolution during heating and intermetallic precipitation during cooling and requires as input 1 the temperaturetime profile for the soldering. Solder joint embrittlement mechanisms, solutions and.
The imc layer is essential to the mechanical strength of the metallurgical bond in the solder joint. The thickness of the imc layer will affect solder joint reliability because it is comprised of one or more. Comparing the reliability and intermetallic layer of solder. Cu3sn the intermetallic cu3sn is important as it forms an interfacial layer between the copper and cu6sn5 imc layer in tinlead and leadfree solder joints formed directly to copper. The microstructure of the imc layer was observed by using a fei quanta 650 scanning electron microscope sem. Understanding the reliability of solder joints used in. Although the formation of an imc layer signifies good bonding between the solder and substrate, its main disadvantage is that it is also known to be the most brittle. An improved numerical method has been developed for calculating the thickness of intermetallic layers formed between cu substrates and solders during the soldering process. Cracking along the intermetallic compound imc interface in solder joints is the most. In this paper, fracture mechanics study of the imc layer for snpb and pbfree solder joints was carried out using finite element numerical computer modelling method. Fracture mechanics analysis of cracks in solder joint intermetallic compounds. Only the pure tin sn in the solder paste composition and copper base for example osp, iag, isn finished or nickel base enig finished in the pcb can cause the diffusion in high temperature and form the firmed interfacial imc layer. The elimination of lead from solder and metallizations has had several consequences in. The results showed that the thickness of intermetallic layer was decreased with increasing weight percentages of ceo2 reinforcements, and the growth of the intermetallic layer was remarkably.
Effects of the intermetallic compound microstructure on the tensile. So far, many papers have reported effects of cooling speed, type of solder pastes and solder fluxes on the reliability of leadfree solder joints. Coefficient of complex correlation of t and t cusn 0. The morphology of the cu 6 sn 5 imc layer has changed from scallop to planar type. Finite element modelling of thin intermetallic compound layer. Solder thickness and strain rate were also found to have a significant influence on the sif values.
Structural changes of the imc in lead free solder joints. Therefore, there is a higher reliability ris fracture mechanics analysis of cracks in solder joint intermetallic compounds ieee conference publication. A solder joint structure according to claim 5, wherein the alloy layer is deposited on the pad by plating. Fracture mechanics analysis of solder joint intermetallic. Physical and mechanical properties of intermetallic. Table 2 measured activation energies for the solder joint type investigated surface mount solder paste bga solder ball metallurgies activation energy kjmol 63sn37pb 63sn37pb 45 63sn37pb 48 sn4.
A brief the formation and thickness of the imc layer can also affect the reliability of the this study will outline the growth kinetics of the imc layers which form between. The cyclic bending cracks always initiate at the point of the acute angle where the solder joint joins the pcb pad, and then propagate in the site between the nisn intermetallic compound imc layer and the bulk solder. Purpose the purpose of this paper is to compare the reliability and intermetallic layer iml of solder joints prepared with infrared ir and vapour phase vp soldering. Growth kinetic studies of cusn intermetallic compound and. Concern arisen that an over growth of intermetallic compound imc can be disadvantageous for solder joint reliability. The formation of a reliable solder joint depends on several factors such as the ability of the molten solder to rapidly and uniformly wet the surface finish and interact with it to form.
Study of intermetallic compound layer formation, growth. Example of a cu3sn interfacial imc of a sac alloy bga solder joint on osp board. Physical and mechanical properties of intermetallic compounds. Formation and growth of intermetallics at the interface. Processing and reliability issues for eutectic ausn solder joints abstract. Suppression of the growth of intermetallic compound layers. The presence of intermetallic compound imc at the soldertoland interfaces of a solder joint is one of the attributes used to indicate proper formation of a solder joint. The iml of the joints was analysed based on image processing algorithm automatically. Review of the impact of intermetallic layers on the. In this study, the effects of ceo2 nanoparticle addition on tensile strength and formation of interfacial intermetallic compound layer for leadfree sn3. After soldering, a solder joint crack was evident at the location of the pin, as shown in figure 2. C, and the growth of interfacial imcs and crack formation at the imc layersolder interface. Types of intermetallic compounds and their positions within the soldered joints. Figure 2 shows the microstructure of a severely embrittled solder joint.