Effects of Resin Thickness on the Stress Intensity Factors of Edge-cracked Adhesive Joints

The effects the thickness of epoxy resin on the stress intensity factors (SIFs) of the edge-cracked adhesive joints subjected to external loads are investigated in the current paper. The three-layered joints composed of Silicon, epoxy resin and FR-4.5 are widely seen in the package solutions of CSP/FBGA for electronic devices. Cracks or delaminations from resin-substrate interface or resin-silicon interface are the common failure modes in plastic IC packages. However, it is difficult to determine the exact stress state of a bi-material interface due to the oscillatory singularity. In this paper, the SIFs of the single edge-cracked joints are determined accurately by using the Crack Tip Stress Method. Then, the effects of resin thickness on the SIFs of various edge interface cracks under uniform tension are investigated by varying the resin thickness and crack length. It was found that the SIFs grow with the increment of resin thickness and reach constants when the resin thickness is larger than the width of the joint.2014 15th International Conference on Electronic Packaging Technology (ICEPT 2014), August 12-15, 2014, Chengdu, Chin

Effects of Resin Thickness on the Stress Intensity Factors of Edge-cracked Adhesive Joints

2014 15th International Conference on Electronic Packaging Technology (ICEPT 2014), August 12-15, 2014, Chengdu, ChinaThe effects the thickness of epoxy resin on the stress intensity factors (SIFs) of the edge-cracked adhesive joints subjected to external loads are investigated in the current paper. The three-layered joints composed of Silicon, epoxy resin and FR-4.5 are widely seen in the package solutions of CSP/FBGA for electronic devices. Cracks or delaminations from resin-substrate interface or resin-silicon interface are the common failure modes in plastic IC packages. However, it is difficult to determine the exact stress state of a bi-material interface due to the oscillatory singularity. In this paper, the SIFs of the single edge-cracked joints are determined accurately by using the Crack Tip Stress Method. Then, the effects of resin thickness on the SIFs of various edge interface cracks under uniform tension are investigated by varying the resin thickness and crack length. It was found that the SIFs grow with the increment of resin thickness and reach constants when the resin thickness is larger than the width of the joint

Evaluation of debonding strength of single lap joint by the intensity of singular stress field

In this paper, the similarity of the singular stress field of the single lap joint (SLJ) is discussed to evaluate the debonding fracture by the intensity of the singular stress field (ISSF). The practical method is proposed for analyzing the ISSF for the SLJ. The analysis method focuses on the FEM stress at the interface end by applying the same mesh pattern to the unknown and reference models. It is found that the independent technique useful for the bonded plate and butt joint cannot be applied to the SLJ because the singular stress field of the SLJ consists of two singular stress terms. The FEM stress is divided to two FEM stresses by applying the unknown and reference models to different minimum element sizes. Then, the practicality of the present method is examined by applying to the previous tensile test results of the SLJ composed of the aluminum alloy and the epoxy resin. The ISSFs for the SLJ were calculated by changing the adhesive thickness t2 and the overlap length l2. In the case of the SLJ with 225mm in total length and 7mm in adherend thickness, it was found that the similar singular stress fields are formed in the range of 0.15mm ≤ t2 ≤ 0.9mm and 15mm ≤ l2 ≤ 50mm. It is shown that the critical ISSFs at the fracture are constant in the range.12th International Conference on Damage Assessment of Structures 10–12 July 2017, Kitakyushu, Japa

A novel method of computing the Stess intensity factors of the interfacial cracks

Bi-material interface and multi-layer systems are widely observed in modern microelectronic applications. When the external load reaches a critical level, the crack either extends along the interface or kinks out of the interface, and finally leads to the catastrophic failure. In fracture mechanics, stress intensity factor, mode mix ratio and strain energy release rate are normally used as parameters to evaluate the adhesive toughness and failure prediction of bi-material interfaces. In this research, a new efficient method based on the finite elements and the extended proportional method using nodal-displacement behind the crack tip was introduced to obtain the stress intensity factors, then the strain energy release rate could be computed by using its relationship with the stress intensity factors. The robustness and accuracy of the current proposed method was discussed by comparing the solution results proposed by other researchers. It was found that the average error is less than 1% for the stress intensity factors, and it can get accurate results with rather coarse finite element meshes. Furthermore, the current method is fairly efficient and less computational resource consuming. The current method could be used as an effective tool in the reliability analysis of the bonded multi-layers in microelectronics.16th International Conference on Electronic Packaging Technology (ICEPT 2015), August 11-14, 2015, Changsha, Chin

Analysis of Interfacial Crack by Means of Hypersingular Integro-Differential Equations

Numerical solutions of hypersingular integro-differential equations are discussed in the analysis of interfacial crack in two and three dimensional bimaterials subjected to general internal pressure. The problem is formulated on the basis of the body force method. In the numerical analysis, unknown body force densities are approximated by the products of the fundamental density functions and power series, where the fundamental density functions are chosen to express singular behavior along the crack front of the interface crack exactly. The present method gives rapidly converging numerical results and highly satisfied boundary conditions throughout the crack boundary. The stress intensity factors are given with varying the material combination and aspect ratio of the crack. It is found that the stress intensity factors KI and II K are determined by the bimaterials constant ε alone, independent of elastic modulus ratio and Poisson\u27s ratio.22rd International Congress of Theoretical and Applied Mechanics (ICTAM 2008), August, 24-30, 2008, Adelaide, Australi

MSAM2019 Preface

2nd International Conference on Material Strength and Applied Mechanics, MSAM2019, 27–30 May 2019, Kiev, Ukrain

Effects of Geometry on Intensity of Singular Stress Fields at the Corner of Single-Lap Joints

This paper discusses effects of adhesive thickness, overlap length and material combinations on the single-lap joints strength from the point of singular stress fields. A useful method calculating the ratio of intensity of singular stress is proposed using FEM for different adhesive thickness and overlap length. It is found that the intensity of singular stress increases with increasing adhesive thickness, and decreases with increasing overlap length. The increment and decrement are different depending on material combinations between adhesive and adherent.WASET 2011:INTERNATIONAL CONFERENCE PROGRAM Holiday Inn Paris Montparnesse-Avenue du Maine, June 24-26, 2011, Paris, Franc

Determination of Stress Intensity Factor for Interface Crack under Uniform Heat Flow by Crack Tip Stress Method

This paper deals with the analysis of the thermal stress intensity factor for interfacial crack in dissimilar materials under uniform heat flow by using the finite element method. This method is based on the fact that the singular stress field near the interface crack tip is controlled by the stress values at the crack tip node calculated by FEM. The calculation shows that the present method has the sufficient accuracy in the interface crack problems under thermal stress.23rd International Congress of Theoretical and Applied Mechanics, August 19-24, 2012, Beijing, Chin

Accurate stress intensity factors for kinked interface crack in bonded dissimilar half-plane

In this study, the stress intensity factor (SIF) of an interface kinked crack is analyzed by the singular integral equation of the body force method. The problem can be expressed by distributing the body force doublets of the tension and shear types along all the boundaries of the kinked and interface crack parts. The SIFs can be obtained directly from the densities of the body force doublets at the crack tips. Although the problem has already been calculated using the crack connection model, the accuracy of the analysis has not been clarified. From the analysis results in this study, it can be seen that the SIFs calculated by the crack connection model have a nonnegligible error, and the present method gives more accurate results. The advantage of the present method is that the SIFs of the kinked and the interface crack tips can be obtained at the same time with high accuracy

Stress Intensity Formulas for Three-dimensional Cracks in the Vicinity of an Interface

In this study, stress intensity formulas are considered in terms of the square root of area parameter to evaluate arbitrary shaped defects or cracks in the vicinity of an interface. Here “area” is the projected area of the defect or crack. Stress intensity factors for an elliptical crack parallel to a bimaterial interface are considered with varying the distance, aspect ratio of the crack, and combinations of material\u27s elastic constants. Also, stress intensity factors of an interface crack and a crack in a functionally graded material are investigated. Then, it is found that the maximum stress intensity factors normalized by the square root of area are always insensitive to the crack aspect ratio. They are given in a form of formulas useful for engineering applications