Prediction of Equilibrium and Stability of Molten Solder Profiles by Finite Element Analysis

2002 ◽  
Author(s):  
Takahiro Nagata ◽  
Takaya Kobayashi ◽  
Hiroshi Sakuta
Keyword(s):  
Surface Tension ◽  
Solder Joint ◽  
Flip Chip ◽  
Deformation Analysis ◽  
Rigid Plastic ◽  
Element Analysis ◽  
Liquid Drops ◽  
Practical Applications ◽  
Updating Procedure ◽  
2D And 3D

In development of surface mount technology for Ball Grid Array (BGA) or flip-chip assemblies, it is important to reduce stress concentration in solder joints as it is immediately effective in improving the fatigue life of the assembly. Thus, the ability to predict and control the joint geometries is critical to obtaining robust and reliable designs of interconnects. Other than the issue of the bump shape, there are many problems concerning soldering such as bridging or self-alignment in which surface tension is definitely involved. This paper attempts to apply the FEM approach in solving these problems. Rigid-plastic FEM which is based on iteration for the velocity field in an incompressible viscous fluid is an approach to large deformation analysis. The flow stress is described by the viscosity of the fluid and the strain rate. By introducing an automatic mesh updating procedure, transient problems with free boundary can be treated. We applied this concept to the prediction of solder joint shapes. In this kind of problem, effects of surface tension dominate. Since surface tension is a distributed load that depends on surface curvature, we employed 2D and 3D methods in which the load is updated based on instantaneous state of surface. To verify the accuracy of this method, we analyzed some shape and stability problems of liquid drops for which theoretical solutions were given. Practical applications of the method were also performed for the 2D and 3D solder joint problems, and the results showed a good agreement with experimental ones.

Prediction of Equilibrium and Stability of Molten Solder Geometries by Finite Element Analysis

2005 ◽  
Author(s):  
Takahiro Nagata ◽  
Takaya Kobayashi
Keyword(s):  
Surface Tension ◽  
Liquid Drop ◽  
Dynamic Effect ◽  
Shell Element ◽  
Molten Solder ◽  
Constitutive Laws ◽  
Constitutive Law ◽  
Creep Model ◽  
Element Analysis ◽  
Liquid Drops

Improving the reliability on solder joints is one of the major tasks to achieve downsizing of electronics products. Taking the molten solder profile as an object of study, a new procedure to model solder liquid with a structural FEM has been developed, which enables us to solve an issue of predefining the geometrical profile of solder liquid drops in a state of static equilibrium taking the surface tension into account, and also a problem concerning dynamic stability of the liquid drops. Molten solder liquid is treated as viscous fluid. Deformation of the material due to its viscosity can be represented by the structural analysis using rheological approach. Two types of the constitutive laws, creep model or viscoelasticity model, can be applied. Such a simple case as the Newtonian fluid, either constitutive law may be employed. Using these types of the constitutive laws in the analysis with time incremental steps, it becomes possible not only to obtain the stabilized shape of liquid drops, but also to analyze problems involved with transient (including dynamic effect) stability. As the size of a liquid drop is microscopic in a range of 100 to 1000 μm, the effect of the surface tension must become so predominant in the loading conditions. In most of the conventional theoretical researches, it is found that the surface tension is treated as the pressure difference varying according to the surface curvature. However, this method is not only so complicated, but also may lead to numerical instability particularly in the transient analysis subjected to large deformations. In this study, an effective method has been developed in which the surface tension can be represented with good accuracy through simplified input data with allocating the shell element generating a constant membrane force over the surface of a liquid drop.

Interconnect Design and Thermal Stress/Strain Analysis of Flip Chip Packaging

2006 ◽  
Vol 326-328 ◽  
pp. 521-524
Author(s):  
Chang Ming Liu ◽  
Chang Chun Lee ◽  
Hsiao Tung Ku ◽  
Chien Chia Chiu ◽  
Kuo Ning Chiang
Keyword(s):  
Solder Joint ◽  
Electronic Packaging ◽  
Flip Chip ◽  
Thermal Loading ◽  
Equivalent Plastic Strain ◽  
Engineering Application ◽  
Stress Strain ◽  
Element Analysis ◽  
Design Guideline ◽  
Solder Balls

As the interconnection density of electronic packaging continues to increase, the fatigueinduced solder joint failure of surface mounted electronic devices become one of the most critical reliability issues in electronic packaging industry. Especially, prediction of the shape of solder joint is a major event in the development of electronic packaging for its practical engineering application. In conventional electronic packages, the geometrical dimensions of solder balls and solder pads of the package are the same. In this research, a hybrid method combined with analytical and energybased methods is utilized to predict force-balanced heights and geometry profiles of solder balls under various solder volume and pad dimensions as well as their relative location during the reflow process. Next, a non-linear finite element analysis is adopted to investigate the stress/strain behavior of solder balls in flip chip package. The results reveal that as the flip chip package contains larger solder balls located at the corner area underneath the chip, the maximum equivalent plastic strain/stress is evidently reduced and the reliability cycles under thermal loading are enhanced. Furthermore, the results presented in this research can be used as a design guideline for area array interconnections.

Predicting the Liquid Formation for the Solder Joints in Flip Chip Technology

2005 ◽  
Vol 128 (4) ◽  
pp. 331-338 ◽  
Author(s):  
Wen-Hwa Chen ◽  
Shu-Ru Lin ◽  
Kuo-Ning Chiang
Keyword(s):  
Surface Tension ◽  
Solder Joint ◽  
Flip Chip ◽  
Solder Joints ◽  
Geometric Method ◽  
External Loading ◽  
Surface Evolver ◽  
Eutectic Solder ◽  
Chip Technology ◽  
Interfacial Surface

An accurate and efficient analytical geometric method is presented for predicting the geometric parameters of the controlled collapse chip connection type solder joint using direct chip attach technology after a reflow process. By this method, the meridian of the solder joint is first discretized as a series of sufficiently fine fragmental arcs. After calculating the internal pressure inside the molten eutectic solder from the forces balance, the meridional and circumferential radii of curvature of each arc are then obtained from the Laplace-Young equation. As a result, the coordinates of each node of the arc and the solder joint geometry can be determined in turn. The factors that affect the final shape of the molten eutectic solder joints, including the solder volumes, external loading, pad size, surface tension of molten eutectic solder, and interfacial surface tension between the molten eutectic solder and the solid high-lead bump are considered herein. The results computed by the analytical geometric method are also compared with those obtained using the Surface Evolver program, the extended Heinrich’s model, and the experimental results. The results of the various approaches are mutually consistent.

Solder Joint Shape Prediction Using a Modified Perzyna Viscoplastic Model

2004 ◽  
Vol 127 (3) ◽  
pp. 290-298 ◽  
Author(s):  
Mudasir Ahmad ◽  
Ken Hubbard ◽  
Mason Hu
Keyword(s):  
Surface Tension ◽  
Numerical Model ◽  
Solder Joint ◽  
Solder Joints ◽  
Element Analysis ◽  
Closed Form Solutions ◽  
Joint Construction ◽  
Shape Prediction ◽  
Applied Forces ◽  
Joint Shape

Ball grid array solder joint reliability is known to be dependent on the shape of solder joints after reflow. To ensure good solder joint formation and prevent solder bridging, it is critical to understand the amount of paste volume needed during assembly and reflow. The final shape of the solder joint is a function of surface tension, wetting area, gravity, and applied forces. In this paper, a new methodology to simulate solder joint shape is presented. Large deformation viscoplastic finite element analysis is used to simulate incompressible fluid flow. A numerical model for surface tension is outlined and validated with closed-form solutions. The results of the numerical model are compared to other known solder joint shape prediction methods. The effects of package weight, coplanarity, warpage, paste volume, pad misregistration, and joint construction on solder joint shape are then analyzed. Recommendations are provided on ways to maximize standoff height and avoid bridging. Finally, the formation of leadless solder joints is studied and compared to experimental data.

Prediction of Solder Joint Geometries in Array-Type Interconnects

1996 ◽  
Vol 118 (3) ◽  
pp. 114-121 ◽  
Author(s):  
S. M. Heinrich ◽  
M. Schaefer ◽  
S. A. Schroeder ◽  
P. S. Lee
Keyword(s):  
Surface Tension ◽  
Solder Joint ◽  
Closed Form ◽  
Flip Chip ◽  
Reaction Force ◽  
Joint Reaction Force ◽  
Optimal Arrangement ◽  
Array Type ◽  
Joint Force ◽  
Uniform Array

An approximate mathematical model is developed for predicting the shapes of solder joints in an array-type interconnect (e.g., a ball-grid array or flip-chip interconnect). The model is based on the assumption that the geometry of each joint may be represented by a surface of revolution whose generating meridian is a circular arc. This leads to simple, closed-form expressions relating stand-off height, solder volume, contact pad radii, molten joint reaction force (exerted on the component), meridian curvature, and solder surface tension. The qualitative joint shapes predicted by the model include concave (hourglass-shaped), convex (barrel-shaped, with a truncated sphere as a special case), and truncated-cone geometries. Theoretical results include formulas for determining the maximum and minimum solder volumes that can be supported by a particular pair of contact pads. The model is used to create dimensionless plots which summarize the general solution in the case of a uniform array (i.e., one comprising geometrically identical joints) for which the contact pads on the component and substrate are of the same size. These results relate the values of joint height and width (after reflow) to the solder joint volume and the molten-joint force for arbitrary values of the pad radius and solder surface tension. The graphs may be applied to both upright and inverted reflow, and can be used to control stand-off for higher reliability or to reduce bridging and necking problems causing low yields. A major advantage of the model is that it is numerically efficient (involving only simple, closed-form expressions), yet generates results that are in excellent agreement with experimental data and more complex models. Thus, the model is ideally suited to performing parametric studies, the results of which may be cast in a convenient form for use by practicing engineers. Although in the present paper the array is assumed to be doubly-symmetric, i.e., possess two orthogonal planes of symmetry, the model may be extended to analyze arrays of arbitrary layout. The motivation for predicting joint geometries in array-type interconnects is two-fold: (1) to achieve optimal joint geometries from the standpoint of improved yield and better reliability under thermal cycling and (2) to take full advantage of the flexibility of new methods of dispensing solder, such as solder-jet and solder-injection technologies, which enable the volume of each individual joint to be controlled in a precise manner. Use of dispensing methods of these types permits the solder volumes in the array to be distributed in a non-uniform manner. Results such as those presented here (in combination with appropriate fatigue studies) can be used to determine the optimal arrangement of solder volumes.

Experimental evaluation of SnAgCu solder joint reliability in 100-μm pitch flip-chip assemblies

2014 ◽  
Vol 54 (5) ◽  
pp. 939-944 ◽  
Author(s):  
Ye Tian ◽  
Xi Liu ◽  
Justin Chow ◽  
Yi Ping Wu ◽  
Suresh K. Sitaraman
Keyword(s):  
Solder Joint ◽  
Experimental Evaluation ◽  
Flip Chip ◽  
Solder Joint Reliability ◽  
Snagcu Solder ◽  
Joint Reliability
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