Plastic Ball Grid Array Solder Research Articles

Validation of a General Fatigue Life Prediction Methodology for Sn–Ag–Cu Lead-Free Solder Alloy Interconnects

A general fatigue life prediction methodology, based on a unified creep plasticity damage (UCPD) model, was developed for predicting fatigue cracks in 95.5Sn–3.9Ag–0.6Cu (wt %) solder interconnects. The methodology was developed from isothermal fatigue tests using a double-lap-shear specimen. Finite element analysis model geometries, mesh densities, and assumptions were detailed for both a full model (an octant-symmetry slice of the entire ball grid array (BGA) assembly) and a submodel (the solder joint deemed most likely to fail and the surrounding package layers) to facilitate fatigue prediction. Model validation was based on the thermal mechanical fatigue of plastic BGA solder joints (250–4000 thermal cycles, −55°Cto125°C, and 10°C∕min). Metallographic cross sections were used to quantitatively measure crack development. The methodology generally underpredicted the crack lengths but, nonetheless, captured the measured crack lengths within a ±2X error band. Possible shortcomings in the methodology, including inaccurate materials properties and part geometries, as well as computational techniques, are discussed in terms of improving both the UCPD constitutive model and the fatigue life prediction methodology fidelity and decreasing the solution time.

Research on parametric analysis for stress of Plastic Ball Grid Array solder joint under shock load

The dynamic response of a Plastic Ball Grid Array (PBGA) assembly under high acceleration load was investigated. Several influencing factors on solder joint stress were studied by using ANSYS. The results indicate that the location of the solder joint is the most important factor and that the outmost solder balls of the PBGA experience maximum stresses. The solder joint height, the modulus of Ball Grid Array (BGA) have little effect on the stress. The peak stress can be reduced effectively by increasing the diameter of the solder joints, reducing the modulus of the solder joint materials.

Plastic Ball Grid Array Solder Joint Reliability for Avionics Applications

The solder-joint reliability of plastic ball grid array (PBGA) packages for an avionics application was assessed. The fatigue life under combined temperature cycling and random vibration conditions was initially simulated using analytical models. Further simulation was used to plan an accelerated test and to estimate an acceleration factor between field conditions and test conditions, and experimentally verified. The combination of simulation and experimental results was then used to reassess the solder-joint reliability under field conditions. Based on the simulation and test results, it was estimated that PBGA packages without underfill would not satisfy the long-term life expectation for the avionics application under study. In addition, the experimental results also show that the simple application of linear damage superposition (Miner's rule), which neglects the interactions between loads, will underestimate the damage and overpredict the product life. Therefore, calculating the acceleration factor is necessary and cost-efficient for providing the basis of product field reliability assessment

Generalized multi-domain method for fatigue analysis of interconnect structures

This paper describes a generalized multi-domain finite element stress analysis method to obtain the stress and strain fields for a variety of packaging styles under cyclic thermal environments. The elastic–plastic analysis was demonstrated on ceramic chip component, gull-wing, plated-through hole, and plastic ball grid array solder joints. The solder joints were modeled by colonies of sub-domains at stress risers identified in advance by finite element analysis. In this approach, the physical domain was mapped into isoparametric regions, which were divided into nested sub-domains according to projected high-stress gradients. The previous multi-domain method, based on Rayleigh-Ritz energy principle, utilized polynomials to interpolate the displacement within sub-domains. On the other hand, the displacements in the main and sub-domains, for the improved method used in this paper, are represented by the nodal displacements through isoparametric interpolation, which is similar to the finite element method. The solution at each domain was formed as the superposition of the results corresponding to their sub-domains. The Broyden-Fletcher-Goldfarb-Shanno (BFGS), a quasi-Newton method with line search, was used for fast convergence. All results were compared with finite element analyses (FEA) for the same loading conditions. The demonstration concluded that the proposed multi-domain method decreases the presented (example) problem's solution time by a factor ranging from 3.4 to 4.5 compared to finite element model (FEM) at a comparable accuracy.

Nonlinear analysis of plastic ball grid array solder joints

A nonlinear finite element analysis was carried out to investigate the viscoplastic deformation of solder joints in a ball grid array (BGA) package under temperature cycling. The effects of constraint on printed circuit board (PCB) and stiffness of substrate on the deformation behavior of the solder joints were also studied. A relative damage stress was adopted to analyze the potential failure sites in the solder joints. The results indicated that high inelastic strain and strain energy density were developed in the joints close to the package center. On the other hand, high constraint and high relative damage stress were associated with the joint closest to the edge of the silicon chip which was regarded as the most susceptible failure site if cavitation instability is the dominant failure mechanism. Increasing the external constraint on PCB causes a slight increase in stress triaxiality \( \left( {\sigma _m /\sigma _{eq} } \right) \) and relative damage stress in the joint closest to the edge of the silicon die. The relative damage stress is not sensitive to the Young's modulus of the substrate.

Nonlinear Analysis of Full-Matrix and Perimeter Plastic Ball Grid Array Solder Joints

The application of Ball Grid Array (BGA) technology in electronic packaging on high I/O plastic and ceramic packages has grown significantly during the past few years. Although PBGA (plastic BGA) has several advantages over fine-pitch Quad Flat Pack (QFP) in terms of smaller package area, higher I/Os, lower switching noise, large pitch, higher assembly yield, and improved robustness in manufacturing process, potential package reliability problems can still occur, e.g., excessive solder joint deformation induced by substrate warpage, moisture ingression (popcorn effect), large variation in solder ball size, voiding as a result of flux entrapment and improper pad/solder mask design (Marrs and Olachea, 1994; Solberg, 1994; Freyman and Petrucci, 1995; Lau, 1995; Donlin, 1996; Lasky et al., 1996; Munroe et al., 1996). Regardless of its improved thermal fatigue performance over the past few years through an extensive amount of research, the BGA solder joint may still pose a reliability issue under harsh environment, e.g., automotive underhood, larger package size, or higher temperature and temperature gradient due to increase in power dissipation of the package. Numerous studies in BGA solder joint deformation and reliability under thermal and mechanical loadings can be found in the literature, e.g., Borgesen et al. (1993), Choi et al. (1993), Guo et al. (1993), Ju et al. (1994), Lau et al. (1994) Lau (1995), and Heinrich et al. (1995). Also, reliability prediction models have been developed by, e.g., Darveaux et al. (1995) and Darveaux (1996). The present study focuses on the application of a detailed nonlinear finite element analysis (FEA) to studying the thermal cyclic response of solder joints in two particular BGA packages, full-matrix and perimeter. Both time-independent plasticity and time-dependent effect, i.e., creep and relaxation, are considered in the constitutive equations of solder joint to evaluate the discrepancy in the results of life prediction. The critical solder joint is identified, and the locations that are most susceptible to fatigue failure in the critical joint are discussed. Some limitations in computation and reliability prediction are also discussed.

Design for Plastic Ball Grid Array Solder Joint Reliability

Computational stress analysis was performed in this study to investigate the solder joint reliability of plastic ball grid array (PBGA) packages with various configurations. The packages under investigation were 27 mm body‐size, 1.27 mm ball‐pitch, perimeter PBGAs with and without thermal balls at the centre. The diagonal cross‐section of the PBGA‐printed circuit board (PCB) assembly was modelled by plane‐strain elements. The model was subjected to a uniform thermal loading and the solder joints were stressed due to the mismatch of coefficient of thermal expansion (CTE). A total number of 24 cases, involving different solder ball populations, chip sizes, and substrate thicknesses, were studied. The accumulated effective plastic strain was evaluated as an index for the reliability of solder joints. The results of this study revealed the effects of the aforementioned parameters on the solder joint reliability of perimeter PBGA assemblies. The findings are very useful for the design of plastic ball grid array packages.

Solder Joint Reliability of Large Plastic Ball Grid Array Assemblies Under Bending, Twisting, and Vibration Conditions

The mechanical and vibration responses of 225‐pin, 324‐pin and 396‐pin PBGA (plastic ball grid array) solder joints have been determined in this study. The effects of overload environmental stress factors on the mechanical responses of the solder joints have been determined by bending and twisting experiments. The effects of shipping and functional environmental stress factors on the vibration responses of the solder joints have been determined by out‐of‐plane vibration experiments and a mathematical analysis.