Solder Joint Shape Prediction Using a Modified Perzyna Viscoplastic Model

Abstract

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.

Anisotropic Crystal Plasticity Finite Element Modeling of the Effect of Crystal Orientation and Solder Joint Geometry on Deformation after Temperature Change

“…However, for the 0-90-0 and the 0-45-0 orientations, the largest r 23 stress locations may be a worse condition, where the shear is uniformly large at the lower edge of the fillet at the substrate interface, where cracks are often observed in similar geometries. 17 The r 23 shear is also very large for the 0-45-0 and 0-0-0 orientations under the upper fillet edge with the component (rather than the substrate). Figures 8 and 9 show the von Mises stress and shear stress contours for the cylindrical geometry.…”

“…For all three orientations, the maximum von Mises stress occurs at the tin-copper interface, which indicates that damage would probably nucleate in a region close to the interface, which is commonly observed experimentally and in other modeling efforts. [16][17][18]39 Comparing the results of the cylindrical and the shear lap geometries, it is clear that the geometry of the joint has significant impact on the damage nucleation sites and the energy dissipated in tin. The shear lap geometry imposes more constraints on the joint for the volume of tin involved, and therefore requires more of the tin to deform to accommodate these constraints.…”

“…To select a lead-free solder for a specific application, the solderÕs response to anticipated creep and thermomechanical fatigue (TMF) conditions needs to be anticipated. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] The reliability of tin-based solders is often examined using phenomenological models. [19][20][21][22][23] Many studies examine the reliability of solder joints arising from evolution of intermetallic morphology in the interface.…”

A nanoindentation study of the viscoplastic behavior of pure lithium

“…Although a mechanism-based model would have been more reliable in describing the viscoplastic behavior of Li, such a model would require detailed information at the atomic scale (e.g., dislocation structure and diffusion coefficient) that is generally unavailable. Instead, several empirical or phenomenological constitutive models, such as Anand model [21,22], Johnson-Cook model [23], and Perzyna model [24,25], have been developed based on somewhat different assumptions to describe viscoplastic deformation of soft metals and alloys [13,14,26,27]. Anand model does not have an explicit yield condition or loading/unloading criterion, such that plastic strain can take place under any nonzero stress.…”

“…Perzyna model has been successfully used to describe the rate-dependent flow behavior of many soft metallic materials (such as Sn-based solder alloys[26,27]). Considering both the elasticity and viscoplasticity, we assume Li as a Perzyna elastic-viscoplastic solid with work hardening.…”