Enhanced Polymer Passivation Layer for Wafer Level Chip Scale ...
Enhanced Polymer Passivation Layer for Wafer Level Chip Scale ... Enhanced Polymer Passivation Layer for Wafer Level Chip Scale ...
elow, where is the total strain rate (1/sec), is the stress (MPa), E is the elastic modulus, T is the temperature, n is 1Mpa, A1 is 4.0 x10 -7 1/sec and A2 is 1.0 x 10 -12 1/sec, D1 is 3223 exp T and D2 7348 is exp . The second term in the equation (5-5) represents the T climb controlled creep strain and the third term represents the combined glide/climb strain. Syed [93] has applied this creep model to develop a fatigue life model for SnAgCu solders. 3 12 AD 1 1 AD 2 2 E n n 102 (5-5) Zhang et a1. [94] and Schubert et a1. [95] generated data from different sources and from their own testing on different compositions of SnAgCu solder. They both modeled the steady state creep behavior using the hyperbolic sine function, and postulated the high stress region as a power law break-down region. The constitutive model proposed by both of them predicted very similar behavior at low stresses but start diverging at higher stresses. On the other hand, the model proposed by Wiese et a1. [92] predicts lower creep rate at low stresses. Figure 5.4 compares the creep curves for SAC solder from different constitutive models as mentioned here. Equation (5-6) represent the constitutive model of Schubert and Zhang, where A1 = 277984 s -1 , =0.02447MPa -1 , n=6.41, H1/k =6500, E(MPa)=61251-58.5T( o K), CTE=20ppm/K, Poisson’s ration = 0.36 . H kT n 1 cr A1 sinh exp (5-6)
Morris et a1 [96] used a double power law constitutive model to represent creep data on single lap shear specimens of SAC305 solder joints. The stress exponents of 6.6 and 10.7 were suggested for the low and high stress regions. Figure 5.4 Comparison of Creep Models for SnAgCu and SnPb solder [92] Elastic-Plastic-Creep Model: Pang et al. [97], Yang et al. [98], Vandevelde et al. [99], and Qian et al. [100] used the bilinear elastic-plastic and hyperbolic sine creep equation to describe the solder deformation response. This approach uses separate constitutive models for time independent plastic deformation and time-dependent creep deformation. The solder is modeled as an elastic- plastic-creep material with temperature and strain rate dependent Young modulus and yield stress material properties expressed by following equations [101]: 103
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Morris et a1 [96] used a double power law constitutive model to represent creep data on<br />
single lap shear specimens of SAC305 solder joints. The stress exponents of 6.6 and 10.7 were<br />
suggested <strong>for</strong> the low and high stress regions.<br />
Figure 5.4 Comparison of Creep Models <strong>for</strong> SnAgCu and SnPb solder [92]<br />
Elastic-Plastic-Creep Model: Pang et al. [97], Yang et al. [98], Vandevelde et al. [99], and<br />
Qian et al. [100] used the bilinear elastic-plastic and hyperbolic sine creep equation to describe the solder<br />
de<strong>for</strong>mation response. This approach uses separate constitutive models <strong>for</strong> time independent<br />
plastic de<strong>for</strong>mation and time-dependent creep de<strong>for</strong>mation. The solder is modeled as an elastic-<br />
plastic-creep material with temperature and strain rate dependent Young modulus and yield<br />
stress material properties expressed by following equations [101]:<br />
103
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