Enhanced Polymer Passivation Layer for Wafer Level Chip Scale ...

5.2.2 Material Properties
Elements used for simulation were the eight node SOLID45 brick and the VISCO107
elements. Other than the solder balls modeled by VISCO107, all the rest of the materials in the
package were modeled by eight nodes SOLID45.
As taken from the ANSYS element library, SOLID45 is used for 3-D modeling of solid
structures. It is defined by eight noded elements and has three degrees of freedom at each node.
It has the capability to model creep, plasticity, swelling, and other deformation features. The
VISCO107 element also has eight nodes and three degrees of freedom at each node. It is used to
model rate dependent plasticity. This element is chosen for solder defined with the Anand model,
while the SOLID 45 element is used for solder defined with elastic-plastic-creep model.
All of the materials in the package were modeled as isotropic except for the PCB
which was modeled as orthotropic. For the Sn3.0Ag0.5Cu solder, material properties used in the
Anand model are shown in Table 5.2. The material properties for the finite element models of
both WLCSP packages are shown below in table 5.3.
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