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Figure 5: a) Grinding teeth shape A; b) Grinding teeth shape B; c) Grinding wheel Figure 6: a) Roughness vs. grinding wheel type; and b) Package strength vs.
A; and d) Grinding wheel B. grinding wheel type.
and 50µm. After the grinding process, the bending stress. The bending test also as the maximum stress that an object can
bottom thinner die resulted in the lower allows the determination of flexibility, withstand before being bent and broken.
ELK material stress ratio, although there is bending strength, breaking strength and the To compare the effect of grinding wheel
a process risk during die bonding because fracture resistance of the material. During type, we selected four types of wheels for a
of die warpage. The summary of die the bending test, deformation occurs at grinding process DOE study. The grit size
thickness impact on ELK stress in a double- the midpoint of the test samples, and the of the grinding wheel ranged from 7~8µm
sided SiP structure is shown in Table 2a. bending force causes a concave surface to 1~2µm, and the grit concentration
A 3-point bending strength test was also or bending fracture. A force is applied to ranged from 75 to 100, and the grit shape
conducted to confirm package strength, the test sample at its midpoint to form a (i.e., block type of grit shape with vitrified
which is modulated by the external concave surface with a pre-defined radius bond structure); these parameters are
of cur vature. The summarized in Table 2b.
package (PKG) die We also measured the die roughness on
strength is defined a double-sided SiP structure with different

Table 2: Structure strength analysis results: a) Summary of die thickness
impact on ELK stress in a double-sided SiP structure; and b) Comparison of the Figure 7: Double-sided SiP of a BGA ball cross-section scanning electron
impact of various grit sizes with respect to grinding wheel types. microscope (SEM) result.

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