SST International utilizes graphite, among other materials, for tooling of microelectronics parts packaging. The superior characteristics of Graphite including CTE match, thermal shock absorption, thermal conduction, high temperature resilience, and machinability makes it a unique material for demanding high reliability tooling.
For tooling of microelectronics packaging with large variation in tolerances, as well as different steps to assemble these packages, SST utilizes inserts with integral springs made out of graphite to locate the parts precisely into their respective assembly location. These spring shapes vary from design to design. To assure the robustness of the design, Finite Element Analysis (FEA) is used to calculate the desired deflection vs. the stresses exerted on the springs.
Figure 1 shows an analysis for a simple curved beam spring. The displacements are in mm. In this example, based on the amount of the deflection to hold the package to one side of the cavity, the stresses are calculated.
Figure 2 shows the amount of Von Misses stresses on the curved spring in Pascal, which is well below the tensile strength of graphite material.
In another application of FEA to graphite materials for microelectronic packaging, a wafer chuck that goes under thermal cycle has been analyzed for reliability. The graphite with good thermal conduction provides an excellent wafer chuck with acceptable thermal uniformity.
See Figure 3 for temperature uniformity of the chuck. Due to symmetry only half of the chuck is analyzed.
A thermal stress analysis is performed with three supports which constitute mechanical constraints on the wafer chuck.
Figure 4 shows the high areas of stress concentration on the chuck at where the chuck is sitting on the pins. The pins are treated in order to reduce friction and subsequently to reduce stress concentration.
These examples show the flexibility and performance of graphite material and its application in electronics packaging. These capabilities can be extended by utilization of FEA to help design an appropriate fixture for many different tooling requirements.
To learn more about SST International, visit www.sstinternational.com
Download these resources for more information:
| Graphite Machining Datasheet | MEMS Device Packaging Datasheet | Model 3130 Datasheet |
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Saeed Sedehi
Director of Engineering
SST International