Thermal control stage assembly

FIGURE 26.57 Thermal control stage assembly, (a) Top view (b) rear view with counter weight removed. 

Another way of automating assembly is to use the epoxy adhesive in the front of a silver filled or oxide filled tape. These tapes are made by impregnating the epoxy adhesive into a glass mesh support, B-staging to form a tack-free film, and then slitting the tape into rolls or diecutting the tape into custom-made preforms. In production, the user places a preform under the part to be bonded, or uses a machine to chop or punch preforms from a roll of tape. In either case, the tape provides precise control of bond thickness, eliminates voids, and avoids an excessive fillet. The tapes can be cured very quickly, at temperatures over 160°C, and the controlled thickness of the bond reduces thermal stresses due to thermal expansion mismatch between bonded part and the substrate. 

The applicability of thermodynamic theory of self-assembly, as described above, is limited to systems that reach an equilibrium state. The attainability of equilibrium depends largely on the strength of the stickers as measured by their association energy as compared to the thermal energy kT. When the stickers are too strong thermodynamic equilibrium may become unattainable. In this case the aggregation is in effect irreversible and thus subject to kinetic control. Note, however, that equilibrium stmctures may obtain if the sample history allows for equilibration at an intermediate stage. 

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