Optimized design of high precision heating stage for die attach equipment

The high-precision die attach technology is a key process in high-density integrated circuits such as WLP Fan-out, Multi-chip stacking, 3D interconnect and other advanced packaging processes. According to WLP Fan-out process requirements, die attach accuracy must be within ±15µm, even ± 6µm, and the stage temperature is required to be over 180°C and its uniformity can't above ± 3 °C. Those requirement is difficult to be obtained, because the heating stage generates a large number of heat sources, and the high temperature will be transmitted from the stage to the rails layer by layer. The uneven temperature's distribution on the rails will lead to its thermal deformation, which will directly affect the die attach accuracy. To ensure the die attach accuracy, the temperature at guide rail should be lower than 35 °C. In this paper, the structure of the precision heating stage is designed. According to the actual working conditions the boundary conditions of the stage are determined. The influence of the factors on the thermal characteristics of the heating stage are studied, such as the thickness of the thermal insulation layer, the thermal insulation material and the structure of thermal insulation pillars. A four-factor and three-level orthogonal test table is designed by orthogonal experiment method. The structural parameters of the heating stage are optimized. The experimental result shows that the temperature of the guide rail is within 28 °C, and the surface temperature uniformity of the heating stage is within ± 2.5 °C. The optimized stage satisfies the WLP Fan-out process requirements.