Localized Induction Heating Packaging And Its Applications

Induction heating has many advantages such as high efficiency, little impact on device itself, and high reliability, it can be used for MEMS device packaging and wafer-level bonding. In addition, not only can it be combined with the usual MEMS packaging technology such as anodic bonding, eutectic bonding, solder bonding, etc., but also be compatible with electroplating process. Therefore, packaging by induction heating can be developed to a semi-standardized MEMS packaging technology. In this dissertation, our research focuses on developing the induction heating equipment and processes for MEMS packaging. Methods used in the research include theoretical analysis, finite element simulation and experiments.Firstly, based on the electromagnetics and thermal conduction theory, the characteristics of micro-systems induction heating are studied. Some impacts on induction heating temperature, such as the frequency of induction power supply, the relative magnetic permeability, induction coil structure, the material performances and geometry of bonding ring and so on, are analyzed theoretically. Moreover, a micro-scale induction heating packaging model is established. Based on micro-systems simulation of induction heating packaging, a novel non-linear and sequentially coupled magnetic-thermal iteration method is developed, the electromagnetic field and temperature field in the packaging by induction heating are well coupled, and the micro-scale induction heating process can be simulated correctly.Secondly, based on the requirements, a high-frequency induction heating system and a RF induction heating system are developed to handle device packaging and wafer-level bonding, respectively. For the RF induction heating, the combined coil can meet the requirement of wafer-level bonding, and it also can provide the vacuum or inert gas protection in the bonding process. For the high-frequency induction heating, cone-shaped coil is used for hermetic packaging of single MEMS devices.Thirdly, using the non-linear and sequentially coupled magnetic-thermal iteration method, the temperature distribution on ceramic crust is simulated in the packaging by induction heating. When the ceramic crust is square, the eddy current density in the middle of each edge of the solder loops and Kovar cap is larger than that of the corner of the edges, which decreases the temperature in the corner. By the high-frequency induction heating system, ceramic crusts are packaged hermetically. Meanwhile, the temperature distribution, as well as the impacts of heating time and pressure on packaging quality is investigated. Hermetical packaging of Gyroscope using ceramic crust by induction heating is carried out and the bonding quality is evaluated.Finally, simulation and induction heating experiments are applied to explore the impact of the geometry and size of solder loops on the induction heating temperature. For the frequency at 13.56MHz, the wider the edges of solder loops are, the higher the induction heating temperature is. The area of the rectangle loop increases along with the edge of metal loops increasing, then the magnetic flux through the rectangular loops increases and the induction heating temperature increases more rapidly, and the local temperature difference is larger. Some tin-loops fused open because of local overheating of the loops, and the opened loops were not heated any more. By optimizing the design of the coil, uniform alternating magnetic field along the vertical direction is promised. Then, the tin-loop array on the PCB boards was heated uniformly, and the temperature on the loops was consistent. That is, the same loops could results in a uniform induction heating. The results from the simulation agree well with the experimental results, which verify the correctness of the simulation method.