Microelectronics Packaging:Package Hierarchy

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Package Hierarchy

Typical electronic systems are made up of several levels of packaging (see Figure 8.2). The zeroth level of packaging is the implementation of gate-to-gate interconnections on a silicon chip (e.g., gold and solder bumps). The semiconductor chip is encapsulated into a package, which constitutes the first level of packaging. A printed circuit board is usually employed (i.e., second level of packaging) because the total circuit and bit count required might exceed that available on a single first-level package. Besides, there may be components that cannot be readily integrated on a chip or first-level package such as capacitors, high-power resistors, and inductors. Therefore, several levels of packaging will be present and each level of packaging has distinctive types of interconnection devices associated with it (see Table 8.2). They are often referred to as a packaging hierarchy. The number of levels within a hierarchy may vary,

Microelectronics Packaging-0114

depending on the degree of integration and the totality of packaging needs [1,2]. In the past, the packaging hierarchy contained more levels. As shown in Figure 8.2, dies were mounted on individual chip carriers, which were placed on a printed circuit board. Cards were then plugged into a larger board, and the boards were cabled into a cabinet. Finally, the cabinets were connected to assemble the computer. Today, higher levels of integration make many levels of packaging unnecessary, and this reduces the circuit path length significantly and improves the performance, cost, and reliability of the computers. Ideally, all circuitry one day may be placed on a single piece of semiconductor. Thus, packaging evolution reflects the integrated circuits (ICs) progress [4–6].

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