a. At first circuits were made with individual components wired together.
b. Later individual components were soldered into circuit boards.
c. The creation of an integrated circuit( frequently called a `chip') was motivated by the quality control problems of soldering individual electronic components into circuit boards. The development was accelerated by the competition between the US and the USSR to build smaller, more accurate guidance systems for military rockets (Military research traditionally has had deep pockets).
d. Integrated circuit technology creates electronic components directly in a silicon wafer, a thin disk of silicon cut from a circular crystal. The production procedure is to create as many 1/4" square integrated circuits as possible on the surface of the wafer. Economic incentives promote the creation of ever larger wafers. The size has increased from 2 to 8 inches.
Initially an insulating layer of silicon dioxide is deposited on the surface of the chip. The integrated circuit is then constructed with a small number of masking, etching and building steps. In the mask step the chip is first coated with photoresist. Then ultraviolet light is shone through a mask, which defines the circuit elements, on the photoresist. Where the photoresist has been exposed to the UV light it becomes soluble. In the etching step the soluble photoresist is removed with acid. This exposes portions of the underlying surface. In the building step several alternatives are possible depending on the chip design. The exposed areas could be doped with impurities to change the electrical properties of the silicon, other materials such as polysilicon, which conducts electricity could be depositied on the exposed surfaces, or the exposed areas could be etched away to create holes where aluminum is deposited.
After the integrated circuits are created on the wafer, they are tested and the good ones are packaged in plastic to protect the embedded circuits. The steps in creating a wafer are presented in your reading, `` From Sand to Circuits''.