Packaging
Plastic or ceramic packaging involves mounting the die, connecting the die pads to the pins on the package, and sealing the die. Tiny wires are used to connect pads to the pins. In the old days, wires were attached by hand, but now purpose-built machines perform the task. Traditionally, the wires to the chips were gold, leading to a "lead frame" (pronounced "leed frame") of copper, that had been plated with solder, a mixture of tin and lead. Lead is poisonous, so lead-free "lead frames" are now mandated by ROHS.
Chip-scale package (CSP) is another packaging technology. A plastic dual in-line package, like most packages, is many times larger than the actual die hidden inside, whereas CSP chips are nearly the size of the die. CSP can be constructed for each die before the wafer is diced.
The packaged chips are retested to ensure that they were not damaged during packaging and that the die-to-pin interconnect operation was performed correctly. A laser etches the chip's name and numbers on the package.
Read more about this topic: Semiconductor Device Fabrication