Page 403 - A Practical Guide from Design Planning to Manufacturing

Glossary 373

Peripheral component interconnect (PCI) An expansion bus standard. The
most common form is 32 bits wide and runs at 33 MHz.
PGA Pin grid array.
Phase-shift mask (PSM) A photolithography mask that allows light to pass
through with different phases in order to use destructive interference to create
sharper shadows on the photoresist and to allow patterning of smaller features.
Photolithography mask A patterned plate through which light is projected
during photolithography to determine the pattern of a particular layer. Masks
are usually made of quartz with the pattern drawn in chrome. Also called a ret-
icle. A complex integrated circuit may require as many as 40 masks.
Photolithography The process of creating extremely small features from masks
containing the desired pattern. The wafer is coated with a light sensitive chem-
ical called photoresist. Light is then shown through the mask causing a chem-
ical reaction in the photoresist that is exposed. The photoresist is developed
leaving behind a pattern determined by the mask and allowing etching to be per-
formed on the layers beneath only where desired. Repeated steps of deposition
and photolithography are used to create integrated circuits.
Photoresist (PR) A light sensitive chemical used during photolithography.
Positive resists become more soluble when exposed to light, and negative resists
become less soluble.
Pin grid array (PGA) An integrated circuit package using multiple rows of pins
on all four sides as leads.
Pipeline The series of steps required to fetch, decode, execute, and store the
results of a processor instruction. Pipelines improve performance by allowing
the next instruction to begin before the pervious instruction has completed.

Planarization A manufacturing process to create a flat surface for the next pro-
cessing step.
Plasma-enhanced chemical vapor deposition (PECVD) Deposition of mate-
rial through the chemical reaction of plasma. Microwaves are used to turn low-
pressure gases into a plasma allowing the high-rate deposition of high-quality
films.
Plasma oxide (PO) Silicon dioxide deposited using PECVD.
Plastic dual in-line package (PDIP) A plastic package with rows of leads on
two sides.
Plastic leaded chip carrier (PLCC) A plastic package with a single row of
J-bend pins on all four sides.

Plastic quad flat pack (PQFP) A plastic package with a single row of gull-wing
pins on all four sides.
Plated through hole (PTH) A package via created by drilling through the sub-
strate and filling the hole with a conductor.