of Microprocessors

786 MUSICAL ApPLICATIONS OF MICROPROCESSORS
Innovations in Packaging
As mentioned earlier, one way to compete in a market in which
equipment specifications have become standardized is to make your product
more compact. Since the late 1960s, the standard package for integrated
circuits has been the dual-inline package or DIP. Common logic functions,
like gates and flip-flops, use 14-, 16-, and 20-pin packages that take up
roughly 1/2 square inch on a printed circuit board. Larger functions like
microprocessors, read-only memories, and peripheral interface chips use 24-,
28-, 40-, and 64-pin packages that take from 1 to 3 square inches. As long as
DIPs are used, everybody is limited to about the same circuit density. The
main advantage of DIPs is that no specialized equipment is required to
handle or insert them onto boards, although some relatively simple handling
equipment is helpful in mass production. They are easy to work with when
prototypes are built and there is a tremendous variety of sockets, wire-wrap
panels, test clips, and other accessories available.
Recently, however, a number of high-density packaging alternatives
have become available. The first ICs to be affected were large advanced
microprocessors requiring 64 and more package pins. The "leadless chip
carrier" (LCC) and "pin-grid array" (PGA) packages, for example, can contain
a 68000 chip in under lin 2 , while the 64-pin DIP equivalent requires 3in 2 •
Even larger mictoprocessors, such as the 80186 and the 68020 are being
offered only in such packages because DIPs with more than 64 pins are not
available. Sockets are required for the LCC package but the PGA type can be
soldered directly onto a board. A third new package type, called "surface
mount" (SMT), has pins that lie parallel to the circuit board surface and are
soldered on top rather than leads that pass through holes to be soldered on
the bottom. Both large and small logic functions as well as ttansistors are
available in SMT packages and are about one-third to one-quarter the area
and much thinner than DIP equivalents. Sockets are generally not available
for SMT components.
Using these new package styles can effect a dramatic increase in circuit
functionality that can fit onto a standard-sized board. SMT 256K RAM
chips, for example, can be packed about three times closer together, thus
making possible 4M bytes of memory on a single 5 X lO-inch S-100 style
board. With DIP packages, only 1M byte would be possible. In a system
requiring 8M bytes of memory, the supplier of 1M byte boards is at a
substantial competitive disadvantage even if his boards are cheaper per byte.
With PGA and SMT components, one could package a 32-bit 68020
processor, 68881 floating-point processor, a hardlfloppy disk controller, a
CRT display generator, a couple of serial and parallel ports, and 2M bytes of
memory all on one board measuring perhaps 8 X 8 X less than 1/2 inch
thick.
The big disadvantage of these new packages, particularly the SMT
types, is that specialized equipment is necessary to handle them. In addition,