With the evolution of central processing units (CPUs), semiconductor manufacturers had to come up with sockets appropriate for physically and electrically connecting them to the motherboard of computer systems. For about two decades, PGA was the most popular type of integrated circuit packaging used for CPUs and their sockets, and one of its most common variants is SPGA.
PGA Description
PGA is an acronym for "Pin Grid Array." The phrase is used to describe the manner of arrangement of the CPU socket's pin holes that accommodate the pins of the processor; they are arranged in a neat, orderly, grid-like layout. PGA came into existence because CPUs were increasingly being manufactured with more pins to handle wider data and address buses, an occurrence that dual in-line packages (DIPs) were unable to accommodate. The first CPU socket to use PGA packaging is Socket 1, which semiconductor company Intel Corp. debuted in 1989.
PGA Limitations
Socket 1 was made with 169 pin holes to accommodate entries of the Intel 80486 microprocessor, which was released the same year as the socket. However, with the introduction of CPUs such as the Intel Pentium in 1993, the number of processor pins began to exceed 200 and, eventually, 300. The original PGA was beginning to appear inadequate, since manufacturers had to put in more pin holes in the same amount of space.
SPGA Introduction
Socket 5, introduced in 1993 for Intel Pentium processors, became the first CPU socket to use a variant of PGA called SPGA. The "S" stands for "staggered," which means that the pin holes are arranged in a rough, staggered layout so that more of them can be fit onto the socket. For instance, Socket 5 has 320 contacts, almost doubling the amount of Socket 1. Socket 7, which arrived in 1994 and was the second Intel socket to use SPGA packaging, added one more contact.
Current Status
At the time of publication, both PGA and SPGA are no longer in wide use. The last major CPU socket to use SPGA packaging was the 387-contact Socket 8, which came along in 1995. But even then, it only used the format on one side while relying on the traditional PGA standard on the other. By the end of the 2000s, PGA in general had been overtaken by other types of integrated circuit packaging -- most prominent of which has been Land Grid Array (LGA) -- primarily due to the ability to fit more pin contacts on the socket than ever before.
Tags: Socket which, circuit packaging, first socket, Grid Array, integrated circuit