DUAL PATTERN MICROPROCESSOR
1. Field of the Invention
The field of the present invention is integrated circuit packaging footprints for use on printed circuit boards and, more particularly, footprints for receiving and servicing pin grid array (PGA) or tape carrier package (TCP) type micro- 10 processor packages.
2. Description of the Prior Art
Presently, two types of packaging systems for mounting microprocessors (for example, Intel p5c or 486 micropro- 15 cessors) to a printed circuit board are preferred by the personal computer industry. The first developed, and most widely utilized, packaging system is the pin grid array (PGA) packaging system. A typical PGA package comprises a casing or housing for supporting and providing electrical 2Q connections to the pins of a microprocessor, a plurality of pins mounted to the base of the housing, and a plurality of leads for connecting selected pins of the microprocessor to selected pins of the PGA package. A typical PGA package is mounted to a printed circuit board by inserting the pins of 25 the PGA package into a plurality of pin receptors formed within the printed circuit board. The pattern of the pin receptors formed within the printed circuit board is commonly referred to as the PGA package footprint, and an exemplary 320 pin PGA package footprint is illustrated in ,Q FIG. 1.
The second packaging system presently utilized by the personal computer industry is the tape carrier package (TCP) system. A typical TCP packaging system comprises a casing or housing for receiving and providing electrical connec- 35 tions to the pins of a microprocessor, a plurality of land patterns each including a plurality of exposed conductor trace segments formed on the underside of the housing, and a plurality of leads for connecting selected pins of the microprocessor to selected conductor trace segments within 4q the land patterns. Typically, a TCP package is mounted to a printed circuit board by coupling the land patterns of the TCP package to a similar set of land patterns provided on the circuit board. The land patterns provided upon the surface of a printed circuit board are commonly referred to as a TCP 45 package footprint. The TCP package is coupled to the circuit board via conventional means (for example, by hot bar bonding techniques). An exemplary footprint for a TCP package is illustrated in FIG. 2.
Those skilled in the art will appreciate that the personal 50 computer manufacturing industry is highly competitive, and that profit margins are often extremely small. Indeed, system design changes capable of yielding a Vi cent per unit savings in production costs are routinely implemented to maintain a competitive market position. With such tight margins, it is 55 readily apparent that fluctuations in the availability or cost of personal computer components may have a substantial effect on the overall profitability of a product line. For example, when large quantities of printed circuit boards are obtained for use with, for example, a PGA type microprocessor 60 packaging system, a fluctuation in the price of PGA packaging systems or the availability of PGA packaging systems may have a profound effect on the profitability of a computer line employing those boards. Further, if PGA packaging systems cannot be obtained, new boards capable of support- 65 ing a different packaging system (for example, a TCP type packaging system) will need to be obtained, resulting not
only in increased costs, but also in substantial manufacturing delays. Such a scenario is unacceptable in the highly competitive personal computer market. Accordingly, where steps can be taken to minimize and stabilize component supply costs or to insure component availability, it is often highly desirable to implement those steps in the personal computer manufacturing process.
To take advantage of, or conversely to protect against, fluctuations in the cost and availability of PGA and TCP microprocessor packaging systems, it would be desirable to provide both a PGA package footprint and a TCP package footprint on the printed circuit (PC) boards utilized by a given line of computers and, hence, to provide the capability of using either packaging system within a personal computer line. However, it will be appreciated by those skilled in the art that, if two distinct footprints are provided upon a circuit board, substantial space may be wasted on the board. This may result in increased manufacturing costs and, more importantly, may make it extremely difficult to meet board design specifications (for example, surface area restrictions).
It follows that a dual footprint for a PC board capable of receiving and servicing both TCP and PGA microprocessor packaging systems, while occupying a minimum amount of PC board space, would be quite beneficial to the personal computer manufacturing industry.
SUMMARY OF THE INVENTION
In a broad aspect, the present invention is directed to a dual footprint for use on a PC board which enables the PC board to receive one of two distinct microprocessor packages, while consuming a minimum amount of PC board area. More specifically, the present invention is directed to an innovative dual PGA and TCP footprint for use on a PC board and, hence, to a dual footprint capable of servicing either a PGA type microprocessor package or a TCP type microprocessor package. The present invention is also directed to methods for forming such a dual footprint on a PC board.
In one preferred embodiment, the dual footprint of the present invention comprises a TCP footprint disposed within a PGA footprint. It may be noted that this implementation insures that only a minimum amount of board surface area is utilized by a dual footprint in accordance with the present invention.
In another preferred embodiment, the TCP footprint is disposed within the PGA footprint and offset from the PGA footprint by a selected angle. By offsetting the TCP footprint in this fashion it is possible to minimize the number of vias and board line layers required to interconnect the TCP and PGA footprints. This implementation also makes it possible to maximize the line widths of conductor traces interconnecting the PGA and TCP footprints.
Accordingly, it is an object of the present invention to provide an improved footprint for use on PC boards and to provide improved methods for implementing the same.
It is a further object of the present invention to provide a dual footprint capable of servicing either a PGA type microprocessor package or a TCP type microprocessor package.
It is a still further object of the present invention to provide a dual footprint which consumes a minimum amount of physical board area on a PC board.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an illustration of a PC board footprint of a pin grid array (PGA) type microprocessor package.