Patent Application
20050164505
Embodiments of the invention relate, generally, to the field of integrated circuit devices and, more specifically, to integrated circuit packaging and land grid arrays.
There are a multitude of electrical connections between the integrated circuits of an electronic device, such as a computer processor and other integrated circuits within the processor and eventually to other devices. With the ever-increasing complexity of components, such as microprocessors and application specific integrated circuits (ASICs), comes greater challenges in forming good electrical connections between the component and a printed circuit board. Some of the options include various small outline packages, plastic leaded chip carrier, dual inline packages, pin grid arrays, ball grid arrays, etc. Land grid array (LGA) sites are a popular way to connect such components to a printed circuit board.
LGA packages are ideal for devices, such as microprocessors, because the LGA package uses an array of contact pads on the component that are merged with similar contact pads on the printed circuit board, thus providing the required electrical connections between the integrated circuit device and the circuit board. The pitch of such electrical contacts can be very small. Typical LGA sockets include a base for seating the LGA package, which has a recessed portion in the middle of the socket base corresponding to the footprint of the LGA package to be inserted in the socket. This recessed portion operates to align the integrated circuit module to the electrical contacts within the socket, but also prevents the integrated circuit module from extending beyond the socket boundary. LGA sockets also typically include the same number of contacts providing electrical connections from the package to the circuit board, as the number of pads on the LGA package. An interposer between the chip package and the printed circuit board provides a frame that supports the chip package and also provides a conductive path for each of the contact pads.
The advantages of LGA socket connectors include: the capability to upgrade electronics in the field; flexibility in starting up and diagnosing an electronic system; reduction of cost required to rework the previously assembled board; reduction of mismatch between the coefficients of thermal expansion between the module and the board; improvement of electrical performance; and the compactness and low profile of the electrical connector designs. The main reason for terminating a device as an LGA may be to achieve higher pin counts with smaller packages. In short, the LGA offers a viable interconnection for high speed, high density integrated circuits.
Typical LGAs are not without disadvantages. In order to form a good electrical contact with such land grid array assemblies, the interposer's conductors need to be compressed. Thus, a normal force is applied to compress together the chip package and printed circuit board with the interposer sandwiched between. This force must be uniform, otherwise some of the contact pads will compress more than others, which may lead to a poor overall electrical contact. More problematic is that the force must be perpendicular to the point of tangency of the LGA contact or risk deforming the contact. That is, since the LGA contact is a very thin, hook-shaped conductor, if the compressive force is not direct the contact may get bent.
The LGA contacts can be deformed due to improper insertion or other handling, and may, as well, be contaminated by foreign material. That is, with the hooked shape of the contacts, it is easy for contaminating material, such as, for example, clothing threads, dust, or even conductive particles, to get lodged in or beneath the LGA contacts. Such contamination can impair the LGA performance or cause failure.
Over the lifetime of the LGA, the likelihood of a failure-causing deformation or contamination is high. Moreover, as the number of contacts on an LGA increases, the contacts will be thinner, and hence, more susceptible to deforming pressure.
The invention may be best understood by referring to the following description and accompanying drawings that are used to illustrate embodiments of the invention. In the drawings:
In the following description, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure the understanding of this description.
Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
Moreover, inventive aspects lie in less than all features of a single disclosed embodiment. Thus, the claims following the Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment of this invention.
In accordance with one embodiment of the invention, a membrane is placed over the LGA contacts, thus reducing deformation due to indirect pressure (i.e., pressure in an unintended direction) and contamination due to foreign material coming in contact with the LGA contacts. For one embodiment, the membrane is placed over the LGA contacts through use of a frame.
At operation 110, an LGA membrane is created. The LGA membrane may be made from a flexible, durable, and non-conductive material for one embodiment. For one embodiment, the LGA membrane is made of a synthetic polymeric resin that is resistant to high temperature, wear, and corrosion (e.g., a polyimide film). The LGA membrane may be created with small holes that correspond to the LGA contacts so that electrical connection is possible between the contacts and the pads of an IC device. For one embodiment, the dimension of each hole corresponds to the portion of the corresponding LGA contact that interfaces with the IC device pads.
At operation 115, the LGA membrane is affixed to the frame. For one embodiment, a membrane material is sized and cut to fit the frame and is then stretched tightly across the frame.
At operation 120, the LGA frame is attached to the LGA socket such that holes in the membrane align to corresponding LGA contacts.
The membrane, in accordance with various embodiments of the invention, reduces indirect pressure on the LGA contacts and reduces contamination of the contacts and the surrounding area. However, indirect pressure and contamination may be reduced further by providing a completely sealed LGA. In accordance with one embodiment of the invention, the membrane does not have holes through which corresponding LGA contacts interface the IC device pads. Instead, the membrane has pads incorporated therein that electrically interface corresponding LGA contacts and IC device pads.
For one embodiment of the invention, a membrane having incorporated pads is created using flexible circuit technology. A flexible interconnect (e.g., a pad) can be created by laminating a flexible polymer film to a thin sheet of conductive metal.
General Matters
Embodiments of the invention provide an LGA membrane that reduces the likelihood and extent of deformation of the LGA contacts, as well as contamination thereof by foreign material. For one embodiment, the membrane has a number of conductive pads that correspond to the LGA contacts. These pads interface, in place of the LGA contacts, with the IC device pads, providing electrical connection between the IC device pads and the LGA contacts.
Though described in reference to an LGA socket, embodiments of the invention are applicable to various types of direct socket loading (DSL) devices. For some DSL devices, an embodiment of the invention may be more applicable in reducing contamination of the contacts, while for other DSL devices, an embodiment of the invention may be more applicable to reducing the deformation of the contacts.
For various embodiments of the invention, the LGA membrane may be formed from a polyimide film, such as, for example, Kapton®, available from Dupont Corporation of Wilmington, Del. For alternative embodiments, the membrane may be any suitable, flexible material.
Embodiments of the invention include various operations. Many of the methods are described in their most basic form, but operations can be added to or deleted from any of the methods without departing from the basic scope of the invention.
While the invention has been described in terms of several embodiments, those skilled in the art will recognize that the invention is not limited to the embodiments described, but can be practiced with modification and alteration within the spirit and scope of the appended claims. The description is thus to be regarded as illustrative instead of limiting.
