Electrical connectors – Preformed panel circuit arrangement – e.g. – pcb – icm – dip,... – With provision to conduct electricity from panel circuit to...
Reexamination Certificate
1998-02-27
2001-04-24
Patel, Tulsidas (Department: 2839)
Electrical connectors
Preformed panel circuit arrangement, e.g., pcb, icm, dip,...
With provision to conduct electricity from panel circuit to...
Reexamination Certificate
active
06220870
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to achieving electrical interfaces between two conductive paths, and more particularly to the construction of sockets for holding the I/O contacts of an IC chip in electrical contact with the compliant tips of an array of conductive probes, typically pogo pin probes. The invention has particular application in contacting ball grid array (BGA) devices wherein electrical contact must be achieved within an array of densely packed solder balls. However, the socket and method of the invention can also be used in connection with IC chips having other contact or lead formations.
Sockets for holding IC chips are well known and widely used in a variety of industrial applications for achieving efficient electrical contact between the I/O contacts of an IC chip and the conductors of a connector, circuit board or the like. Such applications include test sockets for testing IC devices and contactor sockets for removably mounting an IC device to a printed circuit board. The basic function of the socket is to hold the IC chip in a fixed position such that its array of I/O contacts, eg. the solder balls of a BGA, can be contacted by the compliant tips of a corresponding pogo pin array to produce a desired electrical connection. Precise centering of the pogo pins relative to the chip's I/O contacts is critical to this function and generally to the electrical and mechanical performance of the socket. Any misalignment between the pogo pin tips and the I/O contacts can result in a poor electrical interface to the IC chip. Distortion of the I/O contacts can also result when misalignments produce off-center contacts.
In a conventional IC socket, an IC chip is held in a socket base directly over an array of pogo pins. In such socket designs, the chip's I/O contacts are typically centered by referencing the known lateral dimensions of the IC package to the sidewalls of the socket base in which the IC chip is held. The difficulty with this centering approach is that the true position of the I/O contacts within the socket are subject to usual variations that occur in the dimensions of the IC package. The resulting deviations from a true center detrimentally affects the electrical performance of the socket and increases undesirable deformations in the chip's contacts. The problem of contact deformation is particularly acute in BGA devices where deformations in the device's solder balls can detrimentally affect the inspection of the IC device as well as the assembly of the device onto a printed circuit board. Excessive deformation of the extremely small solder balls of micro-BGAs can, for example, cause such IC devices to be rejected during quality control procedures which typically employ laser or other inspection techniques.
Another drawback of conventional IC socket designs is the need to apply a modicum of force to disengage the IC chip from the pogo pins upon removal of the IC chip from the socket. Generally, the tips of the pogo pin probes will, to a certain degree, indent, displace or disturb the chip's I/O contacts, creating a binding force between the chip and pogo pins which must be overcome upon removal. The need therefore exists for an IC socket where the removal of the chip from the pogo pin tips can be facilitated.
The present invention provides an improved IC socket design and method that overcomes the aforementioned drawbacks of conventional IC sockets. The improved IC socket and method of the invention reduces chip positioning errors and more particularly permits extremely accurate centering of the chip's I/O contacts over the tips of the socket's pogo pins. The invention also facilitates the removal of the chip from the IC socket.
SUMMARY OF THE INVENTION
Briefly, the invention herein described and claimed involves a socket which holds an IC chip having lateral edges and a planar array of I/O contacts. The socket is comprised of a base portion having a defined z-axis, and a separate chip docking structure for receiving the IC chip and for fixing the position of the chip's planar array of I/O contacts in an x-y plane perpendicular to the z-axis of the base portion, without reference to the lateral edges of the IC chip. In the preferred embodiment, the docking structure of the socket is provided in the form of a docking platform having a chip-seating surface extending in the x-y plane. This seating surface has an array of locator openings for receiving the chip when the chip is seated on the seating surface with its I/O contacts engaged in the locator openings. The position of the chip's I/O contacts is therefore fixed in the x-y plane in reference to the I/O contacts themselves, without reference to the lateral edges of the chip. Furthermore, the seating plane of the chip docking structure, which is contacted by the underside of the chip package, provides a reference plane for the chip that has relatively true planarity as compared to the planarity of the seating plane of the I/O contacts. Thus, the IC chip will be held within the socket in the true x-y plane established by the chip docking structure.
The socket of the invention also provides for an array of conductive probes which are held in the socket base in opposition to the chip docking structure. The array of conductive probes are configured to correspond to a standardized configuration of I/O contacts of an IC chip. Specifically, the probes have compliant probe tips arrayed in an x-y plane so that the probe tips and the I/O contacts held on the chip docking structure are centered relative to each other in the direction of the z-axis of the socket base. In the preferred embodiment, the probe array is held in a fixed transverse bottom wall of the socket's base portion. However, it will be understood that the probe array can be provided beneath the docking structure by other means, such as a separate probe retention structure that moves within the socket base or that externally connects to the socket base.
The socket of the invention further includes z-axis closure means for operatively bringing the I/O contacts of the IC chip held on the docking structure into contact with the compliant probe tips of the conductive probe array opposed thereto by a relative movement of the contacts and probe tips along the z-axis of the base portion. It is particularly contemplated that the chip docking structure will be movable relative to the probe tip array along the z-axis by providing a docking structure that is depressible in the z-axis against spring supports in the socket base. In the illustrated embodiment of the invention, the docking structure is provided in the form of a rectangular docking platform which is depressibly captured in the socket base along its four corners by means of corner blocks. The corner retention of the docking platform will inhibit any rotational movement of the docking platform in the base portion which would cause positional errors of the outermost I/O contacts of the IC chip seated on the platform.
The invention also involves a method for bringing the I/O contacts of an IC chip into contact with the compliant tips of an interface probe array. The method is generally comprised of fixing the position of the planar array of I/O contacts of an IC chip in the x-y plane in direct reference to the I/O contacts, and providing an array of probes having probe tips centered to such known fixed reference position. The centered probe tips and the I/O contacts of the I/C chip are brought into contact along the z-axis, preferably by moving the IC chip relative to the probe tips.
Therefore, it can be seen that a primary object of the present invention is to provide an IC socket and a method for centering the I/O contacts of an IC chip over the compliant tips of a probe array with minimal positional error. It is a further object of the invention to provide a test socket and method which permits the IC chip to self-release from the probe array upon removal of the IC chip from the test socket. Other advantages of t
Barabi Nasser
Jonaidi Siamak
Beeson Donald L.
Cerprobe Corporation
Patel Tulsidas
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