Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2000-04-29
2004-05-11
Pert, Evan (Department: 2829)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S754090, C324S758010
Reexamination Certificate
active
06734690
ABSTRACT:
TECHNICAL FIELD
The invention relates in general to computer component test equipment, and more particularly to printed circuit board test equipment.
BACKGROUND
When testing computer components on printed circuit boards it is generally desirable to make electrical contact with electrical nodes at particular locations on such printed circuit boards (PCB). Where integrated circuit (IC) packages which have an array of surface contacts are connected to the PCB, electrical contact is most practically made on the side of the board opposite the IC packages, generally employing vias in the board. Herein, the term “board” and “printed circuit board” are generally used interchangeably.
Where IC packages are attached to a board or PCB, an intermediate conductive layer is commonly inserted between the IC packages and the PCB, such as an interposer which includes compression contacts. The compression contacts apply a force against the board, generally causing the board to bow out or bend away from IC package electrical contacts where no restraint is placed on the board. When the board is allowed to bend away from electrical contacts on the IC package, electrical contact between the board and the IC package may be disrupted, thereby disabling proper function of the board and any meaningful diagnostic operation. Accordingly, a back pressure plate or back plate is commonly applied to the side of the PCB opposite the side on which the IC package is attached to prevent such board warpage, thereby ensuring that proper electrical contact is made between the IC package and the board and that proper operation of the equipment on the board as a whole is maintained.
Although installation of the back pressure plate generally solves the problem of the warpage of the PCB while preserving proper function of components interconnected on the PCB, the installation of a plate in this manner generally blocks access to electrical contacts which is needed for testing the operation of the board.
Therefore, it is a problem in the art that, without restraint being applied to PCB, the PCB may bend away from IC packages attached to the PCB causing normal operation of the board to be disrupted and preventing effective diagnosis of the board's function.
It is a further problem in the art that attaching a back plate to the side of a PCB opposite the side on which an IC package is attached generally blocks access to electrical contacts benefical performing testing on the board.
SUMMARY OF THE INVENTION
These and other objects, features and technical advantages are achieved by a system and method which opposes the warpage of a printed circuit board caused by compression contacts or other mechanism disposed between an IC package and a PCB while providing clearance on the side of the PCB opposite a side on which an IC package is attached, thereby providing access to electrical contacts on the circuit board beneficial to performing diagnostic operations on PCB operation. Herein, the term “opposing side” or “opposing surface” generally refers to the side or surface of a PCB opposite to the side of the PCB to which an IC package or other component to be tested is attached.
One approach to providing access to electrical contacts on a PCB for diagnostic purposes involves drilling holes in selected locations on a back pressure plate which is in place to prevent warpage of the PCB. The holes are preferably drilled at locations on the back plate corresponding to locations, on the pertinent side of the PCB, of electrical contacts carrying signals which are of interest to a diagnostic operation. In this manner, even with the back plate firmly secured against the PCB, electrical probes may be inserted through the back plate and make contact with desired locations on the PCT for diagnostic purposes.
A disadvantage which may arise when employing the drilled back pressure plate approach discussed above is that it may be desirable to probe locations on the PCB which are blocked by the back pressure plate. This situation may arise due to a number of circumstances including but not limited to: misalignment between the holes in the back pressure plate and the desired connection locations on the PCB, a change in location of certain desired electrical contact locations on the PCB, between the time when the back pressure plate is designed and machined and the time at which testing is conducted, and a change in the locations on the PCB selected for probing during diagnostic operations. Accordingly, a more flexible approach to opposing warpage of the PCB while still permitting access to electrical contact locations desired for diagnostic purposes is needed.
In a preferred embodiment of the present invention, a mechanism is deployed which opposes warpage in a printed circuit board caused by compression contacts or other device by applying force to an opposing side of a PCB employing one or more selectively located pressure points while exposing electrical contacts on the opposing side of the PCB for attachment of probes for diagnostic purposes.
In a preferred embodiment, a frame may be attached to a PCB. In turn, one or more contact devices may be attached to the frame for applying force to the PCB to oppose warpage of the PCB. The frame could be permanently attached to the PCB or alternatively could be suited for temporary attachment to the PCB during testing or diagnostic operations. Alternatively, the frame could secured in proximity to the PCB through an attachment to a location independent of the PCB.
In a preferred embodiment, the number of contact devices employed to impart force to the PCB may be varied based upon a number of factors, such as, for instance: the size of the PCB, the number locations on the PCB with which electrical contact is sought, and the relative proximity of the desired electrical contact points on the PCB. Moreover, the locations on the PCB at which the one or more contact devices make contact with the PCB may be either variable or fixed. Furthermore, force may be imparted to an opposing side of a PCB employing a number of means including but not limited to: coil spring, electric motor, leaf spring, electromagnetic solenoid, pneumatic pressure, hydraulic pressure. Links disposed above the PCB for imparting force to the PCB may include a range of possible degrees of rigidity.
In a preferred embodiment, the inventive mechanism preferably enables the PCB to be remain substantially straight during testing of the PCB, thereby preferably ensuring proper electrical contact between the PCB and an IC package attached thereto as well as proper operation of the PCB, while simultaneously providing physical access to electrical contact points on the PCB for probes and other devices to enable diagnostic operations to be performed. Moreover, the inventive mechanism preferably presents the ability to flexibly modify the locations on the PCB to which physical access by electrical probes may be granted. Modifying the locations on the PCB to which access is granted in successive testing setups or attachments preferably enables an entirety of contact points of interest on a PCB surface to be accessed, even if a subset of these contact points is blocked by test fixture equipment during an initial test fixture attachment.
Therefore, it is an advantage of a preferred embodiment of the present invention that the inventive mechanism may operate to oppose warpage of a PCB while providing access on the PCB to electrical probes for diagnostic purposes.
It is a further advantage of a preferred embodiment of the present invention that force may be imparted to a PCB at a selectable set of locations on the PCB, thereby enhancing an ability to access all desired electrical contact locations on the PCB.
It is a still further advantage of a preferred embodiment of the present invention that the points on a PCB to which test equipment may be connected may be varied after testing is under way.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the inven
Hewlett--Packard Development Company, L.P.
Hollington Jermele M.
Pert Evan
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