Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
1999-06-07
2001-09-25
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S754090, C324S757020, C324S761010, C324S765010
Reexamination Certificate
active
06294920
ABSTRACT:
This invention relates to burn-in and test of electronic devices in surface mount packages. More particularly, it relates to methods and apparatus for mounting and holding electronic device packages during burn-in and test and to establishing and maintaining positive electrical contact to closely spaced input/output terminal lands or leads on such packages without damaging the electronic device, the device package, its interconnection terminals or the test socket and without introducing signal distortion.
Advances in microelectronics technology tend to develop electronic device chips and packages which occupy less space while performing more functions faster. As a result, the number of electrical interconnections between the device package and external circuitry required for the circuits in the chips to communicate with the outside world increases and the physical size of each such interconnection must decrease. In order to provide electrical communication between the chip and external circuitry, circuit chips are usually contained within a housing or package which supports interconnection pads or lands, leads, balls, etc., on one or more of its external surfaces. In order to reduce overall lead length from chip to external circuitry and to provide adequate spacing between input/output terminals on the package, high pin count devices are sometimes mounted in packages in which the input/output terminals are in the form of conductive lands or pads formed on one or more faces of the package. The lands are often arranged in rows parallel with and adjacent peripheral edges of one face with the surfaces of the lands coplanar and parallel with (but slightly below) the bottom surface of the package. The lands may be arranged in other patterns such as parallel rows which cover the entire bottom surface in a grid pattern; lands grouped near the center of the bottom surface; or various combinations of such arrangements. Such device packages (commonly known as land grid array or LGA packages) may thus be mounted on circuit patterns on the surface of a circuit board or the like so that the terminal lands are bonded to mating lands or pads on the board.
In many cases it is desirable that the completed device package be subjected to test and/or burn-in prior to acceptance and assembly onto a circuit board. While the terminal lands may be directly and permanently surface mounted on a circuit board by soldering, it is much more difficult to establish and maintain temporary electrical contact with each land without destroying or damaging the land, the package or the encapsulated device chip. In order to reliably test and burn-in such packages, the package must be temporarily mounted in a re-useable socket or mounting which makes precision interconnection between the input/output lands and outside circuitry without introducing signal distortion problems and without physically damaging the device package.
As the size of the package decreases and the number of lands increases, the size and spacing of lands become smaller. Smaller and more closely spaced lands are, of course, more difficult to contact with test probes or the like. Furthermore, long or massive contact pins cannot be used for connecting external circuitry to the input/output lands for testing when high frequency devices are involved because such contact pins, particularly when closely spaced in order to contact closely spaced lands, introduce unacceptable signal distortion.
Conventional burn-in and test apparatus employs test sockets mounted on a burn-in board with the pin-out leads of the test or burn-in socket passing through the bottom of the socket and through holes in a circuit board in conventional through-hole mountings. Interconnection of high frequency devices with outside circuitry using such conventional mountings can induce unacceptable signal distortion because of the high density of parallel terminal leads passing through the board.
Miniaturized surface mount device packages have now been devised which have very closely-spaced input/output terminal lands on one face of the package. Such device packages, because of their extremely small size, configuration and physical construction are most difficult to handle without causing damage, yet good electrical contact with all the input/output terminal lands is essential. It is therefore desirable that apparatus be devised in which such small packages may be easily temporarily mounted (preferably by automation) and tested and/or stress-tested by burn-in and the like without damaging the device package or introducing signal distortion problems.
In accordance with the present invention reliable precise electrical contact is provided between input/output lands on LGA packages and external circuitry by re-useable mounting apparatus which employs a support base, a guide plate and contact pins in the form of fingers which extend through guides in the guide plate to engage the input/output lands on an LGA package. The guide plate is formed of electrically insulating material and has a set of guides (such as holes or channels) arranged to correspond with the terminal land arrangement of the LGA package. The guide plate is supported on and spaced from a support base which has a set of guides arranged to correspond with input/output lands on external circuit media such as a circuit board, burn-in board or the like. An axially elongated contact pin or finger having first and second ends supported by a shank is positioned so that the first end of the contact finger extends through a guide in the guide plate and the second end of the contact finger extends through a guide in the support base to contact an input/output land on an external circuit board such as a burn-in board or the like. The shank of each contact finger extends through an aperture in a bending plate positioned intermediate the guide plate and the support base. When the bending plate is moved in a first direction with respect to the guide plate and support base, it bends the contact finger, thus drawing the ends of the fingers toward the bending plate. When moved in the opposite direction, the curvature of the fingers is decreased and the ends move outwardly through the guides in the guide plate and the support base. As the ends of the fingers move outwardly, they engage terminal lands on an LGA package mounted adjacent the guide plate and terminal lands on a circuit board or the like on which the support base is mounted. With the space between the lands on the LGA and the lands of the circuit board fixed by the size of the mounting apparatus, the contact pressure applied to the contact lands can be closely controlled by movement of the bending plate. Extending and retracting the ends of the contact fingers by bending the fingers also causes the ends of the fingers to move slightly laterally (in the direction opposite the direction of movement of the bending plate), thus causing the ends of the fingers to very slightly scrape the surfaces of the terminal lands to insure good electrical contact.
REFERENCES:
patent: 5419710 (1995-05-01), Pfaff
patent: 5508628 (1996-04-01), Pfaff
Deb Anjan K
Griggs Dennis T.
Metjahic Safet
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