SUPPORTO IN SCALA DI CHIP PER OPERAZIONI DI COLLAUDO E VERIFICA

Description

5831.76 / P / Italy -2DESCRIPTIONRM98 A 000201' accompanying an application for a patent for invention entitled: Chip scale support for testing and verification operations in the name of: WAYNE K. PFAFF The present invention relates to the infant mortality testing and inspection of small electronic packages, semiconductor chips, and the like. More particularly, it relates to methods and apparatus for manipulating small electronic devices and device packages, such as chip-scale packages and the like, during infant mortality testing and inspection, and for establishing and maintaining positive electrical contact with closely spaced input / output terminals on such small-scale packages without damaging the chip, its package, its interconnecting terminals, or the test medium. Advances in microelectronics technology tend to develop electronic device chips and their enclosures that take up less space while performing a greater function. WG. BARZANO' & ZANARDO ROMA SpA -3 number of functions. As a result, the number of electrical interconnections between the chip and the external circuitry required for the circuits embedded in the chip to communicate with the outside world increases, and the physical size of each such interconnection must decrease. To provide electrical communication between the chip and the external circuitry, the circuit chips are typically contained within a housing or package that supports the interconnect terminals, connection pads, etc., on one or more of its external surfaces.To reduce the overall length of leads extending from the chip to the external circuitry and to provide adequate spacing between the input / output leads of the package, high-pin-count devices are typically mounted in packaged packages in which the input / output leads are arranged in a grid pattern on one side of the package. The leads may be in the form of pins extending from the package (commonly described as a pin grid array, or PGA) or as contact pads or ridges on the package surface. -4encapsulation (usually described as ridge grid array or LGA). To physically secure the chip to a substrate and to provide an electrical connection between its terminal ridges and similar ridges or interconnect pads on the surface of a substrate, e.g., a circuit board or the like, on which the encapsulation package is to be mounted, a small droplet or bead of solder or the like is affixed to each terminal pad on the device package. Because the solder droplet forms a bead-like prominence extending from the terminal pad, such devices are ordinarily described as bead grid array (or BGA) devices. While the term bead grid array device is commonly applied to a device package that has substantially spherical contacts extending from one face of the package, the term is also applied to other structures. For example, bare (unencapsulated) chips are sometimes provided with a bead grid array of contacts for assembly in a package. ®G. BARIAMO' & ZANARDO ROMA Sp A· -5However, at some point during fabrication, the bare chip with bead-shaped contacts is quite well described as a bead-grid array device. Similarly, finished chips are sometimes provided with terminal pads on a surface with bead-shaped solder deposits forming interconnects on the terminal pads. The chip is then inverted and connected directly to a corresponding configuration of interconnect pads on a substrate. When heated, the solder beads reflow to form electrical and physical connections. This process (sometimes referred to as flip-chip technology) obviously uses devices that can be described as bead-grid array devices.More recently, package designs for miniature devices have been developed that feature closely spaced input / output terminal beads on one side of the chip. These devices are referred to as chip-scale package designs, or micro BGAs, and are, due to their extremely small size, highly susceptible to cracking. ING. BARZANO' & ZANARDO ROMA S.p.A. -6Their configuration and physical construction make them very difficult to manipulate without causing damage, yet good electrical contact with all input / output terminals is essential. With such small encapsulation packages and finely spaced terminals, it is impractical to probe each terminal with a single wire-shaped probe. Such probes tend to flex (and thus become misaligned); overlap two or more terminals; exert sufficient pressure on the terminal ball to break or damage it; or tend to distort and / or bind to the terminal ball.Therefore, it is desirable that apparatus be devised in which devices having a grid array or array of beads, particularly small encapsulation packages such as chip-scale encapsulation packages, can be readily assembled (preferably automatically) and stress tested and / or verified by infant mortality or burn-in tests and the like. For purposes of the present invention, the term "grid array" refers to all such array or array arrangements comprising grids of beads. The term "chip-scale packages" is used. -7used to describe a particularly small bead grid array encapsulation container, but should not be interpreted to exclude other bead grid array devices. In accordance with the present invention, positive electrical contact with each terminal bead of a BGA encapsulation package is achieved by using a flexible interconnect band or strip having electrically conductive ribbons or patterns at various depths thereof, separated by thin layers of insulation with apertures or windows disposed in the insulation to allow the input / output terminals of the bead grid array to make electrical contact with a conductive ribbon on the surface of the interconnect band and / or a conductive ribbon exposed through a window in the insulation layer. By forcing the surface of the terminal bead into contact with the flat surface of a conductive ribbon or pad, all forces applied to the terminal bead are perpendicular to the face of the encapsulation package. Therefore, tangential or other forces ING. BARZANO' & ZANARDO ROMA S.p.A. -8 that could displace or distort the terminal bead are avoided. By forcing the terminal bead into a flat face of a pad or conductive tape, the pad or conductive tape is encouraged to conform to the shape of the terminal bead, thus forming a maximum-area physical contact. Furthermore, the flat surface of the pad or contact tape does not scratch, etch, or otherwise deform the terminal bead. Because there is no point contact, the likelihood of unwanted bonding by migration between the terminal bead and the contact pad is avoided or substantially reduced. Most significantly, the physical distance (the length of the conductor) between the terminal bead and the external circuitry to which it is connected by the conductive tape is substantially reduced.Therefore, the interconnection arrangement according to the invention may be used for testing or infant mortality (bum-in) testing of extremely high frequency devices. Other features and advantages of the invention will be more readily understood from the following detailed description taken in conjunction with the appended claims and with. -9i attached drawings, in which: Figure 1a represents a top perspective view of the preferred embodiment of a chip scale holder utilizing the principles of the invention; Figure 1b represents an exploded view showing the chip scale holder of Figure 1a in the open position and illustrating the placement of the chip scale encapsulation containers therein; Figure 2a is a sectional view of the chip scale holder of Figure 1a, taken along the line 2a-2a, Figure 2b is a sectional view of the chip scale holder of Figure 1b, taken along the line 2b-2b. Figures 3a and 3b are partial sectional views illustrating an array or matrix of terminal beads on a chip-scale encapsulation package that is in contact with a conductive ribbon or strip configuration in the interconnect band of the invention. Figure 4 is a greatly enlarged partial sectional view illustrating the 1NG. BALZANO' & ZANARDO ROMA Sp A -10contact of the output pins of the chip scale holder with the interconnect pads of the interconnect band or strip, Figure 5 is an exploded assembly view of the chip scale holder shown in the preferred embodiment of Figure 1a, Figure 6 is a top perspective view of the base plate of the chip scale holder of Figure 1a, Figure 7a is a top perspective view of the flip-up door of the chip scale holder of Figure 1a, Figure 7b is a bottom perspective view of the flip-up door of the chip scale holder of Figure 1a, Figure 8a is a top perspective view of the main body of the chip scale holder of Figure 1a, Figure 8b is a bottom perspective view of the main body of the chip scale holder of Figure 1a,and Figure 9 is an exploded perspective view of the chip-scale encapsulation carrier assembly of the invention with a grid array mounting socket, -11 of spheres, as described in U.S. Patent No. 5,611,705. It will be recognized that the principles of the invention can be utilized and embodied in many different forms. In order to demonstrate these principles, the invention is now described with reference to a specific preferred embodiment thereof. The invention, however, is not limited to the specific forms described herein. The preferred embodiment shown in the drawings comprises a body 10 supporting a hinged flap or baffle 20 that supports bearing pads 21 aligned with openings 11 in the body 10. A bottom plate 30 carries a plurality of output terminal pins 31 in configured openings 32. An interconnection strip 40 is folded over a bearing pad 50, such that one end section thereof faces the terminal pins 31 and the other end section faces the openings 11. The interconnection strip 40 carries a pattern of electrically conductive ribbons or traces 41 on its surface and at least one layer of electrically conductive traces or tracks 42 encapsulated in the strip and insulated. BARZANO' & ZANARDO ROMA Sp A -12from each other and from the surface strips 41 by means of the top insulation layer 43. By using the multilayer interconnect strip, isolated interconnections can be achieved between the very fine pitch terminal bead array and the outside world circuitry. The interconnection between the terminal pins 31 and the terminal beads 15 is illustrated in detail in Figure 4, and the interconnection of the assembled carrier with a large-scale bead grid array socket is shown in Figure 9. The electrical contact between the terminal beads 15 of an encapsulation container 16 comprising a grid array of beads and the conductive tracks or traces of the interconnect strip of the invention is best illustrated. in Figures 3a and 3b. An enlarged partial section 16 of a BGA package having terminal beads 15 projecting from one face thereof is shown suspended above a partial section 40 of an interconnect strip 40 supported on a support pad 50. As shown in Figures 3a and 3b, the interconnect strip 40 comprises -13two layers 43 of electrically insulating material (e.g., mylar or the like). A plurality of conductive tracks 42 are sandwiched between the insulating layers 43 and a plurality of conductive tracks 41 are disposed on the top surface of the top layer 43 of the interconnect strip 40. In the preferred embodiment, the tracks 42 are formed by depositing a layer of conductive metal (e.g., copper or the like) on the surface of the bottom layer 43 and subsequently forming a pattern of tracks 42 by photomasking, chemical etching, etc. Alternative processes may be employed, such as deposition through a mask or the like. For purposes of the present invention, any process that forms the conductive tracks in the desired pattern between two layers of insulating material may be employed.A second layer of conductive traces 41 are formed on the top surface of the top insulation layer 43. Windows 44 are cut in the top insulation layer 43 at appropriate locations and in the desired configuration to permit electrical interconnection with the pads. BARZANO' & ZANARDO ROMA Sp A. -14conductive pads 42a exposed therethrough. It will thus be appreciated that the conductive traces 42 may be formed in a configuration having a plurality of enlarged contact pads (e.g., pad 42a) connected to thin conductive ribbons or tracks that provide electrical connection to the interconnecting pads 52a elsewhere in the interconnecting strip 40. By appropriate positioning of the traces 42 and the windows 44, a configuration of contact pads 42a exposed through the windows 44 may be formed to coincide with a selected configuration of terminal beads 15. A similar configuration of contact pads 41a may be formed on the top surface of the top layer 43 (with each pad 41a connected to a conductive trace 41) and arranged to coincide with a selected configuration of terminal beads 15.If desired, a conductive ring 41b may be formed adjacent to a window 44. In this arrangement, the terminal ball 15 makes electrical contact with the electrical trace 41b, as well as with the contact pad 42a. As depicted in Figure 3b, each -15 Terminal ball 15 is forced into contact with a top pad 41a or an inner pad 42a exposed through a window 44. The interconnect strip or band 40 is preferably supported on a support pad 50 of resilient material, such as rubber or the like. Accordingly, as the BGA device 16 is moved toward the rubber support pad 50, the terminal balls 15 are forced into intimate contact with the contact pads 41a and 42a. However, because pads 41a and 42a are flexible and because support pad 50 is resilient, pressure is uniformly applied to all of the terminal balls 15 and the pressure is exerted only in a direction perpendicular to the face of BGA device 16 from which the terminal balls 15 extend. Furthermore, no sharp edges or ends of pins, probes, or the like engage the terminal balls 15.Conversely, each terminal ball 15 is forced into contact with a broad face of a contact pad. As the balls are forced into contact with the contact pads, the contact pads 41a, 42a deform to conform to the surfaces of the. BALZANO' & ZANAIO POMA S.p.A. -16 terminal spheres, thus distributing the contact force evenly across each terminal sphere 15. By forming the contact pads 41a, 42a in parallel planes insulated from each other by the top insulation layer 43, the conductive traces 41, 42 can be insulated from each other and the traces of a single layer (e.g., traces 41) can be spaced sufficiently to prevent an electrical short circuit or crosstalk. In this manner, the pads 41a and 41b can be staggered to form an insulated contact with extremely closely spaced terminal balls. In the preferred embodiment, the interconnect strip 40 is formed using mylar films 43 that are only about 0.001 inch thick, or 25.4 microns. The contact pads 41a, 42a and the tracks or tracks 41 are formed of copper of approximately the same thickness. The interconnect strip 40 is therefore flexible and can be formed with contact pads 41a in a grid configuration on 0.5 mm (or less) centers, where each pad and its associated trace are electrically insulated. -17from the others. While the interconnect strip 40 shown in Figures 3a and 3b comprises only two insulating layers and two conductive layers, it will be readily recognized that the invention is not so limited. Interconnect strips 40 of the same general configuration comprising three or more layers of conductive traces may be employed where closer packing of the terminal beads is required and / or where greater separation distance between the traces is desired. In order to provide electrical communication between each of the contact pads 41a, 42a and the outside world, the traces 41, 42 must be connected to external circuitry. In the preferred embodiment shown in the drawings, the contact pads 41a, 42a are arranged in a 0.50 mm pitch configuration (0.50 mm center-to-center separation) with the opposite ends (interconnect pads) of the traces arranged in a 1.27 mm pitch configuration. As shown in Figures 2, 2a, 2b and 4, the interconnect strip 40 is wrapped around the WG. BARZANO' & ZANARDO ROMA S.p.A. -18support pad 50 and interconnection pads 51a and 52a (which are connected to contact pads 41a and 42a via traces 41 and 42, respectively) are positioned on the opposite side of support pad 50. As shown in Figures 2a, 2b, and 5, contact pins 31 are positioned in openings 32 in the base plate 30 (see Figure 6) and are arranged to contact interconnect pads 51a and 52a and to provide electrical communication with circuitry in the outside world. As shown in Figure 5, the chip scale carrier of the invention provides electrical connection to the terminal beads of BGA devices on 0.5 mm centers and distributes output terminals to pins 31 on 1.27 mm centers. The output pins 31 may be connected to conventional external circuitry through a circuit board, infant mortality test board, or the like. Alternatively, the interconnect terminal pins 31 protruding from the bottom plate 30 may be inserted into a larger test or infant mortality (burn-in) socket as shown. -19in Figure 9. In the preferred embodiment illustrated, a chip-scale holder is provided which permits the simultaneous mounting of four BGA devices for verification, infant mortality testing, etc. The holder illustrated includes a base plate 30 (see Figures 5 and 6) which includes four groups or configurations of apertures 32. Output terminal pins 31 positioned in apertures 32 provide electrical connections to the outside world, as discussed above. As illustrated, the interconnect strip 40 is wrapped around the resilient support pad 50 (see Figures 4 and 5) and is mounted such that the output terminal pins 31 engage the interconnect pads 51a and 52a facing in a first direction in predetermined configurations. The contact pads 41a and 42a are arranged in a grid matrix configuration which faces in the opposite direction. The support body 10 has four windows, each of which is aligned with each of the four pad configurations of ING. BARZANO' & ZANARDO ROMA S.p.A. -20contact, such that each configuration of contact pads on the top section of the interconnect strip 40 is exposed through one of the windows (Figures 8a and 8b). The body 10, the interconnect strip or band 40 (wrapped around the support pad 50), and the base 30 are all rigidly secured together by means of rivets 50, screws, bolts, or the like. It will be appreciated that each window 61 in the body 10 is adapted to align and position a BGA device such that the configuration of the terminal balls on the BGA device is in register with the configuration of the contact pads 41a and 42. Various registration means, e.g., keying slots, sloped sides, asymmetrical shapes, etc., may be used to properly orient and position the BGA device in the window.A baffle or door 20 is hingedly mounted to the body 10 and has four openings 63 in which the bearing pads 21 are mounted. The bearing pads 21 are preferably made of a resilient, yielding material, e.g., rubber or the like, and are arranged to fit in register or closely match the windows 61 in the body 10. -21 When the door 20 is rotated to the closed position (see Figures 1a and 2a), the bearing pads 21 rest on the top surfaces of the BGA device encapsulation containers 16. It should be noted that, when the door 20 is closed, the support pads 21 simply rest on the device encapsulation containers 16, without exerting substantial pressure. In order to uniformly apply pressure to the device encapsulation containers 16 (and thus simultaneously bias the end balls extending from all four encapsulation containers into contact with the contact pads 41a and 42a, while applying pressure in only one direction), the door 20 is provided with a pair of ribs 70 that extend in the direction from the hinge to the free end of the door 20. Each rib 70 has a top surface 71 at a first height and a parallel surface 72 at a second height. The surface 72 (positioned toward the free end of the door 20) is parallel to, but spaced further apart from, the bottom surface of the closed door. -22as is the surface 71. A closure member 80 is mounted in the grooves 81 formed by the junction of the body 10 and the base plate 30 so as to span the distance between a first (open) position (see Figures 1b and 2b) and a second (closed) position (see Figures 1a and 2a). A bushing or stopper 82 is formed in the top cover of the closure member 80 and is positioned so as to contact and slide on the surface 71 at the same time that the leading edge 83 contacts and slides on the surface 72. Accordingly, with the chip-scale encapsulation containers 16 in each of the windows 11 and with the flip-up door 20 in the closed position, the bearing pads 21 rest on the surfaces top of the encapsulating containers 16. A closure member 80 is moved to the closed position, the leading edge 83 and the stop member 82 simultaneously contact the ramped surfaces 72a and 71a. As the closure member is moved to the closed position, the leading edge 83 and the stop member 82 move along the rising ramps 72a and 71a to the surfaces 72 and 71. This movement urges -23simultaneously the hinged door 20 (and thus the contact pads 21) in the direction of the base plate 30. The movement of the closure 80 towards the closed position therefore automatically provides uniform downward pressure on all end balls 15. It will be recognized that all components of the chip-scale carrier according to the invention can be fabricated from readily available materials using conventional techniques. Naturally, when the carrier is to be used as a base for infant mortality testing, the materials must be chosen to withstand the temperatures involved, as well as repeated use. It will also be recognized that the loading and unloading operations of the device encapsulation containers 16 can be readily automated using conventional techniques. The chip scale holder described so far as a preferred embodiment may be mounted on a circuit board or the like by connecting the lower ends of the output terminal pins 31 to the surface or into holes provided on a circuit board. Alternatively, the WG. BARIAMO' & ZANARDO ROMA Sp A -24Exposed ends of terminal pins 31 may be temporarily inserted into the BGA device test socket 100, which is mounted in a burn-in panel or the like (see Figure 9). In the arrangement illustrated in Figure 9, the BGA device infant mortality test socket 100 may be a socket such as that described in U.S. Pat. No. 5,611,705 or other convenient mounting apparatus. For purposes of disclosure, U.S. Pat. No. 5,611,705 is hereby incorporated by reference. It will be apparent from the foregoing that the principles of the invention can be used to mount and make temporary electrical contact with the terminal beads of almost any BGA device or encapsulation package without risk of damage to the device or its terminal beads. It should be understood, however, that while numerous features and advantages of the invention have been set forth in the foregoing description, along with details of the construction and operation of the invention, this description is to be considered illustrative only. -25changes and modifications may be made in details, especially in the shape, size, arrangement and combination of parts, without thereby departing from the spirit and scope of the invention, as defined in the appended claims. AN AGENCY for himself and for others Antonio Taliercio BARZANO' & ZANARDO ROMA S.p.A.

Claims

CLAIMS 1. An interconnection tape comprising: (a) at least first and second layers of substantially flexible insulating material; (b) a plurality of electrically conductive traces or tracks positioned between said first layer and said second layer, each of said conductive traces electrically connecting an interconnection pad to a contact pad exposed through a window in said first insulating layer; and (c) a plurality of electrically conductive traces positioned on the surface of said first layer, each of such conductive traces electrically connecting an interconnection pad to a contact pad.

2. The interconnection tape or strip of claim 1 further comprising a third layer of substantially insulating material adjacent to the surface of said second layer and a plurality of electrically conductive traces sandwiched between said second layer and said third layer, each such conductive trace electrically connecting an interconnection pad to an exposed contact pad through a window provided in said first layer and said second layer.

3. An interconnection tape according to claim 1, wrapped around a resilient support pad, such that a first section of the interconnection tape has a grid-like matrix configuration of contact pads facing in a first direction and a second section of said interconnection tape has a configuration of interconnection pads facing in the opposite direction.

4. A mounting apparatus for a ball grid array device, comprising: (a) an elongated flexible interconnection tape having contact pads arranged in a grid pattern corresponding to the terminal ball pattern of the ball grid array to be mounted, interconnection pads spaced from the contact pads, and electrically conductive traces electrically connecting said contact pads to said interconnection pads; (b) a resilient support pad supporting said flexible interconnection tape -28 with a section of said interconnection tape having said grid pattern of contact pads facing in a first direction and a section of said interconnection tape having said interconnection pads facing in the opposite direction; (c) a base plate;(d) a plurality of terminal pins supported in said base plate, each terminal pin having one end in electrical contact with an interconnection pad and the opposite end projecting from said base plate; (e) a support body secured to said base plate and arranged to secure said flexible interconnection strip and said support pad between said support body and said base plate, said support body having a window therein maintained in registration with said grid pattern of contact pads and exposing such grid pattern of contact pads therethrough; and (f) means for urging terminal balls of a grid pattern of balls into contact with the contact pads exposed therethrough; 5. The mounting apparatus of claim 4 wherein said biasing means comprises a door mounted adjacent to said support body for pivoted movement between a closed position and an open position and supporting a resilient pad in register with said window when in the closed position.

6. The mounting apparatus of claim 5, including means for uniformly urging said door towards said base plate.

7. The assembly apparatus of claim 6, wherein said uniformly biased means comprise a closure plate movable alternately between an open position and a closed position, wherein said closure plate is parallel to the door, said closure plate having a first surface contacting the door at a first height and a second surface contacting said door at a second height, such that said first surface and said second surface cooperate with said door to bias said door toward the base plate when the closure plate is moved toward the closed position.

8. The assembly apparatus of claim 7 wherein said first and second surfaces contact ramped surfaces on said door simultaneously.

9. The mounting apparatus of claim 4, wherein said support body includes means for positioning a bead grid array device in said window.

10. Apparatus for temporarily connecting terminal beads of a bead grid array device to external circuitry, comprising: (a) an interconnecting tape or strip comprising: (i) first and second flexible layers of electrically insulating material; and (ii) a plurality of electrically conductive traces encapsulated between said first layer and said second layer, each such trace electrically interconnecting an interconnecting pad and a contact pad exposed through a window provided in said first layer and arranged in a grid configuration ING. BARZANO' & ZANARDO ROMA S.pA.-31 coincides with a grid configuration of terminal beads extending from a bead grid array device; (b) a plurality of input / output terminal pins, each of said terminal pins being in contact with an interconnection pad and providing electrical communication between said interconnection pad and external circuitry; and (c) means for temporarily urging the terminal beads extending from a bead grid array device into physical contact with contact pads exposed through said windows.

11. Apparatus according to claim 10, wherein said interconnecting tape or strip further comprises a plurality of electrically conductive traces disposed on said first layer, each such trace electrically interconnecting an interconnecting pad and a contact pad arranged in a grid pattern coinciding with a grid pattern of terminal beads extending from said bead grid array device. ING. GARZANO' & ZANARDO ROMA S.p.A 12. The apparatus of claim 10 wherein said interconnecting ribbon is wrapped around a resilient support pad to present a grid-like array configuration of contact pads facing in a first direction and a configuration of interconnecting pads facing in the opposite direction.

13. Apparatus according to claim 12, wherein said plurality of input / output terminal pins are arranged and supported in a configuration of apertures in a base plate.

14. The apparatus of claim 13, including a support body secured to said base plate, with said support pad and said interconnect strip positioned between said base plate and said support body, said support body having at least one window thereon in register with a grid pattern of contact pads and arranged to expose such grid pattern of contact pads.

15. The apparatus of claim 14, further comprising a door mounted adjacent to the support body for pivotal rotation movement between a closed position wherein said first edge is the leading edge of said top plate. Rome, 2 7 MAR. 1998 pp WAYNE K. PFAFF ING. BARZANÒ & ZANARDO ROfrd SpJU TA / cc / ec 14702 AN AUTHORIZED REPRESENTATIVE for himself and others Antonio Taliercio WG. B ARIANO' & ZANARDO ROMA S.pA -33 and an open position and having: (i) a pivotal rotation end; (ii) a free end; and (iii) a resilient pad mounted thereon in register with said window in said support body when the door is in the closed position.

16. The apparatus of claim 15, further comprising closing means comprising a top plate mounted for reciprocation above said door between a closed position and an open position and having: (i) a first edge maintained at a first height relative to said door; (ii) a second edge maintained at a second height relative to said door; wherein said first edge and said second edge are in contact with first and second surfaces, respectively, on said door and urge said door toward said support body when said closing means is moved from the open position to the closed position.

17. Apparatus according to claim 16,