Electrostatic discharge protection device for semiconductor chip packages

Abstract: An electrostatic discharge (hereafter referred to as "ESD") protection device (130) is disclosed for use with semiconductor chip packaging (hereafter referred to as "SCP"). The electrostatic protection device comprises electrically conductive shorting devices (132,134,136,138) that may be removably connected to the SCP (104) during the manufacture to short selected pins from the SCP. The ESD protection device (130) remains in place to provide ESD protection during all phases of handling and shipping and may be either automatically unshorted or be manually removed during final assembly when the SCP is installed in its end product.

Description: This invention relates to an electrostatic discharge (hereafter referred to as "ESD") protection device for various semiconductor chip packages (hereinafter referred to as "SCP") of the type having a plurality of connector pins which are either (a) continuously shorted and then, upon insertion of the connector pins into complementary receptacles, automatically unshorted or (b) continuously shorted until the physical removal of the ESD protection device from the SCP. For a plurality of connector pins of a SCP which mates with a corresponding plurality of receptacles in a connector, typically, a printed circuit board, it is frequently necessary to short together the connector pins of the SCP until they are inserted into complementary receptacles in the connector in order to protect the semiconductor's circuity from ESD. Present ESD protection devices consist primarily of ESD packaging of the SCP in electrically conductive strips, pellets, boxes and plastic tubing which provides effective ESD protection until the user is about to insert the connector pins of the SCP into the complementary receptacles in the connector. At that point, however, the user must remove this ESD packaging from the SCP, thus rendering the SCP vulnerable to ESD, in order to position and insert the connector pins into the receptacles. Accordingly, as the user inserts the connector pins of the SCP into the receptacles, the semiconductor dies housed within these SCP's could be destroyed by ESD and would have to be replaced. Moreover, certain types of SCPs typically EPROMs, UVPROMS, and DRAMs, are plug-in devices which have connector pins which are repeatedly inserted into and then removed from the receptacles. These types of SCPs require ESD protection during the repeated insertions into and removals from the receptacles. Specifically, the connector pins of these SCPs require ESD protection from the moment that their connector pins are removed from the receptacles till their connector pins are again inserted therein. Consequently, a need still exists within the semiconductor chip packaging industry for a true ESD protection device, rather than ESD packaging, which effectively protects the semiconductor die from ESD until the connector pins of the SCP are inserted into the receptacles of the connector and then protects the semiconductor die from ESD again when the connector pins are removed from their respective receptacles. DE-OS-2348630 describes a method and device for protecting devices from damage due to electro-static charges by shorting the connectors with individual electrically conducting members. JP-A-59-13353 describes an annular conductor slidable across a package to maintain an electrical connection. In accordance with the present invention, an electrostatic discharge protection device in combination with a semiconductor chip package of the type having a top surface and opposite bottom surface and a plurality of interface surfaces disposed between the top and bottom surfaces, each interface surface having a plurality of connector pins extending outwardly therefrom in a substantially parallel and spaced apart relationship with respect to each other, the electrostatic discharge protection device being characterised by: a) a plurality of electrically conductive bars, each disposed in an overlying relation with respect to a respective plurality of connector pins extending from a respective interface surface; and b) a spring structure mounted to the top surface of the semiconductor chip package for urging the plurality of electrically conductive bars against the conductor pins, the spring structure comprising: i) a central pad securely mounted to the top surface of the semiconductor chip package; and ii) a plurality of spring members integral to the central pad and corresponding in number to the number of electrically conductive bars, each spring member having a cantilevered portion fixedly secured at one end to the central pad and extending outwardly therefrom beyond the edge of the top surface of the semiconductor chip package and two spaced apart depending leg portions integral to the cantilevered portion and extending downwardly on both sides of a respective plurality of connector pins and beyond the bottom surface, the cantilevered portion and the two depending leg portions of each spring member defining an interface therebetween adjacent which a respective one of the plurality of electrically conductive bars is fixedly disposed, each spring member further comprising means for yieldably biasing the spring member to move the cantilevered portion thereof towards the top surface of the semiconductor chip package so as to urge the electrically conductive bar associated therewith against its respective plurality of connector pins thereby creating an electrical interconnection therebetween. Preferably, the device includes an adhesive for securely mounting the central pad to the top surface. Generally, the electrically conductive bars are selected from the group comprising an elastic, electrically conductive foam, plastic, fiber, and foil. Preferably, the cantilevered portion further comprises a thin sheet fixedly secured at one end to the central pad, extending outwardly therefrom beyond the top surface of the semiconductor chip package, and having an aperture disposed therebetween. In one example, an adhesive for securely mounting the respective electrically conductive bar to the cantilevered portion adjacent to the interface between the cantilevered portion and the leg portion is provided. The present invention provides an ESD protection device on a SCP which operates in a simple, economical, and effective manner to automatically short a plurality of connector pins together while the SCP is disconnected from a connector. An embodiment of the present invention provides an ESD protection device on a SCP which operates to automatically open the shorts between the plurality of connector pins upon the SCP's connection to a connector which has not been specifically adapted to effect such opening. The present invention also provides an ESD protection device on a SCP which operates to automatically short a plurality of connector pins until the ESD protection device is physically removed from the SCP. The SCPs are of the type that have a top surface, a bottom surface, and, disposed between the top and bottom surfaces, a plurality of interface surfaces each having a plurality of substantially parallel and evenly spaced apart connector pins disposed thereon. Each connector pin comprises a first portion extending outward from the interface surface, a second portion of substantially the same width as the first portion extending in a downward direction, a bent portion interconnecting the first and second portions, a third portion extending downward to its distal end, and an interface portion interconnecting the second and third portions. In one embodiment, when the SCP is positioned against the surface of a connector, each cantilevered portion moves away from the top surface of the SCP against its yieldable bias so as to disengage its electrically conductive bar from its respective plurality of connector pins on the interface surface to break the electrical connection therebetween. In the accompanying drawings: Figure 1A is an exploded perspective view of an example of an ESD protection device of this invention disposed above a SCP; Figure 1B is a perspective view of the ESD protection device shown in Figure 1A mated to the top surface of the SCP shown in Figure 1A; Figure 1C is a perspective view of the ESD protection device-SCP sub-assembly shown in Figure 1B mated to a printed circuit board; Figure 1D is a side view as seen along line 1D-1D of Figure 1B of the ESD protection device mated to the top surface of the SCP; and, Figure 1E is a side view as seen along line 1E-1E of Figure 1C of the ESD protection device-SCP sub-assembly mated to the printed circuit board. Referring now to Figures 1A-1E, there is shown generally at 102 a PCB-ESD protection device combination of this invention comprising a SCP 104 and a complementary connector 124. The SCP in one embodiment may comprise a top surface 106, a bottom surface (not shown), and, between the top and bottom surfaces, a plurality of interface surfaces 108,110,112,114. A plurality of connector pins 116,118,120,122 are disposed on the interface surfaces 108,110,112,114, respectively, in a substantially parallel and spaced apart relationship with respect to each other. As will be readily understood, the SCP 104 may house either a VLSI, LSI, or MSI semiconductor die or dies. The plurality of connector pins 116,118,120,122 are adapted for physical and electrical connection to the connector 124, typically a printed circuit board, having a substantially planar surface 126 on one selected side thereof. A plurality of surface pads 128 exist on the planar surface 126 in a complementary relationship with respect to the connector pins 116,118,120,122 so as to accommodate the ready soldering of the connector pins 116,118,120,122 to the respective ones of the surface pads 128. In order to ensure that the connector pins 116,118, 120,122 are shorted until they are soldered to the complementary surface pads 128, the ESD protection device 130 is provided. This ESD protection device 130 comprises a plurality of electrically conductive bars 132,134,136,138 disposed in overlying relationship with respect to the plurality of connector pins 116,118,120,122 respectively and a spring structure 140 mounted to the top surface 106 of the SCP 104 for urging the plurality of conductive bars 132,134,136,138 against the respective connector pins 116,118,120,122. The spring structure 140 has a central pad 142 securely mounted with an adhesive (not shown) to the top surface 106 of the SCP 104 and a plurality of spring members 144,146,148,150 integral to the central pad 142 and corresponding in number to the number of electrically conductive bars 132,134,136,138. Each spring member 144,146,148,150 has an integral cantilevered portion 152 fixedly secured at one end to the central pad 142 and extending outwardly beyond the top surface and an integral pair of spaced apart depending leg portions 154,156 extending downwardly on both sides of a respective one of the plurality of connector pins 116,118,120,122 and beyond the bottom surface (not shown). Each corresponding electrically conductive bar 132,134,136,138 is securely mounted with an adhesive (not shown) to its corresponding cantilevered portion 152 adjacent to the interface between its cantilevered portion 152 and its pair of leg portions 154,156 so as to selectively engage its respective one of the plurality of connector pins 116,118,120,122. The plurality of spring members 144,146,148,150 are yieldably biased by means well known in the art such as a built in resilient spring bias so as to urge their respective cantilevered portion 152 towards the top surface 106 and their respective electrically conductive bars 132,134,136,138 against the connector pins 116,118,120,122 respectively thereby creating an electrical interconnection therebetween. Thus, as is readily apparent from Figures 1A-1E, when the plurality of connector pins 116,118,120,122 are not soldered to their complementary surface pads 128, the spring members 144,146,148,150 urge their respective electrically conductive bar 132,134,136,138 against and into electrical connection with their respective connector pins 116,118,120,122. In this manner, the shorting of all of the connector pins 116,118,120,122 is accomplished so as to effectively protect the semiconductor die (not shown) within the SCP 104 from ESD which could operate to damage the electrical circuitry in the semiconductor die. Positioning the connector pins 116,118,120,122 over the complementary surface pads 128 in the connector 124 in readiness for soldering operates to move and deflect upwards the leg portions 154,156 of all the spring members 144,146,148,150 against their yieldable bias, thereby moving all the electrically conductive bars 132,134,136,138 out of physical and electrical connection with the connector pins 116,118,120,122. As will be readily apparent, the connector pins 116,118,120,122 on all the interface surfaces 108,110,112,114 need not be soldered together by this ESD protection device 104 but may be limited to those connector pins found in any select subset of all the interface surfaces.

Claims: An electrostatic discharge protection device (130) in combination with a semiconductor chip package (104) of the type having a top surface (106) and opposite bottom surface and a plurality of interface surfaces (108,110,112,114) disposed between the top and bottom surfaces, each interface surface having a plurality of connector pins (116,118,120,122) extending outwardly therefrom in a substantially parallel and spaced apart relationship with respect to each other, the electrostatic discharge protection device being characterised by: a) a plurality of electrically conductive bars (132, 134,136,138), each disposed in an overlying relation with respect to a respective plurality of connector pins extending from a respective interface surface; and b) a spring structure (140) mounted to the top surface of the semiconductor chip package for urging the plurality of electrically conductive bars against the conductor pins, the spring structure comprising: i) a central pad (142) securely mounted to the top surface of the semiconductor chip package; and ii) a plurality of spring members (144,146,148,150) integral to the central pad and corresponding in number to the number of electrically conductive bars, each spring member having a cantilevered portion (152) fixedly secured at one end to the central pad and extending outwardly therefrom beyond the edge of the top surface of the semiconductor chip package and two spaced apart depending leg portions (154,156) integral to the cantiievered portion and extending downwardly on both sides of a respective plurality of connector pins (116) and beyond the bottom surface, the cantilevered portion (152) and the two depending leg portions (154, 156) of each spring member defining an interface therebetween adjacent which a respective one of the plurality of electrically conductive bars is fixedly disposed, each spring member further comprising means for yieldably biasing the spring member to move the cantilevered portion thereof towards the top surface of the semiconductor chip package so as to urge the electrically conductive bar associated therewith against its respective plurality of connector pins thereby creating an electrical interconnection therebetween. A device according to claim 1, characterised by an adhesive for securely mounting the central pad (142) to the top surface (106). A device according to claim 1, characterised in that the electrically conductive bars (132,134,136,138) are selected from the group comprising an elastic, electrically conductive foam, plastic, fiber and foil. A device according to claim 1, characterised in that the cantilevered portion (152) further comprises a thin sheet fixedly secured at one end to the central pad (142), extending outwardly therefrom beyond the top surface (106) of the semiconductor chip package (104), and having an aperture disposed therebetween. A device according to claim 1, characterised by an adhesive for securely mounting the respective electrically conductive bar (132) to the cantilevered portion (152) adjacent to the interface between the cantilevered portion and the leg portion (154). A device according to claim 1, in combination with a connector (124) for connecting the semiconductor chip package, wherein the spring members and the connector (124) are constructed such that when the semiconductor chip package is positioned against the surface (126) of the connector, each cantilevered portion moves away from the top surface of the semiconductor chip package against its yieldable bias so as to disengage its electrically conductive bar from its respective plurality of connector pins on the interface surface to break the electrical connection therebetween.

Inventors: CRONIN DAVID V, CRONIN, DAVID V.
Applicants: POLAROID CORP, POLAROID CORPORATION
Application year: 1992
Main classification: H01L23
IPC codes: H01L23, H05F3