Electrostatic discharge protection device for semiconductor chip packages

Abstract: An electrostatic discharge (hereafter referred to as "ESD") protection device (46) is disclosed for use with semiconductor chip packaging (hereafter referred to as "SCP"). The electrostatic protection device comprises electrically conductive shorting devices (50) that may be removably connected to the SCP (12) during the manufacture to short selected pins (22,24) from the SCP. The ESD protection device (46) 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 form their respective receptacles. Navy Technical Disclosure Bulletin, vol.6, no.3, March 1981, p.33-36, discloses a device for protecting a SCP from damage due to electrostatic charges by shorting the connectors of the SCP with individual electrically conducting shorting arms. JP-A-59-13353 describes an annular conductor slidable across a package to maintain the 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 pair of interface surfaces disposed between the top and bottom surfaces, each interface surface having a plurality of connector pins disposed thereon in a substantially parallel and spaced apart relationship with respect to each other, each connector pin having a portion extending outward from the interface surface and downward at its distal end so as to extend beyond the bottom surface, the electrostatic discharge protection device including a base section secured to the semiconductor chip package and a plurality of shorting arms integral to the base section, each shorting arm being in electrical engagement with the connector pins for shorting between the plurality of connector pins via the shorting arms and the base section, each shorting arm further including means for yieldably biasing each shorting arm so as to urge the distal end portion thereof against its respective ones of the connector pins thereby creating an electrical connection therebetween, the protection device being characterised in that: a) said base section is secured to the bottom surface of the semiconductor chip package; and b) said shorting arms extend outward from the base section with the distal end portions in spaced apart relationship with respect to each other and transversely disposed with respect to the plurality of connector pins, each shorting arm comprising a first portion fixedly secured to the base section and extending outwardly from the bottom surface, a knee portion extending from the first portion to define a bend in the shorting arm, and an intermediate portion extending from the bend towards at least one of the connector pins so that the distal end portion extends over the respective ones of the connector pins. In one example, an adhesive is provided for securely mounting the base section to the semiconductor chip package. In another example, end portions extend from opposite ends of the base section and integral therewith, each end portion defining a clip which can be removably secured around the top and bottom surfaces of the semiconductor chip package so that the base section is securely mounted to the semiconductor chip package. The present invention thus 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, the means for yieldably biasing each shorting arm urges the distal end portions against the first portions of the respective connector pins thereby creating an electrical connection therebetween when the plurality of connector pins are not inserted into a complementary plurality of receptacles. When the connector pins are inserted into the complementary receptacles, each knee portion may move towards the bottom surface of the SCP against its yieldable bias so as to disengage its distal end portion from the first portion of a respective one of the connector pins to break the electrical connection therebetween. Finally, an adhesive disposed on the base section or a pair of clips disposed on the ends of the base section provide this ESD protection device with a secure attachment to the SCP. In the accompanying drawings: Figure 1A is an exploded perspective view of an example of an ESD protection device of this invention disposed below a SCP; Figure 1B is a perspective view of the ESD protection device shown in Figure 1A mated to the bottom surface of the SCP shown in Figure 1A; and, Figure 1C is a perspective view of the ESD protection device-SCP sub-assembly shown in Figure 1B mated to a printed circuit board. Referring now to Figures 1A-1C, there is shown generally at 10 a SCP-ESD protection device combination comprising an ESD protection device 46 of this invention, a SCP 12, and a complementary connector 38. The SCP 12 in one embodiment may comprise a top surface 14, a bottom surface 16, and, between the top and bottom surfaces, a pair of interface surfaces 18 and 20. A plurality of connector pins 22 and 24, respectively, are disposed on each interface surface 18 and 20, respectively, in a substantially parallel and spaced apart relationship with respect to each other. Each of the plurality of connector pins 22,24 further comprises a first portion 26 extending outwardly from the corresponding interface surface 18,20, a second portion 28 of substantially the same width as the first portion 26 extending in a downward direction, a bent portion 30 interconnecting the first portion 26 and the second portion 28, a third portion 32 narrower than the first portion 26 and extending downward to its distal end 34, and an interface portion 36 which interconnects the second portion 28 and the third portion 32. As will be readily understood, the SCP 12 may house either a VSLI, LSI, or MSI semiconductor die or dies. The plurality of the connector pins 22,24 are adapted for physical and electrical connection to the connector 38, typically a printed circuit board, having a substantially planar surface 42 on one selected side thereof. A plurality of elongated receptacles 44 extend inwardly from the planar surface 42 in a substantially parallel spaced apart insulated relationship and in a complementary relationship with respect to the connector pins 22,24 so as to accommodate the ready insertion of the third portion 32 of the connector pins 22,24 into the respective ones of the receptacles 44. In order to ensure that the connector pins 22,24 are shorted until they are secured in the complementary receptacles 44, the ESD protection device 46 is provided. This ESD protection device 46 comprises a base section 48 secured to the bottom surface 16 of the SCP 12 and a plurality of integral shorting arms 50. The plurality of shorting arms 50 extend outwardly from the base section 48 with their distal end portions 52 in spaced apart relationship with respect to each other and transversely disposed with respect to the connector pins 22,24, respectively. Each shorting arm 50 comprises a first portion 54 fixedly secured to the base section 48 and extending outwardly from the bottom surface 16, a knee portion 56 extending from the first portion 54 to define a bend in the shorting arm below the interface portion 36 of a respective one of the plurality of connector pins 22,24 and an intermediate portion 58 extending from the bend towards the respective one of the plurality of connector pins 22,24 so that the distal end portion 52 extends over the first portion 26 of the respective one of the plurality of connector pins 22,24. An adhesive (not shown) disposed on the base section 48 or a pair of clips 60,62 disposed on the ends of the base section provides the ESD protection device with a secure attachment to the SCP 12. The plurality of shorting arms 50 are yieldably biased by any means well known in the art such as a built in resilient spring bias so as to urge their respective distal end portions 52 against the first portions 26 of respective ones of the plurality of connector pins 22,24 thereby creating an electrical interconnection between the plurality of shorting arms 50 and the plurality of connector pins 22,24. Thus, as is readily apparent from Figures 1A-1C, when the plurality of connector pins 22,24 are not inserted into the corresponding plurality of receptacles 44, the shorting arms 50 urge their respective distal end portions 52 against and into respective electrical connection with the first portions 26 of the respective plurality of connector pins 22,24. In this manner, the shorting of all or some of the plurality of connector pins 22,24 is accomplished so as to effectively protect the semiconductor die (not shown) within the SCP 12 from ESD which could operate to damage the electrical circuitry in the semiconductor die. Insertion of the connector pins 22,24 into the complementary receptacles 44 in the connector 38 operates to move and deflect upwards the knee portion 56 of the shorting arms 50 against their yieldable bias, thereby moving the distal end portions 52 out of physical and electrical connection with the first portions 26 of the connector pins 22,24, respectively. As will be readily apparent, the number of connector pins 22,24 on either interface surface 18,20 to be shorted together by this ESD protection device 46 need not include all the connector pins 22,24 as shown in Figures 1A-1C but may also be limited to any subset of all the conductive pins. Moreover, only a subset of all the connector pins 22,24 on just one interface surface 18,20 may be shorted together by this ESD protection device 46 while all the other connector pins 22,24 remain unshorted.

Claims: An electrostatic discharge protection device (46) in combination with a semiconductor chip package (12) of the type having a top surface (14) and opposite bottom surface (16) and a pair of interface surfaces (18,20) disposed between the top and bottom surfaces, each interface surface having a plurality of connector pins (22,24) disposed thereon in a substantially parallel and spaced apart relationship with respect to each other, each connector pin having a portion extending outward from the interface surface and downward at its distal end so as to extend beyond the bottom surface, the electrostatic discharge protection device including a base section (48) secured to the semiconductor chip package and a plurality of shorting arms (50) integral to the base section, each shorting arm being in electrical engagement with a respective connector pin for shorting between the plurality of connector pins via the shorting arms and the base section, each shorting arm further including means for yieldably biasing each shorting arm so as to urge the distal end portion thereof against its respective ones of the connector pins thereby creating an electrical connection therebetween, the protection device being characterised in that: a) said base section (48) is secured to the bottom surface of the semiconductor chip package; and b) said shorting arms (50) extend outward from the base section with the distal end portions (52) in spaced apart relationship with respect to each other and transversely disposed with respect to the plurality of connector pins, each shorting arm comprising a first portion (54) fixedly secured to the base section and extending outwardly from the bottom surface, a knee portion (56) extending from the first portion to define a bend in the shorting arm, and an intermediate portion (58) extending from the bend towards at least one of the connector pins so that the distal end portion extends over the respective ones of the connector pins. A device according to claim 1, characterised by an adhesive for securely mounting the base section to the semiconductor chip package. A device according to claim 1, characterised by end portions extending from opposite ends of the base section and integral therewith, each end portion defining a clip (60,62) which can be removably secured around the top and bottom surfaces of the semiconductor chip package so that the base section is securely mounted to the semiconductor chip package. An electrostatic discharge protection device according to any of the preceding claims in combination with a connector (38) including a plurality of receptacles (44) for receiving said plurality of connector pins (22, 24) of said semiconductor chip package (12), wherein the shorting arms and the connector (38) are constructed so that the shorting arms (50) automatically move out of engagement with the plurality of connector pins (22,24) when the plurality of connector pins (22,24) are inserted into said receptacles (44).

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