Patent Document

BACKGROUND 
     The present invention relates to techniques for reliably creating a large number of high-speed electrical connections between two circuit assemblies. More specifically, the present invention provides a variety of techniques for establishing such connections with a high cycle life while requiring a very low externally created force to facilitate the connect-disconnect cycle. 
     As electronics becomes more dense, higher speed and complex, the force necessary to establish reliable connections between circuits, especially in semiconductor test systems, is becoming more and more difficult. Moreover, interconnect methods that rely on high contact forces and metal to metal abrasion lower the cycle life due to damage caused to the metal plating on the electrical contacts of the circuit assemblies. This is of particular concern with zero insertion force (ZIF) connectors and test heads used in semiconductor testers, such as the Agilent Technologies, Inc. V5400 and V5500 testers. A typical test head may have thirty-six zero insertion force connectors between the PEFPIF boards on the PE modules and the edge cards on a probe card. 
     Some conventional zero insertion force connector systems are plagued by electrical connectivity issues due to non-uniform force applied to each of the individual contact elements. Several conventional connector systems use flexible substrates to compensate for mechanical dimensional tolerances of the mating circuit assembly. However, the suppleness of the flexible substrate is directly related to the reciprocal of the electrical performance of the contact between the two circuit assemblies. As the electrical performance of the substrate improves, the mechanical flexibility decreases. This limits the dimensional pitch between the individual electrical contact elements. 
     Accordingly, there is a need for a zero insertion force printed circuit board connector system with reliable electrical connectivity and uniform force applied to individual contact elements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An understanding of the present teachings can be gained from the following detailed description, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  illustrates a perspective view of a connector between a test head and a device under test (DUT) board. 
         FIG. 2  illustrates a close-up perspective view of a DUT board of  FIG. 1 . 
         FIG. 3  illustrates a closer view of a DUT board assembly of  FIG. 1  showing detailed features of a plurality of mating board assemblies disposed thereon. 
         FIG. 4  illustrates a close-up view of the connector assembly of  FIG. 1  showing detailed features of a plurality of clamping assemblies of which the connector assembly is comprised. 
         FIG. 5  illustrates a closer view of a clamping assembly of  FIG. 4  and a partial view of a mating board in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a high-speed connection assembly  100  for establishing a large number of high-speed connections between at least one device under test and automatic test equipment (not shown), such as an ZIF connector for use between a DUT board and a V5400 or a V5500 test head. A DUT assembly  102  is provided on the underside of which are large number of electrical contacts (not shown) to one ore more DUTs. Such electrical contacts might be, for example, probe needles if DUT assembly  102  is a probe card for use in wafer sort, or sockets if DUT board  102  is a contactor board for use in package test. The primary function of DUT assembly  102  is to translate electrical signals out of the plane of board  104  so that they are accessible to the connection mechanism, i.e., interface connection assembly  106 . 
     An exemplary high-speed connector is taught in U.S. Pat. No. 6,833,696 entitled “Methods and Apparatus for Creating a High Speed Connection Between A Device Under Test And Automatic Test Equipment”, by Roger Sinsheimer et al. An exemplary automatic test equipment is the V5400 or V5500 by Agilent Technologies, Inc. of Palo Alto, Calif. High-speed connection assembly  100  may include a DUT assembly  102  for translating electrical signals from a board  104  via a plurality of connector circuits  105  to a connection mechanism  106  with a plurality of clamping connectors  108  radially disposed around the connection mechanism to align with connector circuits  105  on the DUT assembly  102 . 
     Referring to  FIG. 2 , an exemplary DUT assembly  102  may have a plurality of mating printed circuit boards  202  disposed radially on the DUT board  104  which facilitate signal translation.  FIG. 3  shows a close-up view of a portion of an exemplary interface connection assembly  106  with clamping connectors  108  that comprise opposing clamp plates  608  with contacts  602  on inner walls  606  of clamp plates  608 . In the prior art, the clamping and release actions for clamp plates  608  are actuated by pneumatic shafts, cylinders or bladders  612  at either end of the clamp plates  608 . There are springs  610  that work against the clamping cylinders  604  to keep the clamping plates  608  apart. 
       FIG. 4  illustrates a blown-up view of one of the connector circuits  105 , which may comprise a mating printed circuit board  302  with contacts  310  on one or both sides and contacts  308  at the bottom of the assembly to mate with corresponding contacts (not shown) on the surface of board  104  when the connector circuit  105  is secured in place on board  104 . 
     Referring now to  FIG. 5 , a zero insertion force connector system according to the invention is shown. Specifically, an overall connector clamp housing  501  of the zero insertion force connector system is comprised of a material that will support the contact force necessary to compress all the individual contact elements. For example, connector clamp housing  501  may be made of non-magnetic stainless steel  300  series; aluminum; case hardened  440  stainless steel; case hardened BeCu; or a similar material or composite. 
     One or more electrical contact substrates  503  are mounted within the connector clamp housing  501 . The electrical contact substrate  503  may comprise Rogers 4350; Nelco 4000-13 SI; standard FR-4; high temperature FR-4; Rogers 3000; or other similar materials or composites. Passive or active components may be mounted on the electrical contact substrate  503 . Directly behind the electrical contact substrates  503  and located between the connector clamp housing  501  and the electrical contact substrates  503  are several mechanical spring elements  506 , which apply the force necessary to compress the electrical contact substrates  503 . The mechanical spring elements  506  may comprise musical wire; BeCu; non-magnetic  300  stainless steel; coil (belville or wave); silicone rubber (solid or foam) or any similar mechanical spring type elements. 
     Around the perimeter of each electrical contact substrate  503  is a vacuum seal  502  that is actuated to unclamp the electrical contact substrates  503 . The vacuum seals may be hollow O-rings; standard O-rings; lip seals; bellows; vacuum cylinder or other similar vacuum sealing mechanism. The electrical contact substrate  503  is electrically connected to the mating printed circuit board  302  by using a board-to-board interconnect  504 . Through out this document, the phrase board-to-board interconnect is used interchangeably with the phrase interposer. The board-to-board interconnect or interposer  504  may be made of a Neoconix stamped metal spring laminated to PCB; KnS leaf spring made with a wire bond machine; Intercom C-stack; HCD super spring; HCD super button or other similar material. The interposer  504  may have individual electrical contact elements ( 602  in  FIG. 3 ) for making electrical contact with the individual electrical contact elements  310  on the mating printed circuit board  302 . Alternatively, the interposer  504  may be a Z-axis conductive member, such as a sheet of rubber or other insulating material with wires or other conductive features embedded therein perpendicular to the plane of the insulating material. This design would be instead of electrical contact elements  602 . 
     Mating printed circuit board  302  is aligned to the connector system  500  by guide pins or other features (not shown) located in the connector housing  501  or larger system that the connector housing is mounted on, such as a test head (not shown). The mating circuit board  302  may be made of Rogers 4350; high temperature FR-4; standard FR-4; Nelco 4000-13 SI; flex circuit wrapped over molded, machined plastic; or other similar material. The electrical signal may flow from the mating printed circuit board  302 , through the board-to-board interconnect  504 , into the electrical contact substrate  503  and then through a signal transfer members  507 , such as coaxial cable, to and from a target system or device, such as a memory tester (not shown). The signal transfer members  507  may be ribbonized RG178; tempflex low Dk coaxial cable; goretex tape wrapped coaxial cable; tensolite standard braid coaxial cable; tempflex serve shielded coaxial cable or other similar signal transfer means. 
     The electrical signals may also flow in the opposite direction as well. This connector system may be mated and unmated several thousand times without significant degradation to the contact resistance. Ribbonized coaxial cables  507  may or may not be mass terminated to the electrical contact substrate  503  by using hot bar process to minimize manufacturing costs. The connector system may be two sided, but may also be one sided either for the vacuum actuation or the contact substrate. In a one-sided case, another member or element may move the stationary jaw to allow insertion of the mating printed circuit board  302 . 
     One application for this connector system  500  is for use as a DUT interface or probe card interface in a high pin count memory test system, such as the Agilent Technologies, Inc. V5400 or V5500 memory test system. However, this connector system  500  may be used in other systems requiring connecting and disconnecting large numbers of signal paths between printed circuit boards. 
     Improved RF performance may be achieved with the connector system  500  of the present invention by using a rigid printed circuit board for the contact substrate  503 . Improved mechanical compressive force may be achieved behind each electrical contact substrate  503  by using an interposer or board-to-board interconnect  504 . Improved mechanical repeatability and reliability is achieved by actuating the connector system  500  using a vacuum mechanism  502 . 
     In prior connectors, if the electrical performance of the ZIF connector was improved, the electrical performance would be decreased and vice versa. Prior solutions used a combined interposer and printed circuit board into a flex circuit with gold bumps (see U.S. Pat. No. 6,833,696), in which improving mechanical contact of the gold bumps required the flex circuit to be thinner, which decreased the electrical performance. Conversely, to increase the electrical performance, the flex circuit would need to be thicker, which would compromise the mechanical flexibility of the substrate, and thus decrease the mechanical performance. 
     The present zero insertion force connector system  500  decouples the relationship between the electrical performance of the contact substrate  503  and the mechanical force applied to each electrical contact element  602 . The present invention uses a rigid printed circuit board  503  and a separate interposer or board-to-board interconnect  504 , each piece can be optimized individually and the electrical performance is improved and the mechanical loading is more uniform for each electrical contact element  602 . Clamping action is supplied by one or several spring members  506 , sized to provide uniform and sufficient clamping force. A vacuum  502  is used to unclamp the connector  500  and retract the contact substrate  503  and the interposer  504 . 
     Some implementations may include active or passive circuitry on the mating printed circuit board  302 . Some implementations of the connector system  500  may or may not require motion of the contact substrates  503  with active circuitry to achieve clamping action. Active circuits may be mounted inside the ZIF connector housing on the printed circuit board. Prior flex circuit solutions do not permit soldering of semiconductor devices or other components to the flex circuit, because the flex circuit would no longer be flexible. In some implementations, a contact substrate  503  may be stationary with the mating circuit assembly moving to actuate the mating and demating processes. 
     As shown in  FIGS. 1 and 3 , many zero insertion force connector systems  500  may be mounted on a test head  106  in order to enable connections between a tester (not shown) and a DUT card or probe card  102 . In such a case, there may be many vacuum seals  502  simultaneously actuated to ensure that all the connectors  500  on the test head are actuated and deactuated simultaneously. Such a connector system enables a machine, such as a memory testor to be programmed for different tasks by switching out a card or board with complex electronics on it that enables different features of the machine. One such use enables a memory testor to be used in wafer sort to test wafers by making connections between the test head and mating printed circuit boards on a probe card and then to test chips by making connections between the test head and mating printed circuit boards on a DUT card. The present invention overcomes of prior mating connectors that either deteriorated the electrical contact elements on the mating printed circuit board or the contacts of the connector, made unreliable connections or the quality of the connections deteriorated after many connections. 
     As will be appreciated by those in the art, the circular layout of the test head and probe card or DUT card may be another physical layout other than circular, such as rectilinear, linear, etc.

Technology Category: 3