Low contact force, dual fraction particulate interconnect

Details Low contact force, dual fraction particulate interconnect Low contact force, dual fraction particulate interconnect

2002-05-02

2003-06-03

Clark, Sheila V. (Department: 2815)

Electricity: electrical systems and devices

Housing or mounting assemblies with diverse electrical...

For electronic systems and devices

C174S262000, C257S698000

Reexamination Certificate

active

06574114

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to interconnection of electronic components, such as integrated circuit devices and other similar devices or burn-in and test structures, all of which may have an array of closely spaced conductive contact sites. More particularly the present invention provides a geometrical array of dual-fraction particulate contacts, distributed through flexible elastomeric sheets, for reliable, low force electrical interconnection between electronic components.
BACKGROUND OF THE INVENTION
The introduction of solid-state semiconductor electronics provided the opportunity for progressive miniaturization of components and devices. One of the benefits of such miniaturization is the capability of packing more components into a given space. A drawback of miniaturization is the reduction in spacing between contacts on one device and the need for accurate alignment with corresponding contacts on a second device to provide reliable electrical interconnection between the two. Lack of planarity also affects interconnection of devices due to variation in the distance between the device contacts and an array of contacts intended to mate with the device contacts. Accurate engagement by some contacts leaves gaps between other contacts unless independent contacts have freedom to move across such gaps. Alternatively the connecting force between an array of contacts and device contacts increases to a level required for reliable interconnection, with potential for compression and damage to some of the contacts. Resilient anisotropically conductive interposers compensate for lack of device planarity to provide conductive pathways between electronic devices. Integrated circuit sockets used for performance testing, burn-in, and semi-permanent mounting to printed circuit boards employ various types of interposer during performance evaluation of finished, packaged, integrated circuit devices.
Interconnection of electronic components with finer and finer contact spacing or pitch has been addressed in numerous ways along with advancements in semiconductor device design. Introduction of ball grid array (BGA) devices placed emphasis on the need to provide connector elements with space between individual contacts at a minimum. One answer, found in U.S. Pat. No. 5,109,596 and U.S. Pat. No. 5,228,189, describes a device for electrically connecting contact points of a test specimen (circuit board) to the electrical contact points of a testing device using an adapter board having a plurality of contacts arranged on each side thereof. Cushion-like plugs made from an electrically conductive resilient material are provided on each of the contact points to equalize the height variations of the contact points of the test specimen. An adapter board is also provided made of a film-like material having inherent flexibility to equalize the height variations of the contact points of the test specimen. Furthermore, an adapter board is provided for cooperating with a grid made of an electrically insulated resilient material and having a plurality of plugs made from an electrically conductive resilient material extending therethrough. Successful use of this device requires accurate registration of contacts from the test specimen, through the three layers of planar connecting elements to the testing device.
U.S. Pat. No. 5,136,359 and U.S. Pat. No. 5,188,702 disclose both an article and a process for producing the article as an anisotropic conductive film comprising an insulating film having fine through-holes independently piercing the film in the thickness direction, each of the through-holes being filled with a metallic substance in such a manner that at least one end of each through-hole has a bump-like projection of the metallic substance having a bottom area larger than the opening of the through-hole. The metallic substance serving as a conducting path is prevented from falling off, and sufficient conductivity can be thus assured. While the bump-like projections of the anisotropic conductive films, previously described, represent generally rigid contacts, U.S. Pat. No. 4,571,542 and U.S. Pat. No. 5,672,978 describe the use of superposed elastic sheets over a printed wiring board, to be tested, and thereafter applying pressure to produce electroconductive portions in the elastic sheet corresponding to the contact pattern on the wiring board under test. In another example of a resilient anisotropic electroconductive sheet, U.S. Pat. No. 4,209,481 describes a non-electroconductive elastomer with patterned groupings of wires, electrically insulated from each other, providing conductive pathways through the thickness of the elastomer. Other known forms of interconnect structure may be reviewed by reference to United States Patents including U.S. Pat. No. 5,599,193, U.S. Pat. No. 5,600,099, U.S. Pat. No. 5,049,085, U.S. Pat. No. 5,876,215, U.S. Pat. No. 5,890,915 and related patents.
Commercial devices require some downward pressure to provide electrical connection between a device under test (DUT) and a printed circuit board or test socket attached to a load board. For this reason, conductive pathways are preferably short for optimum conductivity and ease of activation using a force sufficiently low to prevent damage to solder balls on a DUT. Reduction in activation force benefits testing at elevated temperatures where there is increased potential for damage to ball grid arrays.
In addition to the problem, mentioned previously, of interconnection failure caused by gaps between contacts, interconnection failure may occur by occlusion of a metal contact due to surface contamination with e.g. grease, non-conducting particles or a layer of metal oxide. Such an oxide layer results from air oxidation of the metal. Since oxide layers generally impede the passage of electrical current, reliable contact requires removal or penetration of the oxide layer as part of the interconnection process. Several means for oxide layer penetration, towards reliable electrical connection, may be referred to as particle interconnect methods as provided in U.S. Pat. No. 5,083,697, U.S. Pat. No. 5,430,614, U.S. Pat. No. 5,835,359 and related patents. A commercial interconnect product, described as a Metallized Particle Interconnect or MPI, is available from Thomas & Betts Corporation. The product is a high temperature, flexible, conductive polymeric interconnect which incorporates piercing and indenting particles to facilitate penetration of oxides on mating surfaces. Another commercial, electronic device interconnection product, available from Tecknit of Cranford, N.J., uses “Hard Hat” and “Fuzz Button” contacts in selected arrays. U.S. Pat. No. 4,574,331, U.S. Pat. No. 4,581,679 and U.S. Pat. No. 5,007,841 also refer to the “Fuzz Button” type of contact.
The previous discussion shows that interconnection of electronic devices has been an area subject to multiple concepts and much product development in response to the challenges associated with mechanical issues of interconnection and resultant electrical measurements. Regardless of advancements made, there is continuing need for improvement in three key areas, namely registration between interconnecting devices and electronic components, flexibility of contact sets for reliable device interconnection and minimization of the force required for reliable interconnection with low contact resistance. In view of the continuing needs, associated with interconnect structures, the present invention has been developed to alleviate drawbacks and provide the benefits described below in further detail.
SUMMARY OF THE INVENTION
The present invention provides an interposer for a compliant interconnect assembly that may be used for reliable electrical connection between electronic devices at lower contact forces than other types of particle interconnect structures. An interposer according to the present invention comprises an elastomeric sheet having holes formed in it to accommodate conductive particles that are usually held together using a resilient binder. Conductive particl

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