Z-axis electrical interconnect

[0002] The present invention relates generally to electrical interconnects and, more particularly, to a Z-axis electrical interconnect.

[0003] Electronic devices are commonly made up of individual components electrically connected together to form a single electrical circuit. An example of an electrical component known in the art is a printed circuit board. Another example is a flexible printed circuit, also known as a flexible circuit. Still another example is an integrated circuit or IC chip. Frequently, it is desirable to connect individual electrical components together. Commonly known electrical interconnection techniques include soldering, socketing, wire bonding, wire button contacts and plug-in connectors.

[0004] As electronic devices physically decrease in size, packaging constraints may limit the use of traditional electrical interconnection techniques.

[0005] For example, stacked electrical components necessitate the use of a Z-axis electrical interconnect. In the past, a wire button contact was used. However, a disadvantage of a wire button contact as a Z-axis electrical interconnect is that it requires a strict vertical dimensional tolerance between the stacked electrical components. Another disadvantage is that the wire button electrical interconnect may not fit in a low profile space. Thus, there is a need in the art for a Z-axis electrical interconnect that is packagable within a low profile space and provides a more positive electrical contact in interconnecting electrical devices.

[0006] Accordingly, the present invention is a Z axis electrical interconnect. The Z-axis electrical interconnect includes a flexible printed circuit folded into a U-shape. The Z-axis electrical interconnect also includes a plurality of raised interconnection members arranged on the flexible printed circuit in a predetermined pattern and a circuit trace interconnecting the raised interconnection members. The Z-axis electrical interconnect further includes a spring fixedly positioned on the flexible printed circuit to maintain the U-shape.

[0007] One advantage of the present invention is that a Z-axis electrical interconnect is provided having a low profile to fit within a limited space. Another advantage of the present invention is that the Z-axis electrical interconnect allows a lower insertion force during installation. Still another advantage of the present invention is that the Z-axis electrical interconnect provides a positive contact in interconnecting stacked electrical components having a large vertical tolerance. A further advantage of the present invention is that the Z-axis electrical interconnect has connections which may also be tailored to have different locations between the two boards, i.e., a smaller pitch on one board and a larger pitch on the other board, because the signal carrying element is built on a flexible printed circuit (FPC).

[0008] Other features and advantages of the present invention will be readily appreciated as the same becomes better understood after reading the subsequent description when considered in connection with the accompanying drawings.

[0009] FIG. 1 is a perspective view of a Z-axis electrical interconnect illustrating features of the present invention.

[0010] FIG. 2 is a side view of the Z-axis electrical interconnect of FIG. 1.

[0011] FIG. 3 is a perspective view of an installed Z-axis electrical interconnect.

[0012] FIG. 4 is a perspective view of another embodiment of an installed Z-axis electrical interconnect.

[0013] Referring to FIGS. 1, 2 and 3, one embodiment of a Z-axis electrical interconnect 10 is illustrated. The Z-axis electrical interconnect 10 includes a flexible printed circuit such as a flexible circuit 12. It should be appreciated that, in this example, the flexible circuit 12 is a mandrel built flexible circuit. For example, to construct a mandrel built flexible circuit 12 a circuit (not shown) is imaged on the mandrel (not shown) in photoresist. The circuit is plated with a conductive material, such as copper. The resist is stripped off of the mandrel. A coverlet film is laminated over the circuit on the mandrel. An example of such a film is a material known as Kapton. While still on the mandrel, a layer of a conductive material such as nickel and a layer of gold is plated onto the pad using the coverlet as a plating resist. The flex is then removed from the mandrel, exposing the circuit traces on the other side of the circuit. A layer of electroless gold or tin-lead may be plated onto the nickel surface to establish a solderable surface. A further example of how this type of flexible circuit 12 is constructed is disclosed in a commonly assigned U.S. Pat. No. 5,207,887 to Crumly, et al., which issued on May 4, 1993, entitled “Semi-Additive Circuitry With Raised Features Using Formed Mandrels”, the disclosure of which is hereby incorporated by reference.

[0014] The Z-axis electrical interconnect 10 includes a raised interconnection member 14 protruding from the flexible circuit 12. The raised interconnection member 14 is a bump made from an electrically conductive material such as copper. Preferably, the Z-axis electrical interconnect 10 includes a plurality of raised interconnection members 14 arranged in a predetermined pattern. In this example, the predetermined pattern is a row of raised interconnection members 14 positioned along a proximate end 16 and a distal end 18 of the flexible circuit 12. It should be appreciated that the raised interconnection member 14 provides a removable electrical contact between stacked first and second electrical devices 20, 22 as illustrated in FIG. 3. It should also be appreciated that the stacked electrical devices 20, 22 may be printed circuit boards.

[0015] The Z-axis electrical interconnect 10 also includes a circuit trace 24 positioned on a surface of the flexible circuit 12. The circuit trace 24 electrically connects the raised interconnection member 14 at the proximate end 16 of the flexible circuit 12 with the corresponding raised interconnection member 14 at the distal end 18 of the flexible circuit 12. It should also be appreciated that, because the Z-axis electrical interconnect 10 has a flexible circuit 12, the interconnect 10 can be tailored to have custom mating locations and raised interconnection members 14 on multiple rows.

[0016] The Z-axis electrical interconnect 10 is folded into a U-shape, with the raised interconnection member 14 facing outwardly. To maintain the shape, the Z-axis electrical interconnect 10 includes a spring 26 fixedly positioned between the proximate and distal ends 16, 18 of the folded flexible circuit 12. The spring 26 is bonded to the flexible circuit 12, such as with an adhesive. Preferably, the spring 12 is elastomeric so as to maintain the shape of the Z-axis electrical interconnect 10 while providing conformity and pressure to the raised interconnection members 14 when in contact with the first and second electrical devices 20, 22. Advantageously, the Z-axis electrical interconnect 10 requires a minimal insertion force to install and maintain contact between the stacked first and second electrical devices 20, 22.

[0017] In operation, the Z-axis electrical interconnect 10 is fixedly retained between the stacked first and second electrical devices 20, 22. The Z-axis electrical interconnect 10 may be retained on the electrical devices 20, 22 by known techniques such as soldering, bonding or fixturing. An example of fixturing is shown in FIG. 4. The Z-axis electrical interconnect 10 includes a tab 28 extending from the flexible circuit 12, such as from a side. Preferably, two tabs 28 are used, although there could be as many as four tabs 28. The Z-axis electrical interconnect 10 is positioned such that the raised interconnection member 14 is aligned with a mating contact (not shown) on the first electrical device 20. The tab 28 is aligned with a corresponding slit 30 in the first electrical device 20, inserted into the slit 30, and fixedly retained, such as by folding the tab 28 over. The tab 28 may also be bonded by an adhesive 31 to the first electrical device 20 to secure the Z-axis electrical interconnect 10 to the first electrical device 20.

[0018] Still another example of fixturing is illustrated in FIG. 2. In this example, solder 32 is used to secure the raised interconnection members 14 onto the first electrical device 20. It should be appreciated that conventional pick and place machines can automate this activity in large volumes.

[0019] The Z-axis electrical interconnect 10 is connected to the second electrical device 22 in a similar manner.

[0020] The present invention has been described in an illustrative manner. It is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation.

[0021] Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the present invention may be practiced other than as specifically described.