Stretchable conductor design and methods of making

• US 9,554,465 B1
• Filed: 01/09/2015
• Issued: 01/24/2017
• Est. Priority Date: 08/27/2013
• Status: Active Grant

• Current Assignee: Flextronics America LLC (Flextronics International Limited)
• Original Assignee: Flextronics America LLC (Flextronics International Limited)
• Inventors: Liu, Weifeng, Mohammed, Anwar, Pang, Dick, Kurwa, Murad
• Primary Examiner(s): Nguyen, Hoa C
• Assistant Examiner(s): Tso, Stanley
• Application Number:
  US14/593,849
• Time in Patent Office: 746 Days
• Field of Search: 371/760, 174/255, 290/5
• US Class Current: 1/1
• CPC Class Codes: H05K 1/0283 Stretchable printed circuits
• CPC Class Codes: H05K 1/03 Use of materials for the substrate
• CPC Class Codes: H05K 1/0393 Flexible materials H05K1/038 takes precedence; specific organic compositions are classified in H05K1/0313 and subgroups
• CPC Class Codes: H05K 1/092 Dispersed materials, e.g. conductive pastes or inks
• CPC Class Codes: H05K 1/147 at least one of the printed circuits being bent or folded, e.g. by using a flexible printed circuit H05K1/148 takes precedence
• CPC Class Codes: H05K 1/183 Components mounted in and supported by recessed areas of the printed circuit board
• CPC Class Codes: H05K 2201/0133 Elastomeric or compliant polymer
• CPC Class Codes: H05K 2201/0162 Silicon containing polymer, e.g. silicone
• CPC Class Codes: H05K 2201/09218 Conductive traces
• CPC Class Codes: H05K 2201/09227 Layout details of a plurality of traces, e.g. escape layout for Ball Grid Array [BGA] mounting
• CPC Class Codes: H05K 2201/09263 Meander
• CPC Class Codes: H05K 2201/09281 Layout details of a single conductor
• CPC Class Codes: H05K 3/285 Permanent coating compositions

Abstract

A stretchable interconnect includes a plurality of electrically conductive traces formed as a complex pattern on an elastic substrate. The form of the electrically conductive traces is such that when the elastic substrate is in a relaxed, or non-stretched, state each of the electrically conductive traces forms a tortuous path, such as a waveform, along the elastic substrate. The tortuous path of the electrically conductive traces provides slack such that as the elastic substrate is stretched the slack is taken up. Once released, the elastic substrate moves from the stretched position to the relaxed, non-stretched position, and slack is reintroduced into the electrically conductive traces in the form of the original tortuous path.

Claims

1. A stretchable interconnect comprising:

a. an elastic substrate having a relaxed, non-stretched state, wherein the elastic substrate has an exterior planar surface and is configured to be stretched along any direction within a plane of the exterior planar surface when a stretching force is applied along the plane, and to return to the non-stretched state when the stretching force is removed; and

b. a plurality of electrically conductive traces printed on the exterior planar surface of the elastic substrate, wherein the plurality of electrically conductive traces are electrically isolated from each other, each electrically conductive trace has a tortuous path relative to any direction along the exterior planar surface when the elastic substrate is in the non-stretched state, further wherein the tortuous path comprises a series of connected floral patterns, each floral pattern having multiple connected petal shapes, each petal shape having a first portion that extends away from a longitudinal axis of the exterior planar surface, a circular portion connected to the first portion, and a second portion connected to the circular portion that returns toward the longitudinal axis, thereby enabling bending of each of the electrically conductive traces in any direction along the exterior planar surface upon application and removal of the stretching force.

2. The stretchable interconnect of claim 1 further comprising an elastic mold layer coupled to the plurality of electrically conductive traces and the elastic substrate.

3. The stretchable interconnect of claim 2 wherein the elastic mold layer and the elastic substrate comprise a same material.

4. The stretchable interconnect of claim 2 wherein the elastic mold layer and the elastic substrate comprise a different material.

5. The stretchable interconnect of claim 2 wherein the elastic mold layer and the elastic substrate encapsulate the plurality of electrically conductive traces except for each end of each electrically conductive trace.

6. The stretchable interconnect of claim 1 further comprising an electrical component coupled to an end of each of the electrically conductive traces.

7. The stretchable interconnect of claim 6 further comprising an elastic mold layer coupled to the plurality of electrically conductive traces, the electrical component and the elastic substrate.

8. The stretchable interconnect of claim 1 wherein the elastic substrate comprises one or more of silicone, urethane and polydimethylsiloxane.

9. The stretchable interconnect of claim 1 wherein the elastic substrate comprises an elastomer film.

10. The stretchable interconnect of claim 1 wherein the plurality of electrically conductive traces comprise a conductive ink made from one or more of silver, copper, nickel and their alloys.

11. The stretchable interconnect of claim 1 wherein the plurality of electrically conductive traces comprise a metal powder made from one or more of silver, copper, nickel and their alloys.

12. The stretchable interconnect of claim 1 wherein the complex pattern comprises a series of floral patterns.

13. The stretchable interconnect of claim 1 wherein the complex pattern comprises the plurality of switchbacks along the first direction and a plurality of switchbacks along a second direction, wherein the second direction is perpendicular to the first direction.

14. The stretchable interconnect of claim 1 wherein each of the electrically conductive traces in the plurality of electrically conductive traces are tightly spaced relative to each such that a line pitch between adjacent electrically conductive traces is equal to or less than 150 um.

15. The stretchable interconnect of claim 1 wherein each of the electrically conductive traces in the plurality of electrically conductive traces are positioned serially adjacent to each other and maintain a substantially constant line pitch between adjacent electrically conductive traces within the complex pattern.

16. The stretchable interconnect of claim 1 wherein an entirety of each electrically conductive trace is positioned on the elastic substrate.

17. A stretchable interconnect comprising:

a. an elastic substrate having a relaxed, non-stretched state, wherein the elastic substrate has an exterior planar surface and is configured to be stretched along any direction within a plane of the exterior planar surface when a stretching force is applied along the plane, and to return to the non-stretched state when the stretching force is removed; and

b. a plurality of electrically conductive traces deposited as metal powder and sintered onto the exterior planar surface of the elastic substrate, wherein the plurality of electrically conductive traces are electrically isolated from each other, each electrically conductive trace has a tortuous path relative any direction along the exterior planar surface when the elastic substrate is in the non-stretched state, further wherein the tortuous path comprises a series of connected floral patterns, each floral pattern having multiple connected petal shapes, each petal shape having a first portion that extends away from a longitudinal axis of the exterior planar surface, a circular portion connected to the first portion, and a second portion connected to the circular portion that returns toward the longitudinal axis, thereby enabling bending of each of the electrically conductive traces in any direction along the exterior planar surface upon application and removal of the stretching force.