Patent Application
20130319759
With the continued advancement of integrated circuit (IC) technologies, the size of the transistors used to form the ICs has decreased dramatically. This has allowed engineers and designers to increase the processing power of the ICs while keeping the same footprint, or to decrease the footprint of the ICs themselves. The decrease in IC size has continued to drive new development and open new application space. Unfortunately, however, it is frequently the IC packaging and wiring interconnects that have become the limiting factor in miniaturization.
Although the fabrication of multi-lead flexible cables has helped alleviate some of these wiring challenges, known techniques are becoming increasingly difficult and expensive to employ as the geometry of the leads are forced to decrease. Moreover, single wires typically have a large form-factor, are difficult to align and connect, and they require multiple steps including wire bonding and hand soldering to meet the pad pitch of the package. For example,
Although there has been some limited work performed in the area of fine-pitch connectors, these solutions are typically designed around bulk z-axis conductors such as interposers or rubber compression connectors. For example, U.S. Pat. No. 6,581,276 describes a fine-pitch connector that is formed by interleaving layers of conductors and insulators to form a stack. The stack is then sliced in a direction transverse to an elongated direction of the conductors to make a plurality of stack slices. The stack slices are then stacked on top of one another to form a plurality of greater stacks. The greater stacks are then interleaved side-by-side with dielectric and are further laminated to form the connector. Although this bulk connector structure may be useful for interposer type applications where the conduction occurs in the z-direction, these solutions do nothing to address the need for miniaturized wiring to carry signals over long distances.
Ribbon cables or bonded wires allow an easier attachment mechanism, but are too large for the application to ICs. In ribbon cables or bonded wires, each wire is separately insulated before being joined together. During fabrication, a number of spools of wire are each separately coated with an insulator. Momentarily after the insulator coating, the insulated wires are bonded together as the coating sets up. Unfortunately, this method is not scalable to the IC level as discrete wires become more difficult to handle as their size decreases resulting in uncontrolled wire-pitch.
Therefore there is a need for an improved flexible wiring assembly to address the limitations set forth above.
In accordance with one embodiment a method of making a flexible wire assembly is provided. The method comprises forming a laminate stack of alternating parallel layers of conducting material and insulating material, wherein the layers of conducting material and the layers of insulating material are substantially planar, and wherein the laminate stack is defined by a stack width (SW) dimension, a stack length (SL) dimension, and a stack height (SH) dimension, and wherein the stack width (SW) and the stack length (SL) dimensions are coplanar with the conducting and insulating layers and the stack height (SH) dimension is measured transversely across the conducting and insulating layers; and singulating the laminate stack into at least one long flexible wire assembly having alternating conductors and insulators by dicing the laminate stack at a singulation pitch along a longitudinal axis aligned with the stack length (SL) such that the resulting flexible wire assembly comprises a wire length (wl), a wire width (ww) and a wire height (wh), wherein the wire width (ww) corresponds to the stack height (SH), the wire height (wh) corresponds to the singulation pitch, and the wire length (wl) corresponds to the stack length (SL) and is one or more orders of magnitude greater than the wire width (ww) and the wire height (wh).
In accordance with another embodiment, a flexible wiring system is provided. The flexible wiring system comprises a flexible wire assembly comprising a plurality of elongated conductors and insulators each having a quadrilateral cross section and alternatingly laminated together, the flexible wire assembly having a wire width (ww) measured across the conductor and insulators, a wire height (wh) equivalent to the height of the conductors and insulators, and a wire length (wl) which is measured in a longitudinal direction orthogonal to the wire width and the wire height, wherein the wire length is one or more orders of magnitude greater than the wire width (ww) and the wire height (wh); and a first device comprising a plurality of bond pads spaced to define a bond pad pitch, wherein the flexible wire assembly is coupled to the first device at the bond pads such that spacing of the conductor conductors is matched to the bond pad pitch.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of various embodiments of the present invention. However, those skilled in the art will understand that embodiments of the present invention may be practiced without these specific details, that the present invention is not limited to the depicted embodiments, and that the present invention may be practiced in a variety of alternative embodiments. In other instances, well known methods, procedures, and components have not been described in detail.
Furthermore, various operations may be described as multiple discrete steps performed in a manner that is helpful for understanding embodiments of the present invention. However, the order of description should not be construed as to imply that these operations need be performed in the order they are presented, nor that they are even order dependent. Moreover, repeated usage of the phrase “in one embodiment” does not necessarily refer to the same embodiment, although it may. Lastly, the terms “comprising”, “including”, “having”, and the like, as well as their inflected forms as used in the present application, are intended to be synonymous unless otherwise indicated.
In accordance with one embodiment of the invention, a laminate stack of alternating parallel layers of conducting material and insulating material is formed. The laminate stack is then singulated by dicing the laminate stack along a longitudinal axis into at least one long flexible wire assembly having alternating conductors and insulators. The resulting flexible wire assembly and the related methods described herein provide a cost-effective, reproducible and scalable flexible wiring solution that solves the problems recognized in the prior art.
In accordance with one embodiment, the laminate stack 10 may be formed by alternatingly layering insulating material and conducting material to form a three-dimensional stack in the x, y and z directions. The insulating material and conducting material may be layered in a variety of manners including, but not limited to deposition, spray coating or through the placement of unitary sheets of material on top of one another. One or more of the insulating materials may comprise flexible electrically insulating materials including but not limited to polyimide, polyester, silicone, PTFE, polyacrylate, or flexible borosilicate glass. In one embodiment, the insulating materials may comprise a polyimide material such as KAPTON® or PYRALUX® both available from DuPont™. One or more of the layers of conducting materials may include conductive materials such as metals including but not limited to gold, platinum, silver, copper, tin, lead, zinc, aluminum and alloys thereof. Conducting materials may also include nonmetals such as graphene and carbon nanotubes or nanorods. In one embodiment an adhesive is provided at each interface between an insulating layer 14 and a conducting layer 16. The provision of the adhesive may comprise a separate deposition or layering step or the adhesive may be included as part of the insulating material or the conducting material. For example, the insulating material may comprise an acrylic based laminate sheet adhesive such as Pyralux® LF overlaid on the insulating material. Moreover, in alternative embodiments, the insulating layers 14 and conducting layers 16 may be laminated in the absence of an adhesive.
Each of the constituent insulating layers 14 and conducting layers 16 in the stack need not be placed in the stack separately, but may be first pre-combined into a unitary layer which is then provided as part of the stack to be laminated. In such a case, however, the insulating and conducting functionality of such a combined layer is nonetheless retained when placed in the stack. For example, the insulating material may comprise an all polyimide laminate constructed of polyimide film laminated to a layer of copper on a single side (e.g., Pyralux® AC) or an all polyimide laminate constructed of polyimide film laminated to a layer of copper on two sides (e.g., Pyralux® AP). Additionally, two or more layers of insulating material or two or more layers of conducting material may be combined to respectively form a single insulating layer 14 or a single conducting layer 16. Moreover, in accordance with embodiments of the invention, the conducting layers need not be patterned nor etched, thus saving time and process complexity as compared to conventional processes.
Once the constituent insulating layers 14 and conducting layers 16 are stacked, heat and pressure are applied to form the laminate stack 10. In one embodiment, the alternating layers are inserted into a press and a pressure of approximately 20,000 psi is applied over a temperature range of 50-230 degrees C. If necessary, the edges of the resulting laminate stack 10 may be trimmed or otherwise cleaned to form clean and regular edges.
In one embodiment, the laminate stack 10 resembles a rectangular prism or right rectangular prism and, for the ease of description, can be defined as having a stack width (SW) and a stack length (SL) as illustrated in
In accordance with one embodiment, once formed, the laminate stack 10 is singulated to form one or more flexible wire assemblies.
The laminate stack 10 may be singulated according to a singulation pitch 23, which may remain constant or may vary across the stack width (SW) of the laminate stack 10, depending upon the specific application. In one embodiment, the singulation pitch 23 is less than 200 μm. Once singulated, the resulting flexible wire assembly 20 can be said to have a wire width (ww) corresponding to the stack height (SH), where the thickness tn of each insulating and conducting layer (14, 16) corresponds to the respective widths wn of the elongated insulators 24 and elongated conductors 26. Although in the illustrated embodiment, the flexible wire assembly 20 comprises four elongated insulators 24 and three elongated conductors 26, any number of insulators and conductors can be constructed by varying the number of insulating layers 14 and conducting layers 16 of the laminate stack 10. As with the thicknesses t of the insulating and conducting layers, the widths wn of the elongated insulators 24 and elongated conductors 26 may differ from one another or they may be the same across the width of the flexible wire assembly 20. In one embodiment, the elongated insulators 24 and elongated conductors 26 have a quadrilateral or non-circular cross-section 28 as viewed with respect to a plane orthogonal to both the longitudinal axis 22 and the insulating layers 14 and conducting layers 16. The flexible wire assembly 20 can be said to further have a wire length (wl) corresponding to the stack length (SL), and a wire height (wh) corresponding to the singulation pitch 23. In one embodiment, the wire length (wl) is at least one order of magnitude greater than the wire width (ww) and wire height (wh). In a specific example, the wire length (wl) is multiple orders of magnitude greater than the wire width (ww) and the wire height (wh). In one specific example, the wire height (wh) of the flexible wire assembly 20 is less than 200 μm while the wire length (wl) is approximately 1 m. However, in accordance with the teachings of the invention the wire length can extend up to and beyond multiple meters in length depending upon the intended application. Due to the high ratio of wire length to wire height (or wire width), the flexible wire assembly 20 can achieve great flexibility. Moreover, the wire length (wl) can be extended up to many meters in order to obtain very long, fine-pitched, flexible wiring assemblies that can be utilized in a wide variety of applications where such long, fine-pitched, flexible wiring may be beneficial.
Flexible wiring system 40 includes a flexible wire assembly 20 coupled to two devices (25, 45). In the illustrated embodiment, the first device 25 is coupled to a first (e.g., top) side A of the flexible wire assembly 20, whereas the second device 45 is coupled to a second (e.g., bottom) side B of the flexible wire assembly 20. Similarly, the flexible wiring system 50 includes a flexible wire assembly 20 coupled to two devices (25, 45), however, each device is coupled to the same side (e.g., side A) of the flexible wire assembly 20. In each of flexible wiring system 40 and flexible wiring system 50, the flexible wire assembly 20 is shown in broken form to illustrate the long length of the flexible wire assembly. Lastly, with flexible wiring system 60, the flexible wire assembly 20 is coupled between the first device 25 and the second device 45. That is, the devices are coupled to the endpoints 62 of the flexible wire assembly 20. Although
In one embodiment, device 85 may represent an array of ultrasonic transducers that generate high frequency energy. The energy may be used to burn a target area or to generate and detect reflected sound waves for imaging. The reflected sound waves may be processed by one or more signal processors or microprocessors coupled to device 85. The processors may be co-located with the device 85 on the treatment end of the assembly or the processors may be part of device 95. Device 95 may further include one or more microprocessors, printed circuit boards, or other electronic or structural devices to further process the reflected sound waves to form an image.
In yet another embodiment, device 85 of the flexible instrument assembly 80 may include one or more mechanical tools to perform an action such as grasping, pinching or cutting, or for performing industrial inspection procedures. For example, electronic signals may be transmitted from device 95 at a proximal end along the flexible wire assembly 20 to a device 85 at a distal end where the device 85 would include the mechanical implements necessary to perform the intended application. Device 85 may further include one or more micro-motors coupled to the implements or additionally provided to induce motion. Alternatively, device 85 may include an imaging device such as a camera and an electro-optical converter to convert optical signals received by the camera to electrical signals. The electrical signals are then transmitted via the flexible wire assembly 20 to device 95 for further processing.
Thus, the various embodiments of the flexible wire assemblies, flexible wire systems and flexible instrument assemblies described herein provide long, fine-pitched wiring solutions that solve an existing need. Although prior efforts have attempted to make fine-pitch interconnects, no one has been able to make long length fine-pitch wiring having reduced labor and material costs and easy manufacturability as the embodiments described herein.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
