BRIEF DESCRIPTION OF THE DRAWINGS
The invention can be better understood with reference to the following figures. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the figures, like reference numerals designate corresponding parts throughout the different views.
FIG. 1A shows a cross-sectional side view illustrating an example of an implementation of a known flex-LED.
FIG. 1B shows a cross-sectional end view of the known flex-LED device shown in FIG. 1A.
FIG. 1C shows a cross-sectional side view illustrating another example of an implementation of a known flex-LED with two bonding wires per LED.
FIG. 2 shows a cross-sectional side view illustrating an example of a known implementation of a printed circuit board.
FIG. 3 shows a cross-sectional side view illustrating an example of a known flexible circuit.
FIG. 4A shows a cross-sectional side view illustrating an example of an implementation of a flex-LED in accordance with the invention.
FIG. 4B shows a cross-sectional end view of the flex-LED shown in FIG. 4A.
FIG. 4C shows a cross-sectional end view of the flex-LED with a filled via.
FIG. 5A shows a perspective view of a section of an example of an implementation of a flexible circuit having multiple vias.
FIG. 5B shows a perspective view of a section of another example of an implementation of a flexible circuit having multiple vias.
FIG. 6 shows a cross-sectional side view illustrating an example of an implementation of a flexible circuit having multiple vias for thermal and electrical connections.
FIG. 7A shows a perspective view illustrating an example of an implementation of a flexible circuit having multiple vias.
FIG. 7B shows a top view of an example of a via layout for the flexible circuit shown in FIG. 7A.
FIG. 8 shows a perspective view illustrating another example of an implementation of a flexible circuit without vias.
DETAILED DESCRIPTION
In the following description of examples of implementations, reference is made to the accompanying drawings that form a part hereof, and which show, by way of illustration, specific implementations of the invention that may be utilized. Other implementations may be utilized and structural changes may be made without departing from the scope of the present invention.
In general, a system and a method of improving the thermal dissipation properties of flexible circuits by adding and repositioning vias utilized for thermal dissipation and the reliability of these devices by adding multiple electrical vias and by re-aligning the wire bonding in these devices is disclosed. Turning to FIG. 4A, a cross-sectional side view illustrating an example of an implementation of a flex-LED 400 in accordance with the invention is shown. The flex-LED 400 may include a substrate 402 that may include a flexible dielectric and electrical conductors. Attached to the substrate 402 is a plurality of LEDs 404. A bonding wire 406 may provide one of the two electrical connections required for each of the LEDs 404, for example, an anode connection. A cathode connection may then be located on the bottom surface of the LED 404, in the form of backside metallization (not shown), which may be implemented by attaching a conducting material to the bottom of each LED 404 and mounting LED 404 on the electrode and thermal pad 414.
In FIG. 4A, the wire bonding wire 406 for each LED 404 is aligned perpendicularly to the direction of primary flexing, i.e., perpendicular to the length-wise axis of the flex-LED 400. In another embodiment, a two-wire bond LED chip may be implemented where both anode and cathode electrode contacts are on the same side of the LED chip, i.e., the top surface. Where there are two bond wires per LED chip, both bond wires are positioned to be substantially perpendicular to the longitudinal axis of the flex strip.
The entire assembly may be encapsulated in an encapsulant 408. In another embodiment, the encapsulant and the assembly may be enclosed in a transparent casing (not shown). FIG. 4B shows a cross-sectional end view of the flex-LED 400 across its width. In FIG. 4B, the flex-LED 400 includes an LED 404 attached to a substrate 402. This package may be encapsulated in an encapsulant 408. The bonding wire 406 completes an electrical connection to a second electrode 416 in the substrate 402. The other electrical connection is to a first electrode 414, which may be a fully-filled via, e.g., a blind via, or a filled via, i.e., a via created by a hole drilled through the substrate 402, then plated with a conductive metal such as copper, silver, etc., and filled with a resin/plug material.
In FIG. 4A, the arrows 412 indicate the primary direction of the flexing of the flex-LED 400. In FIG. 4B, the bonding wire 406 is affixed to the LED 406 and connected to the second electrode 416 in an orientation that is perpendicular to the plane of the direction of primary flexing, that is, the plane defined by the arrows 412. Thus, any flexing in this plane will not effect or cause any stress on the bonding wire 406.
In FIG. 4C, a cross-sectional end view illustrating another example of an implementation of the flex-LED device shown in FIG. 4A is shown. As in FIG. 4B, the bonding wire 406 is affixed to the LED 404 and connected to the second electrode 416 in an orientation that is perpendicular to the plane of the direction of primary flexing, that is, the plane defined by the arrows 412. The connection to the first electrode 414 is made through via 418, which is positioned under the LED 404. Thus, any flexing in this plane will not effect or cause any stress on the bonding wire 406 or the via 418.
In FIG. 5A, a perspective view of a section illustrating an example of a flexible circuit 500 having multiple vias in accordance with the invention is shown. Flexible circuit 500 may include a substrate 502 on which a component 504, such as an LED, may be attached. A bonding wire 506 may provide an electrical connection for the component 504 to an anode pad 510, with a connection to a cathode pad 508 made on the bottom surface of the component 504 utilizing a backside metallization (not shown).
Flexible circuit 500 may also include 4 vias 514 that may be positioned near the LED attached to the flexible circuit. As an example, the flexible circuit may include multiple, redundant vias 514 utilized for thermal dissipation positioned near the component 504 at approximately equal distances therefrom. With this configuration of multiple thermal vias utilized for thermal dissipation, at least two of these vias will not be subjected to stress caused by repeated flexing or sharp bending of the flexible circuit of which it is a part.
In FIG. 5B, a perspective view of a section illustrating another example of a flexible circuit 500 having multiple vias in accordance with the invention is shown. A component 504, such as an LED, may be attached to a substrate 502, with a bonding wire 506 providing an electrical connection for the component 504 to an anode pad 510, and a bonding wire 512 providing an electrical a connection to a cathode pad 508. As in FIG. 5A, the flexible circuit 500 may include multiple, redundant vias 514 utilized for thermal dissipation positioned near the component 504 at approximately equal distances therefrom, thus allowing to avoid the stress caused by repeated flexing or sharp bending of the flexible circuit of which it is a part.
Turning to FIG. 6, a cross-sectional side view illustrating an example of an implementation of a flexible circuit having multiple vias for thermal and electrical connections is shown. Flexible printed circuit (“FPC”) 600 may include a dielectric 604 that is positioned between a top metal layer 606 and a bottom metal layer 602. Attached to the top metal layer 606 may be a component 608, which may be, as an example, an LED. A bonding wire 610 may provide one of the two electrical connections required for the component 608, for example, an anode connection. A cathode connection may then be located on the bottom surface of the component 608 in the form of backside metallization (not shown), which may be implemented by attaching a conducting material to the bottom of component 608. The entire assembly may then be covered by an encapsulant 612.
FPC 600 may also include vias 614 and 616 for thermal dissipation that pass through the dielectric 604 and dissipate heat from the component 608 through the top layer 606 to the bottom layer 602, which may be an aluminum or copper plate. For the other electrical connection, i.e., the cathode connection in this example, the FPC 600 may include a blind via 618 under the component 608 that provides an electrical connection to the bottom layer 602.
In FIG. 7A, a perspective view illustrating an example of another implementation of a flex-circuit having multiple vias is shown. Flex-circuit 700 may include a substrate 702 on which a component 704, such as an LED, may be attached. A bonding wire 706 may provide an electrical connection for the component 704 to an anode pad 710, with a connection to a cathode pad 708 made on the bottom surface of the component 704 utilizing a backside metallization (not shown). In one embodiment, the substrate 702 and the LED 704 may be encapsulated with encapsulant 712. In another embodiment, the substrate 702 may be enclosed within a transparent casing (not shown), which may then be filled with an encapsulant.
Flex-circuit 700 may include multiple vias drilled through the substrate 702, such as vias 714, which may be in electrical connection with the anode pad 710, and vias 716, which may be in electrical connection with the cathode pad 708. These vias may be also configured to provide a path for thermal dissipation from the component 708 by being filled with a thermally conductive material.
Flex-circuit 700 may further include a blind via (not shown) located under the component 704 that provides an electrical connection from the component 704 to a ground plane (not shown) below the substrate 702. FIG. 7B shows a top view illustrating an example of a via layout for the flex-circuit 700 shown in FIG. 7A. Vias 714 and 716 may be configured for thermal connections, while blind via 718 may be configured for an electrical connection for the component (not shown) attached to the cathode post 708.
In FIG. 8, a perspective view illustrating an example of an implementation of a flex-circuit without vias is shown. Flex-circuit 800 may include a substrate 802 on which a component 804, such as an LED, may be attached. A bonding wire 806 may provide an electrical connection for the component 804 to an anode pad 810, with a connection to a cathode pad 808 made on the bottom surface of the component 804 utilizing a backside metallization (not shown). In a first embodiment, the substrate 802 and the LED 804 may be encapsulated with encapsulant 812. In a second embodiment, the substrate 802 and the LED 804 may be enclosed within a transparent casing (not shown), which may then be filled with an encapsulant.
In flex-circuit 800, the electrical connection is taken out of the flex-circuit 800 by external terminations 814 and 816 of electrical terminals without utilizing vias or solder pads. The electrical terminals may be positioned so that they are taken out of the flex-circuit 800 on the same side of the flex-circuit 800.
While the foregoing descriptions refer to the use of an LED as the component attached to a flex-LED and a flexible circuit, the subject matter is not limited to LEDs as the component utilized in a flexible circuit or to flex-LEDs or flexible printed circuits as the substrate. Any electronic component and any type of substrate that could benefit from the functionality provided by the components described above may be implemented as the elements of the invention. The flexible circuits described above applies to thin laminated circuits having low thickness compared to conventional PCBs and may or may not be subject to being flexed or bended many multiple times in end applications. In end applications, it may be in a final state or shape of being bent, or curved to conform to a particular shape with straight sections, curved sections or combination thereof.
Moreover, it will be understood that the foregoing description of numerous implementations has been presented for purposes of illustration and description. It is not exhaustive and does not limit the claimed inventions to the precise forms disclosed. Modifications and variations are possible in light of the above description or may be acquired from practicing the invention. The claims and their equivalents define the scope of the invention.
Patent Application
20080067526
