Patent Application
20140374151
The present invention is directed to a method of wire bonding electrical contacts and, more particularly, to a method of wire bonding electrical contacts on flexible substrates.
Electronic devices such as smart phones, tablets, and the like are trending toward being flexible for a myriad of reasons. In addition, electronic devices have become more compact, and less space is available in manufacturing for the placement of electronics and circuitry. Thus, the use of flexible substrates and chips has become more commonplace in the industry.
However, standard wire bonds are not particularly suitable for use with flexible chips. Stresses on the wire loop, the bond at the bond pad, and the stitch bond at the lead contact can be too great due to the flexibility of the substrate, which can lead to breakage of the bond wire or wire bond. In addition, electrical interconnection through solder balls is not a suitable method for use with flexible substrates.
It is therefore desirable to provide a method of electrically interconnecting electrical contacts on a flexible substrate that will minimize stresses and reduce breakage of the bond wire, and which will add few additional steps or components to the wire bonding process.
The present invention is illustrated by way of example and is not limited by embodiments thereof shown in the accompanying figures, in which like references indicate similar elements. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. Notably, certain vertical dimensions have been exaggerated relative to certain horizontal dimensions.
In the drawings:
Referring to the drawings, wherein the same reference numerals are used to designate the same components throughout the several figures, there is shown in
The first electrical contact 12 may be, as shown in the example of
A second electrical contact 16 may also be provided. Although the second electrical contact 16 is shown in
The first and second electrical contacts 12, 16 are electrically interconnected with a bond wire 18. The bond wire is preferably made from gold, although other conductive materials such a copper or aluminium may be used as well. At least a portion of the bond wire 18 may also include an insulating coating (not shown), which can be an insulating organic or polymeric material surrounding at least a portion of the conductive core.
The bond wire 18 includes a first portion 18a that is attached to the first electrical contact 12. A first bond 20 at the first electrical contact 12 is preferably a ball bond, which may be formed by forming a ball at an end of the bond wire 18 with a hydrogen flame or a spark and pressing it against the first electrical contact 12 by a capillary 58 (
The bond wire 18 further includes a second portion 18b that is attached to the second electrical contact 16. A second bond 22 at the second electrical contact 16 is preferably in the form of a stitch bond. The second bond also may include a security bond formed over the stitch bond. The stitch bond may be formed by pressing the second portion 18b of the bond wire 18 against the second electrical contact 16 by the capillary 58 (
The bond wire 18 further includes a third portion 18c that connects the first and second portions 18a, 18b together. The third portion 18c is formed of a plurality of bent sections that form notches 24, which better enables the bond wire 18 and the first and second bonds 20, 22 to alleviate stresses from elongation and compression through flexing of the substrate 14 or bond wire 18. Each notch 24 is defined by at least two corners 26, which are locations where adjacent lengths of the bond wire 18 meet at a generally right angle.
For example,
Multiple bond wires 18 having notch configurations can be used to string together multiple electrical contacts (not shown) in series or in parallel.
Referring now to
A wire shaping tool 60 is provided for forming the notches 24 within the third portion 18c of the bond wire 18. In a preferred embodiment, the wire shaping tool 60 includes at least a first die 62 and a second die 64 spaced apart from one another along a feed direction of the bond wire 18 and disposed on opposite sides of the bond wire 18. The first and second dies 62, 64 are repetitively moved into and out of a feed path of the bond wire 18 to shape the third portion 18c of the bond wire 18 into the plurality of notches 24 (see e.g.,
More preferably, as shown in
The wire shaping tool 60 is disposed between the bond wire feed 52 and the bonding site 12, 16. More particularly, the wire shaping tool 60 is shown in
Preferably, one or more components of the wire bonder 50 are in operative communication with a processor (not shown) which is programmed or configured to calculate the length of the bond wire 18 necessary for the formation of each interconnection 10, identify the first, second, and third portions 18a, 18b, 18c of the bond wire 18 along the calculated length, and prompt the wire shaping tool 60 to move in and out of the feed path of the bond wire 18 as the third portion 18c passes therethrough.
Referring again to
In the foregoing specification, the invention has been described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein without departing from the broader spirit and scope of the invention as set forth in the appended claims.
Those skilled in the art will recognize that boundaries between the above-described operations are merely illustrative. The multiple operations may be combined into a single operation, a single operation may be distributed in additional operations and operations may be executed at least partially overlapping in time. Further, alternative embodiments may include multiple instances of a particular operation, and the order of operations may be altered in various other embodiments.
The terms “front,” “back,” “top,” “bottom,” “over,” “under” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein.
In the claims, the word ‘comprising’ or ‘having’ does not exclude the presence of other elements or steps then those listed in a claim. Further, the terms “a” or “an,” as used herein, are defined as one or more than one. Also, the use of introductory phrases such as “at least one” and “one or more” in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an.” The same holds true for the use of definite articles. Unless stated otherwise, terms such as “first” and “second” are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. The fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.
