News Column

Patent Issued for Integrally Molded Die and Bezel Structure for Fingerprint Sensors and the like

July 23, 2014

By a News Reporter-Staff News Editor at Electronics Newsweekly -- A patent by the inventors Bond, Robert Henry (Plano, TX); Kramer, Alan (Berkeley, CA); Gozzini, Giovanni (Berkeley, CA), filed on August 6, 2013, was published online on July 8, 2014, according to news reporting originating from Alexandria, Virginia, by VerticalNews correspondents.

Patent number 8772884 is assigned to Apple Inc. (Cupertino, CA).

The following quote was obtained by the news editors from the background information supplied by the inventors: "The present disclosure is related to integrated circuit packaging, and more specifically to methods and apparatus for integrally molding a die and one or more bezel structures, with portions of each exposed or at most thinly covered, for fingerprint sensors and the like.

"One relatively common biometric sensing device today is the fingerprint sensor. These devices are used in controlling access to electronic devices such as computers and mobile phones, safes, buildings, vehicles, etc. by scanning a user's fingerprint and comparing it to an authenticating set of fingerprint images. If the proffered (live) fingerprint to be authenticated matches one within a set of pre-enrolled authorized fingerprints, access may be granted. Fingerprint sensors may be stand-alone devices, integrated into other devices such as PC peripherals, or may be integrated into the devices over which they control access. The sensors may be optical or electrical (e.g., resistive, capacitive, etc.)

"Typical electrical-based fingerprint sensors today comprise a semiconductor body, or die, on which is formed an array of sensor elements and related circuitry. When packaged, the sensor elements are often exposed for contact with a user's finger, or through a protective material. Typically, the sensors operate according to principles that use distance between the sensor surface and a region of the user's finger to construct an image of the user's fingerprint. Accurate operation of such sensors can accommodate no more than a minimal gap between the sensor surface and the fingerprint to be sensed. Therefore, the sensor surface itself is most often left uncovered, and a user places a finger directly into contact therewith in the process of fingerprint sensing. However, certain fingerprint sensor designs include thin protective overcoats over the sensor surface to protect the sensors from physical and environmental damage, wear, etc.

"The semiconductor die typically has a sensor array photolithographically (or otherwise) formed on a top surface thereof. The sensor die are typically quite small, with correspondingly small contact pads, necessitating use of a secondary structure to make practical electrical connections between the die and a printed circuit board (PCB) to which the assembly is attached for use. Such secondary structures include lead frames, chip carriers, and the like. In common applications, the die is attached to a lead frame, and fine wires (wirebonds) make the electrical interconnections between the micro-scale bonding pads of the die and the macro-scale bonding leads of the lead frame. To protect the wirebonds and other components, the die, lead frame, and wirebonds are typically encased in an encapsulation material. This is accomplished by placing the bonded and connected die and lead frame in a mold, injecting the encapsulation material into the mold, and hardening the encapsulation material. Typically this is done such that the sensor array portion of the die is left uncovered by the encapsulation material. The encapsulated die structure may then form a component used in subsequent assembly steps.

"A number of fingerprint sensor circuit designs operate by injecting a small current into the finger being sensed. One example of such a circuit is disclosed in U.S. Pat. No. 6,512,381, which is incorporated herein by reference. In order to drive the user's finger with the desired current, a contact structure, for example as disclosed in U.S. Pat. No. 6,636,053, which is also incorporated herein by reference, may be provided. The contact structure may take the form of a bezel located near an edge of the die. The bezel has a generally planar upper surface that is either coplanar with or parallel to the plane of the upper surface of the die. As the user applies a fingertip to the surface of the die, for example by placement on an area sensor or in the swiping motion over a strip sensor, the fingertip is simultaneously in physical and electrical contact with the surface of the die (i.e., the sensor array formed on the top surface of the die) and the bezel, the latter to electrically drive the fingertip during the sensing process.

"Traditionally, the bezel and the encapsulated die have each been separate elements, brought together in the process of assembling or packaging the sensor apparatus. That is, the bezel and die are not encapsulated together. In one known example, the bezel is a metal sheet bent to curl over at its edges, which makes electrical connection with the bottom side of the substrate. The bezel wraps around the sides of the substrate to present a top, contact portion roughly in the plane of the top surface of the encapsulated die. In other example, a metal strip or frame makes contact with the top side of the substrate, and presents a top, contact portion roughly in the plane of the top surface of the encapsulated die.

"Current fingerprint sensor structures require a number of discrete assembly steps. As the number of discrete elements and manufacturing steps increase, manufacturing cost increases and the potential for faulty or inaccurate assembly that negatively affects product consistency and yield losses increase. Discrete element sub-assembly is also a more time consuming process than integrated manufacturing. As in the general art of IC production, there is significant, ongoing commercial pressure to reduce cost, number of components, and number and complexity of manufacturing steps, and size of the completed structure.

"Furthermore, the separate bezel and encapsulated die structures are often undesirably large final devices. Further still, it is desired that the bezel be as physically close to the sensors as possible to optimize the sensitivity of the sensor. However, known separate bezel and encapsulated die designs limit possible options of the final device size and sensor-to-bezel spacing."

In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventors' summary information for this patent: "According to one aspect of the present disclosure, a biometric sensor assembly, such as a fingerprint sensor, comprises a substrate to which is mounted a die containing sensor circuitry and at least one conductive bezel. As used in the description and claims that follow, 'bezel' means a unitary, substantially uniformly composed structure, most typically metal or conductive plastic. The die and the bezel are encased in a unitary encapsulation structure to protect those elements from mechanical, electrical, and environmental damage, yet with a portion of a surface of the die and the bezel exposed or at most thinly covered by the encapsulation or other coating material structure.

"By encasing both the bezel and the sensor die in the encapsulation structure, those elements may be brought closer together than heretofore possible. In addition, the encapsulation structure physically protects the bezel and sensor die, and in particular maintains the spacing therebetween, in a fashion not possible by currently known device designs.

"According to one variation disclosed herein, the bezel may be an electrically conductive arch-shaped structures secured to a substrate. The substrate may have leadlines or the like formed thereon to allow electrically interconnection between the bezel and other circuitry. The bezel may alternatively be a solid body or part of a bezel frame. A single bezel may be integrally molded with the sensor die in an encapsulation structure or a plurality of bezels by be so molded. The bezel may be adjacent a single side of the sensor die, several sides of the sensor die, or may surround the sensor die.

"The molding of the bezel and sensor die may be such that the top surface of the bezel and the top surface of the sensor die are coplanar. Alternatively, the plane of the top surface of the bezel and the top surface of the sensor die may be generally parallel, but not coplanar, such that the plane of the top surface of the bezel is slightly above the plane of the top surface of the sensor die. In this case, the top surface of the bezel may protrude slightly above the encapsulation material, for example to improve physical contact therewith by a user's finger. Also in this case, it may be desirable to provide the bezel with a slightly rounded cross-section for user comfort, for device robustness, to avoid the buildup of contaminants at the bezel edge, etc.

"The above is a summary of a number of the unique aspects, features, and advantages of the present disclosure. However, this summary is not exhaustive. Thus, these and other aspects, features, and advantages of the present disclosure will become more apparent from the following detailed description and the appended drawings, when considered in light of the claims provided herein."

URL and more information on this patent, see: Bond, Robert Henry; Kramer, Alan; Gozzini, Giovanni. Integrally Molded Die and Bezel Structure for Fingerprint Sensors and the like. U.S. Patent Number 8772884, filed August 6, 2013, and published online on July 8, 2014. Patent URL:

Keywords for this news article include: Apple Inc., Electronics, Semiconductor.

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Source: Electronics Newsweekly

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