CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 U.S. National Stage of International Application No. PCT/SE2018/050426, filed Apr. 25, 2018, which claims priority to Swedish Patent Application No. 1750555-3, filed May 8, 2017. The disclosures of each of the above applications are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention generally relates to a fingerprint sensor package and to a method for manufacturing such a fingerprint sensor package.

BACKGROUND OF THE INVENTION

Various types of biometric systems are used more and more in order to provide an increased security for accessing an electronic device and at the same time keep the user convenience at an acceptable level. In particular fingerprint sensors have been successfully integrated in such devices, for example, thanks to their small form factor, high performance and user acceptance. Among the various available fingerprint sensing principles (such as capacitive, optical, thermal etc.), capacitive sensing is most commonly used, in particular in applications where size and power consumption are important.

There has lately been a desire on the consumer electronics market to increase the interaction between electronic devices such as mobile phones, tablets laptops etc., and the end user. The interaction is now not only related to the fingerprint information but also to for example the force applied on the fingerprint sensor. If the force can be measured a further way of providing feedback between the electronic device and the user is enabled, for example for providing feedback in the form of haptic feedback in response to an applied force. A determined force may further provide application possibilities related to improving timing of when to acquire a fingerprint image (e.g. at preferred pressure on the fingerprint sensor) or for spoof detection.

However, adding further functionalities to present fingerprint sensors poses challenges on the integration of components for providing the further functionalities such as force sensing. For example, space within electronic devices is limited, in particular in mobile phones which are typically relatively thin in the direction where the force would be desirable to be measured, typically perpendicular to the sensing surface of the fingerprint sensor. This makes integration of a force sensor in the fingerprint sensor somewhat problematic. Similar problems occur when trying to simply combine a separate force sensor with a separate fingerprint sensor which generally results in a relatively large stack of components.

Thus, there is a need for improvement with regards to integration of force sensing capabilities with fingerprint sensing.

SUMMARY OF THE INVENTION

In view of above-mentioned and other drawbacks of the prior art, it is an object of the present invention to provide a fingerprint sensor package with integrated force sensing capability in the same package. It is a further an object to provide a method for manufacturing such a fingerprint sensor package.

According to an aspect of the present invention, it is therefore provided a fingerprint sensor package comprising: a substrate having thereon a plurality of electrical connection pads; a fingerprint sensor arranged on the substrate and electrically connected to at least one of the electrical connection pads; a bond wire loop formed from a bond wire having two ends of which at least one end is mechanically and electrically attached to a first one of the electrical connection pads, and a force sensing member in electrical contact with the first electrical connection pad via a upper portion of the bond wire loop, and in electrical contact with a second one of the electrical connection pads different from the first electrical connection pad, wherein an electrical property of the force sensing member is alterable in response to a deformation of the force sensing member, wherein a signal indicative of the alternation of the electrical property is measureable across the electrical connection between the first electrical connection pad and the second electrical connection pad.

The present invention is based upon the realization that bond wire loops may provide an advantageous electronic connection for a force sensing member. The bond wire loops may be placed in suitable locations in the same wire bonding step as for wiring of the fingerprint sensor with minor or no changes of the fingerprint sensor with regards to appearance and/or integration in the package. Furthermore, the bond wire loops extend away from the substrate in a substantially orthogonal direction from the substrate surface, thereby providing a free range of options for the distance between the force sensing member and the substrate. The distance from the substrate would almost only depend on the height of the bond wire loop providing for stacked configurations of the fingerprint sensor and force sensing member. The bond wire loops thus provides for a versatile electrical connection type for the force sensing member.

Accordingly, by connecting the force sensing member with bond wire loops provides improvements in the integration of the force sensing capability with the fingerprint sensor.

The electrical property that may be altered in response to a deformation may be e.g. an electrical resistance or a capacitance measured across the force sensing member. The deformation of the force sensing member may be resilient, thus the shape of the force sensing member is recovered after the force is no longer applied, whereby the electrical property is also at least partly recovered to its original state without the applied force. Accordingly, an alteration in the measured electrical property is indicative of the force applied on the force sensing member.

The electric property is measured across the first connection pad and the second connection pad forming the “plus” and “minus” poles for measuring the electrical property. An electronic measuring circuitry which may be electrically connected to the first connection pad and to the second connection pad is configured for measuring the electric property. Such an electronic measuring circuitry has the suitable electronic components to measure e.g. a voltage over (or a current flowing through) the electric connection path from the first connection pad to the second connection pad via the force sensing member. The electronic property may be determined by an application running on e.g. a mobile phone comprising the fingerprint sensing package.

A bond wire loop is formed from a bond wire which has at least one end attached to a first electrical connection pad. The attachment provides the electrical connection of the bond wire loop to the first electrical connection pad. The second end of the bond wire may be mechanically attached to the same electrical connection pad, or to another electrical connection pad being at the same electrical potential (i.e. electrically being the same point) as the first electrical connection pad. The second end may even be connected to a dummy pad to form the bond wire loop, in such case the dummy pad is given the same electrical potential as the first connection pad through the electrical connection provided by the bond wire. It should be noted that a bond wire loop does not necessarily have to be a closed loop formed by the bond wire. However, the bond wire loop forms an upper loop portion extending away from the substrate surface. For example, the bond wire may form an arch from the bond wire which has two ends attached to the substrate.

A bond wire may be made from e.g. gold or aluminum or any other suitable bond wire material known in the art. A bond wire typically has a cross-sectional diameter in the range of 5 to 50 micro-meter.

The substrate may preferably be a printed circuit board (PCB).

According to embodiments, the bond wire loop is a first bond wire loop, wherein the fingerprint sensor package may comprise: a second bond wire loop formed from a second bond wire having two ends of which at least one end is mechanically and electrically connected to the second one of the electrical connection pads, the second bond wire loop provides the electrical connection for the force sensing member with the second electrical connection pad. Accordingly, a second bond wire loop may be included for further improved integration of the force sensing capability in the fingerprint sensor package.

In some embodiments, a first metal contact is comprised in the fingerprint sensor package to provide an electrical connection from one of the bond wire loops to the force sensing member, the first metal contact being arranged in contact with the upper portion of the bond wire loop. The metal contact is advantageous for improved electrical contact between the force sensing member and the bond wire loop. In addition, the metal contact is particularly advantageous for capacitive read out of the force sensing member, whereby the metal contact may serve as a first metal plate for the capacitive read out.

In some embodiments, the metal contact may be provided in the form of a bezel. The bezel may serve functions associated with the fingerprint sensor, such as to provide a ground connection for the finger or to provide a drive signal to the finger during fingerprint sensing. The bezel may also be a separate bezel serving only as a metal contact.

According to embodiments of the invention, the fingerprint sensor package may comprise a molding material covering at least the top surface of the substrate, the fingerprint sensor, and a portion of each of the bond wire loops, wherein the upper portion of at least one bond wire loop is accessible near the molding material outer surface, wherein said force sensing member is connected to said bond wire loop at said upper portion of the at least one bond wire loop. Accordingly, the bond wire loops are accessible near the surface of the molding material such that they may be electrically contacted as the molding material surface. Near the surface should be interpreted as that the bond wire loop upper portion may initially be partly covered by the molding material, whereby part of the molding material may have to be removed to access the bond wire loop upper portion. Alternatively or additionally the bond wire loops may for example be arranged higher than the molding material surface such that they are visible after the molding step. The mold provides a stable mechanical support for the bond wire loops such that they may be reliable electrically connected at their upper portions.

In one embodiment, the upper portion of the at least one bond wire loop is accessible in a cavity formed in the molding material, wherein the force sensing member is arranged in the cavity. In other words, a cavity may be formed by e.g. laser etching, such as to expose the bond wire loop. The first metal contact may in this case be arranged in the cavity in order to electrically contact the bond wire loop exposed in the cavity. It may often occur that the bond wire loops are not possible to electrically connect to at the surface of the molding material after the molding step. Therefore, a step of exposing the bond wire loops is advantageously included.

Furthermore, the upper portion of at least the second bond wire loop is accessible in a second cavity formed in the molding material surface, wherein the force sensing member electrically connected to the second bond wire loop in the second cavity with a second metal contact.

The force sensing member may for example comprise quantum tunneling composite (QTC) material. A QTC material comprises metal particles embedded in a polymer whereby the electrical resistance through the QTC-comprising member is altered when the QTC-comprising is deformed, the alteration of the electrical property is due to that the distance between the metal particles embedded in the polymer is altered when the QTC-comprising member is deformed. The force sensing material may alternatively comprise a piezoelectric material (e.g. PVDF, BiTi, BaTi, etc.).

The force sensing member may alternatively be comprised of a metal arranged in a way that the resistance through the metal responds to a change in force, ie a strain guage. In other words, the force sensing member may provide a measureable electrical property which is alterable in response to a mechanical deformation of the member which thus provides an indication of the force applied to the force sensing member. Both QTC materials and piezoelectric-comprising member are per se well known in the art of making force sensing members.

According to a second aspect of the present invention, there is provided an electronic device comprising the fingerprint sensor package according to anyone of the above embodiments.

Accordingly, the fingerprint sensing package preferably forms part of an electronic device further comprising a device controller for performing an authentication of the finger based on the acquired verification fingerprint image and verification force value, and performing at least one action only if the authentication indicates an authentication success. Such an action may for example be for unlocking a locked portable device, e.g. in case the portable device is a mobile phone. The action may of course be any type of action suitably used when there is a need to authenticate a finger.

This second aspect of the invention provides similar advantages as discussed above in relation to the previous aspect of the invention.

According to a third aspect of the invention there is provided a method for manufacturing a fingerprint sensor package comprising a fingerprint sensor on a substrate having a plurality of connection pads on the substrate, the fingerprint sensor being connected to at least one of the electrical connection pads, the method comprising: forming a bond wire loop from a bond wire, the bond wire loop being formed by two ends of the bond wire, wherein at least one of the ends is mechanically and electrically attached to a first one of the electrical connection pads, arranging a force sensing member in electrical contact with the first electrical connection pad via an upper portion of the bond wire loop and in electrical contact with a second one of the electrical connection pads different from the first electrical connection pad connected with the bond wire loop, wherein an electrical property of the force sensing member is alterable in response to a deformation of the force sensing member, wherein the alternation of the electrical property is measureable across the electrical connection between the first electrical connection pad and the second electrical connection pad.

Advantageously, the fingerprint sensor is connected to the at least one of the electrical connection pads with at least one bond wire, wherein the bond wire loop and the bond wire connections for the fingerprint sensor are formed in the same wire bonding step. The same wire bonding step should be interpreted as that the wire bonds for the fingerprint sensor and the bond wire loops may be bonded with the same wire bonding apparatus without having to remove the substrate from the wire bonding apparatus between the wire bonding of the fingerprint sensing and forming the bond wire loops. However, the substrate may of course be intermediately removed if needed and even be placed in a different wire bonding tool if desirable. Both cases (remove or not remove the substrate) are within the scope of the invention.

According to embodiments of the invention, there may be included to form a second bond wire loop from a second bond wire having two ends, wherein at least one of the ends is attached to the second one of the electrical connection pads, the second bond wire loop provides the electrical connection for the force sensing member with the second electrical connection pad.

According to embodiments of the invention, there may be included to form a first metal contact to provide an electrical connection from one of the bond wire loops to the force sensing member.

According to yet another embodiment, there may be included to apply a molding material covering at least the top surface of the substrate, the fingerprint sensor, and a portion of each of the bond wire loops.

According to yet another embodiment, there may be included to open a cavity in the molding material such as to access the upper portion of the bond wire loop, wherein the force sensing member is arranged in the cavity in electrical contact with the accessible bond wire loop.

According to yet another embodiment, there may be included to form the first metal contact in the cavity, and arrange the force sensing member in the cavity, and in contact with the first metal contact for connecting the force sensitive member to the exposed bond wire loop in the cavity.

According to yet another embodiment, the force sensing member may be attached to a protective plate, wherein the method comprises: arranging the protective plate on the molding material such that the force sensing member makes electrical contact with the exposed bond wire loop.

This third aspect of the invention provides similar advantages as discussed above in relation to the previous aspect of the invention.

The fingerprint sensor may be implemented using any kind of current or future fingerprint sensing principle, including for example capacitive, optical, or thermal sensing technology. However, at present capacitive sensing is most preferred. With a capacitive fingerprint sensor, a measure is detected indicative of the capacitive coupling between each sensing element in an array of sensing elements and a finger surface touching the fingerprint sensor surface. Sensing elements at locations corresponding to ridges in the fingerprint will exhibit a stronger capacitive coupling to the finger than sensing elements at locations corresponding to valleys in the fingerprint. Both one and two-dimensional sensors are possible and within the scope of the invention. Furthermore, the electronic device may advantageously be a mobile phone. However, other electronic devices are of course thinkable such as tablets, laptops desktop computers, smart cards, electronic locks, vehicle applications, etc.

In summary, the present invention generally relates to a fingerprint sensor package comprising: a substrate having thereon a plurality of electrical connection pads; a fingerprint sensor arranged on the substrate and electrically connected to at least one of the electrical connection pads; a bond wire loop formed from a bond wire having two ends of which at least one end is mechanically and electrically attached to a first one of the electrical connection pads, and a force sensing member in electrical contact with the first electrical connection pad via an upper portion of the bond wire loop, and in electrical contact with a second one of the electrical connection pads different from the first electrical connection pad, wherein an electrical property of the force sensing member is alterable in response to a deformation of the force sensing member.

Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled addressee realize that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.

