MANUFACTURING SUCH A FINGERPRINT SENSOR MODULE

Field of the Invention

The present invention relates to a fingerprint sensor module and method for manufacturing a fingerprint sensor module. Background of the Invention

As the development of biometric devices for identity verification, and in particular of fingerprint sensing devices, has lead to devices which are made smaller, cheaper and more energy efficient, the possible applications for such devices are increasing. Fingerprint sensing in particular has been adopted in more and more applications such as consumer electronic devices and smart cards due to small form factor, relatively beneficial cost/performance factor and high user acceptance.

With the increasing use of fingerprint sensors in low cost applications such as smart cards, it is increasingly important to reduce the cost per sensor. Since the sensors are manufactures in large series resulting in high volumes, one way to efficiently reduce the cost per sensor is to reduce manufacturing costs and to increase process yield.

Typically, a fingerprint sensor module comprises multiple

semiconductor dies which need to be assembled to form the finished fingerprint sensing module ready for integration in an end product. The sensor module may be referred to as an SIP (system-in-package) module. A laminate substrate is typically used to connect multiple integrated circuits along with passive components to form a fingerprint sensor module in a single package.

However, such a laminate substrate is costly, and thermal mismatch between the substrate and components mounted on the substrate may lead to warpage of substrate and/or of the components. An alternative assembly method is available but requires an expensive chip-to-wafer assembly process. Accordingly, it is desirable to improve on existing manufacturing methods for forming a fingerprint sensing module.

Summary

In view of above-mentioned and other drawbacks of the prior art, it is an object of the present invention to provide an improved method for manufacturing a fingerprint sensor module.

According to a first aspect of the invention, there is provided a method for manufacturing a fingerprint sensor module, the method comprising:

providing a carrier comprising an adhesive; providing a plurality of fingerprint sensor devices, each sensor device in turn comprising a sensing array comprising a plurality of sensing elements, a backside of the fingerprint sensor device comprising contact pads; attaching the plurality of fingerprint sensor devices on the carrier by means of the adhesive using a pick-and- place method to arrange the fingerprint sensor device on the carrier, such that the sensing array faces the adhesive; arranging an electronic component on the backside of each of the fingerprint sensor devices the backside being the side opposite of the sensing array, and forming a contact between the fingerprint sensor device and the electronic component; and removing the fingerprint sensing device comprising the electrical component from the carrier using a pick-and-place method.

The fingerprint sensor device should in the present context be understood to be a semiconductor die or chip comprising an array of sensing elements for acquiring an image of a finger placed on a sensing surface of the final fingerprint sensing module. The fingerprint sensor device may be an active or passive capacitive device, an ultrasonic or an optical device. The general operating principles of various types of fingerprint sensor devices are considered to be well known to the skilled person.

In order for a fingerprint sensing device to be incorporated in an end product, such as an electronic consumer device, a smart card or a vehicle, the fingerprint sensor device must be provided in an appropriate packaging solution comprising both the additional components required for the functionality of the fingerprint sensing device as well as appropriate

environmental protection. Accordingly, after production of the fingerprint sensor device itself, there are still a number of manufacturing steps remaining to reach the final semiconductor module which is ready to be mounted in an end product.

In view of the above, the present invention is based on the realization that the process of manufacturing a fingerprint sensor module can be simplified by arranging the fingerprint sensing module on a carrier before arranging additional electrical components on the backside of the carrier. Thereby, the size and configuration of the carrier can be selected such that it can be used with various types of manufacturing equipment for placing the sensor device and for arranging the electric component on the sensor device.

The fingerprint sensor devices may advantageously be arranged on the carrier using a pick-and-place method. A pick-and-place method may be performed by SMT (surface mount technology) component placement systems, also referred to as pick-and-place machines. The use of a pick-and- place machine simplifies the assembly process and also makes it possible to implement the assembly process in commonly available assembly lines comprising pick-and-place machines.

Moreover, a pick-and-place method may advantageously be used to also place the electronic component on the backside of the fingerprint sensor device, i.e. on the side opposing the side where the sensing array is located. The use of a pick-and-place machine also here may further simplify the manufacturing method since the steps of attaching the fingerprint sensing device and of arranging the electronic component can in principle be performed in the same assembly station.

According to one embodiment of the invention, arranging the electronic component on the fingerprint sensor device may comprise soldering the electronic component to the fingerprint sensor device. Soldering is a readily available method of attaching the electronic component on the backside of the fingerprint sensor device, including the steps of flux application and solder reflow. However, it is also possible to use other methods such as

thermocompression bonding.

According to one embodiment of the invention, the electric component may be electrically connected to the fingerprint sensor device by means of via connections through the fingerprint sensor device. Thereby, suitable electrical connections can be formed between the fingerprint sensor device and various components arranged on the backside of the fingerprint sensor device.

Moreover, the via connections may be gathered in one area of the device and where conductive traces can be used to form electrical connections to components in selected other locations on the device.

According to one embodiment of the invention, the adhesive may be an adhesive tape. Adhesive tapes are commonly used and readily available in semiconductor manufacturing, and provides advantages in that they can endure common manufacturing steps and that an adhesive tape, such as a Kapton tape, provides for easy removal of the finalized fingerprint sensor module.

According to one embodiment of the invention the carrier may be a leadframe strip. The leadframe strip can in principle be described as a metal sheet having a pattern formed therein. The leadframe strip would then comprise one or more openings for placing the fingerprint sensor, where an adhesive tape is attached to a first side of the leadframe strip side such that an adhesive side of the tape is exposed in the openings of the leadframe strip, there by allowing the fingerprint sensor device to be placed on the adhesive surface.

In an electrically conductive leadframe strip, a suitable metal pattern can be stamped or etched into the leadframe. Thereby, a pattern can for example be formed which guides the semiconductor device and facilitates correct placing of the device. However, it may in principle be possible to use any planar surface as a carrier, where an adhesive material is arranged on the carrier surface for attaching the fingerprint sensor. The carrier may for example be any rigid sheet material, such as a steel or copper plate or disc. According to one embodiment of the invention, the electronic component may be a fingerprint sensor control chip. A fingerprint sensor control chip may for example be used to provide a drive signal to the sensor device and/or to a finger placed on a sensing surface of the fingerprint sensor module. Accordingly, it is advantageous to provide such components in the same module as the fingerprint sensing device in order to provide a complete fingerprint sensor module.

According to one embodiment of the invention, the electronic component may be a passive component required for the overall functionality of the fingerprint sensor module.

According to one embodiment of the invention, the method may further comprise arranging an electrically conductive bezel on the carrier, the bezel surrounding the fingerprint sensor device. The bezel which is arranged to surround the sensor is exposed adjacent to and in substantially the same plane as the sensing surface of the sensor module such that a finger making contact with the sensing surface also contacts the bezel. Thereby, the bezel can be used to provide a drive signal to a finger which in turns facilitates fingerprint sensing in a capacitive fingerprint sensor device.

According to one embodiment of the invention, the method may further comprise arranging an encapsulant surrounding the fingerprint sensor device to mechanically protect the edges of the device. A controlled quantity of low- fluidity encapsulant may be dispensed in between the sensor devices attached to the carrier so that the edges of the sensor device are protected, without covering the backside of the sensor device. Since only the required amount of encapsulant is dispensed, no cleaning or subsequent removal is required after dispensing the encapsulant.

In an embodiment where there is a bezel arranged to surround the fingerprint sensor device, the encapsulant may advantageously be dispensed only between the bezel and the sensor device, such that the bezel acts as a barrier for the encapsulant, thereby protecting the edges of the device and at the same time providing a transition between the bezel and the sensing device. This requires that the bezel has a height which approximately corresponds to the thickness of the fingerprint sensor device such that the entire edge of the fingerprint sensor device is protected by the encapsulant. If desired, the bezel can be electrically connected to the fingerprint sensor device or to associated control circuitry of the fingerprint sensor module by using wire bonding.

According to one embodiment of the invention, the method may further comprise removing the fingerprint sensor device form the carrier using a pick- and-place process, thereby providing the finalized fingerprint sensor module ready for mounting in an end product. However, it is also possible that additional assembly steps are performed after removing the fingerprint sensor module from the carrier. The sensor module may for example be cleaned to remove any residues of the adhesive, and a protective structure may be arranged to cover the sensing array.

There is also provided a fingerprint sensor module comprising: a fingerprint sensor device comprising a sensing array comprising a plurality of sensing elements; an electrically conductive bezel arranged to surround the sensor device, wherein the bezel is exposed adjacent to a sensing surface of the sensor module; and an encapsulant arranged between the bezel and the sensor device. The described fingerprint sensor module is advantageously manufactured using the above described method where a bezel-frame may be formed in a leadframe strip, followed by placement of the sensor in the bezel and subsequent application of an encapsulant. The encapsulant thereby effectively seals the gap between the sensor device and the bezel without any post-processing steps which may otherwise be required if a bezel is attached to an already finalized fingerprint sensor module.

The bezel may advantageously have a thickness corresponding to a thickness of the fingerprint sensor device. Thereby, the bezel reaches from the sensing surface of the sensor module to the opposite surface such that it defines the area where the encapsulant is dispensed. That the bezel has a thickness corresponding to the thickness of the sensor device should in the present context be interpreted to mean that the thickness of the bezel is substantially the same as the thickness of the sensor device, i.e. of the sensor chip. However, it is not required that the height of the bezel is exactly the same as the thickness.

Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person 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. Brief Description of the Drawings

These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing an example embodiment of the invention, wherein:

Fig. 1 schematically illustrates an electronic device comprising a fingerprint sensor module;

Fig. 2 schematically illustrates a fingerprint sensor device used in embodiments of the invention;

Fig. 3 is a flow chart outlining general steps of a method according to an embodiment of the invention;

Figs. 4A-C schematically illustrate steps of a method according to an embodiment of the invention;

Figs. 5A-B schematically illustrate an embodiment of the invention; Figs. 6A-B schematically illustrate an embodiment of the invention; and Figs. 7A-C schematically illustrate steps of a method according to an embodiment of the invention.

Detailed Description of Example Embodiments

In the present detailed description, various embodiments of the device and method according to the present invention are mainly described with reference to a manufacturing method using a pick-and-place process.

Moreover, embodiments of the present invention are mainly described with reference to a capacitive fingerprint sensing device arranged in a smartphone. However, it should be noted that the present invention is applicable for any type of fingerprint sensor. The fingerprint sensor device may for example be an active or passive capacitive device, an ultrasonic or an optical device.

Fig. 1 schematically illustrates a smartphone 10 comprising a fingerprint sensor module 12 manufactured according to an example embodiment of the present invention. The fingerprint sensor module 12 may, for example, be used for unlocking the smartphone 10 and/or for authorizing transactions carried out using the smartphone, etc. A fingerprint sensor module 12 according to various embodiments of the invention may also be used in other devices, such as tablet computers, laptops, smartcards or other types of consumer electronics. The described fingerprint sensing device may also be used in applications such as smartcards, vehicles etc.

Fig. 2 schematically shows the fingerprint sensing device 20 comprised in the fingerprint sensor module 12 in Fig. 1 . As can be seen in Fig. 2, the fingerprint sensing device 20 comprises a plurality of sensing elements 22 arranged in a sensor array 24. The sensor array 24 comprises a large number of individual sensing elements 22, each being controllable to sense a distance between an electrically conductive sensing structure comprised in the sensing element 22 and the surface of a finger contacting the top surface of the sensing module 12 or another surface defined as the sensing surface. The fingerprint sensor module 12 may for example be arranged underneath a display glass or other cover glass of an electronic device. For a capacitive fingerprint sensor, the electrically conductive sensing structure of the sensing element 22 is typically a conductive plate. Further details related to the structure and function of a capacitive fingerprint sensor are well known to the skilled person and will not be discussed in further detail herein.

The method for manufacturing a fingerprint sensor module will be described with reference to the flow chart of Fig. 3 schematically outlining steps of the manufacturing method, and to Fig. 4A-C schematically illustrating selected manufacturing steps. In a first step illustrated in Fig. 4A, a carrier 40 comprising an adhesive 42 is provided 30. The adhesive 42 may be an adhesive tape or film commonly used in semiconductor manufacturing processes, also referred to as a "sticky tape". It is also possible to use other types of adhesives having properties similar to such an adhesive tape.

Fig. 4B illustrates providing 32 a plurality of fingerprint sensor devices 20, with each sensor device comprising a sensing array 24 as described with reference to Fig. 2. In Fig. 4B the sensing array of the fingerprint sensor device 20 is facing downwards towards the adhesive. It is thus the backside 44 of the fingerprint sensor device 20 which is shown. The backside 44 of the fingerprint sensor device 20 comprises contact pads 46 for forming a contact between the device 20 and additional components located on the backside 44 of the device 20. The fingerprint sensor device 20 may also be referred to as a fingerprint sensor chip or die, and is typically formed from a silicon substrate.

The method step that is being illustrated in Fig. 4B is the attaching 34 of fingerprint sensor devices 20 to the carrier 40 by means of the adhesive 42, such that the sensing array faces the adhesive 42. Here, the fingerprint sensor devices 20 are placed on the carrier 40 using a pick-and-place machine 46. The pick-and-place machine 48 picks up the fingerprint sensor devices 20, for example directly from a diced wafer comprising a large number of devices (not shown) directly from the device fabrication process, and places them on the carrier 40 comprising the adhesive 42. The diced wafer may be arranged on dicing tape, commonly referred to as blue tape, sticky tape, or UV-release tape.

In the following step illustrated in Fig. 4C, electronic components 50, 52 are arranged 36 on each of the fingerprint sensor devices 20. The electronic component may for example be a fingerprint sensor control chip 50 or a passive component 52, which is arranged on the backside 44 of the fingerprint sensor device 20 using a pick-and-place method. The electric components 50, 52 may for example be electrically connected to the fingerprint sensor device 20 by means of via connections through the fingerprint sensor device 20. The connections may furthermore be routed using conductive traces on the backside 44 of sensor thereby allowing a flexibility in the placement of components, since they do not need to be located directly at the location of the via connections.

The electric components 50, 52 can be connected by means of soldering, in which case the type of adhesive 44 to use is selected to withstand the temperatures required for soldering. One such adhesive material is Kapton tape which is capable of withstanding the temperatures used during soldering and reflow. As an alternative to, or in combination with soldering, other attachment methods such as a conductive adhesive, compression bonding or thermosonic bonding may be used. It is also possible to attach different components using different attachment methods.

The placement of the fingerprint sensor devices 20 on the carrier 40 and the following placement of electric components 50, 52 on the fingerprint sensor devices 20 may be performed in one and the same pick-and-place machine 48, or it may be performed by separate pick-and-place machines in a sequential manufacturing line.

In a final step, the finalized fingerprint sensor module 12 is removed 38 from the carrier 40. The finalized fingerprint sensor module 12 may then be provided to the next step in the supply chain for integration in an electronic device, such as the smartphone 10 illustrated in Fig. 1 . The fingerprint sensor module 12 comprises connection pads for connecting to the model to external circuitry

Fig. 5A illustrates a plurality of fingerprint sensor devices 20 arranged on a leadframe strip in the form of a metal frame 54 arranged on an adhesive material 42 such as an adhesive tape. The leadframe strip 54 can be formed having desired pattern through patterning and subsequent etching, thereby providing flexibility in how the metal frame is configured, as will be illustrated in the following examples. Moreover, the use of leadframe strips is well established in semiconductor device packaging and can therefore be easily integrated in a method for manufacturing the fingerprint sensor module. The size of the leadframe strip is equipment dependent, and in general a larger strip size can be used when using a pick-and place machine compared to when using e.g. a die attach machine.

Fig. 5B illustrates a finalized fingerprint sensing module 12, comprising the electronic components arranged on the backside 44 thereof, after removal from the adhesive.

Fig. 6B schematically illustrates an optional additional step of the method manufacturing describing forming an encapsulant to mechanically protect the edges of the fingerprint sensor module 20. Here, an encapsulant 60 is dispensed on the carrier 40 in between the fingerprint senor devices 20 to protect the edges of the fingerprint sensor device 20. The distribution of the fluidic encapsulant on the carrier 40 is controlled by means of the frame. The encapsulant can for example be dispensed using jet dispensing equipment or using needle dispensing. Following dispensing, the encapsulant is cured at an elevated temperature to harden. Once the encapsulant has cured, the encapsulant may be cut, separating the sensor devices 20, prior to removal from the adhesive such that the resulting sensor module 12 comprises encapsulant material encircling the module, thereby protecting the silicon edges. A fingerprint sensor module 12 comprising an encapsulant 60 is illustrated in Fig. 6B.

A further advantage of arranging the fingerprint sensor devices on a leadframe strip is illustrated in Fig. 7A where the leadframe strip has been patterned to form a bezel 70 encircling each of the sensor devices 20. The bezel structures 70 are thus formed in the leadframe prior to arranging the sensor devices 20 thereon. Moreover, an encapsulant is dispensed to fill the gap between the fingerprint sensor device 20 and the bezel 70. Thereby, an electrically conductive bezel 70 can be provided adjacent to a sensing surface of the fingerprint sensor module 10. The bezel 70 can be used to provide a drive signal or any other reference voltage to a finger placed on a sensing surface, or to connect the finger to ground potential, in order to facilitate fingerprint image capture in a capacitive fingerprint sensor module. After finalizing the fingerprint sensor module 10 on the leadframe, the entire structure can be diced by cutting the supporting leadframe lines 72 located between adjacent fingerprint sensor devices 20, permitting removal of the individual fingerprint sensor modules 12.

Fig. 7 schematically illustrates a top side of the finalized fingerprint sensor module 12 displaying the array 24 of sensing elements, surrounded by an encapsulant 60 and a bezel 70 exposed adjacent to the sensing surface of the fingerprint sensor module 12. It should be noted that the sensing array is typically covered by a mold layer or by a protective plater or the like, there by protecting the sensing elements and forming an external sensing surface to be touched by a finger. Accordingly, the bezel 70 preferably has a thickness which is equal to the thickness of the fingerprint sensor device 12 including one or more protective layers covering the sensing array.

Even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. Also, it should be noted that parts of the method may be omitted,

interchanged or arranged in various ways, the method yet being able to perform the functionality of the present invention.

Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.