Integrated flexible force sensor assembly

Abstract

The invention provides a force sensor and a manufacturing method of the force sensor. A force sensor may be used to measure a contact force. The force sensor includes a substrate having an electromagnetic sensing element for contactless sensing of a field formed by a target. The target is included in a flexible member that is subjected to a force and can be deformed by the force. The flexible member is processed so that the force sensor is reliable and has long-term durability.

Description

Technical Field

[0001] The present invention relates to the field of force sensors. More particularly, the present invention relates to force sensors using position sensing and their manufacture. Background Art

[0002] Force sensors are used in many applications. Each type needs to meet specific requirements such as compactness, sensitivity range and reliability.

[0003] For example, force sensors can be used as feedback to assist in automated manipulation of objects. In automated manipulation, the forces applied to the object are often difficult to control, which can lead to manipulation errors or incorrect positioning of the manipulated part, or even damage to the manipulated part.

[0004] In the field of robotics, a robot gripper or robot hand may include a force-torque sensor, for example, on a mechanical part that drives the movement of a gripper (claw, finger, etc.). However, this measurement is indirect. It is not simple to measure the deformation of the contact surface with the object to be handled. In order to solve this problem, the actual contact force can be measured. This can be done by using a flexible material, such as an elastomer, whose surface contacts the object to grasp, and the deformation of the surface is measured as an indication of the force applied to the object. The deformation can be measured with a position sensor on a substrate (on which the flexible material is arranged), which detects the position of a target (such as a magnet, etc.) that moves as the flexible material deforms.

[0005] The sensitivity of the force sensor is therefore determined by the deformation resistance of the flexible material. If the flexible material has a very low deformation resistance, the sensitivity will be high, but the response of the force sensor to high forces will be lower. In extreme cases, the electronics of the position sensor may be damaged, for example due to impact forces or large contact forces. These requirements also need to be compatible with the requirements of compactness, so that the force sensor can be integrated in larger systems.

[0006] An important requirement, primarily for object manipulation, is reliability when the contact area is subjected to shear forces. The flexible material should not break or become detached from the substrate due to these forces. Preferably, the position sensor should also be able to reliably measure these forces.

[0007] It is desirable to provide a sensitive and compact force sensor with a long lifetime that is reliable even when subjected to shear forces. Summary of the invention

[0008] An object of embodiments of the present invention is to provide a compact and reliable sensor for sensing forces, in particular contact forces and shear forces, in an accurate manner for a wide range of forces. A further object is to provide an assembly comprising such a sensor, and a method of manufacturing the sensor.

[0009] In one aspect, the present invention provides a method of manufacturing a force sensor. The method includes providing a flexible member, wherein one of the surfaces of the flexible member is an attachment surface, and the flexible member further includes (eg, is embedded with) a target member.

[0010] A substrate is then provided, the substrate comprising a receiving surface and the substrate comprising at least one sensing element. The sensing element(s) can sense changes in the (electro)magnetic field caused by the movement of the target.

[0011] The method comprises attaching the attachment surface of the flexible member to the receiving surface of the substrate by providing surface activation on the attachment surface, and then providing an adhesive layer in contact with at least the attachment surface by sandwiching the adhesive layer between the receiving surface and the attachment surface. An advantage of an embodiment of the present invention is that a reliable force sensor can be obtained by an improved attachment between the flexible member and the sensing portion of the sensor. An advantage is that an elastomer such as rubber or silicone can be reliably attached to a molding compound such as epoxy for long-term use. Since an improved attachment is provided, an advantage is that high shear forces can be measured.

[0012] In some embodiments, the substrate is a semiconductor package and the at least one sensing element is an integrated circuit included in the semiconductor package, thereby forming a chip. Attaching the flex to the substrate includes attaching an attachment surface of the flex to a receiving surface of the semiconductor package.

[0013] An advantage of embodiments of the present invention is that a highly compact device can be obtained with a very small footprint.

[0014] In some embodiments, providing surface activation includes providing plasma treatment. An advantage of embodiments of the present invention is that ion treatment (such as plasma treatment or the like) can be used to locally treat the surface of the flexible member, thereby allowing very controlled surface activation. This advantageously increases the hydrophilicity of the surface, improving the bond between the material of the flexible member and the material of the adhesive layer, thereby enhancing adhesion.

[0015] In some embodiments, providing the flexible member includes forming the flexible member as a single piece by injection molding.

[0016] An advantage of embodiments of the invention is that the piece can also be provided as a single unit without joints and thus with uniform properties and a lower risk of breaking apart. A further advantage is that the method is compatible with injection molding and high volume manufacturing platforms in microelectronic assemblies.

[0017] In some embodiments, providing the flexible member includes providing a target member and encapsulating the target member within the flexible member.

[0018] An advantage of embodiments of the present invention is that no adhesive is required to attach the target member to the flexible member, thereby reducing the likelihood of adhesive failure.

[0019] In some embodiments, providing a substrate including a sensing element includes providing a sensing element adapted to sense magnetic fields in at least two different directions.

[0020] An advantage of embodiments of the present invention is that a multi-directional force sensor can be provided that allows sensing of forces in 2 directions, such as forces in 2 perpendicular directions, such as forces in 3D, rather than just one component. For example, such a sensor can be used as a grasping sensor that allows a firm grasp to lift an object with less grasping force than would be required to damage or deform the object.

[0021] In some embodiments, the method includes providing a cavity to the flexible member. The cavity is at least partially enclosed by the flexible member, and the cavity is adapted to improve the mobility of the target member.

[0022] The advantages of the embodiments of the present invention are that high sensitivity can be obtained. A further advantage is that the stable life of the sensor can be increased.

[0023] In certain embodiments, it may be advantageous to provide a vent for fluidly connecting the cavity of the flexible member with the exterior of the force sensor.

[0024] An advantage of embodiments of the present invention is that the mobility of the target is not hindered by the pressure differential, thereby improving mobility and reducing response time.

[0025] Providing a cavity may include providing an open cavity, wherein the attachment surface includes an opening to the attachment surface. The flexible member may have a bell shape. An advantage of embodiments of the present invention is that a force sensor with high sensitivity can be provided while providing protection for the chip by reducing pressure on the chip surface.

[0026] In one aspect, the present invention provides a force sensor comprising a flexible member that holds a target member. The flexible member has an attachment surface that is away from the target member. The force sensor also includes a semiconductor package that includes at least one sensing element for sensing a magnetic field generated by the target member. The package also includes a receiving surface. The flexible member is attached to the semiconductor package on the attachment surface, and the attachment surface is contained in and attached to the receiving surface. The flexible member includes a cavity positioned between the target member and the semiconductor package. An advantage of an embodiment of the present invention is that the force sensor is highly sensitive and flexible without sacrificing protection of electronic devices.

[0027] In one aspect, the present invention provides a force sensor comprising a flexible member holding a target member. The flexible member has an attachment surface away from the target member. The force sensor further comprises a substrate comprising a receiving surface and a sensing element for sensing a magnetic field generated by the target member. The flexible member is attached to the substrate by an adhesive layer in contact with the attachment surface, and the flexible member and the substrate have a chemical bond provided by activation of the attachment surface. This improves the adhesion of the flexible member to the adhesive layer.

[0028] An advantage of embodiments of the present invention is that the force sensor is reliable and sensitive even for high contact and shear forces.

[0029] In some embodiments, the flexible member having an activated surface further includes a cavity positioned between the target member and the semiconductor package of the force sensor.

[0030] An advantage of embodiments of the present invention is that a highly sensitive force sensor can be obtained even for high contact and shear forces.

[0031] In embodiments including a cavity, the flexible member may further include a vent hole for providing fluid contact between the cavity and the exterior of the force sensor.

[0032] An advantage of embodiments of the present invention is that the mobility of the target is not hindered by the pressure differential, thereby improving mobility and reducing response time.

[0033] Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims where appropriate and not merely as explicitly set out in a claim.

[0034] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A side view of a force sensor according to an embodiment of the present invention is shown, along with exemplary contact forces that may be applied at the force sensor.

[0036] Figure 2 An exploded cross section of a force sensor according to an embodiment of the present invention is shown.

[0037] Figure 3 The steps of the manufacturing method according to the embodiment of the present invention are schematically shown.

[0038] Figure 4 A side view of a force sensor according to an embodiment of the present invention is shown.

[0039] Figure 5 A perspective view of a cavity showing two flexures used in a force sensor according to an embodiment of the present invention.

[0040] Figure 6 Results of shear testing with shear forces up to 1 Kg are shown for flexures with epoxy attached and without surface plasma treatment, and flexures with silicone attached and without surface plasma treatment.

[0041] Figure 7 A cross section of a flexible piece including a cavity is shown. Different locations of vent holes are shown in the piece.

[0042] Figure 8 The force sensor is shown in three stages, at rest on the left and subject to increasing compressive forces in the center and on the right.

[0043] These drawings are only schematic and non-limiting.In the drawings, the size of some of the elements may be exaggerated and not drawn to scale for illustrative purposes.

[0044] Any reference signs in the claims should not be construed as limiting the scope.

[0045] The same reference numbers in different drawings refer to the same or similar elements. DETAILED DESCRIPTION

[0046] The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims.The dimensions and relative dimensions do not correspond to actual reductions to practice of the invention.

[0047] Furthermore, the terms first, second, etc. in the specification and in the claims are used to distinguish between similar elements and not necessarily to describe a sequence in time, space, in ranking, or in any other manner. It should be understood that the terms so used are interchangeable under appropriate circumstances, and that the embodiments of the invention described herein are capable of operation in a sequence different from that described or illustrated herein.

[0048] Furthermore, the terms top, bottom, etc. in the specification and claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in orientations other than those described or illustrated herein.

[0049] It should be noted that the term "comprising" used in the claims should not be interpreted as being limited to the means listed thereafter; it does not exclude other elements or steps. Thus, the term should be interpreted as specifying the presence of the stated features, integers, steps or components as mentioned, but does not exclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Therefore, the term "comprising" covers the case where only the stated features are present as well as the case where these features and one or more other features are present. Thus, the scope of the expression "a device comprising means A and B" should not be interpreted as being limited to a device consisting only of components A and B. This means that for the present invention, the only relevant components in the device are A and B.

[0050] References throughout this specification to "one embodiment" or "an embodiment" mean that a particular feature, structure, or characteristic described in conjunction with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases "in one embodiment" or "in various embodiments" in various places throughout this specification do not necessarily all refer to the same embodiment, but may refer to different embodiments. Furthermore, in one or more embodiments, the particular features, structures, or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure.

[0051] Similarly, it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. However, this method of disclosure should not be interpreted as reflecting an intention that the claimed invention requires more features than those expressly recited in each claim. On the contrary, as reflected in the appended claims, the inventive aspects lie in fewer features than all of the features of a single preceding disclosed embodiment. Thus, the claims appended to the Detailed Description are hereby expressly incorporated into the Detailed Description, with each claim itself representing a separate embodiment of the invention.

[0052] In addition, although some embodiments described herein include some features included in other embodiments but do not include other features included in other embodiments, as will be understood by those skilled in the art, the combination of features of different embodiments is intended to fall within the scope of the present invention and form different embodiments. For example, in the appended claims, any of the claimed embodiments may be used in any combination.

[0053] In the description provided herein, numerous specific details are set forth. However, it should be understood that embodiments of the present invention may be practiced without these specific details. In other instances, well-known methods, structures, and techniques are not shown in detail to avoid obscuring the understanding of this specification.

[0054] In the embodiments of the present invention, when a “target part” or simply “target” is mentioned, it refers to a formed material object, the position change of which is sensed by the sensing element.

[0055] When referring to a "flexible member" in embodiments of the present invention, it is meant a shaped material object having flexible properties, for example, it may be compressible, and preferably elastic, so that it will return to its original shape in the absence of force. The application of force on the flexible member provides displacement, especially compression, of the material matrix forming the member. In some embodiments, the term "elastomer" will be used, but the present invention is not limited to objects made of elastic polymers.

[0056] A class of force sensors includes a force sensor having one or more sensing elements that detects a position displacement of a target member when a force is applied to the sensor. The present invention relates to a force sensor including one or more non-contact sensing elements, wherein the one or more sensing elements are configured to detect the position of a target member and / or the displacement of a target member without physical contact with the target member. More specifically, the force sensor of the present invention is configured to detect mechanical forces, particularly contact forces applied to a flexible member of an integrated target.

[0057] Sensing can be based on electromagnetic sensing. For example, it can be based on the detection of a magnetic field or electromagnetic field as a function of the position of the target. In some embodiments, sensing is based on changes in a magnetic field (or electromagnetic field) caused by the movement of the target. The target can generate a magnetic field, for example, the target can be a magnet or can be a conductor in which a magnetic field can be induced. The sensing element can sense the position or change of the position according to the nature of the field. The sensing element generates a signal, which is processed to obtain a readable output representing the applied force. The target and the sensing element can be appropriately selected and combined to generate or induce an electromagnetic field, the change of which is caused by the movement of the target, and the detection of the electromagnetic field by the sensing element can be related to the displacement of the target. For example, a magnetic sensing element (such as a Hall sensor) can be combined with a magnet as a target. The chip can be configured to generate a signal representing the force causing the displacement of the target. For example, the chip can include a processing device (e.g., an integrated circuit on a semiconductor substrate) configured to apply a nonlinear model, thereby allowing the force to be directly derived. Alternatively, it can calculate the position of the target to obtain the force causing the displacement of the target.

[0058] The movement of the target due to contact is provided by an elastic or flexible member supporting the target. Upon contact, the flexible member deforms according to the contact force. The target, which is a part of the flexible member, also moves.

[0059] Since the relative position of the sensing element and the target is important, reliable attachment is required between the components forming the sensor, in particular the component comprising the sensing element and the target comprised in the flexure.

[0060] The present invention provides an improved force sensor having an improved attachment between a flexible member including a target and a substrate including a sensing element, so that the force sensor exhibits high elasticity to a wide range of applied contact forces (compression or shear forces). In some embodiments, the flexible member is directly attached to a semiconductor package, which includes (one or more) sensing elements with improved attachment. In these embodiments, the flexible member is formed to fit a smaller area of ​​the semiconductor package (chip). By integrating the elastomer and the target directly onto the package and also keeping it within the package outline boundary, significant advantages are provided in terms of compactness and integration with a claw or robot hand, etc. However, the present invention is not limited to this, and the attachment can be completed on a substrate including a chip (e.g., including a connection to the chip). The substrate can be a printed circuit board (PCB).

[0061] In some embodiments, the manufacturing of the flexure includes activation of the attachment surface, which improves the adhesion of the flexure to the chip. The flexure may also include features that improve force sensitivity by improving the deformation and elastic response of the flexure to applied forces.

[0062] Force sensors and aspects of their manufacture such as Figure 1 and Figure 2 as shown in . Figure 1A lateral view of a force sensor according to an embodiment of the present invention is shown. The force sensor includes a flexible member 200 and a substrate 12 including at least one sensing element. The substrate includes a sensing element that can sense a force 500 applied to the flexible member. The sensing element can sense a vertical force (a compression component 501 toward the sensing element) and can additionally sense any shear component 502 of the force perpendicular to the compression component. The flexible member 200 and the substrate 12 are connected by an adhesive layer 300. The adhesive layer extends through one side of the flexible member 200. This side is referred to as the "attachment surface". The adhesive layer covers the so-called receiving surface 11 of the substrate 12. The force sensor in an embodiment of the present invention includes a flexible member having a feature of increasing reliability over time. As further explained below, in some embodiments, the flexible member includes a cavity that reduces the displacement perpendicular to the compression direction relative to the displacement of the flexible member in the compression direction, thereby reducing the strain of the flexible material and improving reliability over time. In some embodiments, the attachment surface of the flexible member 200 is activated. Activation improves chemical bonding with the adhesive layer 300. The substrate includes one or more sensing elements and electronics that can process the signals of the (one or more) sensing elements, and the sensing elements are aligned with the target (not shown) of the flexible member so that the (one or more) sensing elements can sense the field from the target. For example, substrate 12 can be a PCB that includes connections to sensors integrated in the chip for sensing electromagnetic fields and / or changes in electromagnetic fields caused by the target and / or the movement of the target. The substrate can be selected to have a high affinity with the material of the adhesive layer. In some embodiments, the substrate includes fiberglass-epoxy resin.

[0063] Figure 2 A cross section of a force sensor 10 according to some embodiments is shown in an exploded view. A semiconductor package (or chip 100 for short) is located at the bottom. For example, it includes an integrated circuit implemented in a semiconductor die 102. The semiconductor die 102 can be protected from external influences by a packaging material 110 (such as an overmolding material, for example epoxy resin, etc.). The chip 100 further integrates a sensing element 103. As is well known, the signal generated by the sensing element and processed by the circuit can be sent to a readout via a pin 101. The pin 101 can be connected to a substrate (not shown).

[0064] As mentioned above, the force sensor 10 further comprises a flexible member 200 in which a target member 201 is provided. The target member 201 may be a magnet. The sensing element 103 is sensitive to an (electro) magnetic field from the target member 201, for example, to a magnetic field generated by the target. The translation of the target may be measured by the sensing element, for example, a movement towards the sensing element due to a compressive force applied to the flexible member. The sensing element 103 may be a magnetic field sensor such as a Hall sensor.

[0065] Where reference is made to a compressive force in embodiments of the present invention, reference is made to a force applied between the target and the sensing element in the Z direction. Where reference is made to a shear force in embodiments of the present invention, reference is made to a force applied perpendicular to the direction of the compressive force (thus, at least a force perpendicular to the X direction and / or Y direction of the normal to the contact surface, e.g., perpendicular to the Z direction of the compressive force). In the following, the plane containing the direction perpendicular to the compressive force will be referred to as the "XY plane". The force applied to the sensor may have a compressive component and a shear component.

[0066] In some embodiments, the sensor may ultimately also measure torsion, measuring not only the translation of the magnet in a straight vertical direction in space, but also the rotation of the magnet (e.g. defined by two angles). This may be implemented, for example, with a 3D sensor, such as a 3D Hall sensor made of a combination of horizontal Hall elements (sensitive to movement in a direction perpendicular to the IC) and vertical Hall elements (sensitive to movement in a direction parallel to the IC). In some embodiments, the implementation may provide a 3D sensor made of horizontal Hall elements and magnetic concentrators, each magnetic concentrator being configured to concentrate components of the magnetic field in different directions, respectively. In some embodiments, magnetoresistive elements such as AMR, or GMR, or TMR may be used.

[0067] In those embodiments where a flex is attached to chip 100 , the flex should be fabricated such that the footprint of the flex fits the area of ​​chip 100 .

[0068] The flexible member 200 may include a cavity 206 to distance the target member 201 from the sensing element. The flexible member includes an attachment surface 202. If the flexible member has a cavity opening at the attachment surface, the surface in this embodiment is shaped as a ring. Figure 2 Only a cross section of the attachment surface is shown in FIG. The flexible member may have any other suitable shape, so the attachment surface 202 may be a square ring defined by a square nested within another square (e.g., two concentric squares); for example, the inner and outer boundaries may have different shapes, such as a circle and a square, or a square and a circle, depending on factors such as the available space. The flexible member 200 is attached to the chip 100 by an adhesive layer 300 on a suitable receiving surface 111 of the chip 100 (e.g., a surface close to the (one or more) sensing elements 103). The encapsulation material 110 may be part of an outer surface of the encapsulation material 110 (e.g., an outer surface of a chip housing).

[0069] The adhesive layer of the force sensor holds the flexible part and the chip together. This type of force sensor can be attached to the area where the force needs to be measured. In fields such as robotics, accurate force measurement can be beneficial for controlling the applied force, such as the grasping force of a robot claw. The robot grasps objects with the support of computer-assisted visual feedback. In order to achieve human-like dexterity, the robot hand or claw needs to include tactile sensors. These sensors need to be small and able to detect forces within a range that is sensitive enough for the desired application. The present invention provides a force sensor for sensing the contact of a robot hand or claw with an object to be handled. The force sensor as described above can be used not only to measure compression forces, but also to measure shear forces.

[0070] A general problem in force sensors is that reliability decreases when subjected to strong forces. In particular, shear forces are the main cause of reliability problems associated with objects coming loose or even the flexure coming out of the receiving area. In the case of the invention where the receiving area is at least as small as the footprint of the chip, this problem is considerable, since a smaller attachment area means a smaller amount of adhesive and thus a much greater probability of separation with increasing forces, especially shear forces. Furthermore, since the flexure should be smaller to fit the chip, the measurement is also less sensitive, since the displacement allowed by the amount of elastic material is lower.

[0071] In one aspect, the invention is directed to a method of making a force sensor. Figure 3 The method is generally summarized in the schematic diagram of FIG. The method includes providing S10 a flexible member including a target member, providing S20 a substrate having a sensing element and a receiving substrate, and attaching S30 the flexible member to a receiving surface of the substrate. In some embodiments, the substrate is a semiconductor package or chip that integrates one or more sensing elements and circuits for processing sensing signals.

[0072] The manufacturing method includes providing S10 a flexure to increase reliability even under high forces. In some embodiments, the flexure is provided S10 with a shape and size such that the attachment surface 202 fits the surface area on the chip, particularly the largest outer surface area of ​​the chip.

[0073] In particular, the flexible piece can advantageously be provided as a single piece, for example to embed the target. It can include providing an elastomer, such as silicone, rubber, etc. In particular, the piece can be provided S11 by injection molding. In this way, the piece will not include a joint between the flexible material, but will be uniform, so there are fewer "weak" points that are easy to tear. This is not the only possibility, the flexible piece can be manufactured by assembling multiple parts. In some embodiments, the flexible piece can be provided by additive manufacturing (e.g. 3D printing).

[0074] In some embodiments, a flexible member and a target member are provided separately, and the target member is introduced into the flexible member. For example, the flexible member can be formed to include an opening for introducing the target. In a preferred embodiment, the S11 flexible member is formed around the target (e.g., by injection molding), wherein the injected material is in direct contact with the target member (e.g., the magnet is overmolded with the material of the flexible member).

[0075] The distance between the target and the sensing element in a static position (no force applied) must be carefully controlled for calibration. Consideration needs to be given to the strength of the coupling between the target and the sensing element, the need for a reasonably compact device and the level of force to be applied, as well as reasonable protection of the electronics. In some embodiments of the present invention, providing a flexure includes forming an S12 cavity that is used to keep the target at a distance from the attachment surface (and once assembled, from the sensing element).

[0076] Figure 4 A side view of force sensor 10 is shown. Here, flexure 200 is a transparent truncated dome with a flat surface for receiving force, and flexure 200 exposes target 201 and cavity 206 that improves deformation of the flexure. By forming an S12 cavity, the flexure provides higher deformation for smaller contact forces (thereby allowing the target size to be reduced because the sensitivity is less limited by the field strength, while still providing protection for the underlying electronics, such as from impact forces. This improves protection of the electronics without sacrificing sensitivity.

[0077] In an embodiment of the method comprising forming an S12 cavity, the method may include further forming an S13 vent 207 for fluidly connecting the cavity 206 of the flexible member 200 to the exterior of the force sensor 10. It may be formed wide enough to allow the ventilation required to deform the cavity 206 while the force is applied. This reduces the pressure in the cavity when the deforming force is applied to the flexible member. An advantage of embodiments of the present invention is that the mobility of the target is not hindered by the pressure difference, thereby improving mobility and reducing response time. The manufacture of a flexible member with a vent by injection molding may be accomplished by introducing a molded component having the desired shape. In a particularly advantageous embodiment, the molded component that forms the vent 207 is simultaneously used to hold the target member 201, for example during molding. In Figure 4 In the embodiment, the vent 207 has a "chimney" shape, in the area opposite to the attachment surface, the cavity is fluidly connected to the outside via the top of the flexible piece. The vent can be formed by two elongated pieces, which are shaped so that they can hold the target, so the target does not need to be stationary on the top of the mold piece that shapes the cavity, for example. This allows the space between the target and the cavity to be filled with elastomer as well. Once the flexible piece is formed, the elongated pieces can be removed from the top and bottom, so that the vent is formed and the target is released to the interior of the flexible material.

[0078] In some embodiments, providing a flexible member includes manufacturing a structure for holding a target. The one or more structures may include a beam extending between the inner walls of the cavity. Figure 5 Exemplary retaining structures 203, 213 are shown in perspective views of different flexible members 200, 210. In the case of injection molding, components of the mold may support the object before the molding compound that forms the flexible member is injected. The space between these components forms the retaining structures 203, 213. Figure 5 As shown in the right side flexible member 210 of FIG. 2 , other structures such as reinforcement protrusions 204 may be included during manufacturing.

[0079] In some embodiments, an open cavity is formed on the flexible member, the opening being arranged to face the sensing element, such as an opening in the attachment surface.The flexible member has a hollow shape, such as similar to a bell or cowbell. Figure 4 or Figure 5 Such open cavities 206, 206 are shown in bell-shaped flexible members 200, 210. Although the attachment surface 202 is severely reduced, this disadvantage is overcome by the advantage of being able to easily form the member (e.g. by injection molding, which is fast, reliable and provides high quality members, as explained above).

[0080] However, the present invention is not limited thereto. The cavity may be formed with a wall enclosing the cavity on the inside and an attachment surface on the outside. In other words, there is no opening to the cavity through the attachment surface. In this way, the area of ​​the attachment surface can be increased. Such a cavity without an opening at the attachment surface can be formed by assembling separate parts, or by additive manufacturing as described above, or in other ways.

[0081] The method further includes attaching S30 the flexible member on the substrate. Semiconductor package or chip. In some embodiments, the method includes providing an adhesive and using the adhesive to attach the flexible member to the outer surface of the package of the chip 100, such as on the packaging material 110, such as on the epoxy resin shell protecting the sensing element and / or the integrated circuit. The flexible member is positioned so that the portion of the flexible member containing the target is away from the sensing element of the chip. In an embodiment of the present invention in which the flexible member includes a cavity, the flexible member is attached to the chip so that the cavity remains between the chip and the target.

[0082] The adhesive may be any suitable adhesive for chip packaging, for example, the adhesive may include silicone resin, epoxy resin, etc. Figure 4An adhesive layer 300 is shown sandwiched between a flexible member 200 and a semiconductor package 100 (e.g., a chip). The adhesive layer 300 can, for example, be applied to the attachment surface 202 of the flexible member, and the flexible member with the adhesive layer can then be fixed to the semiconductor package on the receiving surface of the semiconductor package. In other embodiments, the adhesive is applied to the receiving surface 111 of the chip 100, and the flexible member is placed in contact with the adhesive. For example, a layer of glue is placed on the receiving surface of the chip 100, and the flexible member is placed on the glue. If the flexible member includes a cavity opening on the attachment surface, this can preferably minimize the amount of adhesive inside the cavity (and in particular, extending along (one or more) cavity walls).

[0083] The presence of the cavity improves the life of the flexible part, as will be explained below, this is due to the reduction of deformation in the direction perpendicular to the compression direction, so it is possible to simply attach the part to the substrate. In a preferred embodiment, before the flexible part is attached S30 on the substrate, the method includes activating S31 the attachment surface 202 of the flexible part 200 before the adhesive of the contact adhesive layer 300. Activation can be completed by applying a treatment that increases the hydrophilicity of the surface, thereby improving adhesion. In some embodiments, activation is completed by exposing the surface to high-energy ionic charges. In some embodiments, activation is completed by applying plasma treatment. Utilizing activation means that (for example, in the case of elastomers, by forming carboxyl groups and / or destroying surface bonds) the surface becomes more hydrophilic. It is worth noting that plasma treatment (parameters, energy, etc.) is suitable for surface activation, not just surface cleaning. Plasma can be generated in, for example, the open air using a plasma torch. Alternatively, plasma can be generated under a controlled environment (for example, in a processing chamber), in a controlled atmosphere (for example, at atmospheric pressure), or at a lower pressure (for example, between 0.1mBar and 10mBar).

[0084] Multiple pieces can be processed simultaneously. For example, a processing chamber (such as an enclosed chamber with a controlled environment) can be used to process multiple flexible pieces. In some embodiments, a pick and place machine can be configured to pick up a flexible piece and contact the flexible piece with a plasma (e.g., generated by a plasma torch) and then assemble the device by placing the flexible piece where needed.

[0085] The plasma can be generated (even in the chamber) using ambient air as input gas or using any suitable gas (e.g. Ar, O2, N2). The plasma can be a DC plasma, an AC plasma or an RF plasma. The generator can have a power between 100 W and several kW, such as 300 W or 500 W, and a frequency between 10 kHz or 200 kHz, such as 20 kHz or 100 kHz. The duration of the plasma activation can be a few tens of seconds, such as 50 s, but it can also be very likely much smaller, such as a few seconds. Any suitable process conditions can be used as long as surface activation is achieved.

[0086] The present invention is not limited to plasma treatments, and other methods of surface activation may be performed, such as other physical and / or chemical methods capable of treating a surface to make it more hydrophilic.

[0087] In some embodiments of the present invention, the attachment surface 202 of the flexible member, once activated, is contacted with the adhesive before hydrophobic recovery occurs, so that the surface 202 is still hydrophilic when contacting the adhesive layer 300. For example, contact with the adhesive can be completed immediately after treating the surface, such as within an hour, such as during sequential assembly.

[0088] Figure 6 A graph showing shear test results for four variations using different processes and materials is shown, where the shear tests were performed on a flexure attached to a die, such as in Figure 4 For example, as shown in the force sensor 10. The first chart 401 shows the results of a flexible part attached to a chip with epoxy resin 3609, wherein the flexible part was not plasma treated. The shear strength (in kg) reached about 0.25 and the adhesive failed. The third chart 403 shows the results of a flexible part attached to a chip with silicone resin 7503, wherein the flexible part was not plasma treated. The shear strength was lower than 0.75 and the adhesive failed. The second chart 402 and the fourth chart 404 show the results of epoxy resin 3609 and silicone resin 7503, respectively, with shear strength exceeding 1 kg and no adhesive failure. In these cases, a plasma treatment is applied to the attachment surface before contacting the attachment surface with the adhesive.

[0089] The manufacturing process can be done in a simple way within the framework of passive alignment. For example, the manufacturing process can be automated with simple tools such as a "pick and place" machine. It can be with or without computer vision. The machine can pick up the flexure and align it in the XY plane. Alignment enables planar placement in the XY plane with an accuracy of about 100 microns. Passive alignment does not require the placement of the flexure while reading the sensing element to optimize positioning. It has been surprisingly found that the present invention provides a sensor for which passive alignment is sufficient, without the need for active alignment.

[0090] Thereafter, the pins 101 of the chip can be connected to a board such as a PCB, etc., for powering the force sensor and providing a signal output. The force is applied directly to the flexible member. Alternatively, the chip can be connected to a substrate or board, and the flexible member can be subsequently attached to the substrate or board after activation of the attachment surface.

[0091] In one aspect, the present invention provides a force sensor with improved sensitivity and reliability. The force sensor includes a flexible member attached to a receiving surface of a substrate (e.g., a chip), wherein the attachment surface of the flexible member does not extend beyond the chip. The flexible member includes a cavity, so the flexible member exhibits high flexibility and is highly sensitive to the applied force. In some embodiments, it can be highly sensitive to a wide range of values ​​of the applied force. The sensor is less susceptible to breaking due to applied shear forces.

[0092] Figure 4 A cross section of a force sensor according to an embodiment of the present invention is shown. It comprises a flexible member 200, which is attached to a chip 100 by an adhesive layer 300 between one of the surfaces of the flexible member 200 (the so-called attachment surface 202) and a receiving surface 111 of the chip 100. The flexible member 200 comprises a target member 201. The flexible member may be cylindrical or conical, or may have a dome shape. These are only examples, and other designs may be customized according to specific applications.

[0093] The cavity 206 between the chip 100 and the target part 201 provides a customized spacing between the target part 201 and the sensing element 103. In some embodiments, the cavity 206 can be open at the attachment surface 202, so that the cavity is open to the receiving surface 111 of the chip 100. Although the presence of the cavity opening at the attachment surface 202 does reduce the attachment area, it is easy to manufacture (e.g., by injection molding) while still providing a high range of deformation (for both compression and shear forces), thereby improving sensitivity on a compact elastomeric piece.

[0094] The force sensor according to the embodiment of the present invention shows less degradation over time. Surprisingly, due to the presence of the cavity, the flexible member shows very limited deformation in the horizontal direction (the direction perpendicular to the compression direction). The elongation in the horizontal direction is less than the elongation in the vertical direction, resulting in less strain in the material and therefore less damage. Repeatability improves over time, so the durability of the force sensor is also improved.

[0095] In some embodiments, the flexible member includes a support beam or generally a retaining structure 203 that prevents the target member 201 from falling into the cavity 206 . Figure 5 The flexible member 200 on the left shows that the retaining structure 203 can extend horizontally from the inner wall of the cavity 206. In some embodiments, as Figure 5 As shown in the flexible member 210 on the right side of the embodiment, a combination of a reinforcing structure 204 and a retaining structure 213 may be provided. The reinforcing structure may be a rib along the vertical direction. For example, in the inner wall of the cavity 216, the structure 204 includes chamfers extending vertically along the wall and also horizontally, thus increasing resistance to compression when needed.

[0096] The flexible member may further include at least one vent hole 207, 217 (e.g. Figure 4 As shown in Figure 5 The vent 207 is shown in the flexible member 210 on the right side. It ensures that the pressure in the cavity is released when force is applied. If air is retained in the cavity when force is applied on the flexible member, deformation (due to compression or shear) will be more difficult. The vent 207 advantageously improves the sensitivity and response time (detection speed) even for 3D forces (compression and shear). It also protects the flexible member from damage or detachment if the applied force is very large. The vent 207 can pass from the inner wall of the cavity to the side or outer wall of the flexible member away from the chip, such as Figure 4 as shown in .

[0097] Figure 7 A cross section of an alternative embodiment of a flexible member 220 is shown, wherein the vent 208 is close to the attachment surface, for example, closer to the attachment surface than the surface of the flexible member for receiving force in, for example, the lower half of the flexible member (considering that half is half the height). The figure also shows an alternative in the same figure, wherein the vent is a groove 209 passing through the attachment surface, between the outer wall of the flexible member and the cavity. In this case, when the attachment surface is in contact with the adhesive layer, the groove should remain free of adhesive so that the vent is not blocked. Although both vents 208 and 209 are shown in the same figure, the flexible member can have a limited number of vents, such as only one vent, to maintain structural integrity.

[0098] In one aspect, the present invention provides a force sensor comprising a flexible member attached to a substrate via an adhesive layer. The attachment surface of the flexible member is treated and activated to improve the attachment to the adhesive layer. The force sensor can be formed by the method of the present invention. Thus, the force sensor can include, for example, cavities, vents, etc.; the substrate can be a PCB with a chip including a sensing element and processing electronics included in the chip; however, the substrate can be a package for the chip. Compared to the rest of the flexible member (again in Figure 4 The attachment surface 202 of the flexible member 200 may show an increase in carbonyl functional groups and a decrease in organic bonds. The open organic bonds of the material in the flexible member react with the adhesive material to form chemical bonds between the flexible material of the attachment surface 202 and the adhesive layer 300, thereby improving adhesion.

[0099] Figure 8 A force sensor in use is shown. The force sensor is configured to receive a (compressive) force 500, which is measured on an area of ​​the flexible member 200 away from the chip 100, for example on the tip of the dome-shaped flexible member 200. The flexible member deforms and the target inside changes position, as shown in the schematic diagram, from the left side where no force is applied to the center and right side where the force 500 is applied. The sensing element detects this change in position and generates a signal, which is processed into a signal representing the applied force. The force sensor can also be adapted to measure forces in different directions, for example, the force sensor can measure shear force or the component of force in the shear direction. The figure also shows that due to the cavity, the deformation in the horizontal direction is limited, smaller than the deformation in the vertical direction, and as mentioned above, the strain of the material is much smaller. The deformation of the elastomer in the horizontal direction dx_elastomer (dx_elastomer) can be measured and compared with the displacement dz_magnet (dz_magnet) of the magnet in the vertical direction (compression direction). The ratio of deformation (dx_elastomer) to displacement (dz_magnet) may be between 10% and 50%, such as between 20% and 40%, such as between 25% and 30%.

[0100] Sensing and processing are completed by the sensing element and the integrated circuit connected thereto, respectively. Both can be provided in the chip. In some embodiments, the force sensor is compact, wherein the attachment surface of the flexible member is confined to the area of ​​the surface of the chip, particularly on the outer surface of the chip mold or housing. The force sensor can be connected to a PCB or substrate on the grasping portion of the robot hand, thereby allowing accurate measurement of the forces in the compression force and the shear force. The shear component of the force can be generated, for example, under the action of gravity when lifting the object grasped by the robot hand. The durability of the force sensor is improved by improved adhesion, the presence of a cavity in the flexible member, or both. In some embodiments, the detachment of the flexible member is reduced or even prevented by the improved adhesion of the flexible member caused by the activation of the attachment surface of the flexible member.

Claims

1. A method for manufacturing a force sensor (10), comprising: - providing (S10) a flexible member (200) comprising an attachment surface (202) and also comprising a target member (201), - providing (S20) a substrate (12, 100) comprising a receiving surface (11, 111) for attaching the flexible member (200), the substrate (12, 100) further comprising a sensing element (103) configured to sense changes in a magnetic field generated by movement of the target member (201), - attaching (S30) the attachment surface of the flexible member to the receiving surface (11, 111) by providing (S31) surface activation on the attachment surface of the flexible member, and providing the adhesive layer in contact with at least the attachment surface by sandwiching the adhesive layer between the receiving surface (11, 111) and the attachment surface (202).

2. The method according to the preceding claim, characterized in that Providing the substrate includes providing a semiconductor package (100), wherein the sensing element is an integrated circuit included in the semiconductor package (100) to form a chip, and wherein attaching the attachment surface includes attaching the attachment surface of the flexible member to the receiving surface (111) of the semiconductor package (100).

3. The method according to any one of the preceding claims, characterized in that Providing (S31) surface activation includes providing plasma treatment.

4. The method according to any one of the preceding claims, characterized in that Providing ( S10 ) the flexible member includes forming ( S11 ) the flexible member as a single piece by injection molding.

5. The method according to any one of the preceding claims, characterized in that Providing the flexible member includes providing the target member and encapsulating the target member in the flexible member.

6. The method according to any one of the preceding claims, characterized in that Providing a substrate including a sensing element includes providing a sensing element adapted to sense magnetic fields in at least two different directions.

7. The method according to any one of the preceding claims, characterized in that Providing ( S10 ) the flexible member includes providing ( S12 ) a cavity at least partially enclosed by the flexible member, the cavity being suitable for improving the mobility of the target member.

8. The method according to the preceding claim, further comprising providing (S13) a vent hole (207, 208, 209) for fluidly connecting the cavity of the flexible member with the exterior of the force sensor.

9. The method according to claim 7 or claim 8, characterized in that: Providing the flexible member includes providing an open cavity, wherein the attachment surface includes an opening to the attachment surface.

10. A force sensor, comprising: A flexible member (200) for holding a target member (201), the flexible member (200) having an attachment surface (202) away from the target member (201); and a semiconductor package (100), the semiconductor package (100) comprising a receiving surface (111) and a sensing element (103) for sensing a magnetic field generated by the target member, the flexible member (200) being attached to the semiconductor package (100), wherein the attachment surface (202) is included in the receiving surface (111) and attached to the receiving surface (111), wherein the flexible member (200) comprises a cavity (206) positioned between the target member (201) and the semiconductor package (100).

11. A force sensor, comprising a flexible member (200) for holding a target member (201), the flexible member (200) having an attachment surface (202) away from the target member (201), the force sensor further comprising a substrate (12, 100), the substrate (12, 100) comprising a receiving surface (111) and a sensing element (103) for sensing a magnetic field generated by the target member, the flexible member (200) being attached to the substrate (12, 100) via an adhesive layer (300) in contact with the attachment surface (202), and having a chemical bond with the adhesive layer (300) through activation of the attachment surface (202) to improve adhesion between the flexible member (200) and the adhesive layer (300).

12. The force sensor of claim 11, further comprising a cavity (206) positioned between the target (201) and the semiconductor package (100).

13. The force sensor according to claim 10 or claim 12, characterized in that: The flexible member (200) further comprises vent holes (207, 208, 209), wherein the vent holes (207, 208, 209) are used to provide the cavity with fluid contact with the outside of the force sensor.

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