Sliding method for detaching thin electronic devices from adhesive tape

Abstract

An electronic device to be removed from the tape is positioned above a pedestal protrusion mounted on the ejector assembly along a first axis. The pedestal protrusion has a relatively fixed position on the ejector assembly along a second axis, which is perpendicular to the first axis. First, the pedestal protrusion pushes against the electronic device adjacent a first edge of the electronic device to lift the first edge of the electronic device off the tape. Then, while the electronic device is being lifted by the pedestal protrusion, the electronic device and the ejector assembly are caused to slide relative to each other along the second axis until the pedestal protrusion is pushing against the electronic device adjacent a second edge of the electronic device, which is opposite the first edge. The electronic device holder then removes the electronic device from the tape.

Description

Technical Field

[0001] This invention relates to the removal of electronic devices, such as semiconductor dies or chips, from tape on which the electronic devices have already been mounted. Background Technology

[0002] During the die bonding process, semiconductor dies are typically removed from a tape on which a wafer, consisting of multiple singlet semiconductor dies, is already mounted. Each die is then picked up sequentially by a die pick-up tool on a die bonding machine and bonded to a substrate using the same tool.

[0003] During the die pickup step, the die can be held in place by the vacuum suction generated at the opening of the chuck of the die pickup tool. Before lifting the die from the tape using the die pickup tool, a die ejector can be used to push upwards against the bottom surface of the tape on which the die is already attached to lift the die. Lifting the die helps it delaminate from the tape. Successful delamination of the die from the tape is crucial to the success of the die pickup process.

[0004] With technological advancements, die thickness is continuously decreasing to meet the requirements of high-density electronic packaging. Currently, very small (e.g., die size less than 10 mm) and thin (e.g., thickness from 20 μm to 50 μm) semiconductor dies are used in a variety of products. Due to bending forces and other delamination forces that can cause die breakage or failure, removing semiconductor dies from the adhesive film without damaging them is becoming increasingly challenging.

[0005] In the prior art, the primary method for delamination of semiconductor dies utilizes a die ejector assembly comprising multiple pins or plates. An example of a die ejector assembly comprising multiple pins can be found in U.S. Patent No. 6,386,815, entitled "Pick-up apparatus for semiconductor chips." This die ejector assembly has one or more ejector pins mounted on a pin holder having one or more platforms.

[0006] Because the localized stress generated at each contact area between the die and the tip of each pin can be high, multi-pin ejector assemblies can damage the die being delaminated. Pin marks caused by such localized stress should also be avoided. In particular, when the die thickness is less than, for example, 3 mils, the induced bending moment and strain on the die surface will increase accordingly as the die becomes thinner.

[0007] On the other hand, a die ejector assembly comprising multiple plates has been described in U.S. Patent No. 8,141,612, entitled "Device for Thin Die Detachment and Pick-Up." Instead of deployment pins, this die ejector assembly has multiple movable plates having quadrilateral contact surfaces arranged adjacent to each other. The contact surfaces of the movable plates together form a combined contact surface for supporting the adhesive film at the die location. Each movable plate is movable relative to the other movable plates away from the die to induce die delamination at a location above the movable plate.

[0008] While using multiple movable plates reduces the risk of damage compared to using multiple pins, there are some drawbacks to using such an ejector assembly that includes multiple plates. One drawback is that the thickness of each movable plate is limited by its material properties and processing capacity. For example, when the die size is less than 5mm, there is not enough space in the die's surface area to accommodate several plates. Another reason is that if the plates are too thin, the wear caused to the plates will affect their lifespan. Finally, the precise movement of the plates is less reliable due to the relatively high friction between adjacent movable plates.

[0009] It may be beneficial to provide a method for disassembling a semiconductor die that avoids at least some of the aforementioned disadvantages of the prior art. Summary of the Invention

[0010] Therefore, the object of the present invention is to provide a method for effectively delaminating small and thin dies while significantly reducing the risk of damage during the delamination process.

[0011] Therefore, the present invention provides a method for removing an electronic device from an adhesive tape on which the electronic device has been mounted, the method comprising the steps of: positioning the electronic device along a first axis on a base protrusion mounted on an ejector assembly, wherein the electronic device has a first edge and a second edge opposite to the first edge, and the base protrusion has a relatively fixed position on the ejector assembly along a second axis perpendicular to the first axis; moving the base protrusion along the first axis to push the base protrusion against the first edge of the electronic device adjacent to the electronic device to lift the first edge of the electronic device away from the tape; sliding the electronic device and the ejector assembly relative to each other along the second axis while lifting the electronic device by the base protrusion until the base protrusion is pushing against the electronic device by the second edge of the electronic device adjacent to the electronic device; contacting the electronic device with an electronic device holder; and removing the electronic device from the tape by the electronic device holder.

[0012] In the following description, for convenience, the invention will be described in more detail with reference to the accompanying drawings, which illustrate specific preferred embodiments of the invention. The particularity of the drawings and related description should not be construed as replacing the generality of the broad approximation of the invention as defined in the claims. Attached Figure Description

[0013] An exemplary die removal method according to the present invention will now be described with reference to the accompanying drawings.

[0014] Figure 1A It is a plan view of the die ejector assembly including the base protrusion, and Figure 1B This is a plan view of the die ejector assembly located behind the semiconductor die matrix to be disassembled.

[0015] Figures 2A to 2C From Figure 1A Side views of different embodiments of the base protrusion viewed from the AA direction.

[0016] Figures 3A to 3C From Figure 1A Side views of different embodiments of the base protrusion viewed from the BB direction.

[0017] Figures 4A to 4I The diagram illustrates the steps involved in separating the semiconductor die from the tape layer.

[0018] Figure 5 This is a flowchart illustrating the steps involved in ensuring die layer separation by adjusting the height of the abutment protrusion when the semiconductor die cannot be picked up from the tape. Detailed Implementation

[0019] Figure 1A This is a plan view of an ejector assembly such as a die ejector assembly 10, which includes a base protrusion 12 centrally positioned relative to an ejector cover 20 of the ejector assembly. The base protrusion 12 typically has a linear profile including a narrow linear stripe. The ejector cover 20 has a rectangular or elliptical opening 21 for exposing the base protrusion 12 from the interior of the housing of the ejector cover 20. The size of the opening 21 is designed according to the size of the base protrusion 12 and the size of the electronic device being disassembled, such as a semiconductor die. Since excessive bending of the die can cause it to break, the opening 21 is preferably small enough to reduce or prevent the risk of the die bending into the opening 21. More preferably, the size of the opening 21 is smaller than the size of the die to prevent the die from being contained within the opening 21.

[0020] Although the base protrusion 12 can extend vertically to protrude from the opening 21, its horizontal position relative to the ejector cover 20 is fixed. This greatly simplifies the assembly of the base protrusion 12 within the ejector cover 20. This is because, especially when disassembling very small dies and when space within the ejector cover 20 is very limited, no additional space is needed within the ejector cover 20 to accommodate a mechanism that allows the base protrusion 12 to move horizontally relative to the die ejector cover 20 within the die ejector assembly 10.

[0021] Figure 1B This is a plan view of a die ejector assembly 10 located behind a matrix of semiconductor dies 15 to be removed from tape 16 on which the semiconductor dies 15 are already mounted. Specifically, a base protrusion 12 is located below a first die 14 to be removed from tape 16. The linear profile of the base protrusion 12 is arranged in use to extend parallel to the width of the first die 14 to be removed, and its dimensions are designed such that the span of the base protrusion 12 is slightly smaller than the width of the first die 14. The span of the linear profile of the base protrusion 12 can also be equal to the width of the first die 14. The narrower width of the linear stripe of the base protrusion 12 is significantly smaller than the width of the first die 14, so that the base protrusion 12 operates to apply a localized force to lift the portion of the first die 14 that the base protrusion 12 is pushing against.

[0022] Figures 2A to 2C From Figure 1A Side views of different embodiments of the base protrusion 12, viewed from the AA direction. The respective base protrusions 12 are shown mounted and arranged on the support 18, and each base protrusion 12 has a specific shape at its top portion for contacting the target die. The dimensions of the top of the base protrusion 12 can also be designed based on the dimensions of the target die.

[0023] exist Figure 2A In the middle, the abutment protrusion 12a always has a uniform rectangular cross-section. Figure 2B In this design, the abutment protrusion 12b has a narrower tip and tapers along its height so that its cross-sectional area gradually increases toward the base of the abutment protrusion 12b. Therefore, the tip portion of the abutment protrusion 12b is narrower than the base of the abutment protrusion 12b. By introducing a wider base, this design helps to improve the stability of the abutment protrusion 12b.

[0024] exist Figure 2C In the design, the abutment protrusion 12c has a pointed tip with a uniform rectangular cross-section. Below the pointed tip, the abutment protrusion 12c begins to widen, and its cross-sectional area gradually increases towards the base of the abutment protrusion 12c. For thinner target dies, the width of the tip of the abutment protrusion may need to be less than 300 μm. Therefore, for even thinner dies, although a narrower width is required at the pointed tip, Figure 2B or Figure 2C The design can still be used to maintain the strength of its tools.

[0025] Figures 3A to 3C From Figure 1A Side views of different embodiments of the base protrusion 12 as viewed from the BB direction. Different shapes of the top of the base protrusion 12 can be selected to meet different device requirements.

[0026] exist Figure 3A In the side view, the outline of the abutment protrusion 12d is generally rectangular, making its cross-sectional area substantially rectangular, and the abutment protrusion 12d has a flat top surface. Figure 3B In the middle, the abutment protrusion 12e has a curved, convex top surface. If this is preferred for delamination of the target die, this curved, convex top surface pushing against the target die can help apply a larger local force to the target die to lift it.

[0027] exist Figure 3C In the middle, the abutment protrusion 12f also has a curved top surface, but its radius of curvature is small, and its force localization effect is better than that of the protrusion 12f. Figure 3B The force localization effect of the base protrusion 12e shown is more pronounced. Although this design may be able to lift the target die more effectively when the base protrusion 12f contacts the tape 16, the stress on the target die may be greater. Therefore, this design is not ideal for avoiding damage to the target die, for example, if the target die is a more fragile and easily broken type.

[0028] The span or longer side of the abutment protrusion 12 should be equal to or slightly less than the length of the shorter edge of the target die. Furthermore, the width or shorter side of the abutment protrusion 12 can range from 200 μm to 800 μm.

[0029] Figures 4A to 4I The steps involved in separating the first die 14 from the tape 16 on which the first die 14 is already mounted are illustrated. A side view of the die removal device is shown, wherein a base protrusion 12 is located within the housing of an ejector cover 20 having an opening 21, from which the base protrusion 12 can protrude along a first axis and extend from the opening of the ejector cover 20. In this arrangement, the first axis is vertical.

[0030] like Figure 4AAs shown, the support member 18 is located inside the housing of the discharge cover 20, and the base protrusion 12 rising above the support member 18 is configured to extend along the first axis from the opening 21 of the discharge cover 20 by correspondingly lifting the support member 18. A vacuum suction 22 is generated inside the discharge cover 20 through the opening 21 (generally also in the direction along the first axis) to hold the tape 16 to the top holding surface of the discharge cover 20.

[0031] The small size of the opening 21 ensures that the first core 14 is not contained within the opening 21 when the tape 16 is held in place by the vacuum suction 22 on the top holding surface of the ejector cover 20. As previously described, the base protrusion 12 is fixed relative to the ejector cover 20 in a horizontal position along the second axis. This horizontal second axis is perpendicular to the aforementioned vertical first axis.

[0032] Adhesive tape 16, on which a matrix of semiconductor dies 15 is already mounted, is supported and extends on tape mounting frame 24. Tape mounting frame 24 may be coupled to a positioning stage (not shown), operable to move tape mounting frame 24 (and thus tape 16 together with the first die 14) relative to die ejector assembly 10, while base protrusion 12 and die ejector assembly 10 are fixed. Preferably, positioning stage is operable to position tape mounting frame 24 along two orthogonal axes in a horizontal plane.

[0033] Alternatively, instead of coupling the tape mounting frame 24 to the positioning stage, the die ejector assembly 10 can be coupled to a drive system operable to move the die ejector assembly 10 (alongside the base protrusion 12 and the ejector cap 20) relative to the tape mounting frame 24. In this embodiment, the entire die ejector assembly 10 may move relative to the tape mounting frame 24 without requiring relative horizontal displacement between the base protrusion 12 and the ejector cap 20.

[0034] With the tape mounting frame 24 coupled to the positioning stage, the positioning stage first moves the tape mounting frame 24 so that the first die 14 is positioned directly above the base protrusion 12. At the start of the die removal process, the first die 14 is vertically positioned on the base protrusion 12 along the first axis. More specifically, the base protrusion 12 is positioned adjacent to the first edge 14a of the first die 14, such that there is an initial offset 30 between the center of the base protrusion 12 and the leftmost first edge 14a of the first die 14. The initial offset 30 can be optimized based on the size and thickness of the first die 14. For example, for a die with dimensions of 3.5mm x 3.5mm x 25μm, the initial offset 30 can range from 200μm to 500μm. With a suitable initial offset, pre-peeling is induced between the tape 16 and the first die 14 at a lower pre-peeling lift height, reducing the risk of die breakage while avoiding excessive bending of adjacent dies.

[0035] like Figure 4B As shown, at a position where there is an initial offset 30 between the base protrusion 12 and the first edge 14a of the first mandrel 14, the base protrusion 12 extends from the ejector cap 20 and rises along the first axis to a pre-peeling height 32, while the support member 18 is being driven by the ejector motor or the ejector cap motor. This lifts the first mandrel 14 to an inclined position relative to the tape 16, such that the first edge 14a is lifted away from the tape 16. Thus, pre-peeling begins between the first edge 14a of the first mandrel 14 and the tape 16. The pre-peeling height 32 is customized in different ways for different mandrel sizes and different types of tape 16 where the level of adhesion between the first mandrel 14 and the tape 16 varies. While the support member 18 located inside the ejector cap 20 is being driven to lift the base protrusion 12, it should be understood that, alternatively, the entire mandrel ejector assembly 10 can also be lifted to push the base protrusion 12 against the first mandrel 14.

[0036] The base protrusion 12 waits for a certain period of time at the pre-peeling height 32 to allow the tape 16 to be successfully pre-peeled from the edge of the first core 14. Afterwards, in Figure 4C In this configuration, the support member 18, together with the base protrusion 12, is slightly lowered to a sliding lift height 34. Since a lower sliding lift height 34 after successful pre-peeling helps reduce the risk of die breakage and die ejection if the first die 14 is accidentally removed prematurely from the tape 16, this lower sliding lift height 34 after successful pre-peeling is preferred during the sliding of the first die 14 relative to the base protrusion 12. A lower sliding lift height 34 also improves die peeling efficiency and reduces excessive or over-bending that may occur to adjacent dies.

[0037] With the base protrusion 12 extending at the sliding lifting height 34, the positioning platform moves the tape mounting frame 24 together with the first core 14 in the horizontal direction 36 along the second axis relative to the discharge cover 20, so that the first core 14 slides across the base protrusion 12 along the width of the first core 14. Figure 4D As shown. The sliding process can be achieved by the movement of the tape mounting frame 24 and / or by the mandrel ejector assembly 10, without any relative horizontal movement between the base protrusion 12 and the ejector cap 20. This sliding movement facilitates further peeling between the tape 16 and the first mandrel 14 at various locations where the tip of the base protrusion 12 pushes upwards.

[0038] This sliding motion continues until the base protrusion 12 is positioned adjacent to the second edge 14b of the first die 14, which is opposite to the first edge 14a; thus, a final offset 38 is obtained between the center of the base protrusion 12 and the second edge 14b of the first die 14, as shown. Figure 4E As shown. At this location, the base protrusion 12 is pushing against the first die 14 near its second edge 14b, while the first die 14 is not yet completely peeled off from the tape 16. An appropriate value is chosen for the ending offset 38 to avoid complete peeling of the first die 14 at this point, which could cause the first die 14 to fly out or shift its position, altering its placement during die pickup. This also reduces bending caused to adjacent dies.

[0039] Then, at this position where the first die 14 has reached the end offset 38, the electronic device holder (which may take the form of a chuck 50 of the bonding head of the die bonder) can be lowered toward the first die 14. During contact between the chuck 50 and the first die 14, the abutment protrusion 12 is located at the end offset 38. The chuck 50 provides vacuum suction to hold the first die 14. It should be noted that... Figure 4F The image depicts the chuck 50 contacting the first die 14, with a chuck offset 42 present between the center of the chuck 50 and the center of the base protrusion 12. Therefore, the chuck 50 and the base protrusion 12 are not aligned along the first axis at this point, which enhances operational control over the position of the first die 14 and prevents premature removal or unnecessary displacement of the first die 14 from the tape 16.

[0040] Before contacting the first die 14, the chuck 50 first stops at the bonding head search height 40, then the chuck 50 gradually lowers at a set speed to the die pickup level, until the chuck 50 fully contacts the first die 14 at the chuck offset position 42. Figure 4G As shown.

[0041] After the chuck 50 has been lowered to the die pickup level, the chuck 50 waits for a short period of time until the second edge 14b of the first die 14 is completely peeled off from the tape 16. Then, the base protrusion 12 can be moved to a standby level, where the base protrusion 12 is flush with or below the top retaining surface of the ejector cap 20. This should further help avoid the risk of the first die 14 flying out by ensuring a controlled separation distance between the first die 14 and the chuck 50 before removing the bias pressure applied to the first die 14 by the base protrusion 12.

[0042] After the chuck 50 contacts the first die 14, vacuum suction in the chuck 50 is activated to secure the first die 14 to the vacuum suction opening in the chuck 50. Then, the chuck 50 lifts the first die 14, which is separated from the tape 16, as... Figure 4H As shown; and the first die 14 is moved to the bonding position for bonding the first die 14.

[0043] After successfully picking up the first die 14 from the tape 16, the positioning stage moves the tape mounting frame 24 until the second die 52 to be picked up is above the base protrusion 12. Then, a new die picking process for the second die 52 is performed, similar to the picking process described above.

[0044] Figure 5 This is a flowchart illustrating the steps involved in ensuring target die delamination by adjusting the height of the abutment protrusion 12 when the target die cannot be picked up from tape 16. Typically, while a lower pre-peel lift height 32 reduces the risk of die breakage, different target dies in corresponding areas of the wafer may exhibit varying degrees of adhesion to tape 16. When the chuck 50 fails to remove and pick up the target die, encountering a lost die error, the die bonding equipment should automatically check whether the target die is still remaining on tape 16. If so, the die bonding equipment can repeat the pick-up process using the adjusted pre-peel lift height 32.

[0045] refer to Figure 5 At step 60, the system determines that the target die is missing from the chuck 50, indicating that the chuck 50 has not successfully picked up the target die. At step 62, the position of the target die on the tape 16 is checked to verify that the target die is still on the tape 16. At step 64, if the target die is no longer on the tape 16, it is not necessary to try to pick up the target die again, and the operator may be prompted that a process error has occurred. If the target die remains on the tape 16, at step 66, the base protrusion 12 is raised to increase the pre-peel lifting height 32.

[0046] At step 68, the system attempts to pick up the target die again. At step 70, if the target die is again unsuccessfully picked up, step 62 is repeated to check tape 16 to verify that the target die is still on tape 16. If the die is not lost this time and the target die has been successfully picked up, at step 72, the base protrusion 12 is lowered to reduce the pre-peel lift height 32. The system then prepares to pick up another die that has been moved above the base protrusion 12 and is adjacent to the target die (step 74).

[0047] For example, in the aforementioned process, if die picking fails when the pre-peel lift height 32 is set to 300 μm, the pre-peel lift height 32 can be increased to 350 μm for repeated pre-peel activation. The adjustment steps and number of repetitions can be set by the operator to ensure automatic and successful picking of each target die.

[0048] It should be understood that the present invention according to the preferred embodiment described above provides a method for removing very thin semiconductor dies 14, 52 from a film 16. This is particularly advantageous for handling ultra-small, thin semiconductor dies with a thickness less than 2 mils and less than 5 mm x 5 mm.

[0049] The smaller opening 21 on the ejector cap 20, implemented through the preferred embodiment, reduces the likelihood of the die bending into the opening 21, which could lead to die breakage. Furthermore, since the chuck 50 picks up the target die at a position offset from the center of the ejector cap 20, this helps reduce the risk of the target die flying out and optimizes efficiency and productivity. The risk of die flying out is further controlled using an optimized process flow for the relative movement between the chuck 50 and the die ejector assembly 10.

[0050] During the pick-up sequence, the detection of a missing die triggers an automatic adjustment algorithm to change the pre-peel lift height 32 of the abutment protrusion 12, thereby increasing the die removal success rate. When the target die cannot be picked up, another attempt is automatically made with a different pre-peel lift height 32 in order to successfully pick up the target die.

[0051] The invention described herein may have other variations, modifications and / or additions besides those specifically described, and it should be understood that the invention includes all such variations, modifications and / or additions falling within the spirit and scope described above.

Claims

1. A method for removing an electronic device from an adhesive tape on which the electronic device has been mounted, the method comprising the following steps: The electronic device is positioned on a base protrusion along a first axis, the base protrusion being mounted on an exhaust assembly, wherein the electronic device has a first edge and a second edge, the second edge being opposite to the first edge, and the base protrusion has a relatively fixed position on the exhaust assembly along a second axis, the second axis being perpendicular to the first axis; The base protrusion is moved along the first axis to push the base protrusion against the first edge of the electronic device adjacent to the electronic device, thereby lifting the first edge of the electronic device away from the tape; The electronic device and the ejector assembly are slid relative to each other along the second axis while the electronic device is lifted by the base protrusion until the base protrusion is pushing against the electronic device near the second edge of the electronic device. The electronic device is brought into contact with the electronic device holder, and the electronic device is removed from the tape through the electronic device holder.

2. The method according to claim 1, wherein, The discharge assembly includes a discharge cover and an opening on the surface of the discharge cover, the base protrusion being able to extend from the interior of the housing of the discharge cover into the opening along the first axis.

3. The method according to claim 2, further comprising the following step: A vacuum suction is generated from the inside of the discharge cap through the opening to hold the tape on the top holding surface of the discharge cap.

4. The method according to claim 3, wherein, The opening is smaller than the size of the electronic device to prevent the electronic device from being housed in the opening when the tape is held in place by the vacuum suction on the top holding surface.

5. The method according to claim 1, wherein, The tape is supported on and extends on a tape mounting frame, which is coupled to a positioning stage such that during the step of sliding the electronic device and the ejector assembly relative to each other, the positioning stage moves the tape relative to the ejector assembly while the base protrusion and the ejector assembly are fixed.

6. The method according to claim 1, wherein, The ejector assembly is coupled to a drive system for moving the ejector assembly, including the base protrusion, together with the tape.

7. The method according to claim 1, further comprising the following step: The base protrusion is actuated to push against the electronic device near the first edge at an initial offset between the first edge of the electronic device and the base protrusion. This initial offset operation initiates a pre-peeling between the first edge of the electronic device and the tape.

8. The method according to claim 7, wherein, The base protrusion is raised to a pre-peeling height that tilts the electronic device relative to the tape to initiate pre-peeling without causing excessive bending of the second electronic device adjacent to the electronic device, so as to avoid damage to the second electronic device.

9. The method according to claim 8, wherein, Before the electronic device and the ejector assembly slide relative to each other, the base protrusion is lowered from the pre-peeling lift height to the sliding lift height, during which the base protrusion remains at the sliding lift height.

10. The method according to claim 1, wherein, As the base protrusion presses against the electronic device near the second edge, the base protrusion is located at the end offset between the base protrusion and the second edge, such that the electronic device is not completely peeled off from the tape at the end of the sliding of the electronic device and the ejector assembly relative to each other along the second axis.

11. The method of claim 10, further comprising the step of: Before the electronic device holder removes the electronic device from the tape, after contacting the electronic device through the electronic device holder and after the tape is peeled off from the second edge of the electronic device, the base protrusion is lowered away from the electronic device.

12. The method according to claim 1, wherein, The electronic device holder contacts the electronic device at an offset point between the center of the electronic device holder and the center of the base protrusion, such that the electronic device holder and the base protrusion are misaligned along the first axis.

13. The method of claim 8, further comprising the step of: If the electronic device retainer fails to remove the electronic device from the tape, and if the electronic device remains on the tape, the pre-peel lift height is increased before the electronic device and the ejector assembly slide relative to each other during subsequent repeated attempts to remove the electronic device from the tape.

14. The method according to claim 1, wherein, The base protrusion includes a narrow linear strip that, when in use, is arranged to extend parallel to the width of the electronic device being disassembled.

15. The method according to claim 14, wherein, The span of the linear strip is equal to or slightly less than the width of the electronic device.

16. The method of claim 14, wherein, The width of the linear strip is significantly smaller than the width of the electronic device, so as to apply a local force to lift the portion of the electronic device that the linear strip is pushing against.

17. The method according to claim 1, wherein, The base protrusion has a tapered profile along the first axis, such that the tip of the base protrusion is narrower than the base of the base protrusion.

18. The method according to claim 1, wherein, The tip of the base protrusion has a protruding surface for pushing against the electronic device.

19. The method according to claim 1, wherein, The cross-section of the abutment protrusion along its width is substantially rectangular.

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