Flip-chip bonding with tilt feedback

Abstract

A method for a flip-chip bonding system includes applying pressure to a chip to press the chip against a mounting surface, measuring a tilt angle between the chip and the mounting surface while the chip is being pressed against the mounting surface, and adjusting the tilt angle by adjusting a pressure distribution while the chip is being pressed against the mounting surface if the measured tilt angle differs from a predetermined threshold.

Description

[Technical Field]

[0001] The present invention relates to bonding of electronic components, and more particularly to flip-chip bonding. The present invention further relates to process control during flip-chip bonding. [Background technology]

[0002] Flip-chip bonding creates a reliable electrical connection between a chip and a mounting surface. During chip manufacturing, contact pads are formed on one side of the chip. These contact pads facilitate electrical access to the chip. Corresponding contact pads are formed on the surface to which the chip is mounted. When the chip is mounted, the contact pads on the chip are electrically connected to the contact pads on the surface by placing a conductive bump between each pair of contact pads. The bumps are then allowed to deform while the chip is pressed against the surface. After the bumps have hardened, additional adhesive may be applied between the chip and the surface.

[0003] A common problem in flip-chip bonding is that if the deformation process does not proceed evenly on each bump, the chip may tilt slightly relative to the mounting surface. This can cause significant errors in circuits containing orientation-sensitive elements. After the flip-chip bonding process is complete, it is possible to check the tilt angle between the chip and the mounting surface, for example, by optical profilometry electron microscopy. However, if the tilt angle is different from the desired value, the sample must often be discarded. Possible corrections can only be performed when the next sample is bonded, and many trial-and-error experiments may be required before the cause of the tilt is identified. Summary of the Invention

[0004] The present disclosure aims to provide a method and apparatus that overcomes the above problems.

[0005] The object of the present disclosure is achieved by a method and an apparatus having the features set forth in the independent claims. Preferred embodiments of the present disclosure are disclosed in the dependent claims.

[0006] This disclosure is based on the idea of ​​measuring possible tilt already during the flip chip bonding process, so that immediate adjustments can be made and the tilt can be eliminated before the flip chip bonding process is completed. An advantage of the disclosed method and apparatus is that there is no need to discard samples due to tilt errors.

[0007] Hereinafter, the present disclosure will be described in more detail by way of preferred embodiments with reference to the accompanying drawings. [Brief explanation of the drawings]

[0008] [Figure 1] Here's how. [Figure 2] 1 shows a flip chip bonding apparatus. [Figure 3a] 1 illustrates an embodiment of an interferometer. [Figure 3b] 1 illustrates an embodiment of an interferometer. [Figure 3c] 1 illustrates an embodiment of an interferometer. [Figure 4a] 1 shows an embodiment of a resonator. [Figure 4b] 1 shows an embodiment of a resonator. [Figure 5a] 1 shows a diffractive embodiment. [Figure 5b] 1 shows a diffractive embodiment. [Figure 6a] 1 illustrates an embodiment of a solder bump. [Figure 6b] 1 illustrates an embodiment of a solder bump. [Figure 7] 1 shows a reflective embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present disclosure describes a method for attaching a chip to a mounting surface in a flip-chip bonding system. The method includes applying pressure to the chip to urge the chip toward the mounting surface. The pressure has a spatial pressure distribution across a surface of the chip. The method also includes measuring a tilt angle between the chip and the mounting surface while the chip is being pressed toward the mounting surface. The method also includes comparing the measured tilt angle to a predetermined threshold, and adjusting the tilt angle by adjusting the pressure distribution while the chip is being pressed toward the mounting surface if the measured tilt angle differs from the threshold.

[0010] If the measured tilt angle exceeds a threshold, for example, adjusting the pressure distribution can decrease the tilt angle, or if the measured tilt angle is below a threshold, adjusting the pressure distribution can increase the tilt angle.

[0011] This method is illustrated in Figure 1. Reference numbers 11 to 14 indicate the various steps involved in the method.

[0012] This method may include, for example, gripping the chip with a movable bonding head and positioning the bonding head above the mounting surface so that the chip is aligned with the mounting surface. The step of applying pressure to the chip may include pressing the bonding head toward the mounting surface. The step of adjusting the tilt angle by adjusting the pressure distribution may include changing the position of the bonding head while the bonding head is pressed toward the mounting surface. This option may be combined with other embodiments presented in this disclosure.

[0013] Alternatively, the bonding head may include a force actuator that allows the pressure distribution to be changed without the bonding head moving. The force actuator may include, for example, a means for generating an electric or magnetic force between the chip and the mounting surface. This option can also be combined with other embodiments presented in this disclosure. Other means for changing the pressure distribution can also be used in any of the embodiments.

[0014] Additionally, any of the methods for changing the pressure distribution described in this disclosure may be supplemented by adjusting the local temperature near one edge of the chip. The temperature change affects the shear stress profile of the solder bumps. Increasing the temperature at the first edge can cause inelastic formation in nearby solder bumps near the first edge with lower stress than in solder bumps near other edges of the chip. This can be used to facilitate changing the tilt angle. In some cases, local temperature change can be used as an independent method for changing the tilt angle without changing the pressure distribution.

[0015] A corresponding flip-chip bonding apparatus may include an actuator coupled to the chip and a control unit coupled to the actuator. The control unit is configured to control the actuator so that the actuator presses the chip toward the mounting surface. The pressure applied by the actuator has a spatial pressure distribution across the surface of the chip. The apparatus also includes a measurement device coupled to the control unit. The measurement device is configured to measure a tilt angle between the chip and the mounting surface when the actuator presses the chip toward the mounting surface. The control unit is configured to adjust the tilt of the chip by adjusting the pressure distribution based on the measured tilt angle.

[0016] 2 shows a flip-chip bonding apparatus including a fixed support 27 for holding a mounting surface 22 and a movable bonding head 23 for gripping a chip 21. The chip 21 is attached to the mounting surface 22 by solder bumps 25 in a flip-chip process. The apparatus also includes an actuator 24 coupled to the chip 21 through the bonding head 23 and a control unit 28 coupled to the actuator. The control unit 28 is configured to move the bonding head 23 by controlling the actuator 24. The apparatus also includes a measuring device 26 coupled to the control unit 28. The measuring device 28 is configured to measure the tilt angle between (i) the chip 21 gripped by the bonding head 23 and (ii) the mounting surface 22 held on the fixed support 27 when the actuator 24 presses the bonding head 23 toward the fixed support 27. The control unit 28 is configured to change the pressure distribution based on the measured tilt angle by adjusting the tilt of the bonding head 23.

[0017] In other words, the measurement device provides the control unit with immediate feedback regarding the current angle between the chip and the mounting surface while the bonding process is ongoing and the chip is being pressed against the mounting surface. The control unit can be programmed to automatically adjust the position of the bonding head to change the angle. This recursive process of measurement and adjustment can ensure that the chip and mounting surface are parallel to each other upon completion of bonding, and that the position of the chip relative to the mounting surface is fixed. A variety of measurement devices can be used to achieve this goal.

[0018] The flip-chip bonding apparatus may include one or more actuators that exert electric or magnetic forces on the chip. These actuators may be, for example, Coulomb electrostatic actuators or Johnsen-Rahbek electrostatic actuators. The actuators may include multiple electrodes that span the surface area of ​​the chip. The pressure distribution may be altered by varying the voltage applied to these electrodes. The electrostatic actuators may be implemented together with other means for altering the pressure distribution (e.g., force actuation generated through the bonding head) or as a standalone solution.

[0019] The mounting surface may be, for example, the top surface of a circuit board or electronic component, or any other surface to which a chip can be physically attached and electrically connected. The mounting surface may define an xy plane and a z axis that is perpendicular to the xy plane.

[0020] The circuit board or component including the mounting surface may be attached to a fixed structure during the flip-chip bonding process. The fixed structure may be referred to as a bonding table, for example. The mounting surface may remain stationary throughout the flip-chip bonding process.

[0021] The bonding head may be any arrangement to which a chip can be temporarily attached during the flip-chip bonding process. In this disclosure, the act of temporarily attaching a chip to a bonding head is referred to as "gripping" the chip with the bonding head. Temporary attachment of the chip to the bonding head may be achieved, for example, by electrical or magnetic forces, adhesives, and / or vacuum suction.

[0022] The bonding head is movable relative to a fixed support. The bonding head may be located, for example, at the end of a robotic bonding arm that includes part of the actuator 24. A control unit may adjust the position of the bonding arm and the bonding head by controlling the actuator. The movement and adjustment generated by the actuator 24 may include horizontal movement parallel to a plane defined by the mounting surface and up and down movement perpendicular to that plane. The former adjustment allows the chip to be aligned with an intended attachment area on the mounting surface, and the latter adjustment allows the chip to be pressed against the mounting surface. The actuator may include different components for generating the downward pressure and the horizontal movement.

[0023] Adjustments that can be made to the position of the bonding head may include rotation of the bonding head in a plane parallel to the plane defined by the mounting surface. The adjustments may include rotation of the bonding head about an axis parallel to the plane defined by the mounting surface. The latter rotation may be achieved, for example, by tilting the bonding arm and may be used to change the angle between the bottom surface of the chip and the mounting surface.

[0024] The flip-chip bonding process includes pressing a chip against a mounting surface in close proximity with a bonding head. Various bonding methods are possible. The chip may have, for example, a bottom surface with one or more first contact pads, and the mounting surface may have one or more second contact pads. The one or more first contact pads may be aligned with the one or more second contact pads when the bonding head is positioned above the mounting surface. The method may include placing conductive solder bumps on the one or more first contact pads and / or the one or more second contact pads before pressing the bonding head against the mounting surface. In any of the embodiments presented in this disclosure, the bumps may be made of, for example, indium.

[0025] By pressing the chip toward the mounting surface, the chip can be firmly attached to the mounting surface with solder bumps, and the first contact pads can be electrically connected to the second contact pads with solder bumps. The pressing and tilt adjustment can be performed at room temperature or at a cryogenic temperature (e.g., below -100°C). The void space between the chip and the mounting surface can be filled with an underfill material after the chip and the mounting surface are bonded together.

[0026] Measuring the tilt angle may include measuring the gap between the chip and the mounting surface at two or more measurement locations. If the gap is measured at only two points on the mounting surface, the tilt angle can be determined only along a line passing through these points. If the gap is measured at three or more points on the mounting surface, and these three or more points are not all on the same line on the mounting surface, the tilt angle in any direction can be determined.

[0027] The measurement apparatus may include a device for measuring the gap between the chip and the mounting surface at two or more measurement positions.

[0028] In an embodiment in which the chip is held by a movable bonding head, the bonding head may include a first transparent portion through which the chip can be illuminated at each of the two or more measurement positions. The bonding head may further include a second transparent portion through which the mounting surface can be illuminated at each of the two or more measurement positions. Measuring the gap between the surface of the chip and the mounting surface at each of the two or more measurement positions may include simultaneously illuminating the chip through the first transparent portion and the mounting surface through the second transparent portion, and measuring an interference pattern between electromagnetic radiation reflected from the chip through the first transparent portion and electromagnetic radiation reflected from the mounting surface through the second transparent portion.

[0029] Figure 3a shows the device with a bonding head 33 holding a chip 31. The chip 31 is aligned with a mounting surface 32. The mounting surface is attached to a fixed structure 37. Solder bumps 35 are simply shown as lines between the chip 31 and the mounting surface 32. Contact pads are not shown.

[0030] The bonding head 33 includes a first transparent portion 331 and a second transparent portion 332. The transparent portion may be an opening in the bonding head. Alternatively, the transparent portion may be a portion made of glass or another material that transmits the electromagnetic radiation 341 / 342 used for illumination in this embodiment. The transparent portion may extend through the bonding head in the z-direction. Although only one first transparent portion and one second transparent portion are shown at one measurement position, the device may include several first and second transparent portions if gap measurements are performed at multiple measurement positions. Each first transparent portion 331 is located in a portion of the bonding head 33 aligned with the chip 31 in the z-direction. Each second transparent portion 332 is located in a portion of the bonding head 33 aligned with the mounting surface 32, rather than the chip 31, in the z-direction.

[0031] The measurement apparatus includes an interferometer 36, which also functions as an electromagnetic radiation source, emitting electromagnetic radiation 341 / 342 through the first transparent portion 331 toward the chip 31 and through the second transparent portion 332 toward the mounting surface 32. Alternatively, the radiation source and the interferometer may be two different devices. The interferometer also receives the radiation 341 / 342 after it has been reflected upward from the chip or mounting surface. The electromagnetic radiation 341 / 342 may be, for example, visible, ultraviolet, or infrared radiation.

[0032] Electromagnetic radiation 341 reaching chip 31 through first transparent portion 331 may be reflected back to the first transparent portion from the top surface of chip 31 close to bonding head 33. The chip may have an upper reflective layer 311 on its top surface that reflects incident radiation 341 towards interferometer 36. Incident electromagnetic radiation 342 may similarly be reflected from mounting surface 32 towards the interferometer. This is shown in Figure 3b. The gap between the bottom surface of chip 31 and mounting surface 32 at this measurement position can be accurately determined by measuring the interference of light beams 341 and 342 in the interferometer.

[0033] Alternatively, electromagnetic radiation 341 reaching chip 31 through first transparent portion 33 may be reflected by the bottom surface of chip 31, which is further away from the bonding head, to first transparent portion 331. The chip may be, for example, a silicon chip that is transparent to infrared light or a sapphire chip that is transparent to visible light. In this case, the bottom surface of chip 31 may be provided with an optional lower reflective layer 312, as shown in FIG. 3c. Any layer deposited on the top side, such as 311 in FIG. 3c, may be provided with an opening that allows radiation 341 to enter chip 31 without being reflected from the top surface.

[0034] In another embodiment, the chip or mounting surface may comprise a superconducting circuit, the superconducting circuit comprising a coplanar waveguide resonator at each of two or more measurement locations, and measuring the gap between the surface of the chip and the mounting surface at each of the two or more measurement locations may include measuring a resonant frequency of the coplanar waveguide resonator at each of the two or more measurement locations.

[0035] In a corresponding apparatus, the chip and / or mounting surface includes a superconducting circuit having a coplanar waveguide resonator at each of two or more measurement locations, and the measurement device includes a resonance measurement device configured to measure the resonant frequency of each coplanar waveguide resonator.

[0036] A superconducting circuit on a chip or on a mounting surface may be used to measure the tilt angle between the chip and the mounting surface while the chip is pressed against the mounting surface during a flip-chip bonding process. The superconducting circuit may include coplanar waveguide resonators at two or more measurement locations where the gap between the chip and the mounting surface is measured. This use may include measuring the resonant frequency of each coplanar waveguide resonator.

[0037] The flip-chip bonding system may be adapted to bring at least some electrical elements on the mounting surface and / or on the chip to a cryogenic temperature at which they exhibit superconductivity. The superconducting circuit may include a coplanar waveguide resonator as one such element. Other circuits on the mounting surface and / or on the chip may include a signal generator and a transmission line capable of transmitting an electrical signal from the signal generator to the coplanar waveguide resonator. The electrical signal may place the resonator in electrical resonance if its frequency is appropriately selected.

[0038] Figure 4a shows a chip 41, a mounting surface 42, and solder bumps 45 that attach and connect the chip 41 to the mounting surface 42. The bonding head and mounting supports are omitted from this view. A coplanar waveguide resonator 44 is located below the chip 41. The thickness of the resonator relative to the thickness of the chip is greatly exaggerated. The resonant frequency of this resonator can be determined using standard measurements. The resonant frequency depends on the electrical environment of the waveguide resonator. The resonant frequency is significantly affected by the proximity of the mounting surface 42. Therefore, the gap 43 between the resonator 44 and the mounting surface 42 can be determined by measuring the resonant frequency. Figure 4b shows an alternative arrangement in which the coplanar waveguide resonator 44 is located on the mounting surface 42. The measurement principle is the same.

[0039] The surface adjacent to the resonator, i.e., the area of ​​the mounting surface 42 directly below the resonator 44 in Figure 4a, or the area of ​​the chip 41 directly above the resonator 44 in Figure 4b, may be coated with a superconducting material, or alternatively, the surface may be insulating.

[0040] Alternatively, coplanar waveguide resonators may be located on both the chip and the mounting surface at each measurement location. The waveguide resonators on the chip may be aligned with the resonators on the mounting surface at each measurement location. This option is not discussed separately.

[0041] In another embodiment, measuring the gap between the surface of the chip and the mounting surface at each of the two or more measurement locations may include illuminating the gap at each of the two or more measurement locations with a light source that emits electromagnetic radiation into the gap so that the electromagnetic radiation is diffracted in the gap, and measuring the gap further includes measuring the diffracted electromagnetic radiation with a radiation detector.

[0042] In this case, the wavelength of the electromagnetic radiation may be in the visible or infrared range. This wavelength may have the same order of magnitude as the expected gap at two or more measurement locations. This wavelength may be, for example, in the range of 400 nm to 1 mm, or in the range of 800 nm to 1 mm, or in the range of 800 nm to 3000 nm. Figure 5a shows a schematic diagram of a flip-chip bonding system in which the gap between the chip 41 and the mounting surface 42 is measured at one measurement location 51.

[0043] A light source L emits a radiation beam 521 toward the gap between the chip 41 and the mounting surface 42 at a measurement location 51. The radiation beam may be parallel to the mounting surface. If the selected wavelength of the electromagnetic radiation is appropriate and the gap is narrow enough, the incident electromagnetic radiation 521 is diffracted in the gap, so that diffracted electromagnetic radiation 522 can be detected by a radiation detector D. The radiation detector may include multiple pixels, which can resolve the spatial intensity variation of the diffracted electromagnetic radiation 522, shown as a diffraction pattern 53 in FIG. 5a. The height of the gap at the measurement location 51 can be determined by analyzing the pattern 53. The same measurement can be repeated at multiple measurement locations.

[0044] The two or more measurement locations may be located at two or more corresponding corners of the chip 41. This is shown in FIG. 5b. By directing the light beam near the corners, the measurement locations can be precisely identified in the xy plane. The tilt of the chip with respect to the mounting surface can then be calculated after measurements have been taken at two or more corners of the chip.

[0045] Alternatively, the tilt angle can be measured by indirect means, without directly measuring the gap between the chip and the mounting surface.

[0046] In one embodiment, the chip has a bottom surface with one or more first contact pads, the mounting surface has one or more second contact pads, the one or more first contact pads are aligned with the one or more second contact pads when a bonding head is positioned above the mounting surface, and the method includes placing conductive solder bumps on the one or more first contact pads and / or the one or more second contact pads before pressing the bonding head toward the mounting surface, and measuring the tilt angle between the surface of the chip and the mounting surface includes measuring the resistance between at least one first contact pad and at least one second contact pad connected to each other by at least one solder bump.

[0047] In the corresponding device, the chip has one or more first contact pads, the mounting surface has one or more second contact pads, the one or more first contact pads are connected to the one or more second contact pads by conductive solder bumps, and the measurement device comprises an electrical resistance measurement device configured to measure the resistance between at least one of the one or more first contact pads and at least one of the one or more second contact pads.

[0048] FIG. 6a shows a schematic diagram of a flip-chip bonding system device in which a chip 61 is bonded to a mounting surface 62. The bonding head and fixed support are again omitted. The chip has first contact pads 611, and the mounting surface has second contact pads 621. A solder bump 651 is located between 611 and 621. The resistance of the solder bump 651 depends on the gap 63 between the chip 61 and the mounting surface at the measurement location 64 where the bump is located. The first and second contact pads may be connected to a measurement device capable of measuring the resistance between them; this resistance measurement can be used as an indication of the height of the gap 63.

[0049] In practice, it can be difficult to measure the resistance of a single bump 651 with high accuracy. This accuracy can be improved by connecting multiple bumps in series and measuring the resistance between the two ends of the series. FIG. 6a shows a system in which a chip 61 includes multiple first contact pads 611-613 and a mounting surface includes multiple second contact pads 621-623. Multiple solder bumps 651-655 are connected in series between the first and second contact pads, so that the sum of the resistances of all of these solder bumps 651-655 can be measured with a measurement device that can measure the resistance between the first and last contact pads in the series. All of the solder bumps and contact pads are located within a measurement location 64. While a linear arrangement of the series in the x direction is shown in FIG. 6b, the bumps and contact pads forming the series may be arranged in a more compact pattern, such as a square, in the xy plane. The measured resistance is then proportional to the average gap at the measurement location 64. The tilt angle can be determined by repeating the same measurement on the bump and contact pad at multiple measurement locations.

[0050] Another method for directly measuring the tilt angle is shown in Figure 7. In this embodiment, measuring the angle between a surface of a chip 71 and a mounting surface 72 may include illuminating the gap between the chip and the mounting surface with a radiation source 74 that emits a beam of electromagnetic radiation 76 into the gap between the chip and the mounting surface at a non-zero angle of incidence 731 relative to the mounting surface. The beam is reflected between the chip 71 and the mounting surface 72. Measuring the tilt angle further includes measuring the exit angle 732 of the beam relative to the mounting surface.

[0051] In this case, the wavelength of the electromagnetic radiation may be in the visible or ultraviolet range. This wavelength may be an order of magnitude or more smaller than the expected gap between the chip and the mounting surface. This wavelength may be, for example, in the range of 10 nm to 800 nm, or 400 nm to 800 nm, or 10 nm to 400 nm. The angle of incidence 731 may be, for example, in the range of 0.1 to 10 degrees, or 0.1 to 5 degrees, or 0.1 to 0.5 degrees. However, the optimal angle of incidence depends on both the size of the chip and the desired gap between the chip and the mounting surface. Therefore, angles of incidence outside the above ranges may also be used for some applications.

[0052] In both Figures 5a-5b and Figure 7, the measurement device comprises a radiation source and a radiation detector, the radiation source configured to illuminate the gap between the chip and the mounting surface with electromagnetic radiation, and the radiation detector configured to measure the electromagnetic radiation exiting the gap.

[0053] In Figures 5a-5b, the radiation source is configured to illuminate the gap between the chip and the mounting surface with electromagnetic radiation, whereby said electromagnetic radiation is diffracted in the gap, and the radiation detector is configured to measure the diffracted electromagnetic radiation. In Figure 7, the radiation source is configured to illuminate the gap between the chip and the mounting surface, whereby said electromagnetic radiation is reflected between the chip and the mounting surface, and the radiation detector is configured to measure the angle of emergence of the reflected electromagnetic radiation.

Claims

1. Used in flip chip bonding systems to attach chips to mounting surfaces, urging the chip toward the mounting surface by applying pressure to the chip, the pressure having a spatial distribution across a surface of the chip; The method also includes: measuring a tilt angle between the chip and the mounting surface while the chip is pressed against the mounting surface; comparing the measured tilt angle with a predetermined threshold, and if the measured tilt angle differs from the threshold, adjusting the tilt angle by adjusting the pressure distribution while the chip is pressed against the mounting surface.

2. The method of claim 1 , wherein measuring the tilt angle includes measuring a gap between the chip and the mounting surface at two or more measurement positions.

3. 3. The method of claim 2, wherein the chip is held by a movable bonding head, the bonding head comprising a first transparent portion through which the chip can be illuminated at each of the two or more measurement positions, and the bonding head further comprising a second transparent portion through which the mounting surface can be illuminated at each of the two or more measurement positions, and wherein measuring the gap between the surface of the chip and the mounting surface at each of the two or more measurement positions comprises simultaneously illuminating the chip through the first transparent portion and the mounting surface through the second transparent portion, and measuring an interference pattern between electromagnetic radiation reflected from the chip through the first transparent portion and electromagnetic radiation reflected from the mounting surface through the second transparent portion.

4. 4. The method of claim 3, wherein the electromagnetic radiation reaching the chip through the first transparent portion is reflected back to the first transparent portion from a top surface of the chip closer to the bonding head.

5. 4. The method of claim 3, wherein the electromagnetic radiation reaching the chip through the first transparent portion is reflected back to the first transparent portion from a bottom surface of the chip that is further away from the bonding head.

6. 3. The method of claim 2, wherein the mounting surface comprises a superconducting circuit, the superconducting circuit comprising a coplanar waveguide resonator at each of the two or more measurement locations, and wherein measuring the gap between the surface of the chip and the mounting surface at each of the two or more measurement locations comprises measuring a resonant frequency of the coplanar waveguide resonator at each of the two or more measurement locations.

7. 3. The method of claim 2, wherein the chip comprises a superconducting circuit, the superconducting circuit comprising a coplanar waveguide resonator at each of the two or more measurement locations, and wherein measuring the gap between the surface of the chip and the mounting surface at each of the two or more measurement locations comprises measuring a resonant frequency of the coplanar waveguide resonator at each of the two or more measurement locations.

8. 3. The method of claim 2, wherein measuring the gap between the front surface of the chip and the mounting surface at each of the two or more measurement positions includes illuminating the gap at each of the two or more measurement positions with a light source that emits electromagnetic radiation into the gap so that the electromagnetic radiation is diffracted in the gap, and measuring the gap further includes measuring the diffracted electromagnetic radiation with a radiation detector.

9. 2. The method of claim 1, wherein the chip has a bottom surface with one or more first contact pads, the mounting surface has one or more second contact pads that align with the one or more second contact pads when the chip is placed over the mounting surface, the method comprising placing conductive solder bumps on the one or more first contact pads and / or the one or more second contact pads before pressing the chip against the mounting surface, and measuring the tilt angle between the surface of the chip and the mounting surface comprises measuring a resistance between at least one first contact pad and at least one second contact pad connected to each other by at least one solder bump.

10. 2. The method of claim 1, wherein measuring the tilt angle between the surface of the chip and the mounting surface at each of the two or more measurement positions comprises illuminating the gap between the chip and the mounting surface with a radiation source that irradiates a beam of electromagnetic radiation into the gap between the chip and the mounting surface at a non-zero angle of incidence with respect to the mounting surface such that the beam is reflected between the chip and the mounting surface, and measuring the tilt angle further comprises measuring an exit angle of the beam with respect to the mounting surface.

11. 1. A flip-chip bonding apparatus comprising: an actuator coupled to a chip; and a control unit coupled to the actuator, whereby the control unit is configured to control the actuator such that the actuator presses the chip against a mounting surface, and the pressure applied by the actuator has a spatial pressure distribution across a surface of the chip, The flip chip bonding apparatus also includes a measurement device coupled to the control unit, the measurement device configured to measure a tilt angle between the chip and the mounting surface when the actuator presses the chip toward the mounting surface, and the control unit configured to adjust the tilt of the chip by adjusting the pressure distribution based on the measured tilt angle.

12. 12. The flip chip bonding apparatus of claim 11, wherein the measurement apparatus comprises a device for measuring the gap between the chip and the mounting surface at two or more measurement locations.

13. 13. The flip chip bonding apparatus of claim 12, wherein the apparatus comprises a bonding head configured to hold the chip, the bonding head comprising a first transparent portion through which the chip held by the bonding head can be illuminated at each of the two or more measurement positions, the bonding head further comprising a second transparent portion through which the mounting surface held by the fixed support can be illuminated at each of the two or more measurement positions, the measurement apparatus comprising one or more electromagnetic radiation sources configured to simultaneously transmit electromagnetic radiation through the first transparent portion and the second transparent portion, and the measurement apparatus comprising an interferometer configured to measure an interference pattern between the electromagnetic radiation reflected through the first transparent portion and the electromagnetic radiation reflected through the second transparent portion.

14. 13. The flip chip bonding apparatus of claim 11 or 12, wherein the measurement apparatus comprises a radiation source and a radiation detector, the radiation source configured to illuminate the gap between the chip and the mounting surface with electromagnetic radiation, and the radiation detector configured to measure the electromagnetic radiation exiting the gap.

15. 1. Use of a superconducting circuit on a chip or on a mounting surface to measure a tilt angle between the chip and a mounting surface while the chip is pressed against the mounting surface in a flip-chip bonding process, the superconducting circuit comprising coplanar waveguide resonators at two or more measurement positions where the gap between the chip and the mounting surface is measured, the use including measuring a resonant frequency of each coplanar waveguide resonator.

16. Use of one or more first contact pads on a chip, one or more second contact pads on the mounting surface, and conductive solder bumps to measure a tilt angle between the chip and a mounting surface while the chip is pressed against the mounting surface in a flip-chip bonding process, the conductive solder bumps connecting the one or more first contact pads to the one or more second contact pads, the use including measuring a resistance between at least one of the one or more first contact pads and at least one of the one or more second contact pads.

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