Ultrasonic bonding apparatus

Abstract

To electrically connect a wiring board and a bonding object by ultrasonic bonding in a short time by a device having a simple and inexpensive configuration without causing positional deviation of an electrode and an increase in contact resistance.SOLUTION: When the two flexible boards 8 and 9 are bonded to each other, the bumps 83 are formed on the exposed portions of the plurality of leads 81 of one flexible board 8, the exposed portions of the plurality of leads 81 of one flexible board 8 and the exposed portions of the plurality of leads 91 of the other flexible board 9 are sandwiched between the support body 2 and the bonding tool 34 in a state of being overlapped with each other, and the flexible boards 8 and 9 are ultrasonically bonded to each other by applying ultrasonic vibration by the ultrasonic vibration means while pressurizing the flexible boards 8 and 9 with a predetermined pressurizing force set in advance by the pressurizing means.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an ultrasonic bonding device that exposes at least two electrodes of a wiring board and ultrasonically bonds at least two electrodes of a bonding object to each of the two electrodes of the wiring board. [Background technology]

[0002] Conventionally, when mounting a bare chip on a flexible substrate by connecting the electrode terminals of the bare chip to the mounting area where the leads, which are the electrodes of the flexible substrate, are exposed, an anisotropic conductive film (hereinafter referred to as ACF) is placed between the mounting surfaces of the flexible substrate and the bare chip as an adhesive, and they are pressed together while being heated to the hardening temperature of the ACF, and the flexible substrate and the bare chip are mechanically and electrically connected via the conductive particles contained in the ACF, as described in Patent Document 1, for example.

[0003] Furthermore, when connecting leads of a flexible substrate to each other, or when connecting a lead of a flexible substrate to a pattern wiring electrode of a printed circuit board, it is common to use an ACF to connect the flexible substrates to each other or to connect a flexible substrate to a printed circuit board, similar to the bare chip connection method described above. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-324127 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when using ACF in this way to connect leads of a flexible substrate, for example, it is necessary to heat and pressurize the ACF at a high temperature of 100°C to 240°C for 10 to 60 seconds to thermocompress the ACF. This necessitates a heating means such as a heater to heat the ACF, making the configuration complicated, and also posing the problem of a long time of 10 to 60 seconds required for a single bonding process.

[0006] Furthermore, when the ACF is heated, the flexible substrate undergoes thermal expansion and deformation, which causes the leads to become misaligned. In particular, in the case of fine electrode wiring, even a small amount of thermal deformation of the flexible substrate can cause the lead to become misaligned to a significant extent, which may result in poor connection between the flexible substrate and other flexible substrates or printed circuit boards that are connected to it.

[0007] Furthermore, the presence of conductive particles in the ACF increases the contact resistance between flexible boards or between a flexible board and a printed circuit board, which can lead to defects such as a decrease in the signal transmission speed between circuit components.

[0008] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a device with a simple and inexpensive configuration that enables electrical connection between a wiring board and an object to be joined by ultrasonic bonding in a short time without causing electrode misalignment or increasing contact resistance. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, the ultrasonic bonding device of the present invention exposes at least two electrodes of a wiring board and ultrasonically bonds at least two electrodes of objects to be bonded to the two electrodes of the wiring board, respectively. The ultrasonic bonding device includes: a support that supports the wiring board and the objects to be bonded with the electrodes of the wiring board and the electrodes of the objects to be bonded in a state where they are in contact with each other; ultrasonic vibration means having a vibrator and a horn that applies ultrasonic vibrations to the wiring board and the objects to be bonded while sandwiching the wiring board and the objects to be bonded between the support and the horn; and pressure means that pressurizes the wiring board and the objects to be bonded sandwiched between the support and the horn, wherein the electrodes of the exposed wiring board have protrusions that protrude toward the electrodes of the objects to be bonded; and the ultrasonic bonding device applies ultrasonic vibrations to the wiring board and the objects to be bonded sandwiched between the support and the horn at room temperature while pressurizing them with the pressure means.

[0010] With this configuration, at room temperature, the wiring board and the object to be joined are held between the support and the horn and pressurized by the pressure means while ultrasonic vibrations are applied by the ultrasonic vibration means. This eliminates the need for heating as occurs when ACF is used, and does not lead to thermal expansion or deformation of the wiring board due to heating. Furthermore, there is no increase in contact resistance due to the conductive particles in the ACF. This prevents the inconveniences of electrode misalignment and increased contact resistance seen in the past, and the wiring board and the object to be joined can be electrically connected by ultrasonic bonding in a very short time using a device with a simple and inexpensive configuration.

[0011] In this case, by forming a protrusion on the electrode of the exposed wiring board that protrudes in the direction of the electrode of the object to be joined, ultrasonic vibration energy can be concentrated on the protrusion, allowing the electrodes of the wiring board and the object to be joined to be directly joined at the metal atomic level, making it possible to achieve a high-strength bond.

[0012] The protrusions may be bumps, which can be formed on the electrodes of the wiring board using existing bump formation technology, eliminating the need for special equipment and allowing the use of well-known equipment, and by forming the bumps, ultrasonic vibration energy can be concentrated on the bumps, effectively bonding the electrodes of the wiring board and the bonding object together at the metal atomic level.

[0013] It is also preferable that both the wiring board and the object to be joined are flexible boards, and that the flexible boards are joined together. Furthermore, the object to be joined may be a printed circuit board, and the flexible board and the printed circuit board may be joined together, and both the wiring board and the object to be joined may be printed circuit boards, and the printed circuit boards may be joined together.

[0014] In this manner, it is possible to bond flexible substrates to each other, a flexible substrate to a printed circuit board, or two printed circuit boards to each other. [Effects of the Invention]

[0015] According to the present invention, it is possible to electrically connect a wiring board and an object to be joined by ultrasonic bonding in a short time using a device with a simple and inexpensive configuration, without incurring the conventional problems of electrode misalignment and increased contact resistance. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a side view of an embodiment of an ultrasonic bonding device according to the present invention. [Figure 2] FIG. 2 is a front view of the device of FIG. 1. [Figure 3] FIG. 2 is a perspective view of one of the flexible substrates to be joined by the device of FIG. 1. [Figure 4] 2 is a perspective view of the other flexible substrate to be joined by the device of FIG. 1. FIG. [Figure 5] 2 is an explanatory diagram showing the operation of joining flexible substrates together using the device of FIG. 1; [Figure 6] FIG. 10 is a diagram illustrating the operation of a connection method using an ACF as a comparative example. [Figure 7] 2 is an explanatory diagram showing a joining operation by the device of FIG. 1. FIG. [Figure 8] 10 is a perspective view of another flexible substrate that can be bonded by the ultrasonic bonding device of the present invention. FIG. [Figure 9] 1 is a perspective view of a printed circuit board that can be joined by the ultrasonic joining device of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] An embodiment of an ultrasonic bonding device according to the present invention will be described with reference to FIGS.

[0018] <Device configuration> 1 and 2 show an ultrasonic bonding device 1, in which the objects to be bonded are sandwiched between a horizontal support surface 21 of a support body 2 and a horn of a head unit 3 that ultrasonically vibrates in the Y-axis direction in FIGS. 1 and 2, which is parallel to the support surface 21, and a pressure means 5 controlled by a control device 4 configured as a microcomputer having a CPU and memory applies pressure to the objects to be bonded (not shown) in the vertical direction (Z-axis direction) while applying ultrasonic vibration energy in the form of so-called lateral vibration in the left-right direction (Y-axis direction), thereby bonding the objects to be bonded.

[0019] Here, the objects to be joined are two flexible substrates 8 and 9. One flexible substrate 8, which is the wiring substrate of the present invention, is configured as shown in FIG. 3 by arranging a plurality of leads 81, which are electrodes of the present invention, in a predetermined wiring pattern on one surface of a resin base material 80 made of a resin material such as polyimide, PET (polyethylene terephthalate), or liquid crystal polymer, and covering the lead arrangement surface with a resist resin (solder resist) 82. Furthermore, a portion of the resist resin 82 is removed to expose a portion of the plurality of leads 81, and a plurality of bumps 83, which serve as protrusions of the present invention, are formed on each of the exposed portions of the plurality of leads 81. The material of the leads 81 is mainly copper, but copper / nickel / gold alloy, aluminum, etc. can also be used. The material of the bumps 83 can be gold, copper, silver, nickel, aluminum, tin, etc.

[0020] The other flexible substrate 9, which is the object to be joined in the present invention, is similar to flexible substrate 8 in that multiple leads 91, which are electrodes in the present invention, are arranged in a predetermined wiring pattern on one surface of a resin base material 90 made of a resin material such as polyimide, PET (polyethylene terephthalate), or liquid crystal polymer, and the lead arrangement surface is covered with resist resin (solder resist) 92. In flexible substrate 9, the resist resin 92 is also partially removed to expose the multiple leads 91, but unlike flexible substrate 8, no bumps are formed on the exposed portions of the leads 91. Bumps similar to bumps 83 may be formed on the exposed portions of the leads 91.

[0021] 1 and 2, which is the pressure direction, a horn 32 connected to one end of the vibrator 31, and a support means 33 for supporting the vibrator 31 and the horn 32 so that they can move freely in the up-down direction (Z-axis direction) which is perpendicular to the left-right direction (Y-axis direction), which is the vibration direction. The vibrator 31 ultrasonically vibrates the horn 32, thereby applying ultrasonic vibrations to the objects to be bonded, and the objects are bonded. Here, the horn 32 has a bonding tool 34 on its underside that presses the objects, and the vibrator 31 and the horn 32 correspond to the ultrasonic vibration means in this invention.

[0022] Specifically, horn 32 resonates with ultrasonic vibrations generated by transducer 31 controlled by control device 4 and ultrasonically vibrates in the left-right direction (the Y-axis direction in FIGS. 1 and 2 ), which is the direction of its central axis. Horn 32 is formed, for example, with a length of one wavelength of the resonant frequency so that its approximate center in the Y-axis direction and its two opposite ends are maximum amplitude points. A welding tool 34 is attached to the maximum amplitude point at the center of horn 32. Two positions spaced a quarter wavelength from each maximum amplitude point in the left-right direction (the Y-axis direction) correspond to a first minimum amplitude point and a second minimum amplitude point of horn 32, respectively, and horn 32 is supported by support means 33 at these first and second minimum amplitude points. Horn 32 is formed in the shape of a column, e.g., an octagonal cross section. Transducer 31 is connected to the right end of horn 32 by a headless screw or the like so as to be coaxial with the central axis of horn 32.

[0023] Here, horn 32 and welding tool 34 may be formed from various metal materials commonly used to form resonators, such as titanium, titanium alloys, iron, stainless steel, aluminum, and aluminum alloys such as duralumin. Horn 32 is preferably configured so that its resonance frequency is about 15 kHz to about 60 kHz and its vibration amplitude (the amplitude of expansion and contraction in the Y-axis direction in FIGS. 1 and 2) is about 1 μm to about 300 μm.

[0024] Support means 33 includes a base 33a, a vertical support pillar 33b (in the Z-axis direction in FIGS. 1 and 2) whose upper end is connected to base 33a, a support portion 33c connected to the lower end of support pillar 33b, and a pair of clamp portions 33d connected to the lower surface of support portion 33c. Support means 33 supports horn 32 by gripping gripped portions of horn 32 at positions corresponding to the first and second minimum amplitude points with both clamp portions 33d.

[0025] Here, each of the clamping portions 33d is made up of two, upper and lower, separable gripping members 33d1 and 33d2, with the upper gripping member 33d1 fixed to the underside of the support portion 33c, and the upper and lower gripping members 33d1 and 33d2 clamp and grip the gripped portion at positions corresponding to the first and second minimum amplitude points of the horn 32.

[0026] The gripped portion of horn 32 may be supported by support means 33 via an elastic member such as an O-ring or a diaphragm.

[0027] The pressure applying means 5 moves the support means 33 that supports the horn 32 in the vertical direction (Z-axis direction), thereby moving the horn 32 in the vertical direction so as to move the horn 32 closer to or further away from the support 2. The pressure applying means 5 includes a drive motor 51, a ball screw 52 in the vertical direction (Z-axis direction) that is rotated by the drive motor 51, a base 53 that is U-shaped in a side view and that rotatably supports the upper and lower ends of the ball screw 52, ​​and a rectangular parallelepiped movable support 54 to whose front side the base 33a of the support means 33 is connected and to which the ball screw 52 is threadedly attached internally in the vertical direction formed in the center.

[0028] The base 53 includes a flat plate portion 53a that is long in the vertical direction (Z-axis direction), horizontal extension portions 53b that are integral with the upper and lower ends of the flat plate portion 53a and rotatably support the upper and lower ends of the ball screw 52, ​​and a vertical (Z-axis) guide rail 53c that is attached to the front side of the flat plate portion 53a between the upper and lower extension portions 53b and along the flat plate portion 53a. Here, the drive motor 51 is placed on the upper surface of the upper extension portion 53b, and the guide rail 53c is inserted into a vertical (Z-axis) guide groove formed on the rear side of the movable support 54. The drive motor 51 is controlled by the control device 4 to rotate, which rotates the ball screw 52, ​​thereby moving the movable support 54 in the vertical direction (Z-axis direction) along the guide rail 53c.

[0029] At this time, movable support 54 moves upward or downward according to the rotation direction of ball screw 52, ​​causing base 33a of support means 33 connected to movable support 54 to move up and down, and horn 32 moves closer to support 2 or away from support 2. Then, the downward movement of base 33a caused by the downward movement of movable support 54 applies pressure to the workpieces sandwiched between welding tool 34 of horn 32 and support 2.

[0030] Incidentally, a pressure sensor (not shown) constituted by a load cell or the like is provided on the support body 2 or the head unit 3, and the pressure sensor detects the pressure applied by the pressure means 5 to the welding object sandwiched between the welding tool 34 and the support body 2. Also, a linear encoder 6 (see FIG. 1) is provided on the movable support body 54, which detects the height of the head unit 3 in the vertical direction (Z-axis direction). Here, the control device 4 controls the drive motor 51 based on the detection signal of the linear encoder 6, thereby adjusting the height of the head unit 3 and thereby adjusting the height of the horn 32 relative to the support body 2.

[0031] <Joining operation> The operation of joining the leads of the two flexible substrates 8 and 9 shown in FIGS. 3 and 4 will be described.

[0032] A portion of the multiple leads 81 of one flexible substrate 8 shown in Figure 8 is exposed, and bumps 83 are formed on each exposed portion of the multiple leads 81 using a bump forming device.A portion of the multiple leads 81 of the other flexible substrate 8 shown in Figure 9 is exposed, and two flexible substrates 8, 9 to be joined are prepared.

[0033] Then, as shown in Figure 5, for example, the other flexible substrate 9 is placed on the support surface 21 of the support body 2 with the exposed leads 91 facing up, and one flexible substrate 8 is placed on top of it with the exposed leads 81 facing down, and the overlapped flexible substrates 8, 9 are sandwiched between the support body 2 and the joining tool 34 of the horn 32.

[0034] In this manner, with the overlapping flexible substrates 8, 9 sandwiched between the support 2 and the joining tool 34, under the control of the control device 4, the pressure means 5 presses the flexible substrates 8, 9 with a predetermined pressure, while the vibrator 31 is driven to apply ultrasonic vibrations, thereby ultrasonically joining the exposed leads 81, 91 of the flexible substrates 8, 9 together.

[0035] At this time, bonding is performed at room temperature, and the time for applying ultrasonic waves under pressure is very short, at 0.2 to 1.0 seconds, so there is no need for a heating means as in conventional connections using ACF, and bonding can be performed in a very short time without incurring thermal expansion or deformation of the flexible substrates 8 and 9. Moreover, by forming bumps 83 on the exposed portions of the multiple leads 81 of the flexible substrate 8, ultrasonic vibration energy can be concentrated on the bumps 83, making it possible to efficiently bond the leads 81 and 91 of the flexible substrates 8 and 9 together at the metal atomic level.

[0036] Furthermore, in the conventional method using ACF, the contact resistance when two flexible substrates are connected together is, for example, 52 mΩ, whereas when two flexible substrates are connected together using the ultrasonic bonding of this embodiment, the contact resistance is 14 mΩ, which is a 72% reduction in contact resistance compared to the conventional method, and there is no risk of problems such as a decrease in signal transmission speed between circuit components due to an increase in contact resistance.

[0037] Furthermore, when connecting two flexible substrates using a conventional ACF, as described above, the substrates are heated to high temperatures of 100°C to 240°C for a long period of time (4 to 60 seconds). As a result, as shown in FIG. 6, thermal expansion and deformation occur in the two flexible substrates F1 and F2, which can cause misalignment between the lead terminals L1 and L2 to be joined, potentially resulting in poor contact.

[0038] In contrast, when two flexible substrates 8, 9 are joined together by ultrasonic bonding as in the present embodiment, they can be joined at room temperature in a short time of 0.2 to 1.0 seconds without heating to a high temperature as is the case when ACF is used. As a result, as shown in FIG. 7, the flexible substrates 8, 9 do not expand or deform thermally, and misalignment of the leads 81, 91 to be joined can be prevented in advance, and poor connection between circuits, etc., does not occur.

[0039] Therefore, according to the above-described embodiment, two flexible substrates 8, 9 are ultrasonically bonded together at room temperature, eliminating the need for heating as occurs when using conventional ACF, and therefore there is no need for heating, which results in no thermal expansion of the flexible substrates 8, 9 due to heating, and no increase in contact resistance due to the conductive particles in the ACF. This makes it possible to prevent problems such as misalignment between the leads 81, 91 of the flexible substrates 8, 9 being bonded and an increase in contact resistance, and the flexible substrates 8, 9 can be ultrasonically bonded together and electrically connected in a very short time using a device with a simple and inexpensive configuration.

[0040] Furthermore, since bumps 83 are formed on the exposed portions of the multiple leads 81 of the flexible substrate 8, ultrasonic vibration energy can be concentrated on the bumps 83, thereby efficiently and firmly bonding the leads 81, 91 of the flexible substrates 8, 9 together at the metal atomic level. In this case, the bumps can be formed using an existing bump forming device, so no special device is required for bump formation and existing equipment can be used.

[0041] The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention.

[0042] For example, in the above embodiment, bumps 83 are formed on exposed portions of the plurality of leads 81 of the flexible substrate 8, but the shape of the bumps 83 is not limited to the shape shown in Fig. 3, and for example, bumps 84 having a truncated cone shape as shown in Fig. 8 may be formed on exposed portions of the plurality of leads 81. Furthermore, bumps having a truncated pyramid shape may also be formed.

[0043] Furthermore, it is undesirable for the tip of the bump to be sharp, as this may damage the flexible substrate, and it is preferable for the tip of the bump to have a flat surface. In this case, the flat surface of the tip may be, for example, a circle with a diameter of 10 to 500 μm or a rectangle with a side length of 10 to 500 μm.

[0044] Furthermore, instead of the above-described bumps 83 and 84, protrusions having a trapezoidal cross section extending in the length direction of the leads 81 may be formed on the exposed portions of the multiple leads 81 of the flexible substrate 8, and one or more such protrusions may be formed for each exposed lead. Furthermore, protrusions may be formed on each of the exposed portions of the multiple leads of the two flexible substrates 8 and 9.

[0045] In the above embodiment, the case where two flexible substrates 8, 9 are joined together has been described, but the present invention can also be applied to a case where, instead of the other flexible substrate 9 as the joining object, exposed portions of a plurality of wiring electrodes 100 of a printed circuit board 10, which is a rigid board as shown in Fig. 9, are ultrasonically joined to leads 81 of the flexible substrate 8. Furthermore, the present invention can also be applied to a case where the wiring substrate and the joining object in the present invention are both printed circuit boards 10, and protrusions are formed on exposed electrodes of one printed circuit board 10 and joined to exposed electrodes of the other printed circuit board 10.

[0046] Furthermore, in one of the flexible substrates 8 in the above-described embodiment, the resin base material 80 of the exposed portions of the multiple leads 81 may also be removed to expose the leads 81 on both the front and back sides, and then ultrasonically bonded to the exposed leads 91 of the flexible substrate 9. In this case, after bonding, it is desirable to cover the exposed leads 81 by attaching a resin cover film to the exposed lead 81 portions.

[0047] The present invention can also be applied to a case where the object to be joined is a bare chip.

[0048] The present invention can be applied to exposing at least two electrodes of the wiring board and ultrasonically bonding at least two electrodes of the object to be bonded to the two electrodes of the wiring board, respectively. [Explanation of symbols]

[0049] 1...Ultrasonic bonding equipment 2...Support 5...Pressure means 8... Flexible board (wiring board) 9... Flexible substrate (object to be joined) 10...Printed circuit board (wiring board, joining object) 31...Vibrator (ultrasonic vibration means) 32...Horn (ultrasonic vibration means) 81, 91 ... Lead (electrode) 83,84...Bump 100...Wiring electrode (electrode)

Claims

1. An ultrasonic bonding apparatus that exposes at least two electrodes of a wiring board and ultrasonically bonds at least two electrodes of a bonding object to the two electrodes of the wiring board, respectively, comprising: a support body that supports the wiring board and the objects to be joined in a state in which the electrodes of the wiring board and the electrodes of the objects to be joined are in contact with each other; an ultrasonic vibration means having a vibrator and a horn, which applies ultrasonic vibration to the wiring board and the object to be joined by sandwiching the wiring board and the object to be joined between the support body and the horn; a pressure applying means for applying pressure to the wiring board and the object to be joined that are sandwiched between the support body and the horn; Equipped with a protrusion that protrudes toward the electrode of the object to be joined is formed on the electrode of the wiring board in an exposed state, At room temperature, the wiring board and the object to be joined, which are sandwiched between the support and the horn, are pressurized by the pressurizing means while ultrasonic vibration is applied by the ultrasonic vibration means.

1. An ultrasonic bonding device comprising:

2. 2. The ultrasonic bonding device according to claim 1, wherein the protrusion is a bump.

3. 3. The ultrasonic bonding apparatus according to claim 1, wherein the wiring board and the object to be bonded are both flexible substrates.

4. 3. The ultrasonic bonding apparatus according to claim 1, wherein the objects to be bonded are printed circuit boards.

5. 3. The ultrasonic bonding apparatus according to claim 1, wherein the wiring board and the object to be bonded are both printed circuit boards.

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