Electronic component mounting method and electronic component mounting system

Abstract

Provided is an electronic component mounting method that makes it possible to produce a highly reliable fluxless bond by means of a simple device. According to the present invention, an electronic component mounting method involves bonding a bump 22 formed on a first electrode 21 of a first electronic component 20 to a second electrode 11 of a second electronic component 10 and includes an etching step for etching the first electronic component and the second electronic component with a weakly acidic organic acid to remove an oxide film formed on the surface of the bump and the second electrode and, after the etching step, a bonding step for bonding the bump formed on the first electrode to the second electrode in a state in which the first electronic component and the second electronic component are accommodated in a bonding device 70 and an inert gas has been supplied to the bonding device.

Description

Electronic component mounting method and electronic component mounting system

[0001] The present invention relates to a method and system for mounting electronic components, in which electrodes of the electronic components are joined together via bumps.

[0002] For example, when bumps formed on electrodes of electronic components such as semiconductor chips are bonded to connection terminals of a wiring board, if an oxide film is formed on the surface of the bumps or the connection terminals of the wiring board, the bonding between the bumps and the electrodes is hindered, resulting in connection defects. Therefore, a method is generally used in which flux is applied to the surface of the wiring board before bonding the bumps to the electrodes of the wiring board. This allows bonding to be performed with the oxide film formed on the surfaces of the bumps and electrodes removed by the flux.

[0003] However, as the pitch of bumps becomes narrower, it becomes more difficult to sufficiently remove the flux. Flux residue can cause wiring corrosion and migration. Therefore, fluxless bonding methods are being investigated as a way to eliminate the effects of flux residue.

[0004] For example, Patent Document 1 describes a method of reflow (fusion bonding) bumps formed on electrodes of electronic components to connection terminals of a wiring board while supplying a carboxylic acid gas such as formic acid into a heat-melting treatment device (bonder). This method makes it possible to remove oxide films formed on the surfaces of the bumps and connection terminals through the reducing action of the carboxylic acid gas.

[0005] Japanese Patent Application Laid-Open No. 2001-244618

[0006] In the method described in Patent Document 1, since a carboxylic acid gas such as formic acid introduced into a thermal melting treatment device (bonder) is corrosive, it is necessary to take sufficient corrosion countermeasures for the inside of the thermal melting treatment device. However, since the thermal melting treatment device has a complex structure including a conveying mechanism, an alignment mechanism, a pressurizing / heating mechanism, etc., it is necessary to take extensive corrosion countermeasures, which leads to a problem of increased costs for the device.

[0007] In the above method, the carboxylic acid gas introduced into the bonder is exhausted and removed from the device after the reduction of the oxide film is completed, but the carboxylic acid salt (organic compound) of the metal that constitutes the bump or connection terminal, which is generated during the reduction process of the oxide film, may not be decomposed, and some of the carboxylic acid salt may remain as residue on the electronic component or wiring board. In this case, there is a problem that highly reliable bonding cannot be obtained because the carboxylic acid salt has high insulating properties.

[0008] In addition, in the above method, the reduction process of the oxide film must be carried out by controlling the temperature inside the bonder to a range above the reduction temperature of the oxide film of the bump by the carboxylic acid gas and below the melting temperature of the bump. However, since the amount of evaporation of the carboxylic acid gas varies with the ambient temperature, it is difficult to control the concentration of the carboxylic acid gas.

[0009] The present invention has been made in view of the above points, and its main object is to provide an electronic component mounting method and an electronic component mounting system that can obtain highly reliable fluxless bonding using simple equipment.

[0010] An electronic component mounting method according to the present invention is a method for bonding bumps formed on a first electrode of a first electronic component to a second electrode formed on a second electronic component, and includes an etching step of etching the first electronic component and the second electronic component with a weak organic acid to remove oxide films formed on the surfaces of the bumps and the second electrodes, and a bonding step of, after the etching step, placing the first electronic component and the second electronic component in a bonding device and bonding the bumps formed on the first electrode of the first electronic component to the second electrode formed on the second electronic component while supplying an inert gas to the bonding device.

[0011] The electronic component mounting system according to the present invention is an electronic component mounting system that bonds bumps formed on a first electrode of a first electronic component to a second electrode formed on a second electronic component, and includes an etching device that removes oxide films formed on the surfaces of the bumps and the second electrodes by etching the first electronic component and the second electronic component with a weakly acidic organic acid, and a bonding device that houses the first electronic component and the second electronic component that have been etched in the etching device and bonds the bumps formed on the first electrode of the first electronic component to the second electrode formed on the second electronic component while supplying an inert gas.

[0012] Another electronic component mounting method according to the present invention is a method for bonding bumps formed on a first electrode of a first electronic component to a second electrode formed on a second electronic component, the method including: an etching step of etching the second electronic component with a weak organic acid to remove an oxide film formed on the surface of the second electrode; and a bonding step of, after the etching step, placing the first electronic component and the second electronic component in a bonding device and, with an inert gas supplied to the bonding device, bonding the bumps formed on the first electrode of the first electronic component to the second electrode formed on the second electronic component. The bonding step is performed by bringing the bumps formed on the first electrode into contact with the second electrode, and then, with the bumps melted, applying vibration to the first electronic component or the second electronic component that causes a relative displacement in a direction parallel to the interface between the bumps and the second electrode.

[0013] According to the present invention, it is possible to provide an electronic component mounting method and an electronic component mounting system that can obtain highly reliable fluxless bonding using a simple device.

[0014] FIG. 1A is a cross-sectional view schematically showing steps of an electronic component mounting method according to a first embodiment of the present invention. FIG. 1B is a cross-sectional view schematically showing steps of an electronic component mounting method according to a first embodiment of the present invention. FIG. 1C is a cross-sectional view schematically showing steps of an electronic component mounting method according to a first embodiment of the present invention. FIG. 1D is a cross-sectional view schematically showing steps of an electronic component mounting method according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing steps of an electronic component mounting method according to another embodiment. FIG. 3 is a diagram illustrating a bump bonding step according to a second embodiment of the present invention. FIG. 4 is a diagram illustrating a bump bonding step according to the second embodiment of the present invention. FIG. 5A is a cross-sectional SEM photograph of a bump bonding portion in sample A. FIG. 5B is a cross-sectional SEM photograph of a bump bonding portion in sample B. FIG. 6 is a diagram illustrating a bump bonding step according to a third embodiment of the present invention. FIG. 7 is a cross-sectional SEM photograph of a bump bonding portion according to the third embodiment of the present invention. FIG. 8 is a cross-sectional view schematically showing the configuration of an electronic component mounting system according to one embodiment of the present invention. Fig. 9 is a cross-sectional view schematically showing another configuration of a bonding device. Fig. 10 is a cross-sectional view schematically showing another configuration of a bonding device. Fig. 11 is a cross-sectional view schematically showing the configuration of an electronic component mounting system according to another embodiment.

[0015] (Embodiment 1) The present invention relates to an electronic component mounting method for bonding bumps formed on a first electrode of a first electronic component to electrodes formed on a second electrode of a second electronic component. Here, the first electronic component and the second electronic component include semiconductor chips, BGA (ball grid array) packages, printed circuit boards, interposers, electronic component mounting boards, etc. Furthermore, the bumps include bumps made of high-melting-point metals such as copper and gold, low-melting-point metals such as solder bumps, and other metals. Furthermore, the first electrode and the second electrode include metals such as copper, gold, and nickel.

[0016] 1A to 1D are cross-sectional views schematically illustrating steps of an electronic component mounting method according to the first embodiment. In the first embodiment, a case will be described in which bumps formed on electrodes (first electrodes) of a semiconductor chip (first electronic component) are fusion-bonded (hereinafter sometimes referred to as "bump bonding") to connection terminals (second electrodes) of a printed circuit board (second electronic component). The semiconductor chips may be diced into a wafer.

[0017] 1A, the semiconductor chip 20 and the printed circuit board 10 are immersed in an aqueous solution containing citric acid (hereinafter referred to as "citric acid aqueous solution") 51 contained in an etching bath (etching device) 50. Here, the semiconductor chip 20 has a plurality of electrodes 21 formed on its surface, and bumps 22 formed on each electrode 21. In addition, connection terminals 11 are formed on the surface of the printed circuit board 10.

[0018] Citric acid has the property of dissolving metal oxides such as copper. For example, copper oxide (CuO) dissolves in an aqueous solution of citric acid (C6H8O7) according to the following reaction formula:

[0019] 3CuO + 2C6H8O7 → Cu3(C6H8O7)2 + H2O Therefore, by immersing the semiconductor chip 20 and the printed circuit board 10 in a citric acid solution 51, the oxide film (hereinafter referred to as the "metal oxide film") formed on the surfaces of the bumps 22 and the connection terminals 11 is etched away by the citric acid solution 51.

[0020] Here, the concentration of citric acid is preferably 0.1% by mass or more and 10% by mass or less. A citric acid concentration of less than 0.1% by mass is undesirable because the etching rate of the metal oxide film becomes slow. On the other hand, a citric acid concentration of more than 10% by mass is undesirable because citric acid crystals precipitate in the citric acid aqueous solution and the surface roughness of the treated metal oxide film deteriorates.

[0021] The temperature of the citric acid aqueous solution is preferably in the range of 20° C. to 90° C. In particular, by setting the temperature of the citric acid aqueous solution to 40° C. or higher, the etching rate of the metal oxide film can be increased.

[0022] Citric acid is weakly acidic and easy to handle, so that etching of metal oxide films can be performed simply by preparing an etching tank 50 containing an aqueous citric acid solution as an etching apparatus. Therefore, compared to conventional reduction treatments of metal oxide films using carboxylic acid gas, metal oxide films can be removed with a simpler etching apparatus.

[0023] Furthermore, even if the substrate is made of a resin with low acid resistance, the etching process for the metal oxide film is performed using a weakly acidic citric acid aqueous solution, so that the substrate can be prevented from being corroded during the etching process.

[0024] In this embodiment 1, the metal oxide film is removed by immersing the semiconductor chip 20 and the printed circuit board 10 in a citric acid aqueous solution, but it may also be removed by spraying a mist of citric acid aqueous solution onto the surfaces of the semiconductor chip 20 and the printed circuit board 10.

[0025] The etching material for removing the metal oxide film is not particularly limited as long as it exhibits an etching effect on the oxide film of the bumps 22 and the connection terminals 11, and in addition to citric acid, it is possible to use weakly acidic organic acids with a pH of 2 to 6, such as acetic acid, tartaric acid, malonic acid, succinic acid, and adipic acid. The etching material may also be a mixture of these organic acids.

[0026] Next, as shown in FIG. 1B, the semiconductor chip 20 and the printed circuit board 10 that have been etched with the citric acid aqueous solution are immersed in pure water 61 contained in a cleaning tank 60 by a well-known method, and the surfaces of the semiconductor chip 20 and the printed circuit board 10 are cleaned under running water.

[0027] It is preferable that the semiconductor chips 20 and the printed circuit board 10 are transported to the cleaning tank 60 in an inert gas atmosphere such as nitrogen so as to prevent the surfaces of the bumps 22 and the connection terminals 11 from being re-oxidized during the transport from the etching tank 50 to the cleaning tank 60. The semiconductor chips 20 and the printed circuit board 10 may be cleaned using an ultrasonic cleaning device.

[0028] After cleaning, the semiconductor chip 20 and printed circuit board 10 are subjected to a drying process (not shown) by a well-known method. It is preferable that the drying process be performed in a drying chamber in an inert gas atmosphere such as nitrogen so that the surfaces of the bumps 22 and connection terminals 11 are not re-oxidized during the drying process. Drying by applying heat from the outside is not preferable because it accelerates the oxidation of the surfaces of the bumps 22 and connection terminals 11.

[0029] Next, as shown in FIG. 1C, the semiconductor chip 20 and printed circuit board 10 that have been cleaned and dried are placed in a bonding device (flip-chip bonder) 70, and the bumps 22 formed on the electrodes 21 of the semiconductor chip 20 are positioned opposite the connection terminals 11 of the printed circuit board 10.

[0030] Then, as shown in Figure 1D, after the bumps 22 are brought into contact with the connection terminals 11 of the printed circuit board 10, the semiconductor chip 20 is heated to melt the bumps 22, and the bumps 22 formed on the electrodes 21 of the semiconductor chip 20 are melt-bonded to the connection terminals 11 of the printed circuit board 10 (bonding process).

[0031] In the above bonding step, it is preferable to keep the inside of the bonding device 70 in an inert gas atmosphere such as nitrogen so that the surfaces of the bumps 22 and the connection terminals 11 are not re-oxidized.

[0032] In addition, it is preferable that the semiconductor chip 20 and printed circuit board 10 that have been cleaned and dried are transported to the bonding device 70 in an inert gas atmosphere such as nitrogen so that the surfaces of the bumps 22 and connection terminals 11 are not re-oxidized during transport.

[0033] In the electronic component mounting method of this embodiment 1, before performing the bonding process of bonding the bumps 22 formed on the electrodes 21 of the semiconductor chip (first electronic component) 20 to the connection terminals 11 of the printed circuit board (second electronic component) 10, the semiconductor chip 20 and the printed circuit board 10 are etched with a weakly acidic organic acid such as citric acid to remove the oxide film (metal oxide film) formed on the surfaces of the bumps 22 and the connection terminals 11, thereby making it possible to perform bump bonding in a state in which the oxide film formed on the surfaces of the bumps 22 and the connection terminals 11 has been removed.

[0034] The etching process of the metal oxide film in this embodiment 1 is carried out using a weakly acidic organic acid, which makes it easy to handle. Compared to conventional reduction processes of the metal oxide film using carboxylic acid gas, there is no need to take measures against corrosion caused by the carboxylic acid gas or against carboxylic acid salt residues, and highly reliable fluxless bump bonding can be obtained with simple equipment.

[0035] In this embodiment 1, before the etching process of the metal oxide film, as shown in FIG. 2, an irradiation process may be performed in which the semiconductor chip 20 and the printed circuit board 10 are placed in an ultraviolet irradiation device 80 and ultraviolet (UV) rays are irradiated onto the surfaces of the semiconductor chip 20 and the printed circuit board 10 from an ultraviolet light source 81.

[0036] During the manufacturing process of the semiconductor chip 20 and the printed circuit board 10, unwanted contaminants may adhere to the surfaces of the semiconductor chip 20 and the printed circuit board 10. If contaminants adhere to the surfaces, the metal oxide film may not be sufficiently removed during the etching process of the metal oxide film. Furthermore, there is a risk that the contaminants may enter the citric acid aqueous solution during the etching process and contaminate the citric acid aqueous solution.

[0037] Therefore, prior to the etching step, it is preferable to irradiate the surfaces of the semiconductor chip 20 and the printed circuit board 10 with ultraviolet light to remove contaminants adhering to the surfaces of the semiconductor chip 20 and the printed circuit board 10. This allows the metal oxide film to be removed in a short time during the etching step of the metal oxide film, and also allows the citric acid solution to be kept clean.

[0038] Here, in the ultraviolet irradiation process, it is preferable to perform ultraviolet irradiation in a state where an inert gas such as nitrogen (N2) is supplied to the ultraviolet irradiation device 80 (inert gas atmosphere) so that the surfaces of the bumps 22 and the connection terminals 11 are not oxidized.

[0039] Although the wavelength of the ultraviolet light is not particularly limited, vacuum ultraviolet light (having a wavelength of 200 nm or less) having a short wavelength and high energy is preferable. A mercury lamp, an excimer lamp, a plasma UV lamp, or the like can be used as the ultraviolet light source 62. Instead of irradiating the surfaces of the semiconductor chip 20 and the printed circuit board 10 with ultraviolet light, plasma irradiation may be used.

[0040] Furthermore, in the bonding process of this embodiment 1, in order to prevent the surfaces of the bumps 22 and the connection terminals 11 from being re-oxidized, instead of creating an inert gas atmosphere such as nitrogen inside the bonding device 70, the bonding process may be performed in a state where an inert gas is supplied around the semiconductor chip 20 and the printed circuit board 10 inside the bonding device 70.

[0041] The etching step in the first embodiment may be performed in the bonding apparatus 70. In this case, the etching step and the bonding step are preferably performed in a state where the bonding apparatus 70 is filled with an inert gas.

[0042] (Embodiment 2) In the above-mentioned embodiment 1, the semiconductor chip 20 and the printed circuit board 10 are etched with a weakly acidic organic acid such as citric acid to remove the oxide film formed on the surfaces of the bumps 22 and the connection terminals 11, thereby making it possible to perform bump bonding in a state in which the oxide film formed on the surfaces of the bumps 22 and the connection terminals 11 has been removed.

[0043] However, for example, when solder is used as the material of the bumps 22 and copper is used as the material of the connection terminals 11, etching with citric acid or the like may take longer to remove the oxide film formed on the surface of the bumps 22 than to remove the oxide film formed on the surface of the connection terminals 11. Therefore, variations in the thickness of the oxide film formed on the surface of the bumps 22 or variations in the concentration of the etching solution such as citric acid may result in insufficient removal of the oxide film formed on the surface of the bumps 22. As a result, if fusion bonding is performed in a state where the oxide film has not been sufficiently removed, this may result in variations in the joint resistance.

[0044] One possible solution to this problem is to perform fusion bonding while controlling the distance between the electrodes 21 of the semiconductor chip 20 and the connection terminals 11 of the printed circuit board 10 so that it is smaller than the height of the bumps 22. In this method, the fused bumps 22 are significantly deformed by the pressure from the semiconductor chip 20 and the printed circuit board 10, causing the oxide film formed on the surface of the bumps 22 to break and exposing the intrinsic surface of the bumps 22. This causes an intermetallic compound to form at the interface between the bumps 22 that have wrapped around the side surfaces of the connection terminals 11 and the connection terminals 11, thereby reducing variations in the joint resistance.

[0045] However, with the above method, the molten bumps 22 wrap around the side surfaces of the connection terminals 11, and as the pitch of the bumps 22 becomes narrower, there is a risk of short-circuiting between adjacent connection terminals 11. Therefore, in order to accommodate the narrower pitch of the bumps 22, it is necessary to perform fusion bonding while controlling the distance between the electrodes of the semiconductor chip 20 and the connection terminals 11 of the printed circuit board 10 to a distance that prevents the molten bumps 22 from wrapping around the side surfaces of the connection terminals 11.

[0046] Therefore, in this embodiment 2, as shown in Figure 3, in the bonding process of the bumps 22, the bumps 22 (with the oxide film 30 remaining on the surface) formed on the electrodes 21 of the semiconductor chip 20 are brought into contact with the connection terminals 11 of the printed circuit board 10, and then, while the bumps 22 are melted, vibration is applied to the printed circuit board 10 to cause a relative displacement in a direction parallel to the interface between the bumps 22 and the connection terminals 11.

[0047] Here, in the bonding process of the bumps 22, in order to prevent the molten bumps 22 from wrapping around the sides of the connection terminals 11, it is preferable that the vibration applied to the semiconductor chip 20 be performed while controlling the distance between the electrodes 21 of the semiconductor chip 20 and the connection terminals 11 of the printed circuit board 10 so that no pressure is applied to the molten bumps 22 from the semiconductor chip 20 and the printed circuit board 10.

[0048] When the bump 22 is bonded using this method, as shown in Figure 4, vibration applied to the printed circuit board 10 causes the molten bump 22 to flow, and the flow pressure of the bump 22 breaks the oxide film 30 remaining on the surface of the bump 22 that is in contact with the connection terminal 11, exposing the true surface of the bump 22. This forms an intermetallic compound at the interface between the bump 22 and the connection terminal 11. As a result, even if the oxide film formed on the surface of the bump 22 is not sufficiently removed in the etching process using citric acid or the like, it is possible to reduce variations in the bonding resistance.

[0049] The vibration may be applied to the semiconductor chip 20. The vibration applied to the printed circuit board 10 or the semiconductor chip 20 may be controlled by a servo motor to control the stage on which the printed circuit board 10 is placed or the mounting head that holds the semiconductor chip 20. The vibration applied to the printed circuit board 10 or the semiconductor chip 20 may be divided into directions perpendicular to each other at the interface between the bump 22 and the connection terminal 11.

[0050] In the second embodiment, the frequency of the vibration applied to the printed circuit board 10 or the semiconductor chip 20 is preferably in the range of 1 / 20 Hz to 50 Hz, and more preferably in the range of 1 / 5 Hz to 10 Hz. A frequency lower than 1 / 20 Hz is not preferable because it lengthens the bonding process of the bumps 22 and increases production costs. Also, a frequency higher than 50 Hz is not preferable because it becomes difficult for the vibration applied to the printed circuit board 10 or the semiconductor chip 20 to follow the control by the servo motor.

[0051] The amplitude of the vibration applied to the printed circuit board 10 or the semiconductor chip 20 is preferably at least 1 / 20, and more preferably at least 1 / 10, of the width of the bump 22. If the amplitude of the vibration is less than 1 / 20 of the width of the bump 22, the flow pressure of the bump 22 acting on the oxide film 30 remaining on the surface of the bump 22 will be weak, making the oxide film 30 less likely to break, which is undesirable. In addition, the amplitude is preferably within a range that does not cause contact with adjacent bumps 22.

[0052] Furthermore, when vibration is applied to the printed circuit board 10 or the semiconductor chip 20 in the bonding process of the bumps 22, the etching process using citric acid or the like, which is performed as a pretreatment for the bonding process, may be performed only on the printed circuit board on which the bumps 22 are not formed. In this case, the oxide film formed on the surface of the connection terminals 11 is removed in the etching process, and the oxide film formed on the surface of the bumps 22 is removed in the bonding process, which is performed while vibration is applied to the printed circuit board 10 or the semiconductor chip 20.

[0053] <Effect of Vibration> The following samples A to C were prepared, and the effect of vibration was confirmed.

[0054] [Sample A] After etching the semiconductor chip 20 and the printed circuit board 10 with citric acid, the bumps (solder) 22 formed on the electrodes (copper) 21 of the semiconductor chip 20 were melt-bonded to the connection terminals (copper) 11 formed on the printed circuit board 10 without applying vibration to the printed circuit board 10.

[0055] [Sample B] After etching the semiconductor chip 20 and the printed circuit board 10 with citric acid, the bumps (solder) 22 formed on the electrodes (copper) 21 of the semiconductor chip 20 were melt-bonded to the connection terminals (copper) 11 formed on the printed circuit board 10 while applying vibration to the printed circuit board 10.

[0056] [Sample C] Using a conventional flux method, bumps (solder) 22 formed on electrodes (copper) 21 of a semiconductor chip 20 were fused and joined to connection terminals (copper) 11 formed on a printed circuit board 10.

[0057] Table 1 shows the results of measuring the interface resistance between the bump 22 and the connection terminal 11 for each of Samples A to C. The interface resistance was measured by the two-terminal method using a tester.

[0058]

[0059] As shown in Table 1, sample A, in which the bumps 22 were fusion-bonded to the connection terminals 11 without applying vibration to the printed circuit board 10, had a large variation in interface resistance.

[0060] In contrast, sample B, in which bumps 22 were melt-bonded to connection terminals 11 while applying vibration to printed circuit board 10, exhibited an interface resistance with the same variation as sample C, in which bumps 22 were melt-bonded to connection terminals 11 using the conventional flux method.

[0061] 5A is a cross-sectional SEM photograph of the bump bonding portion of sample A, and FIG. 5B is a cross-sectional SEM photograph of the bump bonding portion of sample B. As shown in FIG.

[0062] As shown in Figure 5A, in sample A, the molten bump 22 does not wet and spread over the surface of the connection terminal 11, and it can be seen that no intermetallic alloy is formed at the interface between the bump 22 and the connection terminal 11.

[0063] On the other hand, as shown in Figure 5B, in sample B, the molten bump 22 wets and spreads over the surface of the connection terminal 11, and an intermetallic alloy 40 is formed at the interface between the bump 22 and the connection terminal 11.

[0064] (Embodiment 3) The bump 22 bonding process is performed by bringing the bump 22 into contact with the connection terminal 11 of the printed circuit board 10, and then heating the mounting head holding the semiconductor chip 20 to melt the bump 22, and then melt-bonding the bump 22 formed on the electrode 21 of the semiconductor chip 20 to the connection terminal 11 of the printed circuit board 10.

[0065] At this time, the mounting head, semiconductor chip 20, printed circuit board 10, and the stage on which printed circuit board 10 is placed all undergo thermal expansion, and if the height of the mounting head is not adjusted, the thermal expansion will narrow the distance between semiconductor chip 20 and printed circuit board 10, crushing the molten bumps 22. For this reason, the step of bonding bumps 22 is usually performed by raising the height of the mounting head in accordance with the thermal expansion of the mounting head, etc., so that pressure from the semiconductor chip 20 and printed circuit board 10 is not applied to the molten bumps 22 and the distance between electrodes 21 and connection terminals 11 does not change.

[0066] In this embodiment 3, in the process of bonding the bumps 22, instead of raising the height of the mounting head in accordance with the thermal expansion of the mounting head, etc., the height of the mounting head is raised to a predetermined height prior to the thermal expansion of the mounting head, etc., and then vibration is applied to the printed circuit board 10 or the semiconductor chip 20.

[0067] FIG. 6 is a diagram showing a bonding process of the bumps 22 in the third embodiment.

[0068] As shown in Figure 6, after the bumps 22 formed on the electrodes 21 of the semiconductor chip 20 are brought into contact with the connection terminals 11 of the printed circuit board 10 (step A), the mounting head 72 holding the semiconductor chip 20 is heated to melt the bumps 22, and the height of the mounting head 72 is raised to a predetermined height, provided that the bumps 22 do not separate from the connection terminals 11, and the distance H between the electrodes 21 and the connection terminals 11 is increased to a predetermined distance, and then vibration is applied to the stage 71 on which the printed circuit board 10 is placed (step B).

[0069] At this time, the molten bump 22 flows due to the vibration applied to the stage 71 (printed circuit board 10), and the oxide film 30 remaining on the surface of the bump 22 in contact with the connection terminal 11 is broken by the flow pressure of the bump 22, exposing the true surface of the bump 22 and spreading it over the surface of the connection terminal 11.

[0070] Thereafter, while maintaining the height of the mounting head 72 at a predetermined height, the application of vibration is continued while the distance H between the electrodes 21 and the connection terminals 11 is narrowed in accordance with the thermal expansion of the mounting head 72, semiconductor chip 20, printed circuit board 10, and stage 71 (steps C and D). As a result, the molten bumps 22 wet and spread over the entire surfaces of the connection terminals 11, and an intermetallic alloy is formed at the interfaces between the bumps 22 and the connection terminals 11.

[0071] 7 is a cross-sectional SEM photograph of the bonded portion of the bump in this embodiment. As shown in FIG. 7, the molten bump 22 spreads over the entire surface of the connection terminal 11, and an intermetallic alloy 40 is formed at the interface between the bump 22 and the connection terminal 11. This reduces the interfacial resistance between the bump 22 and the connection terminal 11.

[0072] In the third embodiment, the distance H between the electrodes 21 and the connection terminals 11 is increased to a predetermined distance, and then vibration is applied to the stage 71 (printed circuit board 10), thereby applying vibration to the elongated bumps 22, i.e., the bumps 22 with a small contact surface with the connection terminals 11. This makes it possible to reduce the amplitude of the vibration applied to the stage 71 (printed circuit board 10), thereby preventing short circuits with adjacent electrodes 21 even if the pitch of the bumps 22 becomes increasingly narrow.

[0073] 8 is a cross-sectional view showing a schematic configuration of an electronic component mounting system according to one embodiment of the present invention. This embodiment will be described by taking as an example a case where bumps formed on electrodes (first electrodes) of a semiconductor chip (first electronic component) are fused and bonded to connection terminals (first electrodes) of a printed circuit board (second electronic component). The semiconductor chips may be a plurality of diced semiconductor chips in a wafer state.

[0074] 8, the electronic component mounting system 100 in this embodiment is an apparatus for bonding bumps 22 formed on electrodes 21 of a semiconductor chip 20 to connection terminals 11 of a printed circuit board 10, and includes an irradiation apparatus 80, an etching apparatus 50, and a bonding apparatus 70. The etching apparatus 50 is also provided with a cleaning / drying apparatus (not shown) for cleaning and drying the etched semiconductor chip 20 and printed circuit board 10.

[0075] The irradiation device 80 irradiates the surfaces of the semiconductor chip 20 and the printed circuit board 10 with ultraviolet (UV) light to remove contaminants adhering to the surfaces of the semiconductor chip 20 and the printed circuit board 10 .

[0076] The etching device 50 removes the oxide film formed on the surfaces of the bumps 22 and the connection terminals 11 by etching the semiconductor chip 20 and the printed circuit board 10 with an etching solution containing a weakly acidic organic acid such as citric acid.

[0077] The bonding device 70 accommodates the semiconductor chip 20 and printed circuit board 10 that have been etched by the etching device 50, and while supplying an inert gas, bonds the bumps 22 formed on the electrodes 21 of the semiconductor chip 20 to the connection terminals 11 of the printed circuit board 10.

[0078] In the electronic component mounting system 100 of this embodiment, before the bumps 22 formed on the electrodes (first electrodes) 21 of the semiconductor chip (first electronic component) 20 are joined to the connection terminals (second electrodes) 11 of the printed circuit board (second electronic component) 10 in the joining device 70, the semiconductor chip 20 and the printed circuit board 10 are etched in the etching device 50 with a weakly acidic organic acid such as citric acid to remove the oxide film (metal oxide film) formed on the surfaces of the bumps 22 and the connection terminals 11, thereby making it possible to perform bump joining with the metal oxide film removed.

[0079] In this embodiment, the etching removal of the metal oxide film is performed using a weakly acidic organic acid, which is easy to handle. Compared to conventional reduction treatments of metal oxide films using carboxylic acid gas, there is no need to take measures against corrosion caused by carboxylic acid gas or against carboxylic acid salt residues, and highly reliable fluxless bump bonding can be obtained with simple equipment.

[0080] Furthermore, before etching away the metal oxide film in the etching device 50, the irradiation device 80 irradiates the surfaces of the semiconductor chip 20 and the printed circuit board 10 with ultraviolet light to remove contaminants adhering to the surfaces of the semiconductor chip 20 and the printed circuit board 10 in advance, thereby enabling the metal oxide film to be removed in a short time and keeping the etching solution clean.

[0081] Hereinafter, specific configurations of the irradiation device 80, the etching device 50, and the bonding device 70 will be described with reference to FIG.

[0082] <Irradiation Device> The irradiation device 80 includes a chamber 80a that accommodates the semiconductor chip 20 and the printed circuit board 10, a vacuum pump 83 that evacuates the chamber 80a, and a supply means 84 that supplies an inert gas such as nitrogen into the chamber 80a. Inside the chamber 80a, there are provided an ultraviolet light source 81 that irradiates ultraviolet light, and a stage 82 on which the semiconductor chip 20 and the printed circuit board 10 are placed.

[0083] After the chamber 80a is evacuated by a vacuum pump 83, an inert gas such as nitrogen is supplied into the chamber 80a by a supply means 84, and ultraviolet light is irradiated onto the surfaces of the semiconductor chip 20 and the printed circuit board 10 from an ultraviolet light source 81. This removes contaminants adhering to the surfaces of the semiconductor chip 20 and the printed circuit board 10.

[0084] The ultraviolet light source 62 may be a mercury lamp, a xenon amplifier, an excimer lamp, etc. The wavelength of the ultraviolet light is not particularly limited, but vacuum ultraviolet light (having a wavelength of 200 nm or less) which has a short wavelength and high energy is more preferable.

[0085] The irradiation device 80 may be an irradiation device that irradiates the surfaces of the semiconductor chip 20 and the printed circuit board 10 with plasma instead of irradiating with ultraviolet light.

[0086] <Etching Apparatus> The etching apparatus 50 includes an etching tank 50a containing an aqueous solution (etchant) 51 containing a weakly acidic organic acid such as citric acid. By immersing the semiconductor chip 20 and the printed circuit board 10 in the etching solution 51 contained in the etching tank 50a, the oxide films formed on the surfaces of the bumps 22 and the connection terminals 11 are etched away.

[0087] The etching solution 51 is not particularly limited as long as it exhibits an etching effect on the oxide films of the bumps 22 and the connection terminals 11, and in addition to citric acid, it is possible to use weakly acidic organic acids such as acetic acid, tartaric acid, malonic acid, succinic acid, and adipic acid. The etching solution 51 may also be a mixture of these organic acids.

[0088] The semiconductor chip 20 and the printed circuit board 10 etched by the etching device 50 are washed and dried by a washing and drying device (not shown).

[0089] The etching device 50 may be an etching device that sprays the etching solution 51 in a mist onto the surfaces of the semiconductor chip 20 and the printed circuit board 10 instead of immersing the semiconductor chip 20 and the printed circuit board 10 in the etching solution 51 .

[0090] <Bonding Apparatus> The bonding apparatus 70 includes a chamber 70 a that houses the semiconductor chip 20 and the printed circuit board 10 , a stage 71 on which the printed circuit board 10 is placed, and a mounting head 72 that holds the semiconductor chip 20 .

[0091] The mounting head 72 is disposed at a position opposite the stage 71, and holds the semiconductor chip 20 in an inverted state (face down) so that the bumps 22 formed on the electrodes 21 of the semiconductor chip 20 face the connection terminals 11 of the printed circuit board 10. The mounting head 72 is also provided with a heater 75 for heating the semiconductor chip 20.

[0092] The chamber 70a is evacuated by a vacuum pump 73, and then an inert gas atmosphere such as nitrogen is supplied into the chamber 70a from a container 74.

[0093] With an inert gas supplied into the chamber 70a, the mounting head 72 holding the semiconductor chip 20 is lowered toward the printed circuit board 10, thereby pressing the bumps 22 of the semiconductor chip 20 against the connection terminals 11 of the printed circuit board 10. Thereafter, the semiconductor chip 20 is heated by a heater 75 to a temperature at which the bumps 22 melt, thereby melt-bonding the bumps 22 to the connection terminals 11 (see FIGS. 1C and 1D).

[0094] The bonding device 70 is not limited to the above configuration, and may adopt, for example, a general configuration of a well-known flip-chip bonder.

[0095] After the semiconductor chip 20 and printed circuit board 10 have been etched in the etching device 50, they are preferably washed and dried, and then transported to the bonding device 70 in an inert gas atmosphere such as nitrogen to prevent the surfaces of the bumps 22 and connection terminals 11 from being re-oxidized during transport to the bonding device 70.

[0096] Furthermore, as shown in FIG. 9, the bonding device 70 may be provided with a supply means 76 for supplying an inert gas such as nitrogen to the periphery of the semiconductor chip 20 and the printed circuit board 10 when the bumps 22 formed on the electrodes 21 of the semiconductor chip 20 are melt-bonded to the connection terminals 11 of the printed circuit board 10.

[0097] The supply means 76 is attached to the mounting head 72 so as to surround the side of the mounting head 72, and a through-hole 77 through which the inert gas passes is provided on the side of the supply means 76. A storage chamber 78 storing the inert gas is connected to the through-hole 77 via a pipe 79, and the inert gas is sprayed from the tip of the through-hole 77 toward the stage 71. This forms an air curtain around the semiconductor chip 20 and the printed circuit board 10, preventing air from entering from outside. As a result, oxidation of the surfaces of the bumps 22 and the connection terminals 11 can be prevented without filling the entire interior of the bonding device 70 with inert gas.

[0098] 10 , the bonding device 70 may include a vibration applying unit 85 that applies vibration to the stage 71 on which the printed circuit board 10 is placed, causing a relative displacement in a direction parallel to the interface between the bumps 22 and the connection terminals 11. After the bumps 22 are brought into contact with the connection terminals 11 and melted, vibration applied to the printed circuit board 10 causes the melted bumps 22 to flow. The flow pressure of the bumps 22 breaks the oxide film 30 remaining on the surface of the bumps 22 that are in contact with the connection terminals 11, exposing the intrinsic surface of the bumps 22. As a result, an intermetallic compound can be formed at the interface between the bumps 22 and the connection terminals 11. The vibration applying unit 85 may also apply vibration to the mounting head 72 that holds the semiconductor chip 20. The application of vibration by the vibration applying unit 85 can be controlled, for example, by a servo motor or the like.

[0099] 11 , the etching apparatus 50, together with an accompanying cleaning and drying apparatus (not shown), may be incorporated into a bonding apparatus 70. After the etching process is completed, the semiconductor chip 20 and the printed circuit board 10 are respectively transferred by a transfer mechanism (not shown) such that the semiconductor chip 20 is held by a mounting head 72 and the printed circuit board 10 is placed on a stage 71.

[0100] When conventional reduction treatment of metal oxide films using carboxylic acid gas is performed inside a bonding apparatus, there is a possibility that the components inside the bonding apparatus may corrode, making it difficult to incorporate the treatment into the bonding apparatus. However, the present invention makes this possible.

[0101] When etching is performed on a plurality of diced semiconductor chips 20 in a wafer state in the etching apparatus 50, the etching and cleaning / drying processes may also be performed on the plurality of semiconductor chips 20 in a wafer state in the bonding apparatus 70. In this case, after the etching and cleaning / drying processes are completed, each semiconductor chip 20 is picked up from the wafer and held in an inverted state by the mounting head 72.

[0102] In the electronic component mounting system 100 of this embodiment, if the amount of contaminants adhering to the surfaces of the semiconductor chip 20 and the printed circuit board 10 is small enough not to affect the removal of the oxide film formed on the surfaces of the bumps 22 and the connection terminals 11 during the etching process, the irradiation device 80 may not be provided.

[0103] Although the present invention has been described above with reference to preferred embodiments, such description is not intended to be limiting and various modifications are possible.

[0104] REFERENCE SIGNS LIST 10 Printed circuit board (second electronic component) 11 Connection terminal (second electrode) 20 Semiconductor chip (first electronic component) 21 Electrode (first electrode) 22 Bump 30 Oxide film 40 Intermetallic 50 Etching device 50a Etching bath 51 Citric acid aqueous solution (etchant) 60 Cleaning bath 61 Pure water 62 Ultraviolet light source 70 Bonding device 70a Chamber 71 Stage 72 Mounting head 73 Vacuum pump 74 Container 75 Heater 76 Supply means 77 Through hole 78 Storage chamber 79 Piping 80 Irradiation device 80a Chamber 81 Ultraviolet light source 82 Stage 83 Vacuum pump 84 Supply means 85 Application means 100 Electronic component mounting system

Claims

1. An electronic component mounting method for bonding a bump formed on a first electrode of a first electronic component to a second electrode formed on a second electronic component, comprising: an etching step of removing an oxide film formed on the surface of the bump and the second electrode by etching the first electronic component and the second electronic component with a weak organic acid; and a bonding step of housing the first electronic component and the second electronic component in a bonding device after the etching step, and bonding the bump formed on the first electrode of the first electronic component to the second electrode formed on the second electronic component while supplying an inert gas to the bonding device.

2. The electronic component mounting method according to claim 1, further comprising an irradiation step of irradiating surfaces of the first electronic component and the second electronic component with ultraviolet light or plasma before the etching step.

3. The electronic component mounting method according to claim 1, wherein the weak organic acid is an organic acid selected from the group consisting of citric acid, acetic acid, tartaric acid, malonic acid, succinic acid, and adipic acid.

4. The electronic component mounting method according to claim 1, wherein the bonding step is performed in the bonding device while an inert gas is supplied to the periphery of the first electronic component and the second electronic component.

5. The electronic component mounting method according to claim 1, wherein the etching step is carried out within the bonding device, and the etching step and the bonding step are carried out in a state where the bonding device is filled with an inert gas.

6. The electronic component mounting method according to claim 1, wherein the bonding step is performed by bringing the bump formed on the first electrode into contact with the second electrode, and then, in a state in which the bump is melted, applying vibration to the first electronic component or the second electronic component that causes a relative displacement in a direction parallel to the interface between the bump and the second electrode.

7. The electronic component mounting method according to claim 6, wherein in the bonding step, the vibration applied to the first electronic component or the second electronic component is performed while controlling the distance between the first electrode and the second electrode so that no pressing force is applied from the first electronic component or the second electronic component to the bump in a molten state.

8. The electronic component mounting method according to claim 6, wherein in the bonding step, the frequency of the vibration applied to the first electronic component or the second electronic component is in the range of 1 / 20 Hz to 50 Hz.

9. The electronic component mounting method according to claim 6, wherein in the bonding step, the amplitude of the vibration applied to the first electronic component or the second electronic component is 1 / 20 or more of the width of the bump.

10. The electronic component mounting method according to claim 6, wherein the bonding process includes the steps of: bringing the bump formed on the first electrode into contact with the second electrode, and then, in a state in which the bump is melted, separating the first electrode and the second electrode to a predetermined distance under the condition that the bump does not separate from the second electrode, and then starting to apply the vibration to the first electronic component or the second electronic component; and continuing to apply the vibration while narrowing the distance between the first electrode and the second electrode.

11. An electronic component mounting system for bonding a bump formed on a first electrode of a first electronic component to a second electrode formed on a second electronic component, comprising: an etching device for etching the first electronic component and the second electronic component with a weak organic acid to remove an oxide film formed on the surface of the bump and the second electrode; and a bonding device for housing the first electronic component and the second electronic component etched by the etching device and bonding the bump formed on the first electrode of the first electronic component to the second electrode formed on the second electronic component while supplying an inert gas.

12. The electronic component mounting system of claim 11, further comprising an irradiation device that irradiates ultraviolet light or plasma onto surfaces of the first electronic component and the second electronic component, and in the etching device, the first electronic component and the second electronic component irradiated by the irradiation device are etched with the weakly acidic organic acid.

13. The electronic component mounting system according to claim 11, wherein the weak organic acid is an organic acid selected from the group consisting of citric acid, acetic acid, tartaric acid, malonic acid, succinic acid, and adipic acid.

14. An electronic component mounting system as described in claim 11, wherein the bonding device has a supply means for supplying an inert gas to the periphery of the first electronic component and the second electronic component when bonding the bump formed on the first electrode of the first electronic component to a second electrode formed on the second electronic component.

15. The electronic component mounting system according to claim 11, wherein the etching device is incorporated within the bonding device, and the bonding device has a filling means for filling the inside of the bonding device with an inert gas.

16. The electronic component mounting system of claim 11, wherein the bonding device has an application means for applying vibration to the first electronic component or the second electronic component, the vibration causing a relative displacement in a direction parallel to the interface between the bump and the second electrode, while the bump is in a melted state.

17. An electronic component mounting system as described in claim 16, wherein the vibration applied to the first electronic component or the second electronic component by the application means is performed while controlling the distance between the first electrode and the second electrode so that no substantial pressing force is applied from the first electronic component and the second electronic component to the bump in the molten state.

18. An electronic component mounting system as described in claim 16, wherein the frequency of the vibration applied to the first electronic component or the second electronic component by the applying means is in the range of 1 / 20 Hz to 50 Hz.

19. An electronic component mounting system as described in claim 16, wherein the amplitude of the vibration applied to the first electronic component or the second electronic component by the applying means is equal to or greater than 1 / 20 of the width of the bump.

20. An electronic component mounting method for bonding a bump formed on a first electrode of a first electronic component to a second electrode formed on a second electronic component, comprising: an etching step of etching the second electronic component with a weak organic acid to remove an oxide film formed on the surface of the second electrode; and a bonding step of, after the etching step, housing the first electronic component and the second electronic component in a bonding device and, while supplying an inert gas to the bonding device, bonding the bump formed on the first electrode of the first electronic component to the second electrode formed on the second electronic component, wherein the bonding step is performed by bringing the bump formed on the first electrode into contact with the second electrode, and then, while melting the bump, applying vibration to the first electronic component or the second electronic component that relatively displaces the bump in a direction parallel to the interface between the bump and the second electrode.

21. The electronic component mounting method according to claim 20, wherein in the bonding process, the vibration applied to the first electronic component or the second electronic component is performed while controlling the distance between the first electrode and the second electrode so that no pressing force is applied from the first electronic component or the second electronic component to the bump in a molten state.

22. The electronic component mounting method according to claim 20, wherein in the bonding step, the frequency of the vibration applied to the first electronic component or the second electronic component is in the range of 1 / 20 Hz to 50 Hz.

23. The electronic component mounting method according to claim 20, wherein in the bonding step, the amplitude of the vibration applied to the first electronic component or the second electronic component is equal to or greater than 1 / 20 of the width of the bump.

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