Electronic component mounting method and electronic component mounting system

Abstract

To provide an electronic component mounting method capable of obtaining a fluxless joint of high reliability by a simple device.SOLUTION: There is provided an electronic component mounting method for joining 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 the method includes: an etching process of performing etching processing, using weakly acidic organic acid on the first electronic component and the second electronic component to remove an oxide film formed on the surfaces of a bump and the second electrode; and a joining process of housing the first electronic component and the second electronic component in a joining device 70 after the etching process, and joining the bump formed on the first electrode to the second electrode while supplying an inert gas to the joining device.SELECTED DRAWING: Figure 1A

Description

Technical Field

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

Background Art

[0002] For example, when joining bumps formed on an electrode of an electronic component such as a semiconductor chip to a connection terminal 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 joining between the bumps and the electrodes is inhibited, which may cause a connection failure. Therefore, a method of joining the bumps to the electrodes of the wiring board while applying a flux to the surface of the wiring board is generally performed. Thereby, joining is performed in a state where the oxide film formed on the surface of the bumps and the electrodes is removed by the flux.

[0003] However, as the pitch of the bumps becomes narrower, it becomes difficult to sufficiently remove the flux. If there is a residue of the flux, there is a risk of causing wiring corrosion and migration. Therefore, a fluxless joining method has been studied as a method of eliminating the influence of the flux residue.

[0004] For example, Patent Document 1 describes a method of reflowing (fusion bonding) bumps formed on an electrode of an electronic component to a connection terminal of a wiring board while supplying a carboxylic acid gas such as formic acid into a heat melting treatment apparatus (bonder). By this method, the oxide film formed on the surface of the bumps and the connection terminals can be removed by the reducing action of the carboxylic acid gas.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the method described in Patent Document 1, since carboxylic acid gases such as formic acid introduced into a heat melting treatment apparatus (bonder) are corrosive, it is necessary to take sufficient corrosion countermeasures against the inside of the heat melting treatment apparatus. However, since the heat melting treatment apparatus has a complex structure including a transport mechanism, an alignment mechanism, a pressurization / heating mechanism, etc., it is necessary to take large-scale corrosion countermeasures, which causes a problem of increasing the cost of the apparatus.

[0007] Also, in the above method, after the reduction of the oxide film is completed, the carboxylic acid gas introduced into the bonder is exhausted and removed outside the apparatus. However, the carboxylate (organic compound) of the metal constituting the bump or connection terminal generated during the reduction treatment of the oxide film may not be decomposed, and there is a risk that a part of the carboxylate remains as a residue on the electronic component or the wiring board. In that case, since the carboxylate has high insulation properties, there is a problem that a highly reliable joint cannot be obtained.

[0008] In addition, in the above method, the reduction treatment of the oxide film needs to be performed by controlling the temperature inside the bonder within a range not lower than the reduction temperature of the oxide film of the bump by the carboxylic acid gas and lower than the melting temperature of the bump. However, since the evaporation amount of the carboxylic acid gas varies with the ambient temperature, there is a problem that it is difficult to control the concentration of the carboxylic acid gas.

[0009] The present invention has been made in view of such points, and its main object is to provide an electronic component mounting method and an electronic component mounting system capable of obtaining a highly reliable fluxless joint with a simple apparatus.

Means for Solving the Problems

[0010] The electronic component mounting method according to the present invention is an electronic component mounting method for joining a bump formed on a first electrode of a first electronic component to a second electrode formed on a second electronic component, including an etching step of removing an oxide film formed on the surfaces of the bump and the second electrode by etching the first electronic component and the second electronic component with a weakly acidic organic acid, and a joining step of, after the etching step, accommodating the first electronic component and the second electronic component in a joining apparatus and joining the bump formed on the first electrode of the first electronic component to the second electrode formed on the second electronic component in a state where an inert gas is supplied to the joining apparatus.

[0011] The electronic component mounting system according to the present invention is an electronic component mounting system for joining a bump formed on a first electrode of a first electronic component to a second electrode formed on a second electronic component, including an etching apparatus that removes an oxide film formed on the surfaces of the bump and the second electrode by etching the first electronic component and the second electronic component with a weakly acidic organic acid, and a joining apparatus that accommodates the first electronic component and the second electronic component that have been etched by the etching apparatus and joins the bump formed on the first electrode of the first electronic component to the second electrode formed on the second electronic component in a state where an inert gas is supplied.

[0012] Another method for mounting an electronic component according to the present invention is a method for mounting an electronic component in which bumps formed on a first electrode of a first electronic component are joined to a second electrode formed on a second electronic component, the method including an etching step of removing an oxide film formed on the surface of the second electrode by etching the second electronic component with a weakly acidic organic acid, and after the etching step, accommodating the first electronic component and the second electronic component in a bonding apparatus, and in a state where an inert gas is supplied to the bonding apparatus, joining the bumps formed on the first electrode of the first electronic component to the second electrode formed on the second electronic component. The joining step is performed while applying vibration that relatively displaces the first electronic component or the second electronic component in a direction parallel to the interface between the bump and the second electrode in a state where the bump formed on the first electrode is in contact with the second electrode and then the bump is melted.

Effect of the Invention

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

Brief Description of the Drawings

[0014]

Figure 1A

Figure 1B

Figure 1C

Figure 1D

Figure 2

Figure 3

Figure 4

Figure 5A

Figure 5B

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

[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 an electrode formed on a second electrode of a second electronic component. Here, the first electronic component and the second electronic component include a semiconductor chip, a BGA (Ball Grid Array) package, a printed circuit board, an interposer, an electronic component mounting board, and the like. Further, the bumps include bumps made of high melting point metals such as copper and gold, low melting point metals such as solder bumps, and bumps made of other metals. Further, the first electrode and the second electrode include metals such as copper, gold, and nickel.

[0016] Figs. 1A to 1D are cross-sectional views schematically showing the steps of the electronic component mounting method according to Embodiment 1. In Embodiment 1, a case where bumps formed on an electrode (first electrode) of a semiconductor chip (first electronic component) are melt-bonded (hereinafter, also referred to as "bump bonding") to connection terminals (second electrodes) of a printed circuit board (second electronic component) will be described as an example. Note that the semiconductor chip may be a plurality of diced semiconductor chips in a wafer state.

[0017] First, as shown in Fig. 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 in an etching tank (etching apparatus) 50. Here, the semiconductor chip 20 has a plurality of electrodes 21 formed on its surface, and bumps 22 are formed on each electrode 21. Also, 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 the citric acid aqueous solution 51, the oxide films (hereinafter referred to as "metal oxide films") formed on the surfaces of the bumps 22 and the connection terminals 11 are etched and removed by the citric acid aqueous solution 51.

[0020] Here, the concentration of citric acid is preferably 0.1 mass% or more and 10 mass% or less. If the concentration of citric acid is less than 0.1 mass%, the etching rate of the metal oxide film becomes slow, which is not preferable. Also, if the concentration of citric acid exceeds 10 mass%, crystals of citric acid precipitate in the citric acid aqueous solution or the surface roughness of the treated metal oxide film deteriorates, which is not preferable.

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

[0022] Since citric acid is weakly acidic and easy to handle, as an etching apparatus, an etching treatment of the metal oxide film can be performed simply by preparing an etching tank 50 filled with an aqueous citric acid solution. Therefore, compared with the conventional reduction treatment of the metal oxide film using carboxylic acid gas, the metal oxide film can be removed with a simple etching apparatus.

[0023] Also, even if the substrate is made of a resin with weak acid resistance, since the etching treatment of the metal oxide film is performed with a weakly acidic aqueous citric acid solution, it is possible to prevent the substrate from being corroded during the etching treatment.

[0024] In the first embodiment, the removal of the metal oxide film was performed by immersing the semiconductor chip 20 and the printed circuit board 10 in an aqueous citric acid solution. However, it may also be performed by spraying the aqueous citric acid solution in a mist form 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 films of the bumps 22 and the connection terminals 11. In addition to citric acid, for example, weakly acidic organic acids with a pH of 2 to 6 such as acetic acid, tartaric acid, malonic acid, succinic acid, and adipic acid can be used. Also, the etching material may 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 aqueous citric acid 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 while flowing water.

[0027] Note that, when transporting the semiconductor chip 20 and the printed circuit board 10 from the etching tank 50 to the cleaning tank 60, it is preferable to transport them to the cleaning tank 60 in an environment of an inert gas atmosphere such as nitrogen so that the surfaces of the bumps 22 and the connection terminals 11 are not oxidized again. Further, the cleaning of the semiconductor chip 20 and the printed circuit board 10 may be performed using an ultrasonic cleaning device.

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

[0029] Next, as shown in FIG. 1C, the semiconductor chip 20 and the printed circuit board 10 after the cleaning and drying processes are accommodated in a bonding device (flip chip bonder) 70, and the bumps 22 formed on the electrodes 21 of the semiconductor chip 20 are arranged to face the connection terminals 11 of the printed circuit board 10.

[0030] Then, as shown in FIG. 1D, after bringing the bumps 22 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 step).

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

[0032] Further, the semiconductor chip 20 and the printed circuit board 10 that have undergone the cleaning and drying processes are preferably transported to the bonding device 70 in an environment of an inert gas atmosphere such as nitrogen so that the surfaces of the bumps 22 and the connection terminals 11 are not oxidized again during transportation.

[0033] Before performing the bonding step 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, so that bump bonding can be performed in a state where the oxide film formed on the surfaces of the bumps 22 and the connection terminals 11 is removed.

[0034] Since the etching treatment of the metal oxide film in the first embodiment is performed using a weakly acidic organic acid, it is easy to handle, and compared with the conventional reduction treatment of the metal oxide film using carboxylic acid gas, there is no need to take measures against corrosion of the carboxylic acid gas and measures against residues of carboxylate salts. A highly reliable fluxless bump bonding can be obtained with a simple device.

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

[0036] In the manufacturing process of the semiconductor chip 20 and the printed circuit board 10, unnecessary contaminants may adhere to the surfaces of the semiconductor chip 20 and the printed circuit board 10. If contaminants adhere to the surface, there is a possibility that the metal oxide film cannot be sufficiently removed in the etching step of the metal oxide film. Also, during the etching process, there is a possibility that the contaminants may enter the citric acid aqueous solution and contaminate the citric acid aqueous solution.

[0037] Therefore, before the etching process, it is preferable to irradiate the surfaces of the semiconductor chip 20 and the printed circuit board 10 with ultraviolet rays in advance to remove the contaminants adhering to the surfaces of the semiconductor chip 20 and the printed circuit board 10. Thereby, in the etching process of the metal oxide film, the removal of the metal oxide film can be performed in a short time, and the aqueous citric acid solution can 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] Also, the wavelength of the ultraviolet ray is not particularly limited, but it is more preferable that it is vacuum ultraviolet ray (wavelength of 200 nm or less) with a short wavelength and high energy. Further, as the ultraviolet light source 62, a mercury lamp, an excimer lamp, a plasma UV lamp, or the like can be used. Further, instead of irradiating with ultraviolet rays, the surfaces of the semiconductor chip 20 and the printed circuit board 10 may be irradiated with plasma.

[0040] Also, in the bonding process in the first embodiment, instead of making the inside of the bonding device 70 into an inert gas atmosphere such as nitrogen so that the surfaces of the bumps 22 and the connection terminals 11 are not oxidized again, in the bonding device 70, it may be performed in a state where an inert gas is supplied to the periphery of the semiconductor chip 20 and the printed circuit board 10.

[0041] Also, the etching process in the first embodiment may be performed inside the bonding device 70. In this case, it is preferable that the etching process and the bonding process are performed in a state where the inside of the bonding device 70 is filled with an inert gas.

[0042] (Embodiment 2) In the above-described Embodiment 1, the semiconductor chip 20 and the printed circuit board 10 are subjected to an etching treatment 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, whereby bump bonding can be performed in a state where 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 bump 22 and copper is used as the material of the connection terminal 11, in the etching treatment with citric acid or the like, the removal of the oxide film formed on the surface of the bump 22 may take more time than the removal of the oxide film formed on the surface of the connection terminal 11. Therefore, due to variations in the film thickness of the oxide film formed on the surface of the bump 22, variations in the concentration of the etching solution such as citric acid, etc., the removal of the oxide film formed on the surface of the bump 22 may be insufficient. As a result, when fusion bonding is performed in a state where the removal of the oxide film is insufficient, there is a risk of causing variations in the bonding resistance.

[0044] As a countermeasure against this, a method of performing fusion bonding while controlling the distance between the electrode 21 of the semiconductor chip 20 and the connection terminal 11 of the printed circuit board 10 to be smaller than the height of the bump 22 can be considered. In this method, the melted bump 22 is greatly deformed by the pressing force from the semiconductor chip 20 and the printed circuit board 10, whereby the oxide film formed on the surface of the bump 22 is broken, and the true surface of the bump 22 is exposed. As a result, an intermetallic compound is formed at the interface between the bump 22 that has wrapped around the side surface of the connection terminal 11 and the connection terminal 11, so that variations in the bonding resistance can be reduced.

[0045] However, in the above method, since the melted bump 22 wraps around the side surface of the connection terminal 11, when the pitch of the bump 22 is reduced, there is a risk of short circuit occurring between adjacent connection terminals 11. Therefore, in order to cope with the reduction in the pitch of the bump 22, it is necessary to perform fusion bonding while controlling the distance between the electrode of the semiconductor chip 20 and the connection terminal 11 of the printed circuit board 10 to a distance at which the melted bump 22 does not wrap around the side surface of the connection terminal 11.

[0046] Therefore, in the second embodiment, as shown in FIG. 3, in the bump 22 bonding process, after the bump 22 (with the oxide film 30 remaining on the surface) formed on the electrode 21 of the semiconductor chip 20 is brought into contact with the connection terminal 11 of the printed circuit board 10, while the bump 22 is in a molten state, the printed circuit board 10 is vibrated in a direction parallel to the interface between the bump 22 and the connection terminal 11 while being relatively displaced.

[0047] Here, in the bump 22 bonding process, in order to prevent the molten bump 22 from flowing around the side surface of the connection terminal 11, the vibration applied to the semiconductor chip 20 is preferably performed while controlling the distance between the electrode 21 of the semiconductor chip 20 and the connection terminal 11 of the printed circuit board 10 so that no pressing force from the semiconductor chip 20 and the printed circuit board 10 is applied to the molten bump 22.

[0048] When the bump 22 bonding process is performed in such a manner, as shown in FIG. 4, due to the vibration applied to the printed circuit board 10, the molten bump 22 flows, 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, and the true surface of the bump 22 is exposed. As a result, an intermetallic compound is formed at the interface between the bump 22 and the connection terminal 11. Consequently, even when the removal of the oxide film formed on the surface of the bump 22 is insufficient in an etching process such as citric acid, the variation in the bonding resistance can be reduced.

[0049] Note that the vibration may be applied to the semiconductor chip 20. Further, the vibration applied to the printed circuit board 10 or the semiconductor chip 20 can be controlled by a servo motor for the stage on which the printed circuit board 10 is placed or the mounting head that holds the semiconductor chip 20. Also, the vibration applied to the printed circuit board 10 or the semiconductor chip 20 may be applied separately in 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. If the frequency is less than 1 / 20 Hz, the bonding process of the bumps 22 becomes longer and the production cost increases, which is not preferable. Also, if the frequency exceeds 50 Hz, the vibration applied to the printed circuit board 10 or the semiconductor chip 20 becomes difficult to follow the control by the servo motor, which is not preferable.

[0051] The width of the vibration applied to the printed circuit board 10 or the semiconductor chip 20 is preferably 1 / 20 or more of the width of the bump 22, and more preferably 1 / 10 or more. If the width of the vibration is less than 1 / 20 of the width of the bump 22, the hydrodynamic pressure of the bump 22 acting on the oxide film 30 remaining on the surface of the bump 22 becomes weak, and the oxide film 30 becomes difficult to break, which is not preferable. Also, the width of the amplitude is preferably within a range where it does not contact the adjacent bumps 22.

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

[0053] <Effect of vibration application> The following samples A to C were prepared to confirm the effect of vibration application.

[0054] [Sample A] After the semiconductor chip 20 and the printed circuit board 10 were etched with citric acid, the bump (solder) 22 formed on the electrode (copper) 21 of the semiconductor chip 20 was fusion-bonded to the connection terminal (copper) 11 formed on the printed circuit board 10 without applying vibration to the printed circuit board 10.

[0055] [Sample B] After the semiconductor chip 20 and the printed circuit board 10 were etched with citric acid, while applying vibration to the printed circuit board 10, the bump (solder) 22 formed on the electrode (copper) 21 of the semiconductor chip 20 was fusion-bonded to the connection terminal (copper) 11 formed on the printed circuit board 10.

[0056] [Sample C] Using the conventional flux method, the bump (solder) 22 formed on the electrode (copper) 21 of the semiconductor chip 20 was fusion-bonded to the connection terminal (copper) 11 formed on the printed circuit board 10.

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

[0058]

Table 1

[0059] As shown in Table 1, for Sample A in which the bump 22 was fusion-bonded to the connection terminal 11 without applying vibration to the printed circuit board 10, the variation in the interfacial resistance was large.

[0060] In contrast, for Sample B in which the bump 22 was fusion-bonded to the connection terminal 11 while applying vibration to the printed circuit board 10, an interfacial resistance with a variation equivalent to that of Sample C in which the bump 22 was fusion-bonded to the connection terminal 11 using the conventional flux method was obtained.

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

[0062] As shown in FIG. 5A, in sample A, it can be seen that the melted bump 22 does not wet and spread on the surface of the connection terminal 11, and 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 FIG. 5B, in sample B, it can be seen that the melted bump 22 wets and spreads on 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) In the bump 22 joining process, after bringing the bump 22 into contact with the connection terminal 11 of the printed circuit board 10, the mounting head holding the semiconductor chip 20 is heated to melt the bump 22, and the bump 22 formed on the electrode 21 of the semiconductor chip 20 is melt-joined to the connection terminal 11 of the printed circuit board 10.

[0065] At this time, since the mounting head, the semiconductor chip 20, the printed circuit board 10, and the stage on which the printed circuit board 10 is placed all thermally expand, if the height of the mounting head is not adjusted, the distance between the semiconductor chip 20 and the printed circuit board 10 will become narrow due to thermal expansion, and the melted bump 22 will be crushed. Therefore, usually, in the bump 22 joining process, while increasing the height of the mounting head in accordance with the thermal expansion of the mounting head etc., so that no pressing force from the semiconductor chip 20 and the printed circuit board 10 is applied to the melted bump 22, and the distance between the electrode 21 and the connection terminal 11 does not change.

[0066] In this Embodiment 3, instead of increasing the height of the mounting head while increasing it in accordance with the thermal expansion of the mounting head etc. in the bump 22 joining process, prior to the thermal expansion of the mounting head etc., after raising the height of the mounting head to a predetermined height, vibration is applied to the printed circuit board 10 or the semiconductor chip 20.

[0067] Figure 6 is a diagram showing the bonding process of the bump 22 in Embodiment 3.

[0068] As shown in FIG. 6, after bringing the bump 22 formed on the electrode 21 of the semiconductor chip 20 into contact with the connection terminal 11 of the printed circuit board 10 (step A), by heating the mounting head 72 that holds the semiconductor chip 20, in a state where the bump 22 is melted and under the condition that the bump 22 does not separate from the connection terminal 11, the height of the mounting head 72 is raised to a predetermined height, and the distance H between the electrode 21 and the connection terminal 11 is separated to a predetermined distance, and then vibration is started to be applied to the stage 71 on which the printed circuit board 10 is placed (step B).

[0069] At this time, the melted bump 22 is vibrated by the vibration applied to the stage 71 (printed circuit board 10), and as the melted bump 22 flows, 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, the true surface of the bump 22 is exposed, and it wets and spreads on the surface of the connection terminal 11.

[0070] Thereafter, while maintaining the height of the mounting head 72 at a predetermined height, vibration is continuously applied while narrowing the distance H between the electrode 21 and the connection terminal 11 as the mounting head 72, the semiconductor chip 20, the printed circuit board 10, and the stage 71 thermally expand (steps C and D). As a result, the melted bump 22 wets and spreads over the entire surface of the connection terminal 11, and an intermetallic alloy is formed at the interface between the bump 22 and the connection terminal 11.

[0071] FIG. 7 is a cross-sectional SEM photograph of the bonded portion of the bump in the embodiment. As shown in FIG. 7, it can be seen that the melted bump 22 wets and 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. Thereby, the interface resistance between the bump 22 and the connection terminal 11 can be reduced.

[0072] In the third embodiment, after separating the distance H between the electrode 21 and the connection terminal 11 to a predetermined distance, vibration is applied to the stage 71 (printed circuit board 10), so that vibration is applied to the bump 22 elongated in a slender shape, that is, the bump 22 in a state where the contact surface with the connection terminal 11 is small. Thereby, since the amplitude of the vibration applied to the stage 71 (printed circuit board 10) can be reduced, even if the pitch of the bump 22 is narrowed, a short circuit with the adjacent electrode 21 can be prevented.

[0073] FIG. 8 is a cross-sectional view schematically showing the configuration of an electronic component mounting system according to an embodiment of the present invention. In this embodiment, a case where a bump formed on an electrode (first electrode) of a semiconductor chip (first electronic component) is melt-bonded to a connection terminal (first electrode) of a printed circuit board (second electronic component) will be described as an example. The semiconductor chip may be a plurality of diced semiconductor chips in a wafer state.

[0074] As shown in FIG. 8, the electronic component mounting system 100 in this embodiment is a device that bonds the bump 22 formed on the electrode 21 of the semiconductor chip 20 to the connection terminal 11 of the printed circuit board 10, and includes an irradiation device 80, an etching device 50, and a bonding device 70. The etching device 50 is provided with a cleaning and drying device (not shown) for cleaning and drying the etched semiconductor chip 20 and printed circuit board 10 as an accompaniment thereto.

[0075] The irradiation device 80 removes contaminants adhering to the surfaces of the semiconductor chip 20 and the printed circuit board 10 by irradiating ultraviolet rays (UV) onto 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 bump 22 and the connection terminal 11 by etching the semiconductor chip 20 and the printed circuit board 10 with an etching solution containing a weak organic acid such as citric acid.

[0077] The bonding device 70 houses the semiconductor chip 20 and the printed circuit board 10 that have been etched by the etching device 50, and in a state where an inert gas is supplied, bonds the bumps 22 formed on the electrode 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 according to the present embodiment, in the bonding device 70, before bonding the bumps 22 formed on the electrode (first electrode) 21 of the semiconductor chip (first electronic component) 20 to the connection terminal (second electrode) 11 of the printed circuit board (second electronic component) 10, in the etching device 50, the semiconductor chip 20 and the printed circuit board 10 are etched with a weak acidic organic acid such as citric acid, and the oxide film (metal oxide film) formed on the surfaces of the bumps 22 and the connection terminals 11 is removed, so that bump bonding can be performed in a state where the metal oxide film has been removed.

[0079] In the present embodiment, since the etching removal of the metal oxide film is performed using a weak acidic organic acid, it is easy to handle, and compared with the conventional reduction treatment of the metal oxide film using carboxylic acid gas, there is no need to take measures against corrosion of the carboxylic acid gas or measures against residues of carboxylate salts, and a highly reliable fluxless bump bonding can be obtained with a simple device.

[0080] Also, in the etching device 50, before etching and removing the metal oxide film, in the irradiation device 80, ultraviolet rays are irradiated onto the surfaces of the semiconductor chip 20 and the printed circuit board 10 to remove in advance the contaminants adhering to the surfaces of the semiconductor chip 20 and the printed circuit board 10, so that the removal of the metal oxide film can be performed in a short time and the etching solution can be kept clean.

[0081] Hereinafter, with reference to FIG. 8, the specific configurations of the irradiation device 80, the etching device 50, and the bonding device 70 will be described.

[0082] <Irradiation Device> The irradiation device 80 includes a chamber 80a that houses the semiconductor chip 20 and the printed circuit board 10, a vacuum pump 83 that evacuates the inside of the chamber 80a, and a supply means 84 that supplies an inert gas such as nitrogen into the chamber 80a. Inside the chamber 80a, 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 are provided.

[0083] After evacuating the inside of the chamber 80a with the vacuum pump 83, in a state where an inert gas such as nitrogen is supplied into the chamber 80a by the supply means 84, ultraviolet light is irradiated from the ultraviolet light source 81 onto the surfaces of the semiconductor chip 20 and the printed circuit board 10. Thereby, contaminants adhering to the surfaces of the semiconductor chip 20 and the printed circuit board 10 are removed.

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

[0085] Note that 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 ultraviolet light.

[0086] <Etching device> The etching device 50 includes an etching tank 50a containing an aqueous solution (etching solution) 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 and removed.

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

[0088] Note that the semiconductor chip 20 and the printed circuit board 10 that have been etched by the etching apparatus 50 are cleaned and dried by a cleaning / drying apparatus (not shown).

[0089] The etching apparatus 50 may be an etching apparatus that sprays the etching solution 51 in a mist form 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 70a 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 facing the stage 71, and holds the semiconductor chip 20 in an inverted state (face down) such 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. Further, the mounting head 72 is provided with a heater 75 that heats the semiconductor chip 20.

[0092] After the inside of the chamber 70a is evacuated by a vacuum pump 73, an inert gas such as nitrogen is supplied into the chamber 70a from a container 74, thereby creating an inert gas atmosphere.

[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 the heater 75 to a temperature at which the bumps 22 melt, thereby melting and bonding the bumps 22 to the connection terminals 11 (see FIGS. 1C and 1D).

[0094] Note that the bonding device 70 is not limited to the above configuration. For example, a general configuration of a well-known flip chip bonder can be adopted.

[0095] After the semiconductor chip 20 and the printed circuit board 10 that have completed the etching process in the etching device 50 are cleaned and dried, it is preferable to transport them to the bonding device 70 in an environment of an inert gas atmosphere such as nitrogen so that the surfaces of the bumps 22 and the connection terminals 11 are not oxidized again during the transportation.

[0096] Also, as shown in FIG. 9, when the bonding device 70 melt-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, it 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.

[0097] The supply means 76 is attached to the mounting head 72 so as to surround the side surface of the mounting head 72. A through hole 77 through which the inert gas passes is provided in the side portion of the supply means 76. A storage chamber 78 in which the inert gas is stored is connected to the through hole 77 via a pipe 79, and the inert gas is jetted from the tip of the through hole 77 toward the stage 71. Thereby, an air curtain is formed around the semiconductor chip 20 and the printed circuit board 10, and the intrusion of external air is blocked. As a result, even if the entire inside of the bonding device 70 is not filled with the inert gas, it is possible to prevent the surfaces of the bumps 22 and the connection terminals 11 from being oxidized.

[0098] Also, as shown in FIG. 10, the bonding apparatus 70 may include an applying means 85 that applies vibrations causing relative displacement in a direction parallel to the interface between the bump 22 and the connection terminal 11 to the stage 71 on which the printed circuit board 10 is placed. Thereby, after the bump 22 is brought into contact with the connection terminal 11, in a state where the bump 22 is melted, due to the vibrations applied to the printed circuit board 10, the melted bump 22 flows, and as a result, 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, and the true surface of the bump 22 can be exposed. As a result, an intermetallic compound can be formed at the interface between the bump 22 and the connection terminal 11. Note that the applying means 85 for applying vibrations may be performed on the mounting head 72 that holds the semiconductor chip 20. Further, the addition of vibrations by the applying means 85 can be controlled by, for example, a servo motor or the like.

[0099] Also, as shown in FIG. 11, the etching apparatus 50 may be incorporated into the bonding apparatus 70 together with an accompanying cleaning and drying apparatus (not shown). The semiconductor chip 20 and the printed circuit board 10 that have undergone the etching process are each held by a mounting head 72 by a transport mechanism (not shown), and the printed circuit board 10 is placed on a stage 71.

[0100] When performing a reduction process of a metal oxide film using a conventional carboxylic acid gas in a bonding apparatus, there is a possibility of corroding the constituent devices in the bonding apparatus, so it is difficult to incorporate it into the bonding apparatus, but the present invention enables this.

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

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

[0103] As described above, the present invention has been described with reference to the preferred embodiments. However, such descriptions are not limiting matters, and of course, various modifications are possible.

Explanation of Reference Numerals

[0104] 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 tank 51 Aqueous citric acid solution (etching solution) 60 Cleaning tank 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 Pipe 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 surfaces of the bump and the second electrode by etching the first electronic component and the second electronic component with a weakly acidic organic acid; a bonding step of accommodating the first electronic component and the second electronic component in a bonding apparatus 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 apparatus; An electronic component mounting method including the above steps.

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

3. The electronic component mounting method according to claim 1, wherein the weakly acidic organic acid is an organic acid selected from the group including 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 a state where an inert gas is supplied to the periphery of the first electronic component and the second electronic component in the bonding apparatus.

5. The etching step is performed in the bonding apparatus. The electronic component mounting method according to claim 1, wherein the etching step and the bonding step are performed in a state where the inside of the bonding apparatus is filled with an inert gas.

6. The electronic component mounting method according to claim 1, wherein in the bonding step, after bringing the bump formed on the first electrode into contact with the second electrode, while melting the bump, vibration is applied to the first electronic component or the second electronic component in a direction parallel to the interface between the bump and the second electrode to relatively displace them.

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 from the first electronic component and the second electronic component is applied to the melted bump.

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 width 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 bonding step is a step of bringing the bump formed on the first electrode into contact with the second electrode, then melting the bump, and separating the distance between 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; a step of continuing to apply the vibration while narrowing the distance between the first electrode and the second electrode The electronic component mounting method according to claim 6, comprising:

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, an etching device for removing an oxide film formed on the surfaces of the bump and the second electrode by etching the first electronic component and the second electronic component with a weakly acidic organic acid; a bonding device that houses the first electronic component and the second electronic component that have been etched by the etching device, and supplies an inert gas, and bonds the bump formed on the first electrode of the first electronic component to the second electrode formed on the second electronic component An electronic component mounting system comprising:

12. The electronic component mounting system according to claim 11, further comprising an irradiation device that irradiates ultraviolet rays or plasma onto the surfaces of the first electronic component and the second electronic component, wherein in the etching device, the first electronic component and the second electronic component that have been 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 weakly acidic organic acid is an organic acid selected from the group including citric acid, acetic acid, tartaric acid, malonic acid, succinic acid, and adipic acid.

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

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

17. In the applying means, 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 substantially no pressing force is applied to the molten bump from the first electronic component and the second electronic component. The electronic component mounting system according to claim 16.

18. In the applying means, 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. The electronic component mounting system according to claim 16.

19. In the applying means, the width 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. The electronic component mounting system according to claim 16.

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, An etching step of removing an oxide film formed on the surface of the second electrode by etching the second electronic component with a weakly acidic organic acid; After the etching step, the first electronic component and the second electronic component are housed in a bonding device, and the bump formed on the first electrode of the first electronic component is bonded to the second electrode formed on the second electronic component while supplying an inert gas to the bonding device. A bonding step including The bonding process is an electronic component mounting method in which the bump formed on the first electrode is brought into contact with the second electrode, and then while the bump is in a molten state, vibration is applied to the first electronic component or the second electronic component in a direction parallel to the interface between the bump and the second electrode while relatively displacing them.

21. 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 the pressing force from the first electronic component and the second electronic component is not applied to the bump in a molten state. The electronic component mounting method according to claim 20.

22. In the bonding process, 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. The electronic component mounting method according to claim 20.

23. In the bonding process, the width 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. The electronic component mounting method according to claim 20.

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