JP2008034683A - Method for preprocessing of metal bonding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a preprocessing of metal bonding portions by plasma exposure which obtains satisfactory bonding of metals to each other. <P>SOLUTION: As the preprocessing in the case of bonding two metal matters 91a and 91b to be bonded, a first plasma exposure process is carried out which makes a first processing gas plasmatic and makes it contact with at least one of the matters to be bonded. The first processing gas uses a gas containing no oxygen substantially, and preferably uses gaseous nitrogen. Next, a second plasma exposure process is carried out which makes the second processing plasmatic and makes it contact with the matter to be bonded which has been processed by the first plasma exposure process. The second processing gas is a gas containing oxygen and is preferably a mixed gas of nitride and oxygen. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a pretreatment method that is performed prior to a joining step when joining two joining objects made of metal in the field of manufacturing electronic devices, for example.

For example, when an IC chip is mounted on a circuit board, bumps or the like are provided on the chip and bonded to electrodes on the circuit board. The bumps and electrodes of the objects to be joined are made of gold or other metal. Generally, since the surface of these metal-based objects to be joined has an oxide film or dirt, pretreatment such as cleaning is performed prior to the joining process. As pretreatment means, plasma irradiation or the like is employed. The processing gas used for plasma irradiation is, for example, argon (see Patent Document 1), and irradiation is completed once.
JP 2004-119701 A JP 2006-013479 A

  An object of the present invention is to provide a pretreatment capable of obtaining a good bonding state between metals in a metal bonding pretreatment by plasma irradiation.

In order to solve the above problems, the present invention is a pretreatment method that is performed prior to joining two joining objects made of metal,
A first plasma irradiation step of bringing the first processing gas substantially free of oxygen into plasma (including activation, radicalization, and ionization; hereinafter the same) and contacting at least one object to be joined;
A second plasma irradiation step in which a second processing gas containing oxygen is turned into plasma and brought into contact with the object to be bonded that has undergone the first plasma irradiation step;
It is characterized by performing.
If the objects to be joined are joined after the above-described metal joining pretreatment by plasma irradiation, a good joining state of these objects to be joined can be obtained.
The phrase “substantially free of oxygen” means that oxygen is less than the content that can affect the reaction on the surface of the object to be joined. Specifically, the oxygen content in the first processing gas is preferably less than 3 vol%, and more preferably almost 0%.

The first processing gas is preferably nitrogen gas (N ₂ ). The second processing gas is preferably a mixed gas of nitrogen (N ₂ ) and oxygen (O ₂ ). Thereby, a favorable joining state can be obtained reliably.

The volume flow ratio of nitrogen (N ₂ ) and oxygen (O ₂ ) in the second processing gas is preferably N ₂ : O ₂ = 9: 1 to 99: 1, and N ₂ : O ₂ = 29: About 1 is more preferable. Thereby, a favorable joining state can be obtained reliably.

In the first and second plasma irradiation processes, it is preferable to generate a plasma by preparing a pair of electrodes and applying an electric field between the electrodes to cause a discharge. It is preferable that the object to be bonded is disposed outside the pair of electrodes, and the processing gas that has been converted into plasma between the electrodes is blown out to the object to be bonded to the outside. The electrode and the object to be joined are preferably placed in an environment near atmospheric pressure, a glow discharge near atmospheric pressure is generated between the electrodes, and plasma irradiation is preferably performed under atmospheric pressure. The vicinity of atmospheric pressure refers to a range of 1.013 × 10 ^{4 to} 50.663 × 10 ⁴ Pa, and 1.333 × 10 ^{4 to} 10.664 considering the ease of pressure adjustment and the simplification of the apparatus configuration. × 10 ⁴ Pa (100 to 800 Torr) is preferable, and 9.331 × 10 ^{4 to} 10.9797 × 10 ⁴ Pa (700 to 780 Torr) is more preferable.

  ADVANTAGE OF THE INVENTION According to this invention, in the metal-bonding pre-process by plasma irradiation, the pre-process which can acquire the favorable joining state of metals can be performed.

Hereinafter, a first embodiment of the present invention will be described.
FIG. 1 schematically shows a metal bonding pretreatment apparatus M. The apparatus M includes a base material installation unit 10 and a plasma irradiation unit 20 disposed above the base material installation unit 10. In the base material installation unit 10, a circuit board 91 (first joining target base material) and an IC chip 92 (second joining target base material) to be mounted on the circuit board 91 are installed. The circuit board 91 is provided with electrode terminals 91a (first object to be joined) made of metal such as gold. The IC chip 92 is provided with bumps 92a (second bonding target). The bump 92a is made of a metal such as gold.
In the figure, the thickness of the substrate 91 and its electrode terminal 91a, and the IC chip 92 and its bump 92a are exaggerated.
After the pretreatment by the metal bonding pretreatment apparatus M, the electrode terminals 91a of the circuit board 91 and the bumps 92a of the IC chip 92 are joined to each other.

  A pair of electrodes 21 and 22 are provided on the plasma irradiation unit 20 of the metal bonding pretreatment apparatus M so as to face each other. A solid dielectric layer (not shown) is provided on at least one opposing surface of the electrodes 21 and 22. An inter-electrode space 23 at atmospheric pressure is formed between the electrodes 21 and 22. A power source 30 is connected to one electrode 21 and the other electrode 22 is electrically grounded. The power supply 30 supplies a high frequency voltage or a pulse voltage to the electrode 21. By this voltage supply, an atmospheric pressure glow discharge is generated between the electrodes 21 and 22, and the interelectrode space 23 becomes a discharge space.

A processing gas supply unit 40 is connected to the upper end of the interelectrode space 23. The processing gas supply unit 40 includes a nitrogen supply line 42 extending from the nitrogen gas source 41 and an oxygen mixing line 44 extending from the oxygen gas source 43. The downstream end of the nitrogen supply line 42 is connected to the interelectrode space 23. A mixer 45 is provided in the middle of the nitrogen supply line 42. An oxygen mixing line 44 is connected to the mixer 45.
The nitrogen gas supply line 42 alone constitutes the first process gas supply unit. A nitrogen gas supply line 42, an oxygen mixing line 44, and a mixer 45 constitute a second processing gas supply unit.

A blowout port 24 is provided at the lower end (downstream end) of the interelectrode space 23.
A movement mechanism (not shown) is connected to one of the plasma irradiation unit 20 and the base material installation unit 10. By adjusting the relative position of the plasma irradiation unit 20 and the base material setting unit 10 by this moving mechanism, the blowout port 24 can be made to face the electrode terminal 91a of the circuit board 91 or the bump 92a of the IC chip 92. It is like that.

  As shown in FIG. 2, a tube 25 may be extended from the downstream end of the interelectrode space 23, and the tip of the tube 25 may be used as the outlet 24. As the material of the tube 25, an olefin resin, glass or the like may be used. The length of the tube 25 is, for example, about 50 to 500 mm.

Prior to mounting the IC chip 92 on the circuit board 91, the following pretreatment is performed on the electrode terminals 91 a of the circuit board 91 and the bumps 92 a of the IC chip 92 using the metal bonding pretreatment apparatus M having the above configuration. Apply.
First, the pretreatment for the circuit board 91 will be described first.
The outlet 24 of the plasma irradiation unit 20 is disposed above the circuit board 91. Then, nitrogen (N ₂ ) in the nitrogen supply line 42 is introduced into the interelectrode space 23 as the first processing gas. The oxygen mixing line 44 is closed so that the first processing gas (N ₂ ) does not contain oxygen. The flow rate of the first processing gas (N ₂ ) is preferably about 10 to 50 L / min, and more preferably about 30 L / min. In parallel, voltage supply from the power supply 30 to the electrode 21 is performed. The supply voltage is preferably about Vpp = 7 to 15 kV, and the frequency is preferably about 10 to 100 kHz. As a result, an atmospheric pressure glow discharge is generated between the electrodes 21 and 22, the first processing gas composed of nitrogen is turned into plasma, and nitrogen plasma is obtained. This nitrogen plasma is blown out from the blow-out port 24 and irradiated to the electrode terminal 91a of the circuit board 91. The distance (working distance) between the blowout port 24 and the circuit board 91 is preferably about 3 to 10 mm. The irradiation time is preferably about 1 to 5 seconds.

Second Plasma Irradiation Process After the first plasma irradiation process is completed, the second plasma irradiation process is preferably performed within 1 to 60 seconds. In the second plasma irradiation step, nitrogen (N ₂ ) in the nitrogen supply line 42 is mixed with oxygen (O ₂ ) from the oxygen mixing line 44 by the mixer 45, and a second processing gas composed of a mixed gas of nitrogen and oxygen is mixed. Generate. The volume flow ratio of nitrogen (N ₂ ) and oxygen (O ₂ ) in the second process gas is preferably N ₂ : O ₂ = 9: 1 to 99: 1, and N ₂ : O ₂ = 29: 1. The degree is more preferred. The total flow rate of the second processing gas (sum of nitrogen and oxygen) is preferably 10 to 50 L / min, and more preferably about 30 L / min. This second processing gas is introduced into the interelectrode space 23. In parallel with the introduction of the second processing gas into the inter-electrode space 23, an atmospheric pressure discharge is generated between the electrodes 21 and 22 by supplying a voltage from the power source 30 to the electrode 21, and the second processing gas is turned into plasma. This plasma gas is blown out from the inter-electrode space 23 and applied to the electrode terminals 91 a of the circuit board 91. The irradiation time is preferably about 1 to 5 seconds.

  The IC chip 92 is preprocessed in the same manner as the preprocessing of the circuit board 91. That is, the outlet 24 of the plasma irradiation unit 20 is disposed above the IC chip 92, the first plasma irradiation process is performed on the bumps 92a of the IC chip 92 in the same manner as described above, and then the second plasma irradiation process is performed. Execute.

  The processing order may be the order of the first plasma irradiation step and the second plasma irradiation step for each of the circuit board 91 and the IC chip 92, and the first plasma irradiation step and the second plasma irradiation step of the circuit board 91 are performed. After the completion, the first plasma irradiation process and the second plasma irradiation process of the IC chip 92 may be performed. After the first plasma irradiation process and the second plasma irradiation process of the IC chip 92 are completed, the circuit board 91 is completed. The first plasma irradiation step and the second plasma irradiation step may be performed. The first plasma irradiation process is performed in the order of the circuit board 91 and the IC chip 92, or the IC chip 92 and the circuit board 91 in this order, and then the second plasma irradiation process is performed in the order of the circuit board 91 and the IC chip 92, or the IC. You may decide to carry out in order of the chip | tip 92 and the circuit board 91. FIG.

After the pretreatment (the first plasma irradiation step and the second plasma irradiation step) of the bonding process circuit board 91 and the IC chip 92 is completed, the circuit board 91 or the IC chip 92 is heated. The heating temperature is preferably about 100 to 200 ° C. The bumps 92a of the IC chip 92 are pressed against the electrode terminals 91a of the heated circuit board 91. The pressing load is preferably about 200 to 1000 gf, and the pressing time is preferably about 2 to 5 seconds.
Thereby, the bump 92a of the IC chip 92 can be firmly bonded to the electrode terminal 91a of the circuit board 91, and a good metal bonded state can be obtained.

The present invention is not limited to the above embodiment, and various modifications can be made.
For example, the preprocessing device M for the circuit board 91 and the preprocessing device M for the IC chip 92 may be prepared separately and preprocessed separately.
Only one of the circuit board 91 and the IC chip 92 may be preprocessed, and the other may not be preprocessed. In that case, it is preferable that the pre-processing side is the circuit board 91.
The bonding target is not limited to the electrode terminal 91a of the circuit board 91 and the bump 92a of the IC chip 92, and can be applied to various metal bonding.
The first processing gas in the first plasma processing step is not limited to a pure nitrogen gas, and other gas species substantially free of oxygen (for example, argon) may be used. The second processing gas in the second plasma processing step is not limited to a mixed gas of nitrogen and oxygen, and a mixed gas of a gas other than nitrogen (for example, argon) and oxygen may be used. The gas species may be selected according to the metal component of the object to be joined.

Examples will be described. Needless to say, the present invention is not limited to this embodiment.
The apparatus M with a tube of FIG. 2 was used. The material of the tube 25 is glass and the length is 300 mm. The entire front surface of the circuit board 91 is made of gold, and the gold on the front surface is used as one joining object 91a. Four bumps 92a made of gold were formed on the IC chip 92, and this was used as the other bonding object.
First Plasma Irradiation Step The first plasma irradiation step was performed on both the circuit board 91 and the IC chip 92 under the same processing conditions listed below.
First processing gas: pure nitrogen (N ₂ ) 30 L / min
Plasma irradiation time: 5 seconds Supply voltage: Vpp = 16.6 kV
Supply current: 2.8A
Frequency: 80kHz
Working distance: 2mm
Processing temperature: 30 ° C

Second Plasma Irradiation Step After the first plasma irradiation step, the second plasma irradiation step was performed on both the circuit board 91 and the IC chip 92, respectively. The processing conditions were the same as those in the first plasma irradiation step except for the processing gas components as follows.
Second processing gas: nitrogen (N ₂ ) 29 L / min
Oxygen (O ₂ ) 1 L / min
Plasma irradiation time: 5 seconds Supply voltage: Vpp = 16.6 kV
Supply current: 2.8A
Frequency: 80kHz
Working distance: 2mm
Processing temperature: 30 ° C

Bonding process After the pretreatment (the first plasma irradiation process and the second plasma irradiation process) is completed, the circuit board 91 is heated to 150 ° C., and the bumps 92 a of the IC chip 92 are pressed against the surface of the circuit board 91. It was. The time interval from the end of the second plasma irradiation process to the start of pressing was 1 minute. The pressing load was 150 gf, and the load application time was 10 seconds. As a result, the bump 92 a of the IC chip 92 was bonded to the gold 91 a on the surface of the circuit board 91.

Thereafter, the bonding strength was measured by a destructive test. In the destructive test, a shearing force of 1000 gf / mm ² was applied to the bump 92 a to inspect whether the bump 92 a was peeled off from the circuit board 91.
As a result, three of the four bumps 92a were not peeled from the circuit board 91, and the bonding was maintained. Thereby, it was confirmed that a favorable joining state was obtained.

[Comparative Example 1]
As Comparative Example 1, a second plasma irradiation step of irradiating a plasma of a mixed gas of nitrogen (N ₂ ) and oxygen (O ₂ ) is performed first, and then a first plasma irradiating a plasma of only nitrogen (N ₂ ). Irradiation was performed. In the second plasma irradiation process of Comparative Example 1, the processing conditions were the same as those of the second plasma irradiation process of Example 1, except that the supply voltage was Vpp = 17.0 kV and the supply current was 2.9 A. . The processing conditions of the first plasma irradiation step were the same as those of the first plasma irradiation step of Example 1 except that the supply voltage was Vpp = 17.0 kV.
Then, the joining process was performed by the same operation as in Example 1, and further, the destructive test was performed by the same operation as in Example 1. As a result, all four bumps 92a of the IC chip 92 were peeled from the circuit board 91. .
As a result, it was confirmed that when the order of the first plasma irradiation step and the second plasma irradiation step was reversed, a desired bonding state could not be obtained.

[Comparative Example 2]
As Comparative Example 2, only the first plasma irradiation step using only nitrogen (N ₂ ) was performed, and the second plasma irradiation step was omitted. In the first plasma irradiation process of Comparative Example 2, the processing conditions were the same as those in Example 1 except that the supply voltage was Vpp = 16.8 kV, the supply current was 2.9 A, and the plasma irradiation time was 30 seconds. It was the same as 1 plasma irradiation process.
Then, the joining process was performed by the same operation as in Example 1, and further, the destructive test was performed by the same operation as in Example 1. As a result, all four bumps 92a of the IC chip 92 were peeled from the circuit board 91. .
As a result, it was confirmed that the desired bonding state could not be obtained even if the plasma irradiation time was increased if the pretreatment was only the first plasma irradiation step.

[Comparative Example 3]
As Comparative Example 3, the first plasma irradiation step was omitted in the pretreatment, and only the second plasma irradiation step using a mixed gas of nitrogen (N ₂ ) and oxygen (O ₂ ) was performed. In the second plasma irradiation process of Comparative Example 2, the processing conditions were the same as those of the second plasma irradiation process of Example 1, except that the supply voltage was Vpp = 16.8 kV and the plasma irradiation time was 10 seconds. .
Then, the joining process was performed by the same operation as in Example 1, and further, the destructive test was performed by the same operation as in Example 1. As a result, all four bumps 92a of the IC chip 92 were peeled from the circuit board 91. .
As a result, it was confirmed that the desired bonding state could not be obtained even if the plasma irradiation time was increased if the pretreatment was only the second plasma irradiation step.

  The present invention can be used, for example, in a process of mounting an IC chip on a circuit board in the field of manufacturing electronic devices.

It is a front view showing typically the metal joining pretreatment device concerning a 1st embodiment of the present invention. It is a front view which shows the modification of the said metal joining pre-processing apparatus.

Explanation of symbols

M Metal Bonding Pretreatment Device 20 Plasma Irradiation Unit 40 Processing Gas Supply Unit 41 Nitrogen Gas Source 42 Nitrogen Supply Line 43 Oxygen Gas Source 44 Oxygen Mixing Line 45 Mixer 91 Circuit Board (First Bonding Target Substrate)
91a Electrode terminal (first joining object)
92 IC chip (second bonding target substrate)
92a Bump (second bonding object)

Claims (3)

A pretreatment method that is performed prior to joining two joining objects made of metal,
A first plasma irradiation step in which a first processing gas substantially free of oxygen is converted into plasma and brought into contact with at least one object to be joined;
A second plasma irradiation step in which a second processing gas containing oxygen is turned into plasma and brought into contact with the object to be bonded that has undergone the first plasma irradiation step;
A pre-bonding method for joining metal, characterized in that: Wherein the first process gas is a nitrogen gas (N _2), the second process gas, nitrogen (N ₂₎ and oxygen according to claim 1, wherein the mixture is a gas (O ₂₎ Bonding pretreatment method. The volumetric flow ratio of nitrogen (N ₂ ) and oxygen (O ₂ ) in the second processing gas is N ₂ : O ₂ = 9: 1 to 99: 1, The bonding according to claim 2, Pre-processing method.

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