JPH04313373A - Method for cleaning part mounted substrate - Google Patents

Abstract

PURPOSE:To clean a part mounted substrate with argon gas plasma while preventing the oxidation of a copper pattern formed on the substrate surface. CONSTITUTION:Argon gas is introduced into a vacuum chamber 10, a high-frequency high voltaage is impressed between the electrodes 16 and 18 provided in the chamber 10 to convert the argon gas into plasma, the plasma is allowed to impinge on the surface of the electronic part mounted substrate 22 placed on the electrode 16 connected to a high-frequency power source 20, and the substrate 22 surface is cleaned. In this case, 5-10vol.% of hydrogen gas is introduced into the argon gas to convert the hydrogen gas into plasma along with the argon gas to clean the substrate 22 surface.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of cleaning a component mounting board using argon gas plasma.

[0002] When mounting an IC on a substrate, a wire bonding connection method is used to directly electrically connect the terminals of the IC chip to an external circuit. In the wire bonding connection method, an IC chip is die-bonded onto a lead frame or wiring board using Au-Si eutectic solder or epoxy resin adhesive, and then chip electrode terminals and external terminals are connected using Au or Al thin wires. Connect by thermocompression bonding or ultrasonic bonding. This connection method is
Since a wire is connected to each terminal, I
With C chips, it takes time to connect, and there is a problem of reduced reliability. For this reason, mass production factories have introduced automatic bonding equipment to streamline connection work and improve reliability.

[0003] The surface of the conductor pad of the substrate to which wire bonding is performed is contaminated by the formation of oxides and carbides due to heat treatment in each process, and the adhesion of organic matter and flux due to cleaning, resulting in significantly poor bonding properties. Therefore, it is necessary to clean the bonding surface of the substrate prior to wire bonding.

0004

2. Description of the Related Art A method using argon (Ar) gas plasma is known as a method for cleaning the surface of a conductor pad on a substrate prior to wire bonding.

[0005] This method involves introducing argon gas into a vacuum chamber, applying a high frequency high voltage between electrodes provided in the vacuum chamber, and turning the argon gas into plasma.
This is a method of cleaning the surface of an electronic component mounting substrate placed on an electrode connected to a high-frequency power source by colliding plasma with the surface of the substrate.

The principle of the plasma cleaning method will be explained with reference to FIG. When the electrode on which the substrate 2 is placed is connected to a high-frequency high-voltage power source and the argon gas is turned into plasma by glow discharge, Ar ions collide with the substrate 2 and adhere to the substrate surface, as shown in Figure 2 (A). Contaminants (4) are knocked out as shown by the broken line, and the substrate surface is cleaned.

[0007] Furthermore, the degree of vacuum in the vacuum chamber is between 1 and 0.
．． Since it is about 1 Pascal, the oxygen (O) remaining in the vacuum chamber collides with the surface of the substrate 2 and combines with the carbide 6 formed on the substrate surface, converting the carbide 6 into CO2.
, in the form of CO2, also cleans the substrate surface. A suitable cleaning time is 4 to 5 minutes.

[0008]

[Problems to be Solved by the Invention] However, oxygen in the vacuum chamber combines with carbides formed on the substrate surface.
At the same time, this carbide is removed in the form of CO and CO2,
As shown in FIG. 3, conductive pads 8 formed on the surface of the substrate 2
There is a problem in that the Cu film reacts with Cu such as oxidation and discoloration occurs. This discoloration of the Cu film is particularly noticeable when plasma cleaning is performed for a long time.

The present invention has been made in view of these points, and its purpose is to provide a component mounting method using argon plasma that can prevent oxidation of copper patterns formed on the surface of a substrate. An object of the present invention is to provide a method for cleaning a substrate.

0010

[Means for Solving the Problems] The present invention introduces argon gas into a vacuum chamber, applies a high frequency high voltage between electrodes provided in the vacuum chamber to turn the argon gas into plasma, and uses a high frequency power source to turn the argon gas into plasma. 5 to 10 volume percent hydrogen gas in the argon gas; The method is characterized in that the surface of the substrate is cleaned by introducing hydrogen gas into plasma along with argon gas.

[0011]

[Operation] By introducing a mixed gas of Ar + H2 into the vacuum chamber and performing plasma cleaning on the component mounting board, hydrogen can reduce both the board surface and the oxygen in the vacuum chamber. It does not combine with the copper formed on the substrate surface, and can effectively remove oxides on the substrate surface.

0012

[Example] DuPont 9922 (trade name of DuPont) Cu paste was coated on a ceramic substrate and baked at a maximum temperature of 900°C for about 10 minutes in a nitrogen gas atmosphere for a total of 1 hour to form a Cu thick film ceramic substrate. Created. The binder in the Cu paste is attached to this Cu thick film ceramic substrate, and the Cu is oxidized during firing and storage, so wire bonding is extremely difficult as it is.

Therefore, this Cu thick film ceramic substrate was subjected to plasma cleaning according to the method of the present invention in a plasma cleaning apparatus shown in FIG.

In FIG. 1, reference numeral 10 indicates a vacuum chamber, which is provided with a gas introduction port 12 through which a mixed gas of argon and hydrogen is introduced, and an exhaust port 14 through which gas within the vacuum chamber is exhausted. . Reference numeral 16 denotes a cathode electrode, which is connected to a high frequency AC power source 20 of 13.56 MHz and 500 V. Further, the anode electrode 18 is grounded.

A mixed gas of argon and hydrogen containing 10% hydrogen gas by volume is introduced into the vacuum chamber 10 through the introduction port 12, and a Cu thick film ceramic substrate 22 is placed on the cathode electrode 16. A high frequency AC voltage of 13.56 MHZ and 500 V was applied to the cathode electrode 16 to generate a glow discharge. As a result, the mixed gas in the vacuum chamber 10 becomes plasma, and the Cu thick film ceramic substrate 22 placed on the cathode electrode 16 is biased to a negative potential. Membrane ceramic substrate 22
and cleans the substrate surface.

In this embodiment, the hydrogen gas introduced into the vacuum chamber 10 covers the surface of the substrate 22 and the vacuum chamber 1.
Plasma cleaning was performed for about 5 minutes to reduce the oxygen in the substrate, and the thick Cu film was able to cleanly remove oxides, carbides, etc. from the substrate surface without discoloring due to oxidation. When a gold wire was wire-bonded to the Cu thick-film ceramic substrate that had been surface-treated in this manner, very excellent bonding properties could be obtained. The bonding property is 25-3 compared to conventional Au balls.
A 0% improvement in shear strength was observed.

[0017] Furthermore, in the case of a through-hole board, the board is cleaned with an organic solvent after parts are reflow soldered, but the residue of the cleaning liquid remains around the through-hole, and the bonding performance at the pad area around the through-hole becomes extremely poor. . When this through-hole substrate was subjected to plasma cleaning under the same conditions as described above, the cleaning residue of the organic solvent could be completely removed, and a remarkable improvement in bonding properties was observed.

In addition, on glass epoxy boards, flux residue after surface mounting of components by soldering contaminates the bonding pad surface and deteriorates bonding performance. However, plasma cleaning of glass epoxy boards was performed under the same conditions as above. As a result, we were able to significantly improve bonding properties.

In the plasma cleaning of the present invention, it is desirable to set the degree of vacuum in the vacuum chamber to 1 to 0.1 Pascal and to set the high frequency AC voltage to 500 to 1,000V. Further, from the viewpoint of safety, the content of hydrogen gas in the argon gas is suitably 5 to 10 percent by volume.

[0020]

Effects of the Invention As described in detail above, the present invention performs plasma cleaning of a component mounting board by introducing 5 to 10 volume percent hydrogen gas into argon gas. The copper pattern is not oxidized during cleaning, and oxides, carbides, organic residues from cleaning, flux residues, etc. on the substrate surface can be removed cleanly.

According to the method of the present invention, the bonding property is A
The shear strength of the u-ball can be improved by 25 to 30%, and the wettability of solder can be significantly improved.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a plasma cleaning apparatus suitable for implementing the invention.

FIG. 2 is an explanatory diagram of a plasma cleaning method.

FIG. 3 is a diagram illustrating problems in the conventional cleaning method.

[Explanation of symbols]

10 Vacuum chamber 16 Cathode electrode 18 Anode electrode 20 High frequency AC power supply 22 Cu thick film ceramic substrate

Claims (2)

[Claims] 1. Introducing argon gas into a vacuum chamber (10) and applying a high frequency high voltage between electrodes (16, 18) provided in the vacuum chamber (10) to turn the argon gas into plasma, An electronic component mounting board (
22) In a method for cleaning a component mounting board in which the surface of the board (22) is cleaned by bombarding the surface with the plasma, 5 to 10 volume percent of hydrogen gas is introduced into the argon gas, and the hydrogen gas is mixed with the argon gas. A method for cleaning a component mounting board, characterized by cleaning the surface of a board (22) by converting it into plasma. [Claim 2] The degree of vacuum in the vacuum chamber (10) is set to 1.
~0.1 Pascal, high frequency high voltage 500 ~1,
2. The method of cleaning a component mounting board according to claim 1, wherein the voltage is set to 000 V.