A packaging method for improving the sealing property of IC package

Abstract

The application discloses a packaging method for improving the sealing property of IC packaging, which comprises the following steps: preparing a packaging substrate, the electrode of the packaging substrate comprising a silver plating layer; fixing a die on the packaging substrate and welding a bonding wire; forming a dense silver oxide film on the surface of the silver plating layer of the electrode of the packaging substrate after the bonding wire is welded; and plastic packaging. The dense silver oxide film is formed on the surface of the silver plating layer of the electrode of the packaging substrate after the bonding wire is welded, the bonding wire is directly welded on the silver plating layer of the electrode of the packaging substrate, the welding quality is high, the bonding force is good, and the resistance of the welding point is small; the surface of the silver plating layer of the electrode has the dense silver oxide film during the plastic packaging, the bonding force between the electrode of the packaging substrate and the packaging plastic can be improved, and the electrode and the packaging plastic can be prevented from delaminating.

Description

[Technical Field]

[0001] This invention relates to IC packaging, and more particularly to a packaging method for improving the hermeticity of IC packaging. [Background Technology]

[0002] In the packaging process of IC products, the electrodes of the frame and carrier are usually silver-plated surfaces. Silver has good conductivity. Although the silver plating layer formed on the metal substrate by the existing technology helps the soldering process, there is a disadvantage that the silver plating layer and the packaging plastic have insufficient bonding force, which makes the packaging plastic prone to delamination after absorbing moisture.

[0003] To meet the airtightness requirements in harsh environments, existing technology provides a metal surface treatment technique that uses etching to roughen the surface of the metal substrate of the leadframe, and then forms a silver plating layer on the roughened metal substrate, thus giving the surface of the silver plating layer a corresponding roughening treatment. The roughened surface of the silver plating layer can increase the contact area between the encapsulation plastic and the surface of the silver plating layer, thereby improving the adhesion between the silver plating layer and the encapsulation plastic.

[0004] While metal surface treatment technology can reduce the possibility of delamination between the encapsulation layer and the silver plating layer, the roughened surface will reduce the bonding force of wire bonding, making the electrodes prone to wire breakage due to insufficient bonding force, or even causing the chip to break the circuit with the external circuit.

[0005] Application No. 201610116809.X discloses a leadframe comprising a metal substrate, a silver plating layer, and a silver oxide layer. The silver plating layer is formed between the metal substrate and the silver oxide layer. The outer surface of the silver oxide layer is polarized, and the thickness of the silver oxide layer is 1.3 nanometers or more. The silver oxide layer helps to improve the adhesion between the leadframe and the encapsulating plastic, thereby preventing delamination and meeting more stringent environmental moisture-sensitive conditions.

[0006] The electrochemical method for generating silver oxide layers requires high current (8 ASD) and an alkaline environment, making it unsuitable for most substrates, especially those already covered by solder mask. The electrochemical method involves the emission of heavy metals and harmful substances, making it environmentally unfriendly and costly. Furthermore, the thickness of the silver oxide layer is difficult to precisely control due to variations in current, plating time, solution composition, fluid state, electric field distribution, and temperature. Silver oxide has low conductivity and can be considered an insulator, resulting in high resistance. The surface properties of silver oxide differ significantly from those of pure silver, further reducing the bonding strength of wire bonding. This can lead to wire detachment due to insufficient bonding strength, or even disconnection between the chip and external circuitry. [Summary of the Invention]

[0007] The technical problem to be solved by the present invention is to provide a packaging method that can improve the bonding strength of wire bonding and enhance the sealing performance of IC packaging.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is a packaging method for improving the sealing performance of IC packages, comprising the following steps:

[0009] 101) Prepare a packaging substrate, the electrodes of which include a silver plating layer;

[0010] 102) Die bonding is performed on the packaging substrate, and bonding wires are soldered;

[0011] 103) A dense silver oxide film is formed on the surface of the silver-plated electrode layer on the packaging substrate where the bonding wires have been soldered.

[0012] 104) Plastic sealing.

[0013] The encapsulation method described above, step 103 includes the following steps:

[0014] 201) Place the packaged carrier board with the bonded wires into the plasma chamber, which is equipped with a plasma generator.

[0015] 202) Inject inert working gas into the plasma chamber, adjust the gas pressure in the plasma chamber to the working gas pressure for plasma cleaning to remove oxides and / or impurities from the surface of the packaged substrate electrode.

[0016] 203) Inject oxygen-containing gas into the plasma chamber and adjust the gas pressure in the plasma chamber to the working gas pressure; enter the plasma working state and adjust the discharge time and power of the plasma generator to obtain the required thickness of the silver oxide film.

[0017] The encapsulation method described above includes step 202, which involves evacuating the plasma chamber, injecting working gas to a set pressure, and removing oxides and / or impurities from the surface of the encapsulation substrate electrodes by plasma discharge.

[0018] The encapsulation method described above uses argon and nitrogen as the working gases. The plasma cleaning process conditions include: an argon flow rate of 80-200 sccm and a nitrogen flow rate of 60-200 sccm; a plasma generator operating frequency of 13.56 MHz and a power of 200-1000 W; a vacuum degree of 8-20 Pa and a temperature of 25-100 °C in the plasma chamber; and a cleaning time of 100-800 s.

[0019] The encapsulation method described above includes the following process conditions for preparing the silver oxide film in step 203: the oxygen injection flow rate is 80-200 sccm, the plasma generator operating frequency is 13.56 MHz, and the power is 200-1000 W; the vacuum degree in the plasma chamber is 8-20 Pa, the temperature is 25-100 °C, and the oxidation time is 50-300 s.

[0020] This invention involves forming a dense silver oxide film on the surface of the electrode silver plating layer after the bonding wires are soldered onto the packaging substrate. The bonding wires are directly soldered onto the silver plating layer of the packaging substrate electrode, resulting in high welding quality, good bonding force, and low welding point resistance. During plastic encapsulation, the surface of the electrode silver plating layer has a dense silver oxide film, which can improve the bonding force between the packaging substrate electrode and the packaging plastic and prevent the electrode from delaminating from the packaging plastic. [Detailed Implementation]

[0021] The packaging method for improving IC packaging hermeticity according to embodiments of the present invention includes the following steps:

[0022] 1. Prepare the encapsulation substrate. The electrodes on the encapsulation substrate have a silver plating layer on their surface.

[0023] 2. Die bonding is performed on the packaging substrate, and bonding wires are soldered.

[0024] 3. A dense silver oxide film is formed on the surface of the silver-plated electrode layer on the packaging substrate where the bonding wires have been soldered.

[0025] Forming a dense silver oxide film on the surface of the silver-plated electrode includes the following steps:

[0026] 1) Place the packaged carrier board with the bonded wires into the plasma chamber, which is equipped with a plasma generator.

[0027] 2) Inject inert working gas into the plasma chamber, adjust the gas pressure in the plasma chamber to the working gas pressure, and perform plasma cleaning to remove oxides and / or impurities from the surface of the packaged substrate electrode.

[0028] 3) Inject oxygen-containing gas into the plasma chamber and adjust the gas pressure in the plasma chamber to the working gas pressure; enter the plasma working state and adjust the discharge time and power of the plasma generator to obtain the required thickness of the silver oxide film.

[0029] 4. Plastic sealing epoxy resin adhesive.

[0030] Step 2) above includes evacuating the plasma chamber, injecting working gas to the set pressure, and removing oxides and / or impurities from the surface of the encapsulation substrate electrode through plasma discharge.

[0031] The working gases include argon and nitrogen. The plasma cleaning process conditions are as follows: the flow rate of injected argon is 80-200 sccm, and the flow rate of injected nitrogen is 60-200 sccm; the working frequency of the plasma generator is 13.56 MHz, and the power is 200-1000 W; the vacuum degree in the plasma chamber is 8-20 Pa, the temperature is 25-100℃, and the cleaning time is 100-800 s.

[0032] For example, the following process conditions can be used for cleaning: the flow rate of injected argon is 120 sccm, the flow rate of injected nitrogen is 100 sccm; the working frequency of the plasma generator is 13.56 MHz and the power is 500 W; the vacuum degree in the plasma chamber is 10 Pa and the temperature is 25 °C, and the cleaning time is 100 s.

[0033] The process conditions for preparing the silver oxide film in step 3) above are as follows: the oxygen injection flow rate is 80-200 sccm, the plasma generator operating frequency is 13.56 MHz, and the power is 200-1000 W; the vacuum degree in the plasma chamber is 8-20 Pa, the temperature is 25-100℃, and the oxidation time is 50-300 s.

[0034] For example, the following process conditions can be used to prepare a silver oxide film: the oxygen injection flow rate is 80 sccm, the plasma generator operates at a frequency of 13.56 MHz and a power of 500 W; the vacuum level in the plasma chamber is 10 Pa, the temperature is 25 °C, the oxidation time is 50 s, and the thickness of the resulting dense silver oxide film is 2.5 nm.

[0035] Silver oxide film significantly improves the bonding between epoxy resin adhesive and silver electrodes. However, due to silver's excellent antioxidant properties, obtaining silver oxide film through natural processes or heating is time-consuming and ineffective, hindering production. Oxidation in an oxygen-containing plasma atmosphere greatly improves the chemical reaction process because ionic oxygen participates in the reaction. A chemical reaction is essentially a process of electron transfer among reacting substances; the plasma state provides the chemical energy, making the reaction much more vigorous and the resulting products much stronger. In the IC packaging method of the above embodiments of the present invention, a dense silver oxide film is formed on the surface of the electrode silver plating layer after the bonding wires are soldered onto the packaging substrate. The bonding wires are directly soldered to the silver plating layer of the packaging substrate electrodes, resulting in high soldering quality, strong bonding, and low solder joint resistance. During molding, the dense silver oxide film on the electrode silver plating layer surface enhances the bonding strength between the packaging substrate electrodes and the packaging plastic, increasing it by approximately 3-5 times compared to without oxidation treatment. This significantly improves packaging quality and prevents electrode delamination from the packaging plastic.

[0036] The IC packaging method of the above embodiments of the present invention uses a physical environment to process the formation of a dense silver oxide film on the surface of the silver plating layer, using only gas as the reactant, which does not damage the surface of the substrate; the above embodiments of the present invention have low cost in forming a dense silver oxide film, no harmful substances are emitted, and the process is convenient and efficient.

Claims

1. A packaging method for improving the sealing property of an IC package, characterized by, The method comprises the following steps: 101) preparing a packaging board, the electrodes of the packaging board comprising silver-plated layers; 102) fixing dies on the packaging board and welding bonding wires; 103) forming a dense silver oxide film on the silver-plated layer surface of the electrodes of the packaging board with welded bonding wires; 104) plastic packaging; Step 103 comprises the following steps: a) placing the packaging board with welded bonding wires into a plasma working chamber in which a plasma generator is installed; b) injecting an inert working gas into the plasma working chamber, adjusting the gas pressure in the plasma working chamber to a working gas pressure to perform plasma cleaning to remove oxides and / or impurities on the electrode surface of the packaging board; c) injecting an oxygen-containing gas into the plasma working chamber, adjusting the gas pressure in the plasma working chamber to a working gas pressure; entering a plasma working state, adjusting the discharge time and power of the plasma generator to obtain a required thickness of the silver oxide film.

2. The packaging method according to claim 1, characterized in that, Step 102 comprises vacuumizing the plasma working chamber, injecting a working gas to a set pressure, and removing oxides and / or impurities on the electrode surface of the packaging board through plasma discharge.

3. The packaging method according to claim 2, wherein, The working gas comprises argon and nitrogen, and the plasma cleaning process conditions comprise: the flow rate of injected argon is 80-200 sccm, the flow rate of injected nitrogen is 60-200 sccm; the working frequency of the plasma generator is 13.56 M, and the power is 200-1000 W; the vacuum degree in the plasma working chamber is 8-20 pa, the temperature is 25-100℃, and the cleaning time is 100-800 s.

4. The packaging method of claim 1, wherein, The process conditions for preparing the silver oxide film in step 103 comprise: the flow rate of injected oxygen is 80-200 sccm, the working frequency of the plasma generator is 13.56 M, and the power is 200-1000 W; the vacuum degree in the plasma working chamber is 8-20 pa, the temperature is 25-100℃, and the oxidation time is 50-300 s.