High-corrosion-resistance sintered nano-copper surface modification method suitable for packaging

Abstract

The invention discloses a high-corrosion-resistance sintered nano-copper surface modification method suitable for packaging. According to the method, argon serves as working gas, hexamethyldisiloxane HMDSO serves as a reaction medium, the two kinds of gas flow are mixed and then fed into a plasma generation area of an atmospheric pressure plasma jet APPJ system, Si-O cross-linked thin film deposition is conducted on the surface of a sintered nano-copper sample, and the Si-O cross-linked thin film is obtained. And the surface of the sintered nano-copper is completely covered with the film for surface modification. The method has the beneficial effects that the atmospheric pressure plasma jet APPJ technology is adopted, a vacuum system is not needed, the equipment cost is reduced, the process flexibility is improved, and the method is suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of integrated circuit packaging. Specifically, it relates to a surface modification method of highly corrosion-resistant sintered nanocopper suitable for packaging. Background Art

[0002] Copper and its alloys are widely used in fields such as electronic packaging. However, they are prone to corrosion in humid or sulfur-containing environments, resulting in performance degradation. Existing protection technologies mainly include organic coatings, electroplated metal protective layers, chemical vapor deposition (CVD), etc. However, organic coatings have poor adhesion, are prone to aging and peeling, and have poor long-term protection effects; harmful waste liquids are generated during the electroplating process, causing serious environmental pollution; while CVD equipment is complex and costly.

[0003] In recent years, plasma deposition technology has received attention due to its high efficiency and environmental friendliness. Low-pressure plasma-enhanced chemical vapor deposition (PECVD) technology forms a protective film by exciting reaction gases (such as HMDSO) under a low-pressure environment. However, it relies on a vacuum system, resulting in complex equipment, high energy consumption, high cost, and the film uniformity is limited by the reaction chamber size, making it difficult to achieve large-area and rapid deposition, with low deposition efficiency. Summary of the Invention

[0004] Aiming at the deficiencies of the above-mentioned existing technologies, the purpose of the present invention is to provide a highly corrosion-resistant sintered nanocopper surface modification method that is efficient, environmentally friendly and can be applied on a large scale. The present invention deposits a dense Si-O cross-linked film on the surface of sintered nanocopper through atmospheric pressure plasma jet (APPJ) technology, which can significantly improve the hydrophobicity and corrosion resistance of sintered nanocopper, and solves the problem that sintered nanocopper materials are prone to corrosion in corrosive environments (such as environments containing H2S gas). The method of the present invention can achieve efficient and uniform film deposition under atmospheric pressure without a complex vacuum system. The present invention can simplify the process flow, reduce production costs, and meet the requirements of industrial large-scale application.

[0005] The technical solution of the present invention is specifically introduced as follows.

[0006] The present invention provides a surface modification method of highly corrosion-resistant sintered nanocopper suitable for packaging, which uses argon as the working gas and hexamethyldisiloxane HMDSO as the reaction medium. After mixing these two gas flows, they are sent into the plasma generation area of the atmospheric pressure plasma jet APPJ system, and the surface of the sintered nanocopper sample is completely covered by depositing a Si-O cross-linked film to achieve the purpose of surface modification.

[0007] In the present invention, in the atmospheric pressure plasma jet APPJ system, a needle-ring structure electrode design is adopted, with a high-voltage copper needle as the positive electrode and a copper ring as the grounded electrode.

[0008] In the present invention, the atmospheric pressure plasma jet is an argon / HMDSO plasma jet; the flow rates of argon and hexamethyldisiloxane (HMDSO) are set to 1000 - 3000 mL / min and 10 - 50 mL / min respectively, the plasma discharge frequency is 4 - 7 kHz, and the applied voltage is 5 - 15 kV. Further preferably, the flow rates of HMDSO are set to 1200 - 1800 mL / min and 20 - 40 mL / min respectively, the plasma discharge frequency is 4 - 6 kHz, and the applied voltage is 8 - 12 kV.

[0009] In the present invention, the single APPJ thin film deposition process lasts for 1 - 5 minutes, and the sample is deposited 2 - 5 times repeatedly.

[0010] In the present invention, the thin film deposited on the surface of the sintered nano - copper sample is a cross - linked structure composed of the combination of one silicon atom and three oxygen atoms and the combination of one silicon atom and four oxygen atoms.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0012] The present invention adopts the atmospheric pressure plasma jet (APPJ) technology, which does not require a vacuum system, can reduce the equipment cost and improve the process flexibility, and is suitable for large - scale industrial production.

[0013] By optimizing the electrode design and gas flow rate, the present invention realizes rapid and uniform thin film deposition and improves the deposition efficiency.

[0014] By depositing the Si - O cross - linked thin film multiple times to form a dense protective layer, the present invention significantly improves the hydrophobicity and corrosion resistance of the sintered copper. The polarization curve shows that the corrosion potential moves positively, the corrosion current moves negatively, the corrosion tendency is significantly reduced, and the corrosion degree decreases; in the 384 - hour H2S corrosion experiment, the thin film remains intact, and no sulfur element penetration is detected, showing excellent long - term protection ability.

[0015] The present invention is green and environmentally friendly, without harmful by - products.

[0016] The process parameters of the present invention are adjustable, adapting to different corrosion environments, and expanding the application of sintered nano - copper in electronic packaging and industrial scenarios with high humidity and high sulfur.

[0017] The present invention is superior to the low - pressure PECVD technology in terms of simplifying the process, reducing the cost, improving the environmental friendliness and protection performance, and provides an efficient and reliable industrial solution for the corrosion protection of sintered nano - copper. Description of the Drawings

[0018] Figure 1 .(a) Plasma thin film deposition system, (b) Process diagram.

[0019] Figure 2. (a) Surface and cross-sectional microtopographies, (b) surface chemical states, and (c) water contact angles of sintered copper samples with / without thin film deposition.

[0020] Figure 3 . (a) Polarization curves, (b) corrosion potential, and corrosion current density of sintered copper samples with / without thin film deposition. The inset shows the surface image of the sample after testing.

[0021] Figure 4 . Optical microscope images of the surfaces of sintered copper samples with / without thin film deposition at different corrosion times.

[0022] Figure 5 . Characterization of morphology and elemental composition based on SEM / EDS: (a) surface characteristics of sintered copper samples without thin film deposition at different corrosion times; (b) cross-sectional characteristics of sintered copper samples without thin film deposition aged for 336 h; (c) surface characteristics of sintered copper samples with thin film deposition at different corrosion times; (d) cross-sectional characteristics of sintered copper samples with thin film deposition aged for 336 h. Detailed implementation manners

[0023] The technical solutions of the present invention will be introduced in detail below in conjunction with the accompanying drawings and embodiments.

[0024] (1) Plasma film-forming system

[0025] Figure 1 Shows an atmospheric pressure plasma jet (APPJ) surface thin film deposition system for sample corrosion protection. The system adopts a needle-ring structure electrode design, with a high-voltage copper needle as the positive electrode and a copper ring as the grounded electrode. The quartz glass tube serves as the reaction chamber, with an outer diameter of 8 mm, an inner diameter of 6 mm, and a length of 140 mm. The power supply parameters include a voltage of 10 kV, a frequency of 5 kHz, a pulse width of 1000 ns, and a rise / fall time of 100 ns. The system monitors the discharge voltage and current in real time through a high-voltage probe (Tektronix P6015A), a current coil (Pearson 4100), and an oscilloscope (TDS2014B, Tektronix). One gas pipeline uses high-purity argon (Ar, purity 99.999%) as the working gas, while the other pipeline introduces HMDSO (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) as the reaction medium through the bubbling method. These two gas flows are mixed and then sent into the reaction chamber. The gas flow rates are controlled by mass flow controllers (D07-19, Sevenstar), and the flow rates of argon and HMDSO are set to 1500 ml / min and 35 ml / min respectively. To achieve good thin film deposition effects, the distance between the reaction chamber outlet and the sample surface is maintained at about 2 cm, as Figure 3(as shown in (b)). The single APPJ thin film deposition process lasts for 3 minutes, and the sample is deposited 4 times repeatedly. Therefore, the total processing time for each sample is 12 minutes.

[0026] (2) Analysis of Plasma-Deposited Thin Films

[0027] To analyze the physical state and elemental composition of the deposited thin films, surface and cross-sectional analyses were performed on sintered copper samples with / without thin film deposition, and the results are as Figure 2 (a) shown. The surface SEM results show that the surface of the initial sample is relatively flat. After atmospheric pressure APPJ treatment, a typical particle agglomeration thin film is formed on the surface of the sintered copper sample, which significantly increases the surface roughness. The cross-sectional SEM results show that the bottom layer of the thin film is composed of spherical particles that are squeezed and cross-linked with each other, forming a dense film structure. The surface of the deposited thin film shows a wavy morphology, indicating that during the plasma treatment process, the thin film shows a tendency of vertical growth. The EDS surface scanning results show that the APPJ-deposited thin film is mainly composed of Si and O atoms. To further analyze the specific chemical states of the elements in the thin film, XPS analysis of the thin film was carried out, and the results are as Figure 2 (b) shown. No Cu atoms were detected in the full spectrum of the sintered copper sample with deposition, which confirms that the deposited thin film completely covers the surface of the sintered copper. The spectrum of Si2p can be decomposed into two curves. Among them, the curve with a peak at 102.84 eV corresponds to -Si-O3 (Si atom combined with 3 O atoms), and the curve with a peak at 105.32 eV corresponds to -Si-O4 (Si atom combined with 4 O atoms). By integrating the area covered by the curves, it can be known that the ratios of -Si-O3 and -Si-O4 are 92% and 8% respectively. Due to the large number of O atoms combined with Si atoms, the deposited thin film shows a high degree of cross-linking. The surface of the sintered copper sample without deposition is mainly composed of Cu and its oxides. Figure 2 (c) shows the water contact angle (WCA) values and water droplet images on the surfaces of sintered copper samples with / without thin film deposition. Among them, the average contact angle of the sample without deposition is 101.0°, while the average contact angle of the deposited sample is 134.8°. After APPJ thin film deposition treatment, the contact angle increases by 33%, and the hydrophobicity of the sintered copper sample increases by about 33%.

[0028] (3) Analysis of Corrosion Protection Performance

[0029] Through electrochemical research, the effect of the APPJ-deposited thin film on the corrosion tendency of sintered copper was investigated. Figure 3 (a) shows the polarization curves of sintered copper samples with / without thin film deposition, and the inset shows the surface images of the samples after testing. The corrosion potential (E corr ) and corrosion current density (I corr), such as Figure 3 shown in (b). The test results show that after APPJ deposition, the E corr of the sintered copper plate sample increases from -0.003 V to 0.033 V, and its I corr decreases from 0.34 μA to 0.25 μA, and the corrosion current density decreases by 26.5%. The positive shift of E corr indicates that the corrosion thermodynamic tendency of the thin-film deposited sample decreases, thus confirming its weak corrosion tendency. The decrease of I corr confirms that the corrosion intensity of the deposited sample is low. The inset also shows that the non-deposited sample is severely corroded and there are crystalline corrosion products, while the deposited sample only shows slight corrosion.

[0030] In the 384-h H2S gas corrosion experiment, a batch of sintered copper samples with / without thin-film deposition were taken out every 96 h. Figure 4 shows the optical microscope images of the sample surfaces at different aging times. During the entire 384-h corrosion process, the corrosion products gradually accumulated on the surface of the sample without thin-film deposition, and finally cracks appeared and peeled off. In contrast, the sample with thin-film deposition maintained the integrity of the deposited thin-film throughout the aging process and successfully protected the sample surface from generating visible corrosion products.

[0031] The surface morphology of the samples at different aging times and the cross-sectional morphology of the 384-h aged samples were analyzed by SEM / EDS. The morphology test results are as Figure 5 shown, and the elemental compositions of the surface and cross-section are summarized in Table 1 and Table 2, respectively.

[0032] Table 1 Surface elemental contents of sintered copper samples with / without thin-film deposition at different aging times

[0033]

[0034] Table 2 Cross-sectional elemental contents of sintered copper samples with / without thin-film deposition aged for 384 h

[0035] Sample type Aging time / h Cu / at% O / at% S / at% Si / at% C / at% No thin film deposition 384 46.4 11.3 31.5 0 10.8 With thin film deposition 384 54.9 9.3 1 18 16.9

[0036] As Figure 5 (a) shown, after the sintered sample without deposited thin-film was corroded by 2 ppm H2S gas for 384 h, layered corrosion products were formed. As the corrosion products continuously accumulated on the sample surface, the corrosion product layer experienced cracking (aging time about 192 h), peeling off (aging time about 288 h), and continued to grow a new corrosion layer on the newly exposed substrate (aging time about 384 h). It should be noted that once cracks appeared in the corrosion product layer, H2S gas began to penetrate through the corrosion product layer and react with the newly exposed sintered copper material below. Figure 5(b) shows the cross-sectional view of the sample without thin film deposition aged for 336 h prepared by FIB. The thickness of the surface corrosion product is observed to be approximately 6.23 μm and it has been separated from the underlying sintered copper matrix. The corrosive gas passes through the surface corrosion product layer and reacts with the newly exposed sintered copper matrix, further causing damage to the sample. The corrosion depth of the newly exposed sintered copper is approximately 3 μm, and the corrosion products mainly consist of Cu2O, Cu2S, CuO, and CuS.

[0037] Figure 5 (c) shows the surface characteristics of the thin film deposited and sintered samples at different aging times. As can be seen from the figure, the deposited thin film did not change during the entire corrosion process and remained in its original state. EDS analysis also indicates that the surface of the deposited thin film does not contain S element at different aging times, which proves that the APPJ deposited thin film did not react with H2S under the experimental conditions of this study. Figure 5 (d) shows the cross-sectional characteristics of the thin film deposited sample aged for 336 h. It can be found that the deposited thin film remains intact and is firmly connected to the surface of the sintered copper. In addition, no S element is detected in the cross-section, which further indicates that the APPJ deposited thin film effectively resists the erosion of H2S, O2, and other possible corrosive substances.

Claims

1. A method for surface modification of highly corrosion-resistant sintered nano-copper suitable for encapsulation, characterized in that, Using argon as the working gas and hexamethyldisiloxane (HMDSO) as the reaction medium, these two gas flows are mixed and then fed into the plasma generation region of the atmospheric pressure plasma jet (APPJ) system. Under atmospheric pressure, by depositing a Si-O crosslinked film on the surface of the sintered nano-copper sample, complete coverage of the surface of the sintered nano-copper sample is achieved to achieve the purpose of surface modification.

2. The high-corrosion-resistant sintered nano-copper surface modification method according to claim 1, wherein In the atmospheric pressure plasma jet (APPJ) system, a needle-ring structure electrode design is adopted, with a high-voltage copper needle as the positive electrode and a copper ring as the grounded electrode.

3. The high corrosion-resistant sintered nano-copper surface modification method according to claim 1, characterized in that, The atmospheric pressure plasma jet is an argon / hexamethyldisiloxane (HMDSO) plasma jet; the flow rates of argon and hexamethyldisiloxane (HMDSO) are set to 1000 - 3000 mL / min and 10 - 50 mL / min respectively, the plasma discharge frequency is 4 - 7 kHz, and the applied voltage is 5 - 15 kV.

4. The high corrosion-resistant sintered nano-copper surface modification method according to claim 1, characterized in that The process of single-time atmospheric pressure plasma jet (APPJ) film deposition lasts for 1 - 5 minutes, and the sample is deposited 2 - 5 times repeatedly.

5. The high-corrosion-resistant sintered nano-copper surface modification method according to claim 1, characterized in that The film deposited on the surface of the sintered nano-copper sample has a crosslinked structure composed of the combination of one silicon atom and three oxygen atoms and the combination of one silicon atom and four oxygen atoms.

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