A micron Ag, micron In and micron Cu@In core-shell mixed material preform and a preparation method and application thereof

Abstract

A hybrid core-shell material preform of micron-sized Ag, micron-sized In, and micron-sized Cu@In, along with its preparation method and applications, belongs to the field of electronic packaging micro-interconnect technology. The specific method involves: preparing a micron-sized Cu@In core-shell material via chemical plating, and mixing it with micron-sized In particles and micron-sized Ag particles to obtain a hybrid core-shell material preform of micron-sized Ag, micron-sized In, and micron-sized Cu@In. The hybrid core-shell material preform is placed on a substrate, and the chip, preform, and substrate are assembled into a sandwich structure to obtain an integrated device. The integrated device is then connected under a certain pressure to obtain an interconnect device. This invention can be well applied in the fields of semiconductor device manufacturing, microelectronic packaging, and power electronic packaging.

Description

Technical Field

[0001] This invention belongs to the field of electronic packaging micro-interconnect technology, specifically relating to a micron-sized Ag, micron-sized In, and micron-sized Cu@In core-shell hybrid material preform for low-temperature connection and high-temperature service, its preparation method, and its application. Background Technology

[0002] With the rapid development of third-generation power semiconductor devices such as silicon carbide (SiC) and gallium nitride (GaN), their operating temperatures can reach up to 300℃. However, traditional packaging technologies and interconnect materials are increasingly unable to meet the interconnection and packaging requirements of high-power, high-temperature chips. Metal nanoparticles, due to their size effect, can undergo solid-state reaction sintering at temperatures far below the melting point of metal materials. Furthermore, the physical properties of the sintered connectors are close to those of pure metals, thus perfectly meeting the requirement of "low-temperature sintering, high-temperature service," making them ideal chip interconnect materials. Currently, nano-silver (Ag) and nano-copper (Cu) particles are the most researched in the field of electronic packaging. Both Ag and Cu have good electrical and thermal conductivity; however, Ag is prone to electromigration, and Cu is easily oxidized. Additionally, nanoparticles exhibit significant porosity and pore problems during the sintering process.

[0003] Low-temperature transient liquid phase bonding (TLP) technology uses two metals with significantly different melting points as bonding materials. Upon heating, the liquid, lower-melting-point component comes into close contact with the solid, higher-melting-point component, undergoing a metallurgical reaction to generate a high-melting-point interphase (IMC) phase. TLP, as a simple and low-cost low-temperature bonding technology, can be applied to the packaging interconnects of high-temperature power devices. Indium (In) not only possesses excellent electrical and thermal conductivity but also has a low melting point (156°C), enabling it to react with Cu and Ag at relatively low temperatures to generate high-melting-point IMC. Therefore, using In as the bonding material in TLP bonding technology to achieve "low-temperature connection, high-temperature service" has broad application prospects. Summary of the Invention

[0004] To address the aforementioned problems with existing micro / nano particle materials, this invention provides a preform of a hybrid core-shell material consisting of micron-sized Ag, micron-sized In, and micron-sized Cu@In, along with its preparation method and applications. The hybrid interconnection process of this invention reduces the porosity and voids of the joints, significantly lowering the interconnection temperature and conditions while maintaining the conductivity of the interconnecting materials.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A preform of a hybrid core-shell material of micron-sized Ag, micron-sized In, and micron-sized Cu@In comprises micron-sized Ag particles, micron-sized In particles, and micron-sized Cu@In core-shell particles, wherein the mass percentage of the micron-sized Ag particles, micron-sized In particles, and micron-sized Cu@In core-shell particles is 8-16%: 20-60%: 32-64%.

[0007] Furthermore, the particle size of the micron-sized Ag particles is 1–10 μm, which can be 1 μm, 1.8 μm, 5 μm, or 10 μm; the particle size of the micron-sized In particles is 5–10 μm, which can be 5 μm, 8.5 μm, or 10 μm; and the particle size of the micron-sized Cu@In core-shell particles is 20–45 μm, which can be 20 μm, 30 μm, or 45 μm.

[0008] Furthermore, the thickness of the core-shell hybrid material preform of micron Ag, micron In and micron Cu@In is 50 to 200 μm.

[0009] Furthermore, the preparation method of micron-sized Cu@In core-shell particles is an existing technology. Taking chemical plating as an example, the specific preparation method is as follows: First, the micron-sized Cu particles are pre-treated to remove the oxide film and oil on their surface. Then, micron-sized Cu@In core-shell particles are obtained by chemical plating. The specific chemical plating method is as follows: An alkaline plating solution containing a complexing agent, indium salt, and antioxidant is added to the dispersion system of micron-sized Cu particles, and chemical plating occurs on the surface of the micron-sized Cu particles to form a Cu@In core-shell particle solution.

[0010] A method for preparing a preform of a core-shell hybrid material consisting of micron-sized Ag, micron-sized In, and micron-sized Cu@In, comprising the following steps:

[0011] Step 1: Mix micron-sized Ag particles, micron-sized In particles, and micron-sized Cu@In core-shell particles evenly to obtain a mixed powder;

[0012] Step 2: Place the mixed powder in the preform mold, gently vibrate and shake to spread the powder evenly at the bottom of the mold, apply a pressure of 3MPa above the mold and hold the pressure for 1 minute to form a preform of micron Ag, micron In and micron Cu@In core-shell mixed material with uniform thickness and metallic luster.

[0013] Furthermore, in step one, micron-sized Ag particles and micron-sized In particles are added to a solution of micron-sized Cu@In core-shell particles, ultrasonically separated by centrifugation, and the precipitate is vacuum dried to obtain a mixed powder; the vacuum drying conditions are -1MPa vacuum and drying at 50℃ for 4 hours; or the micron-sized Ag particles, micron-sized In particles and micron-sized Cu@In core-shell particles are placed in an agate mortar and ground thoroughly to mix them evenly to obtain a mixed powder.

[0014] An application of the aforementioned micron-sized Ag, micron-sized In, and micron-sized Cu@In core-shell hybrid material preform involves selecting molds of different shapes or cutting the preform into specific shapes for connection based on the different pad sizes when preparing weld seams. The specific steps include:

[0015] Step S1: Add a preform of a hybrid core-shell material of micron Ag, micron In and micron Cu@In onto a substrate, and place the chip on top of the preform of the hybrid core-shell material of micron Ag, micron In and micron Cu@In to form a sandwich structure;

[0016] Step S2: Place the sandwich structure in a constant temperature drying oven for preheating to remove contaminants between the chip, preform, and substrate, avoid the formation of excess pores in the connection structure, and reduce welding stress; then perform thermoforming or laser welding.

[0017] Furthermore, in step S1, before use, the substrate is treated with acetone to remove oil stains on the surface, with dilute hydrochloric acid to remove surface oxides, and then the substrate is dried and polished to further remove the surface oxide film. The treated substrate is then placed in a vacuum drying oven and stored at room temperature under a vacuum of -1MPa for later use.

[0018] Furthermore, in step S2, the preheating temperature is 110–140°C, and the preheating time is 5–30 min.

[0019] Furthermore, in step S2, the hot pressing connection involves placing the assembled sandwich structure into a hot press for connection. The heating method is double-sided heating, with a temperature rise rate of 5℃ / min, a pressure of 1~10MPa, a heating temperature of 250~400℃, and a heating time of 5~60min.

[0020] Furthermore, in step S2, laser welding involves applying a certain pressure to the assembled sandwich structure sample and placing it in a laser micro-welding device for rapid connection. The parameters are: heating power of 30-75W, heating time of 10-30s, applied pressure of 1-10MPa, and defocusing distance of 0-1.2cm.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] 1. In the core-shell hybrid material of micron-sized Ag, micron-sized In, and micron-sized Cu@In, the melting point of In is only 156.6℃, so bonding can be performed at a relatively low temperature. Once In is completely depleted to form intermetallic compounds, its service temperature increases. Therefore, low-temperature bonding and high-temperature service are possible.

[0023] 2. Micron-sized Ag particles, micron-sized In particles, and micron-sized Cu@In core-shell particles have different particle sizes, allowing them to fit together after welding and fully utilize space. Furthermore, at temperatures above 156.6℃, In melts first, and the molten indium begins to diffuse and fill the pores between the micron-sized particles, improving wettability and reducing porosity. This significantly reduces raw material costs, providing a major advantage in large-scale industrial production.

[0024] 3. In can form intermetallic compounds with both Ag and Cu, improving joint strength. Even after the reaction is complete, the internal Cu core remains. Compared to traditional all-IMCs (Intermetallic Compound) welds, the Cu core can better absorb external stress, thus alleviating localized stress concentration and improving the weld's shear resistance. Furthermore, due to Cu's excellent electrical and thermal conductivity, the final weld exhibits significantly improved electrical and thermal conductivity compared to traditional all-IMCs welds.

[0025] 4. In can form intermetallic compounds with Ag and Cu, improving resistance to thermal aging. The shear strength of the welded joint does not decrease significantly after high-temperature aging; in fact, it may even increase with prolonged high-temperature aging time.

[0026] 5. Precast weld beads reduce weld porosity and increase weld shear strength compared to solder paste. During welding, the rising temperature causes the flux and other organic substances in solder paste to volatilize, creating voids and resulting in high porosity in the weld, thus reducing its shear strength. Using precast weld beads eliminates the need for flux, preventing the formation of pores or voids due to flux volatilization, effectively reducing weld porosity and increasing shear strength.

[0027] 6. This invention relates to a connecting material formed by mixing micron-sized Ag, micron-sized In, and micron-sized Cu@In core-shell particles. In the micron-sized Cu@In core-shell particles, the micron-sized Cu core serves as the conductive matrix, while the outer In shell primarily prevents oxidation of the internal Cu core. The micron-sized In mainly reduces porosity, and the micron-sized Ag forms an IMC (internal matrix structure), improving the shear strength of the connector and acting as a secondary conductive matrix. Furthermore, the micron-sized Ag deforms under pressure, giving it a certain degree of porosity-filling ability. This allows for low-temperature connection and high-temperature service, not only reducing interconnection temperature and conditions but also effectively reducing porosity and voids in the connector, improving shear strength and resistance to thermal aging. It enables the interconnection of chips and substrates at low temperatures, completing the connection and packaging of semiconductor devices, and maintains good mechanical properties at high temperatures. It can be well applied in semiconductor device manufacturing, microelectronic packaging, and power electronic packaging. Attached Figure Description

[0028] Figure 1 This is a morphology image of the micron-sized Cu@In core-shell structure obtained by chemical plating in Example 1;

[0029] Figure 2 This is a schematic diagram of the core-shell hybrid material preform of micron-sized Ag, micron-sized In, and micron-sized Cu@In prepared in Example 1;

[0030] Figure 3 The sample is a preform of a core-shell hybrid material of micron Ag, micron In and micron Cu@In in Example 1, wherein (a) is a front view of the preform and (b) is a side view of the preform.

[0031] Figure 4 This is a schematic diagram of the hot-pressed connection of preforms made of micron-sized Ag, micron-sized In, and micron-sized Cu@In core-shell hybrid materials in Example 1;

[0032] Figure 5 This is a morphology diagram of the solder joint formed between the micron Ag, micron In and micron Cu@In core-shell hybrid material preform and the copper substrate in Example 1;

[0033] Figure 6 Line scan image of the solder joint formed between the core-shell hybrid material preform of micron Ag, micron In and micron Cu@In in Example 1 and the copper substrate;

[0034] Figure 7 The image shows a comparison of the shear strength of the micron Ag, micron In, and micron Cu@In core-shell hybrid material preforms in Examples 1 and 2 with the micron Ag, micron In, and micron Cu@In core-shell hybrid material solder pastes made with different fluxes in Example 3.

[0035] Figure 8 This is a schematic diagram of the laser rapid connection of preforms made of micron-sized Ag, micron-sized In, and micron-sized Cu@In core-shell hybrid materials in Example 9. Detailed Implementation

[0036] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of the invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0037] Example 1:

[0038] This embodiment provides an interconnection process for a hybrid core-shell material preform of micron-sized Ag, micron-sized In, and micron-sized Cu@In. The micron-sized Cu@In core-shell material is prepared by chemical plating and then mixed with micron-sized In and Ag particles to obtain a hybrid core-shell material preform. The micron-sized Ag, micron-sized In, and micron-sized Cu@In core-shell material preform is placed on a substrate, and the chip, preform, and substrate are assembled into a sandwich structure to obtain an integrated device. The integrated device is then connected under a certain pressure to obtain an interconnect device. The specific implementation steps are as follows:

[0039] Step 1: Preparation of micron-sized Cu@In core-shell material. First, the micron-sized Cu particles are pre-treated to remove the oxide film and oil on their surface, and then a solution of micron-sized Cu@In particles is obtained through chemical plating.

[0040] Step 2: Preparation of preforms of micron-sized Ag, micron-sized In, and micron-sized Cu@In core-shell hybrid materials. A certain amount of dried micron-sized In and Ag particles are weighed and poured into a solution of micron-sized Cu@In core-shell particles. The mixture is ultrasonicated, centrifuged, and then dried in a vacuum drying oven. The dried mixed powder is then placed into a preform mold, gently vibrated and shaken to evenly spread the powder at the bottom of the mold. Pressure is applied above the mold and held for a certain time to obtain the preforms of micron-sized Ag, micron-sized In, and micron-sized Cu@In core-shell hybrid materials. The mass percentages of micron-sized Cu@Ag core-shell particles, micron-sized Ag, and micron-sized In particles in the mixed powder are 48%:12%:40%. The particle size of the micron-sized Ag particles is 10 μm, the particle size of the micron-sized In particles is 5 μm, and the particle size of the micron-sized Cu@In core-shell particles is 20 μm.

[0041] Step 3: Substrate Treatment. First, use acetone to remove oil stains from the substrate surface, and use dilute hydrochloric acid to remove surface oxides. After drying, polish the cleaned copper substrate sequentially with 1000# and 2000# sandpaper to further remove the surface oxide film and increase surface roughness, which helps with the wetting of the preforms during the soldering process. Store the treated substrate in a vacuum drying oven.

[0042] Step 4: Addition of the preform. A preform of micron-sized Ag, micron-sized In, and micron-sized Cu@In core-shell hybrid material is added to the substrate treated in Step 3. The thickness of the preform is 100 μm. The chip, preform, and substrate are assembled into a sandwich structure and placed in a constant temperature drying oven. It is preheated at 120°C for 10 minutes to remove contaminants between the chip, preform, and substrate, avoid the formation of excess pores in the bonding structure, and reduce welding stress.

[0043] Step 5: Place the assembled sandwich structure into a hot press for connection. The heating method uses double-sided heating, which provides more uniform heating and reduces thermal stress compared to single-sided heating. The temperature rise rate is 5℃ / min, the pressure is 5MPa, the heating temperature is 350℃, and the heating time is 30min.

[0044] Example 2:

[0045] The difference between this embodiment and Embodiment 1 is that in step two, after washing and centrifuging the prepared micron-sized Cu@In particles, the supernatant is poured out and placed in a vacuum drying oven for drying. Then, the three types of particles—micron-sized Ag particles, micron-sized In particles, and micron-sized Cu@In core-shell particles—are weighed according to a mass ratio of 12%:40%:48%, respectively, and placed in an agate mortar and ground thoroughly for a certain period of time to ensure uniform mixing.

[0046] Example 3:

[0047] The difference between this embodiment and embodiment 1 is that in step two, three fluxes, UV223, MK504, and RMA223, are added to the three dried micron Ag particles, micron In particles, and micron Cu@In core-shell particles mixed powder to prepare three solder pastes; in step four, the three mixed solder pastes are uniformly coated onto the substrate by screen printing.

[0048] Example 4:

[0049] The difference between this embodiment and Embodiment 1 is that in step five, the selected heating temperature is 350℃ and the heating time is 60 minutes.

[0050] Example 5:

[0051] The difference between this embodiment and Embodiment 1 is that in step five, the selected heating temperature is 250℃ and the heating time is 30 minutes.

[0052] Example 6:

[0053] The difference between this embodiment and Embodiment 1 is that in step five, the selected heating temperature is 250℃ and the heating time is 60 minutes.

[0054] Example 7:

[0055] The difference between this embodiment and embodiment 1 is that in step five, the selected heating temperature is 400℃ and the heating time is 30 minutes.

[0056] Example 8:

[0057] The difference between this embodiment and embodiment 1 is that in step five, the selected heating temperature is 400℃ and the heating time is 60 minutes.

[0058] Example 9:

[0059] The difference between this embodiment and embodiment 1 is that in step five, a laser micro-welding equipment is used for rapid connection, with a heating power of 75W, a sintering time of 18s, an applied pressure of 5MPa, and a defocusing amount of 0.8cm.

[0060] Example 10:

[0061] The difference between this embodiment and embodiment 1 is that in step five, a laser micro-welding equipment is used for rapid connection, with a heating power of 75W, a sintering time of 30s, an applied pressure of 5MPa, and a defocusing amount of 0.8cm.

[0062] Example 11:

[0063] The difference between this embodiment and embodiment 1 is that in step five, a laser micro-welding equipment is used for rapid connection, with a heating power of 75W, a sintering time of 18s, an applied pressure of 10MPa, and a defocusing amount of 0.8cm.

[0064] Example 12:

[0065] The difference between this embodiment and embodiment 1 is that in step five, a laser micro-welding equipment is used for rapid connection, with a heating power of 75W, a sintering time of 18s, an applied pressure of 5MPa, and a defocusing amount of 1.2cm.

[0066] Example 13:

[0067] The difference between this embodiment and embodiment 1 is that in step five, a laser micro-welding equipment is used for rapid connection, with a heating power of 50W, a sintering time of 18s, an applied pressure of 5MPa, and a defocusing amount of 1.2cm.

[0068] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A preform of a core-shell hybrid material consisting of micron-sized Ag, micron-sized In, and micron-sized Cu@In, characterized in that: It includes micron-sized Ag particles, micron-sized In particles, and micron-sized Cu@In core-shell particles, wherein the mass percentage of the micron-sized Ag particles, micron-sized In particles, and micron-sized Cu@In core-shell particles is 8-16%: 20-60%: 32-64%.

2. The preform of the core-shell hybrid material of micron-sized Ag, micron-sized In, and micron-sized Cu@In according to claim 1, characterized in that: The micron-sized Ag particles have a diameter of 1–10 μm, the micron-sized In particles have a diameter of 5–10 μm, and the micron-sized Cu@In core-shell particles have a diameter of 20–45 μm.

3. The preform of the core-shell hybrid material of micron-sized Ag, micron-sized In, and micron-sized Cu@In according to claim 1, characterized in that: The thickness of the core-shell hybrid material preform of micron-sized Ag, micron-sized In, and micron-sized Cu@In is 50–200 μm.

4. A method for preparing a preform of a core-shell hybrid material of micron-sized Ag, micron-sized In, and micron-sized Cu@In as described in claim 1, 2, or 3, characterized in that, Includes the following steps: Step 1: Mix micron-sized Ag particles, micron-sized In particles, and micron-sized Cu@In core-shell particles evenly to obtain a mixed powder; Step 2: Place the mixed powder in the preform mold, spread it evenly, and apply pressure to the mold to form the mixed powder inside into a core-shell mixed material preform of micron Ag, micron In and micron Cu@In.

5. The preparation method according to claim 4, characterized in that: In step one, micron-sized Ag particles and micron-sized In particles are added to a solution of micron-sized Cu@In core-shell particles, ultrasonicated and centrifuged, and the precipitate is vacuum dried to obtain a mixed powder; or micron-sized Ag particles, micron-sized In particles and micron-sized Cu@In core-shell particles are placed in a mortar and ground thoroughly to mix them evenly to obtain a mixed powder.

6. An application of the micron-sized Ag, micron-sized In, and micron-sized Cu@In core-shell hybrid material preform as described in claim 1, 2, or 3, characterized in that, Includes the following steps: Step S1: Add a preform of a hybrid core-shell material of micron Ag, micron In and micron Cu@In onto a substrate, and place the chip on top of the preform of the hybrid core-shell material of micron Ag, micron In and micron Cu@In to form a sandwich structure; Step S2: Place the sandwich structure in a constant temperature drying oven for preheating, and then perform hot pressing or laser welding on it.

7. The application according to claim 6, characterized in that: In step S1, before use, the substrate is treated with acetone to remove oil stains on the surface, with dilute hydrochloric acid to remove surface oxides, and then the substrate is dried and polished to further remove the surface oxide film. The treated substrate is then placed in a vacuum drying oven and stored at room temperature for later use.

8. The application according to claim 6, characterized in that: In step S2, the preheating temperature is 110–140°C, and the preheating time is 5–30 min.

9. The application according to claim 6, characterized in that: In step S2, the heating method for hot-press connection is double-sided heating, with a temperature rise rate of 5℃ / min, a pressure of 1~10MPa, a heating temperature of 250~400℃, and a heating time of 5~60min.

10. The application according to claim 6, characterized in that: In step S2, the parameters for laser welding are: heating power of 30-75W, heating time of 10-30s, applied pressure of 1-10MPa, and defocusing range of 0-1.2cm.

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