High strength low bond stress packaging method for a metal periodic structure

Abstract

The application provides a high-strength low-bonding stress packaging method of a metal periodic structure, comprising the following steps: S1: part preparation; S2: metal part pretreatment, all metal parts need to be formed through high-precision machining; S3: sintering and welding, in the process of glass sintering and solder welding, the temperature curve and atmosphere adopted for different glasses and solder types (including components and size) need to be paid attention to; S4: pre-plating treatment, oil stains, contamination and oxide layers on the surface of the product must be removed before electroplating; S5: electroplating, the requirements are met through the method of plating nickel on the metal surface first and then plating gold. The application uses high-strength metal as the packaging material of a semiconductor chip, and through polishing, sintering, welding and electroplating treatment of the metal, the strength of the metal is improved as a whole and the stress is reduced, so that the strength of the whole metal packaging shell is improved, and the purpose of improving the packaging reliability is achieved.

Description

Technical Field

[0001] This invention belongs to the field of semiconductors, specifically a high-strength, low-bonding-stress packaging method for metal periodic structures. Background Technology

[0002] Periodic metal deposition structures can achieve high mechanical strength and stiffness through precise control of the deposition process, primarily relying on their unique geometric layout and material distribution characteristics. The advantage of this structure lies in its periodic arrangement, which allows for a more uniform distribution of externally applied stress, thereby improving the material's resistance to fatigue and crack propagation. Specifically, the mechanisms of action include the following:

[0003] For example, periodic metal deposition structures offer advantages such as uniform stress distribution, internal material support and conduction, control of mechanical properties, fatigue resistance, crack propagation resistance, material strengthening mechanisms, strengthening phases and phase transitions, localized reinforcement effects, and energy absorption and dissipation. Through precise design of their geometric arrangement, material distribution, and multi-level, multi-scale structural characteristics, periodic metal deposition structures effectively enhance mechanical strength, stiffness, fatigue resistance, and crack propagation resistance. External stress can be uniformly dispersed, and crack propagation is effectively prevented, resulting in superior performance under high-load, long-term use conditions. These characteristics make periodic metal deposition structures promising for applications in semiconductors, aerospace, automotive, energy, and high-performance materials. Semiconductor chip packaging refers to the process of using precision welding technology to attach and fix chips to a base such as a frame or PCB board, connecting the chip's bonding area to the base using gold, copper, aluminum wires, or other media, and then protecting them with insulating materials to form independent electronic components.

[0004] The purpose of semiconductor chip packaging is to protect the chip from or minimize its exposure to external environmental influences and to provide it with a suitable operating environment to perform its functions stably, reliably, and normally. However, chip packaging only limits, not enhances, the chip's functionality. Therefore, the world is constantly researching and developing new packaging methods to maximize the inherent functionality of semiconductor chips, especially integrated circuits, and minimize the impact of packaging on chip performance. The semiconductor chip packaging process can be divided into two parts: the "front-end" process and the "back-end" process. The "front-end" process includes two crucial steps: surface mount and bonding. These two steps determine the success or failure of the entire semiconductor chip packaging process. The "back-end" process includes molding, post-curing, high-temperature storage, deflashing, tin plating (electroplating), lead trimming (bending), testing and sorting, marking, and packaging. The back-end process is the so-called packaging, which refers to the casing used to mount the semiconductor integrated circuit chip. It not only serves to place, fix, seal, and protect the chip and enhance its electrothermal performance, but also acts as a bridge connecting the internal and external circuits of the chip. The contacts on the chip are connected to the pins of the package casing by wires, and these pins are then connected to other devices through wires on the printed circuit board. Therefore, packaging is an important component of the device and plays a very important role. With the miniaturization and high performance of electronic systems, packaging has become as important as the chip itself, and the proportion of packaging costs in semiconductor sales value is increasing. As a result, electronic packaging has received unprecedented attention. In countries such as the United States and Japan, electronic packaging is developed as a separate industry. For Asian countries and regions such as Singapore, electronic packaging and assembly technology is regarded as a pillar of their industry and is given absolute priority in development.

[0005] Currently, ultrasonic bonding is commonly used in the bonding of semiconductor chips, and materials such as plastic, ceramic and glass are often used for packaging. Since these three materials are not very strong, the reliability of these three types of packaging is not strong.

[0006] In summary, this invention provides a high-strength, low-bonding-stress encapsulation method with a metal periodic structure to solve the above-mentioned problems. Summary of the Invention

[0007] The purpose of this invention is to provide a high-strength, low-bonding-stress encapsulation method for metal periodic structures to solve the problems mentioned in the background art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a high-strength, low-bonding-stress encapsulation method for a metal periodic structure, comprising the following steps:

[0009] S1: Component preparation. The packaging of metal components generally includes a base plate, frame, glass beads, leads, solder, cap or cover plate. Depending on the performance requirements of the packaging, there are many materials that can be selected, such as iron-nickel-cobalt alloy, copper, tungsten copper, molybdenum copper, stainless steel, aluminum and aluminum alloy.

[0010] S2: Pre-treatment of metal parts. All metal parts must be formed by high-precision machining. Special attention should be paid to the roughness of the sealing surface during the forming process, because both too rough and too smooth surfaces will result in poor sealing quality and affect airtightness.

[0011] S3: Sintering and welding. During the glass sintering and solder welding process, it is important to pay attention to the temperature profile and atmosphere adopted for different types of glass and solder (including composition and size). That is, it is necessary to control the temperature of each temperature zone, the speed of the furnace chain, and the flow rate of the protective gas. Also, the product should be covered with a special box during glass sintering.

[0012] S4: Pre-plating treatment. Before electroplating, oil stains, dirt and oxide layer on the product surface must be removed. In general, chemical methods are used for pre-treatment. Different cleaning and polishing methods are used for different packaging materials. When the appearance requirements of the packaging are very high, mechanical ball milling, sandblasting and chemical polishing can be combined.

[0013] S5: Electroplating, which meets the requirements by first plating nickel and then gold on the metal surface. For packaging with multiple metal combinations, in order to make the potential of the shell surface consistent, the plating layer uniform and without chemical displacement affecting the bonding force, a layer of copper can be plated first.

[0014] S6: Inspection, observe the surface of the metal shell after electroplating, and check whether it meets the standards and requirements;

[0015] S7: Packaging and shipping. The qualified and standard metal casings are packaged and shipped out using a packaging machine.

[0016] Preferably, the base plate, frame, cap, or cover plate in S1 are generally made of iron-nickel-cobalt alloy. If there are special requirements for the base plate and frame, copper alloy, steel, stainless steel, or aluminum alloy may be used.

[0017] Preferably, the lead material in S1 is generally an iron-nickel-cobalt alloy, copper, or an iron-nickel alloy coated with copper or a copper-coated iron-nickel-cobalt alloy.

[0018] Preferably, the glass bead material in S1 is generally selected to be a material whose expansion is compatible with the base plate or frame and lead wires that are directly sintered. If necessary, a material with a smaller coefficient of expansion can also be selected for compression sealing.

[0019] Preferably, the solder in S1 is a pure metal or an alloy.

[0020] Preferably, the surface roughness of the metal part in S2 should be Ra = 3.2-6.3 μm.

[0021] Preferably, step S2 further includes cleaning, decarburizing, and pre-oxidizing the parts.

[0022] Preferably, the cleaning process involves repeatedly cleaning the parts with gasoline, alkaline solution, and alcohol.

[0023] Preferably, the purpose of decarburization is to remove surface contaminants, reduce the carbon content on the metal surface and the gas content molten inside, and reduce stress. The decarburization process used is to hold the metal at 1050°C in a hydrogen atmosphere for 30 minutes.

[0024] Preferably, in step S3, some activated carbon balls are also placed inside the box.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] This invention utilizes high-strength metal as the packaging material for semiconductor chips, and improves the overall strength of the metal and reduces stress by grinding, sintering, welding and electroplating the metal, thereby increasing the strength of the entire metal packaging shell and achieving the goal of improving packaging reliability. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the process structure of the present invention. Detailed Implementation

[0028] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0029] like Figure 1As shown, this invention provides a high-strength, low-bonding-stress encapsulation method for a periodic metal structure, comprising the following steps: S1: Component preparation. The encapsulation of metal components generally includes a base plate, frame, glass beads, leads, solder, cap, or cover plate. Depending on the performance requirements of the encapsulation, various materials can be selected, including iron-nickel-cobalt alloys, copper, tungsten copper, molybdenum copper, stainless steel, aluminum, and aluminum alloys. In addition to the previously mentioned selection of materials for the base plate, frame, and glass beads, the components related to the periodic metal structure are specifically designed and prepared. Periodic metal deposition structures can achieve high mechanical strength and stiffness through precise control of the deposition process. Their unique geometric layout and material distribution characteristics give them many advantages. For example, the unit shape of the periodic metal structure can be designed as square, circular, or hexagonal, and its size is determined according to the overall performance requirements of the encapsulation. The unit side length or diameter can be in the range of 0.5-5 mm. Regarding materials, iron-nickel-cobalt alloys or copper alloys that match the main structure can be selected to ensure that their coefficient of thermal expansion is compatible with other encapsulation components, avoiding encapsulation failure due to differences in thermal expansion and contraction. These periodic metal structural parts can be formed using high-precision manufacturing processes such as precision stamping, photolithography, or electrical discharge machining, ensuring their shape and dimensional accuracy is within ±0.05 mm to meet the stringent precision requirements of subsequent packaging processes. Periodic metal structures often possess regular geometric units, such as arrays, meshes, or layers. Through precise design, these structures allow for uniform distribution of external loads within the material. While traditional metal materials may experience cracking or fatigue damage in certain areas due to stress concentration, periodic metal structures, due to the symmetry and geometric characteristics of their repeating units, can significantly reduce this stress concentration phenomenon. For the base plate, frame, cap, or cover plate in S1, iron-nickel-cobalt alloys are generally preferred. If the base plate and frame have special requirements, copper alloys, steel, stainless steel, or aluminum alloys can be used. For the lead wires in S1... The materials are generally iron-nickel-cobalt alloys, copper, and iron-nickel alloys clad in copper or copper clad in iron-nickel-cobalt alloys. In S1, the glass bead material is generally selected based on expansion matching that of the base plate or frame and leads to which it is directly sintered. If necessary, materials with a smaller expansion coefficient can be used for compression sealing. The solder in S1 is generally pure metal (such as copper, silver, tin) or alloy (such as silver-copper, gold-silver-copper, silver-copper-tin, palladium-silver-copper, tin-lead). S2: Pre-treatment of metal parts. For periodic metal structural parts, after machining, the surface roughness must be strictly controlled within the range of Ra = 3.2-6.3 μm. During the cleaning process, due to the potential presence of numerous fine gaps or pores in the structure, ultrasonic oscillation cleaning combined with high-pressure gas purging is required to ensure that cleaning agents such as gasoline, alkaline solutions, and alcohol can fully contact and remove oil and impurities from all parts. The decarburization process is the same as for other metal parts, involving holding at 1050℃ in a hydrogen atmosphere for 30 minutes to reduce surface carbon content and internal gas content, and to reduce stress.During pre-oxidation, a special oxidation device is used to address the unique shape of the periodic metal structure, ensuring a uniform oxide layer of appropriate thickness, primarily composed of low-valence oxides, is formed on its surface. For example, by controlling the flow rate and temperature distribution of the oxidation atmosphere, the oxide thickness is uniformly distributed between 0.1 and 0.5 micrometers, providing favorable interface conditions for subsequent sintering and welding. The units of the periodic structure typically act as stress-sharing points; each unit is equivalent to a small support point. Under external stress, they work together to evenly distribute the load, thus avoiding localized overload. S3: Sintering and Welding. During glass sintering and solder welding, the presence of the periodic metal structure affects heat transfer and gas flow. For glass sintering, the coating method and amount of glass are adjusted according to the density and unit shape of the periodic metal structure. For example, in denser areas, the amount of glass coating is appropriately reduced to prevent bubbles or cracks from excessive accumulation during sintering; in looser areas, a small amount of glass can be added to enhance connection stability. During welding, the welding temperature profile and shielding gas flow rate are optimized based on the distribution of connection points between the periodic metal structure and other parts. For areas with numerous connection points, the welding speed is appropriately reduced while the welding time is increased to ensure each connection point is fully welded. Simultaneously, the protective gas flow rate is controlled to create a stable protective atmosphere within the structure, reducing oxidation during welding. Furthermore, during glass sintering, to better adapt to the shape characteristics of the periodic metal structure, the internal structure of the specially designed box is optimized, incorporating grooves or support components that match the periodic structure to prevent deformation or displacement during sintering. The number and placement of activated carbon balls within the box are also adjusted according to the structural characteristics to ensure effective adsorption of sintering fumes. By changing the size (e.g., period length, porosity) and arrangement (e.g., square, hexagonal, triangular) of the periodic structural units, the stiffness and strength of the structure can be precisely adjusted. The impact of these factors on the welding effect must be considered during welding; for example, smaller units typically increase stiffness, requiring more precise welding parameters to ensure reliable connections. S4: Pre-plating treatment. For removing oil stains, contaminants, and oxide layers from the surface of the periodic metal structure, when using chemical methods, a specialized chemical cleaning agent is formulated based on the structural characteristics. For example, adding appropriate amounts of penetrants and complexing agents can improve the cleaning effect by targeting dirt in the gaps and pores inside the structure.When high aesthetic requirements are needed, mechanical ball milling uses specially designed spherical abrasives, the diameter of which is selected based on the minimum size of the periodic structure, generally 1 / 10 to 1 / 5 of the minimum size, to avoid excessive wear on the structure. During sandblasting, the sandblasting pressure and angle are controlled to ensure uniform application to the surface of the periodic structure. Chemical polishing uses a mild polishing solution formula to avoid corrosion or damage to the structure during the polishing process. S5: Electroplating. In the electroplating stage, due to the relatively large surface area and complex shape of the periodic metal structure, special electroplating fixtures are used to ensure uniform plating. The fixtures are designed to fit the shape of the periodic metal structure, and by rationally distributing electrode positions and current density, the current can be evenly distributed across the entire surface of the structure. When copper plating is performed first, the copper plating process parameters, such as plating solution concentration, temperature, pH value, and electroplating time, are adjusted according to the structural characteristics. For example, the copper plating time is appropriately increased in the recessed areas of the structure to ensure uniform plating thickness. During nickel and gold plating, process parameters are optimized based on the complexity of the structure to ensure the plating quality meets the requirements of salt spray testing, bonding, solderability, and lead wire strength tests. This ensures the plating forms a uniform, dense, and well-adhered metal coating on the surface of the periodic metal structure, with the thickness controlled within specified ranges, such as 3-5 micrometers for nickel plating and 0.1-0.3 micrometers for gold plating. At the nanometer or micrometer scale, periodic metal deposition structures often exhibit size effects, meaning that as the structure size decreases, the strength and stiffness of the material often increase. The electroplating process must also consider the potential impact of this size effect on the bonding force between the plating and the periodic structure to ensure overall packaging performance. S6: Inspection. For the inspection of periodic metal structures, in addition to the conventional metal shell surface inspection items, the integrity and dimensional accuracy of the periodic structure are also inspected. Optical or electron microscopes are used to perform microscopic inspections of the unit shape, size, and connection points of the structure to ensure there are no structural deformations, cracks, or plating defects caused by the packaging process. Simultaneously, X-ray diffraction or energy dispersive spectroscopy is used to detect the composition and crystal structure of the coating to ensure that the coating quality meets the standard requirements. Using specially designed testing fixtures and software, various parameters of the periodic metal structure are precisely measured and analyzed, and compared with design standards to determine whether they meet the requirements. Periodic metal structures have significant advantages under fatigue loads because they can disperse external periodically changing stresses into multiple small areas, resulting in a more uniform stress distribution in each area. Therefore, each unit has a longer fatigue life. During the testing process, simulated fatigue tests can be used to further verify whether its fatigue resistance meets the packaging expectations. S7: Packaging and Shipping. In the packaging stage, a dedicated packaging mold or pallet is designed according to the shape and size of the periodic metal structure to ensure that the structure is not damaged by compression or collision during packaging.For example, grooves made of foam or sponge material can be created to match the periodic structure, and the metal casing can be fixed within them before overall packaging. After packaging, the relevant parameters and special precautions for the periodic metal structure should be noted on the packaging label to ensure proper handling during transportation and storage. Finally, the shipment process should proceed according to normal procedures.

[0030] By integrating the above methods, the characteristics and advantages of periodic metal structures are fully incorporated into all aspects of the high-strength, low-bond-stress packaging approach. This results in superior, high-performance packaging that meets the stringent requirements of aerospace, automotive, energy, and high-performance materials industries for packaged products.

[0031] The embodiments of the present invention are given for the purposes of illustration and description. Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A high-strength, low-bonding-stress encapsulation method for a metal periodic structure, characterized in that, Includes the following steps: S1: Component preparation. The packaging of metal components generally includes a base plate, frame, glass beads, leads, solder, cap or cover plate. Depending on the performance requirements of the packaging, there are many materials that can be selected, such as iron-nickel-cobalt alloy, copper, tungsten copper, molybdenum copper, stainless steel, aluminum and aluminum alloy. S2: Pre-treatment of metal parts. All metal parts must be formed by high-precision machining. Special attention should be paid to the roughness of the sealing surface during the forming process, because both too rough and too smooth surfaces will result in poor sealing quality and affect airtightness. S3: Sintering and welding. During the glass sintering and solder welding process, it is important to pay attention to the temperature profile and atmosphere adopted for different types of glass and solder (including composition and size). That is, it is necessary to control the temperature of each temperature zone, the speed of the furnace chain, and the flow rate of the protective gas. Also, the product should be covered with a special box during glass sintering. S4: Pre-plating treatment. Before electroplating, oil stains, dirt and oxide layer on the product surface must be removed. Generally, chemical methods are used for pre-treatment. Different cleaning and polishing methods are used for different packaging materials. When the appearance requirements of the packaging are very high, mechanical ball milling, sandblasting and chemical polishing are combined. S5: Electroplating, which meets the requirements by first plating nickel and then gold on the metal surface. For packaging with multiple metal combinations, in order to make the potential of the shell surface consistent, the plating layer uniform and without chemical displacement affecting the bonding force, a layer of copper is first plated. S6: Inspection, observe the surface of the metal shell after electroplating, and check whether it meets the standards and requirements; S7: Packaging and shipping. The qualified and standard metal casings are packaged and shipped out using a packaging machine.

2. The high-strength, low-bonding-stress encapsulation method for a metal periodic structure as described in claim 1, characterized in that: The preferred materials for the base plate, frame, cap, or cover plate in S1 are generally iron-nickel-cobalt alloys. If there are special requirements for the base plate and frame, copper alloys, steel, stainless steel, or aluminum alloys may be used.

3. The high-strength, low-bonding-stress encapsulation method for a metal periodic structure as described in claim 1, characterized in that: The lead material in S1 is iron-nickel-cobalt alloy, copper, or iron-nickel alloy coated with copper or copper coated with iron-nickel-cobalt alloy.

4. The high-strength, low-bonding-stress encapsulation method for a metal periodic structure as described in claim 1, characterized in that: In S1, the glass bead material is selected to be compatible with the expansion of the base plate or frame and lead wires that are directly sintered with it.

5. The high-strength, low-bonding-stress encapsulation method for a metal periodic structure as described in claim 1, characterized in that: The solder used in S1 is either pure metal or alloy.

6. The high-strength, low-bonding-stress encapsulation method for a metal periodic structure as described in claim 1, characterized in that: The surface roughness of the metal part in S2 is Ra = 3.2-6.3 μm.

7. The high-strength, low-bonding-stress encapsulation method for a metal periodic structure as described in claim 1, characterized in that: The S2 further includes cleaning, decarburizing and pre-oxidizing the parts.

8. The high-strength, low-bonding-stress encapsulation method for a metal periodic structure as described in claim 7, characterized in that: The cleaning process requires repeated cleaning of the parts with gasoline, alkaline solution, and alcohol.

9. The high-strength, low-bonding-stress encapsulation method for a metal periodic structure as described in claim 7, characterized in that: The purpose of decarburization is to remove surface contaminants, reduce the carbon content on the metal surface and the gas content molten inside, and reduce stress. The decarburization process used is to hold the metal at 1050°C in a hydrogen atmosphere for 30 minutes.

10. The high-strength, low-bonding-stress encapsulation method for a metal periodic structure as described in claim 1, characterized in that: In step S3, some activated carbon balls should also be placed inside the box.

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