High-strength low-bonding-stress packaging method of metal periodic structure

Abstract

The invention provides a high-strength low-bonding stress packaging method of a metal periodic structure. The method comprises the following steps: S1, preparing parts; s2, metal parts are pretreated, and all the metal parts need to be subjected to high-precision machining forming; s3, sintering and welding, wherein temperature curves and atmospheres adopted for different types (including components and sizes) of glass and welding fluxes need to be paid attention to in the glass sintering and welding flux welding process; s4, pre-plating treatment, wherein oil stains, stains and an oxide layer on the surface of the product must be removed before electroplating; and S5, electroplating, wherein the requirements are met through a method of plating nickel on the metal surface and then plating gold on the metal surface. According to the invention, the high-strength metal is used as a packaging material of the semiconductor chip, and the metal is polished, sintered, welded and electroplated, so that the strength of the metal is integrally improved, the stress is reduced, the strength of the whole metal packaging shell is improved, and the purpose of improving the packaging reliability is achieved.

Description

Technical Field

[0001] The invention belongs to the field of semiconductors, and in particular relates to a high-strength and low-bonding stress packaging method for a metal periodic structure. Background Art

[0002] The periodic metal deposition structure can obtain high mechanical strength and stiffness by precisely controlling the deposition process, which mainly depends on its special geometric layout and material distribution characteristics. The advantage of this structure is that it allows the externally applied stress to be more evenly distributed through periodic arrangement, thereby improving the material's fatigue resistance and crack propagation resistance. Specifically, there are the following mechanisms of action:

[0003] For example: uniform stress distribution, support and conduction inside the material, regulation of mechanical properties, fatigue resistance, crack propagation resistance, material strengthening mechanism, strengthening phase and phase change, local enhancement effect, energy absorption and dissipation, etc.; periodic metal deposition structure effectively improves mechanical strength, stiffness, fatigue resistance and crack propagation resistance by precisely designing its geometric arrangement, material distribution and its multi-level and multi-scale structural characteristics. External stress can be evenly dispersed and crack propagation is effectively prevented, which makes the periodic metal structure show superior performance under high load and long-term use conditions. These characteristics make the periodic metal deposition structure have broad application prospects in semiconductors, aerospace, automotive industry, energy and high-performance materials. Among them, semiconductor chip packaging refers to the process of using precision welding technology to paste and fix the chip on a base such as a frame or PCB board, and connect the bonding area of ​​the chip to the base through gold wire, copper wire, aluminum wire or other media, and then protect them with insulating materials to form independent electronic components.

[0004] The purpose of semiconductor chip packaging is to protect the chip from or reduce the impact of the external environment, and provide it with a good working environment for the semiconductor chip to function stably, reliably and normally. However, chip packaging will only limit but not improve the chip's function. Under such circumstances, the world is working hard to research and continuously introduce new packaging forms to maximize the original functions of semiconductor chips, especially semiconductor integrated circuits, and reduce the impact of packaging on chip functions. The semiconductor chip packaging process can be divided into two parts: the "front-end" process and the "back-end" process. Among them, the "front-end" process includes two processes, namely, patch and bonding, which are two crucial processes in the entire semiconductor chip packaging process and determine the success or failure of the entire packaging process; the "back-end" process includes plastic sealing, post-curing, high-temperature storage, deburring, tinning (electroplating), rib cutting (bending), testing and classification, marking, packaging and other processes. The back-end process is the so-called packaging, which refers to the shell used to install semiconductor integrated circuit chips. It not only plays the role of placing, fixing, sealing, protecting chips and enhancing electrical and thermal performance, but also serves as a bridge to communicate the internal and external circuits of the chip. The contacts on the chip are connected to the pins of the package shell with wires, and these pins are connected to other devices through wires on the printed circuit board. Therefore, packaging is one of the important components of the device and plays a very important role. With the miniaturization and high performance of electronic systems, packaging has become as important as chips, and the proportion of packaging costs in semiconductor sales value is also increasing. Therefore, electronic packaging has received unprecedented attention. In the United States, Japan and other countries, electronic packaging is developed as a separate industry, while for Asian countries and regions such as Singapore, electronic packaging and assembly technology are regarded as their industrial pillars and are in an absolutely priority position for development;

[0005] At present, semiconductor chips are often bonded using ultrasonic bonding, and packaging often uses materials such as plastic, ceramic and glass. Since the strength of these three materials is not high, the reliability of these three types of packaging effects is not very strong.

[0006] In summary, the present invention provides a high-strength and low-bonding stress packaging method for a metal periodic structure to solve the above problems. Summary of the invention

[0007] The purpose of the present invention is to provide a high-strength and low-bonding stress packaging method for a metal periodic structure to solve the problems raised in the above background technology;

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

[0009] S1: Parts preparation. The packaging of metal parts generally includes base plate, frame, glass beads, pins, solder, caps or cover plates. There are many materials to choose from according to the different performance requirements of the packaging, including 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 need to be processed by high-precision machining. In the molding process, special attention should be paid to the roughness of the sealing surface, because too rough a surface or too smooth a surface will lead to poor sealing quality and affect air tightness.

[0011] S3: Sintering and welding. During the glass sintering and soldering process, attention should be paid to the temperature curve and atmosphere adopted for different types of glass and solder (including composition and size). In other words, the temperature of each temperature zone, the rotation speed of the furnace chain belt, and the flow rate of the protective gas should be controlled. In addition, the product should be covered with a special box during glass sintering.

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

[0013] S5: Electroplating, the requirements are met by first plating nickel and then gold on the metal surface. For packages with multiple metal combinations, in order to make the potential on the shell surface consistent, the plating layer is uniform and chemical replacement does not occur to affect the bonding strength, a layer of copper can be plated first;

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

[0015] S7: Packing and shipping: The qualified and standard metal shells are packed and shipped out using a packaging machine.

[0016] Preferably, the material of the bottom plate, frame, pipe cap or cover plate in S1 is generally iron-nickel-cobalt alloy. If there are special requirements for the bottom plate and frame, copper alloy, steel, stainless steel or aluminum alloy can be selected.

[0017] Preferably, the lead material in S1 is generally iron-nickel-cobalt alloy, copper, and iron-nickel alloy clad copper or copper clad iron-nickel-cobalt alloy.

[0018] Preferably, the glass bead material in S1 is generally selected to have an expansion coefficient that matches that of the base plate or frame and leads to which it is directly sintered. If necessary, a material with a smaller expansion coefficient may also be selected for compression sealing.

[0019] Preferably, the solder in S1 is made of pure metal or alloy.

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

[0021] Preferably, S2 also includes: cleaning, decarburizing and pre-oxidation treatment of the parts.

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

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

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

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

[0026] The present invention utilizes high-strength metal as the packaging material of the semiconductor chip and polishes, sinters, welds and electroplates the metal to improve the overall strength of the metal and reduce stress, thereby improving the strength of the entire metal packaging shell and achieving the purpose of improving packaging reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the process structure of the present invention. DETAILED DESCRIPTION

[0028] The following embodiments of the present invention are described in further detail in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0029] like Figure 1As shown, the present invention provides a high-strength and low-bonding stress packaging method for a metal periodic structure, comprising the following steps: S1: Part preparation. The packaging of metal parts generally includes a base plate, a frame, glass beads, pins, solder, a cap or a cover plate. There are also many materials that can be selected according to the different performance requirements of the packaging, including iron-nickel-cobalt alloy, copper, tungsten-copper, molybdenum-copper, stainless steel, aluminum and aluminum alloy. In addition to the selection of materials for parts such as the base plate, frame, and glass beads mentioned above, the parts related to the periodic metal structure are specially designed and prepared. The periodic metal deposition structure can obtain higher mechanical strength and rigidity by precisely controlling the deposition process, and its special geometric layout and material distribution characteristics give it many advantages. For example, the unit shape of the periodic metal structure can be designed as a square, circular or hexagonal geometric shape, and its size is determined according to the overall performance requirements of the package. The unit side length or diameter can be in the range of 0.5-5 mm. In terms of materials, an iron-nickel-cobalt alloy or copper alloy that matches the main structure can be selected to ensure that its thermal expansion coefficient is compatible with other packaged parts to avoid package failure due to differences in thermal expansion and contraction. These periodic metal structural parts can be formed through high-precision manufacturing processes such as precision stamping, photolithography or electrospark machining to ensure that their shape and size accuracy is within ±0.05 mm to meet the strict requirements of subsequent packaging processes for part accuracy. Periodic metal structures often have regular geometric units, such as arrays, meshes, layers, etc. These structures are precisely designed to evenly distribute external loads in the material. Traditional metal materials may cause cracks or fatigue damage due to stress concentration in certain areas, but periodic metal structures can significantly reduce this stress concentration phenomenon due to the symmetry and geometric characteristics of their repeating units. In S1, the preferred material for the base plate, frame, cap or cover plate is generally iron-nickel-cobalt alloy. If there are special requirements for the base plate and frame, copper alloy, steel, stainless steel or aluminum alloy can be used. The lead material in S1 The materials are generally iron-nickel-cobalt alloy, copper, and iron-nickel alloy clad copper or copper clad iron-nickel-cobalt alloy. The glass bead material in S1 generally selects the material whose expansion matches the base plate or frame and lead to which it is directly sintered. If necessary, materials with a smaller expansion coefficient can also be selected for compression sealing. The solder in S1 generally uses 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: Pretreatment of metal parts. For periodic metal structural parts, after mechanical processing and forming, the surface roughness must also be strictly controlled within the range of Ra=3.2-6.3μm. In the cleaning process, since there may be many fine gaps or holes in its structure, ultrasonic oscillation cleaning combined with high-pressure gas purging is required to ensure that cleaning agents such as gasoline, alkali solution, and alcohol can fully contact and remove oil and impurities from various parts. The decarburization process is the same as other metal parts. Keep warm in a hydrogen atmosphere at 1050℃ for 30 minutes to reduce the surface carbon content and internal gas content and reduce stress.During the pre-oxidation treatment, a special oxidation device is used for the special shape of the periodic metal structure to ensure that an oxide layer with appropriate thickness and mainly low-valent oxides can be uniformly formed on its surface. For example, by controlling the flow rate and temperature distribution of the oxidizing atmosphere, the oxide thickness is uniformly distributed between 0.1-0.5 microns, providing good interface conditions for subsequent sintering and welding. The units of the periodic structure usually play a role in sharing stress. Each unit is equivalent to a small support point. Under the action of external stress, they work together to transfer the load evenly, thereby avoiding local overload; S3: Sintering and welding, in the process of glass sintering and solder welding, it is considered that the existence of the periodic metal structure will affect 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 areas with dense structures, the amount of glass coating is appropriately reduced to prevent bubbles or cracks from being generated due to excessive accumulation of glass during the sintering process; for areas with loose structures, a small amount of glass can be added to enhance the connection stability. During the welding process, the welding temperature curve and the protective gas flow are optimized according to the distribution of the connection points between the periodic metal structure and other parts. For areas with more connection points, the welding speed is appropriately reduced and the welding time is increased to ensure that each connection point can be fully welded. At the same time, the flow rate of protective gas is controlled to form a stable protective atmosphere inside the structure and reduce oxidation during welding. In addition, during glass sintering, in order to better adapt to the shape characteristics of the periodic metal structure, the internal structure of the specially made box is optimized, and grooves or supporting parts matching the periodic structure are set to prevent the structure from deforming or displacing during the sintering process. The number and placement of activated carbon balls in the box are also adjusted according to the structural characteristics to ensure effective adsorption of sintering fumes. By changing the size of the periodic structural unit (such as period length, porosity, etc.) and the arrangement (such as square, hexagon, triangle, etc.), the stiffness and strength of the structure can be accurately adjusted. The influence of these factors on the welding effect needs to be considered during the welding process. For example, smaller units can usually improve stiffness, and more accurate welding parameters need to be used during welding to ensure the reliability of the connection; S4: Pre-plating treatment, for the removal of oil stains, stains and oxide layers on the surface of the periodic metal structure, when using chemical methods, a special chemical cleaning agent is prepared according to its structural characteristics. For example, for dirt in the gaps and holes inside the structure, adding appropriate amounts of penetrants and chelating agents can improve the cleaning effect.When the appearance requirements are high, mechanical ball milling uses special spherical abrasives, and its diameter is selected according to the minimum size of the periodic structure, generally 1 / 10-1 / 5 of the minimum size, to avoid excessive wear on the structure; during the sandblasting process, the sandblasting pressure and angle are controlled to ensure that the sandblasting can act evenly on the surface of the periodic structure, and the chemical polishing uses a mild polishing liquid formula to avoid corrosion or damage to the structure due to the polishing process; S5: electroplating, in the electroplating process, due to the relatively large surface area and complex shape of the periodic metal structure, in order to ensure the uniformity of the coating, a special electroplating tool is used. The tool is designed to match the shape of the periodic metal structure, and the current can be evenly distributed on the entire surface of the structure by reasonably distributing the electrode position and current density. When copper plating first, adjust the copper plating process parameters according to the structural characteristics, such as plating solution concentration, temperature, pH value, and electroplating time. For example, the copper plating time is appropriately increased in the concave part of the structure to ensure uniform coating thickness. In the nickel plating and gold plating process, the process parameters are also optimized according to the complexity of the structure to ensure that the quality of the coating meets the test requirements of salt spray test, bonding, solderability and lead firmness, so that the coating forms a uniform, dense and well-adhesive metal covering layer on the surface of the periodic metal structure, and the thickness is controlled within the specified range, such as 3-5 microns for nickel plating and 0.1-0.3 microns for gold plating. At the nanometer or micrometer scale, periodic metal deposition structures often show size effects, which means that as the size of the structure decreases, the strength and stiffness of the material tend to increase. The electroplating process also needs to consider the possible impact of this size effect on the bonding force between the coating and the periodic structure to ensure the overall packaging performance; S6: Detection, for the detection of periodic metal structures, in addition to the conventional metal shell surface detection items, the detection of the integrity and dimensional accuracy of the periodic structure is added. Use an optical microscope or an electron microscope to perform a microscopic inspection of the unit shape, size and connection parts of the structure to ensure that there are no problems such as structural deformation, cracking or coating defects caused by the packaging process. At the same time, X-ray diffraction or energy spectrum analysis is used to detect the composition and crystal structure of the coating to ensure that the quality of the coating meets the standard requirements. Through specially designed testing tools and testing software, the various parameters of the periodic metal structure are accurately measured and analyzed, and compared with the design standards to determine whether they meet the requirements. The periodic metal structure has significant advantages under fatigue loads because it can disperse the external periodic stress to multiple small areas. The stress condition of each small area is relatively uniform, so the fatigue life of each unit is longer. During the testing process, simulated fatigue tests and other means can be used to further verify whether its fatigue resistance meets the packaging expectations; S7: Packaging and delivery. In the packaging process, a special packaging mold or pallet is designed according to the shape and size of the periodic metal structure to ensure that the structure will not be damaged by extrusion or collision during the packaging process.For example, a groove matching the periodic structure is made of foam or sponge material, and the metal shell is fixed in it before the whole is packaged. After packaging, the relevant parameters and special precautions of the periodic metal structure are marked on the packaging label so that it can be properly handled during transportation and storage, and finally the warehouse is shipped according to the normal process.

[0030] Through the above integration, the characteristics and advantages of periodic metal structures are fully integrated into all aspects of high-strength and low-bonding stress packaging methods to achieve better quality and high-performance packaging effects, meeting the strict requirements of aerospace, automotive industry, energy field and high-performance materials field for packaging products.

[0031] The embodiments of the present invention are provided for the purpose of illustration and description. Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations of the present invention. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A high-strength and low-bonding stress packaging method for a metal periodic structure, characterized in that: The following steps are involved: S1: Parts preparation. The packaging of metal parts generally includes base plate, frame, glass beads, pins, solder, caps or cover plates. There are many materials to choose from according to the different performance requirements of the packaging, including iron-nickel-cobalt alloy, copper, tungsten-copper, molybdenum-copper, stainless steel, aluminum and aluminum alloy. S2: Pre-treatment of metal parts. All metal parts need to be processed by high-precision machining. In the molding process, special attention should be paid to the roughness of the sealing surface, because too rough a surface or too smooth a surface will lead to poor sealing quality and affect air tightness. S3: Sintering and welding. During the glass sintering and soldering process, attention should be paid to the temperature curve and atmosphere adopted for different types of glass and solder (including composition and size). In other words, the temperature of each temperature zone, the rotation speed of the furnace chain belt, and the flow rate of the protective gas should be controlled. In addition, the product should be covered with a special box during glass sintering. S4: Pre-plating treatment. Before electroplating, the oil stains, stains and oxide layers on the product surface must be removed. In general, chemical methods are used for pre-treatment. There are different cleaning and polishing methods for different packaging materials. When the appearance requirements of the package are very high, mechanical ball milling, sandblasting and chemical polishing can be combined to treat it. S5: Electroplating, the requirements are met by first plating nickel and then gold on the metal surface. For packages with multiple metal combinations, in order to make the potential on the shell surface consistent, the plating layer is uniform and chemical replacement does not occur to affect the bonding strength, a layer of copper can be plated first; S6: Inspection: observe the surface of the metal shell after electroplating to check whether it meets the standards and requirements; S7: Packing and shipping: The qualified and standard metal shells are packed and shipped out using a packaging machine.

2. A high-strength and low-bonding-stress packaging method for a metal periodic structure as claimed in claim 1, characterized in that: In the S1, the material of the bottom plate, frame, pipe cap or cover plate is generally preferably iron-nickel-cobalt alloy. If there are special requirements for the bottom plate and frame, copper alloy, steel, stainless steel or aluminum alloy can be selected.

3. A high-strength and low-bonding-stress packaging method for a metal periodic structure as claimed in claim 1, characterized in that: The lead wire material in S1 is iron-nickel-cobalt alloy, copper, iron-nickel alloy clad copper or copper clad iron-nickel-cobalt alloy.

4. A high-strength and low-bonding-stress packaging method for a metal periodic structure as claimed in claim 1, characterized in that: The glass bead material in S1 is selected to have expansion matching with the base plate or frame and leads to which it is directly sintered.

5. The high-strength and low-bonding-stress packaging method of a metal periodic structure according to claim 1, characterized in that: The solder in S1 is pure metal or alloy.

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

7. A high-strength and low-bonding-stress packaging method for a metal periodic structure as claimed in claim 1, characterized in that: The S2 also includes: cleaning, decarburizing and pre-oxidation treatment of the parts.

8. A high-strength and low-bonding-stress packaging method for a metal periodic structure as claimed in claim 7, characterized in that: During the cleaning, the parts need to be cleaned repeatedly with gasoline, alkali solution and alcohol.

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

10. The high-strength and low-bonding-stress packaging method of a metal periodic structure according to claim 1, characterized in that: In the S3, some activated carbon balls are also placed in the box.

Images