High-reliability Schottky axial diode and production process thereof

Abstract

The invention relates to a high-reliability Schottky axial diode and a production process thereof, two sides of a chip of the high-reliability Schottky axial diode are provided with leads, and the chip is sequentially coated with four layers of materials from inside to outside: a silicon nitride layer, an oxygen-containing polycrystalline silicon layer, a silicon dioxide layer and a polyimide adhesive layer, the production process comprises the following specific steps of cleaning and drying, inner layer protection of the chip, surface layer PI glue protection of the chip, metallization, vacuum pre-welding of a PUMP solder ball process, welding, silica white glue protection and reinforcement, and epoxy resin wrapping. The invention provides a more comprehensive high-reliability process for respectively protecting the surface and the interior: the surface adopts the PI glue coating to increase the surface protection of the chip, and the interior adopts the silicon nitride layer, the oxygen-containing polycrystalline silicon layer and the silicon dioxide layer, so that the chip has the advantages of high reliability, high efficiency, high reliability, strong compatibility and environmental protection.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and in particular to a high-reliability Schottky axial diode and its manufacturing process. Background Technology

[0002] Schottky axial diodes are widely used in industrial and automotive electronics due to their high efficiency and fast response time. However, silver ion migration is one of the key factors affecting their long-term reliability. Figure 1 As shown, traditional high-reliability technologies typically employ a two-layer structure: SIOPS (Semi-Insulating Polycrystalline Silicon) combined with a silicon dioxide layer to protect the chip surface. However, in practical applications, the durability and reliability of such diodes remain insufficient in extreme environments. They suffer from poor reliability, low efficiency despite high reliability, and poor compatibility.

[0003] Moreover, with increasingly stringent environmental regulations, the environmental requirements of halogen-free, phosphorus-free, and antimony-free materials have become a new trend in the industry, and the materials used in existing production processes do not meet these environmental requirements.

[0004] If different coatings are added, due to the limitations of the passivation process, there will be contamination and oxide layers between the layers, which makes this multi-layer structure very unstable. The layers will separate, which will greatly affect the performance of the product. Summary of the Invention

[0005] To address the aforementioned problems, the purpose of this invention is to provide a high-reliability Schottky axial diode and its manufacturing process, which produces a Schottky axial diode with high reliability, better compatibility, and is more environmentally friendly.

[0006] To achieve the above objectives, the first technical solution of the present invention is: a high-reliability Schottky axial diode having a chip, with leads on both sides of the chip, the chip employing multiple protective layers, the protective layers being, from the inside out, a SIN layer, a SIPOS layer, a SiO2 layer and a polyimide adhesive layer, the coating area of ​​the SIN layer, SIPOS layer, SiO2 layer and the polyimide adhesive layer decreasing layer by layer from the inside out.

[0007] To achieve the above objectives, the second technical solution of the present invention is: a manufacturing process for a Schottky axial diode, used to produce the Schottky axial diode as described in claim 1, comprising the following specific steps:

[0008] S1 cleans the Schottky axial diode chip, removes surface contaminants, and then dries it.

[0009] Internal protection of the S2 chip

[0010] The chip undergoes the following processes in sequence: photoresist coating, photolithography, development, etching, CVDSiN passivation deposition, acid washing before deposition to expand the effective area of ​​the subsequent coating, CVDSIPOS deposition, acid washing again before deposition to further expand the coating area, glass coating, glass sintering, LTO, SiO2 formation, and a third acid washing before film formation to ensure sufficient LTO coverage and remove excess photoresist.

[0011] Surface protection of S3 chip

[0012] A layer of polyimide (PI) adhesive is coated on the chip surface, with a thickness of 5µm to 15µm and a width of 300µm to 500µm. The PI adhesive is cured and excess adhesive is removed to form the initial barrier protective layer; S4 metallization.

[0013] A metal layer of titanium (0.3–0.5 μm), nickel (0.5–1 μm), and silver (2–5 μm) is evaporated or sputtered onto the chip surface;

[0014] S5 Vacuum Pre-soldering Pump Ball Process

[0015] The chip mask is aligned using a printed stencil, and the amount of solder is controlled. The amount of solder is mainly controlled by the diameter of the opening on the stencil and the thickness of the stencil (30-50 N / cm under normal tension). The opening diameter is 70%-85% of the effective size of the chip window, and the thickness of the stencil is 0.05mm-0.2mm. After printing, the wafer is moved into a vacuum soldering boat.

[0016] S6 welding

[0017] Use no-clean, residue-free flux for welding. If necessary, ion cleaning can be used to prevent organic solvents from damaging or leaving residues on the PI adhesive.

[0018] S7 silicone sealant for protection and curing

[0019] A high-viscosity silicone sealant of 6500-10000 cP is evenly applied to the side of the chip. The wrapped semi-finished product is then placed in an oven. After the oven is evacuated, nitrogen gas is introduced and continuously introduced until the oven temperature is less than or equal to 80°C. The baking process is divided into four temperature zones. The first zone is a 70°C heating phase, which is maintained at a constant temperature for 1 hour. The main purpose is to use a low-temperature baking and degassing zone. The second zone is a 150°C pre-baking zone, where the temperature is increased from 70°C to 150°C with precise control of the heating rate, which is no more than 2°C per minute. The temperature is maintained at 150°C for 1 hour. The third zone is a high-temperature curing zone, where the temperature is increased from 150°C to the maximum temperature. The oven temperature is maintained at 200°C-220°C for at least 5 hours. The fourth zone is a cooling zone, where heating is stopped, but the fan continues normally to gradually lower the temperature. Once the temperature drops to 100°C, the oven door can be opened to accelerate heat dissipation. The nitrogen gas is not turned off. When the temperature drops below 80°C, the nitrogen gas can be turned off.

[0020] S8 is encapsulated in epoxy resin.

[0021] The chip is surrounded by spherical silicon micropowder particles with a particle size of 400-700 mesh, with a filling ratio of not less than 35%, forming a tightly encapsulated structure. The molding (encapsulation) curing time is 120-200 seconds.

[0022] In the above technical solution, the graphite boat is heated by electrodes during vacuum pre-welding of S5. Inert gas is introduced for protection during cooling. The welding temperature is controlled by a high-precision temperature controller combined with a P-TYPE temperature measuring rod to control the temperature change of the graphite boat.

[0023] In the above technical solution, the vacuum pre-soldering of S5 uses a high-temperature lead-tin-silver solder that is clean-free and leaves no residue. When using it, the chip to be sintered is placed in a vacuum soldering furnace, the vacuum furnace is turned off, a vacuum is first drawn, then nitrogen is added, a vacuum is drawn again, and heating and sintering are started. The temperature is between 285 and 328°C, and the high-temperature time is not less than 8 minutes. Heating is then stopped, and nitrogen is introduced for cooling. When the temperature reading is below 80 degrees, the nitrogen valve is closed, the vacuum furnace is opened, and the chip is taken out.

[0024] In the above technical solution, the positioning process in the vacuum pre-soldering of S5 is as follows: place the chip on the bottom of the printed stencil, align and fix it, perform a trial brushing, check the difference between the corresponding points of the solder paste and the chip position under the positioning mechanism, adjust and correct it using the chip positioning worktable, and after confirming that the chip position meets the requirements, print the chip, and check the size and position after printing.

[0025] In the above technical solution, after the trial brushing, a dual CCD positioning mechanism is used in conjunction with a large-size display to position the chip.

[0026] In the above technical solution, the epoxy resin coating of S8 is preferably filled with spherical silica powder particles with a particle size of 600 mesh or larger.

[0027] In the above technical solution, the CVD SIN passivation deposition in S2 is to passivate the chip using a silicon nitride (SIN) thin film, with a SIN thickness of 300-500 nm.

[0028] In the above technical solution, the passivation of the SIN layer and SIPOS layer in S2 is carried out by deposition without separate furnace. After the SIN layer is completed, the product is not removed from the furnace, and the gas is directly replaced to form the SIPOS layer.

[0029] In summary, the advantages of the technical solution of this invention compared to traditional methods are as follows: This invention proposes a more comprehensive high-reliability process that provides protection both on the surface and internally: a wider and thicker PI adhesive coating is used on the surface to increase chip surface protection, making it more difficult for moisture intrusion and silver ion migration; combined with the use of no-clean, residue-free flux and ion cleaning, it avoids damage to the PI by organic cleaning solutions. The chip uses a vacuum pre-soldering pump ball process to avoid solder or overflow contamination, and a tunnel furnace soldering process with rapid heating and slow cooling. It is suitable for high-requirement consumer products, industrial control, and automotive-grade products.

[0030] Internally, an ultra-thick silicon nitride (SIN) passivation layer provides protection, resulting in extremely low leakage current at high temperatures. This represents an order-of-magnitude advantage over traditional Schottky products in terms of high-temperature leakage current. The encapsulation utilizes high-viscosity 6500-10000cP silicone white glue, cured in a nitrogen-oxygen-free oven (to prevent lead oxidation and reduce the bonding strength between the product and the molding compound) at 200-220 degrees Celsius. It employs a low-stress epoxy resin material with at least 35% filler of 400-700 mesh spherical silicon micropowder. This not only improves the Schottky axial diode's resistance to silver ion migration but also meets the environmental requirements of being halogen-free, phosphorus-free, and antimony-free, making it suitable for industrial and automotive applications. The SIPOS layer ensures the chip's high-temperature stability, while the SIN layer guarantees its insulation.

[0031] Furthermore, acid pickling is performed before forming the silicon nitride (SIN) passivation layer, SIPOS layer, and SIN layer. On the one hand, acid pickling can clean the oxide layer and contaminants, preventing delamination between layers. On the other hand, acid pickling can also widen the coating area, and a larger coating area can also increase the contact area between layers and make the connection tighter.

[0032] In summary, it has the following advantages:

[0033] 1. High Reliability: This invention uses silicon nitride (SIN) as the core passivation material, combined with a dual protection mechanism of silicone sealant and epoxy resin, enabling the entire process to meet the stringent reliability requirements of industrial control and even automotive-grade standards. The process performs exceptionally well, especially in high-temperature and high-humidity environments.

[0034] 2. The product has high reliability, thanks to its multi-layered protection design, which includes PI chip surface protection, silicone white glue metal ion curing protection, and high-mesh epoxy resin water vapor protection.

[0035] 3. High compatibility: This process is applicable to various types of Schottky axial diodes and can be implemented without large-scale modifications to existing production equipment.

[0036] 4. Environmentally friendly: The materials used in this process are all halogen-free, phosphorus-free, and antimony-free, complying with environmental standards such as RoHS and REACH, reducing potential harm to the environment. Attached Figure Description

[0037] The foregoing and other objects, features and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.

[0038] Figure 1 This is a schematic diagram of a Schottky axial diode in the prior art;

[0039] Figure 2 This is a structural diagram of the invention's flowchart;

[0040] Figure 3 A schematic diagram of a Schottky axial diode produced using this invention;

[0041] Figure 4 This is a schematic diagram of the chip portion in this invention;

[0042] Figure 5 for Figure 4 A cross-sectional view;

[0043] The labels are as follows: 100, chip; 110, solder paste; 200, lead; 300, protective layer; 310, SIN layer; 320, SIPOS layer; 330, SiO2 layer; 340, polyimide adhesive layer; 400, solder; 500, silicone sealant. Detailed Implementation

[0044] The following description is based on preferred embodiments of the present invention. Those skilled in the art can make various changes and modifications without departing from the inventive concept. The scope of this invention is not limited to the contents of the specification but must be determined according to the claims.

[0045] The invention will be further described with reference to the following figures:

[0046] Example 1:

[0047] like Figure 5As shown, a high-reliability Schottky axial diode has a chip with leads on both sides and a circumferential multilayer protective layer on the chip surface. The protective layers, from the inside out, are a SIN layer, a SIPOS layer, a SiO2 layer and a polyimide adhesive layer.

[0048] The silicon nitride (SIN) passivation layer prevents leakage current, the SIPOS layer ensures the high-temperature stability of the chip, the SIN layer ensures the chip insulation, and the outermost polyimide adhesive layer plays a role in adsorption and barrier.

[0049] Example 2:

[0050] like Figure 2 As shown, a manufacturing process for Schottky axial diodes includes the following steps:

[0051] S1 cleans the Schottky axial diode chip, removes surface contaminants, and then dries it.

[0052] Internal protection of the S2 chip

[0053] The chip is subjected to the following processes in sequence: photoresist coating, photolithography, development, etching, CVD SIN passivation deposition, CVDSIPOS deposition, glass coating, glass burning, LTO SiO2 formation, and removal of excess photoresist. Acid washing is performed before CVDSIN passivation deposition, CVDSIPOS deposition, and LTO SiO2 to widen the coating area.

[0054] Surface protection of S3 chip

[0055] A layer of polyimide (PI) adhesive is coated on the chip surface. The PI thickness is 5um to 15um and the width is 300um to 500um. The PI adhesive is cured and the excess PI adhesive is removed to form an initial barrier protective layer. The PI adhesive has good insulation and chemical corrosion resistance, which can effectively isolate the chip from the influence of the external environment.

[0056] S4 Metallization

[0057] A metal layer of titanium (0.3–0.5 μm), nickel (0.5–1 μm), and silver (2–5 μm) is evaporated or sputtered onto the chip surface;

[0058] S5 Vacuum Pre-soldering Pump Ball Process

[0059] The chip mask is aligned using a printed stencil, with precise control over the solder amount. This control primarily involves adjusting the stencil aperture diameter and thickness (30-50 N / cm under normal tension). The aperture diameter is 70%-85% of the effective chip window size, effectively preventing solder overflow. The stencil aperture diameter and thickness are controlled to be 0.05mm-0.2mm. Sufficient tension is provided by the stencil. Dual CCDs combined with a large-size display are used for precise positioning, preventing solder paste misalignment and contamination of the isolation ring due to visual errors. After printing, the wafer is transferred into a vacuum soldering boat. An electrode-heated graphite boat system is used, resulting in rapid heating. Cooling requires nitrogen purging or other inert gas or other auxiliary cooling methods. High-precision temperature controllers combined with P-TYPE temperature probes are used to precisely control the graphite boat temperature. The solder paste used is a no-clean, residue-free, high-temperature lead-tin-silver solder. The vacuum pre-soldering positioning process involves placing the chip on the bottom of the printed stencil and aligning and fixing it. First, a test run is performed. The solder paste is checked against the chip position using a positioning mechanism to ensure accuracy. Adjustments are made using a chip positioning stage. Once the chip position is confirmed to meet requirements, the chip is printed. After printing, the size and position are checked. During pre-soldering, an electrode-heated graphite boat is used. The soldering temperature is controlled by a high-precision temperature controller combined with a P-TYPE temperature probe. The pre-soldering solder paste is a no-clean, residue-free high-temperature lead-tin-silver solder. When using it, the chip to be sintered is placed in a vacuum soldering furnace. The furnace is closed, a vacuum is first created, then nitrogen is added, and the furnace is vacuumed again. Heating and sintering begin at a temperature between 285 and 328°C, with a duration of at least 8 minutes. Heating is then stopped, and nitrogen is introduced for cooling. Once the temperature reading is below 80 degrees Celsius, the nitrogen valve is closed, and the vacuum furnace is opened. During soldering, a no-clean, residue-free flux is used to avoid silver ion migration problems that may be caused by traditional flux residues. This flux evaporates naturally after high-temperature soldering, leaving no residue.

[0060] S6 welding

[0061] Use no-clean, residue-free flux for welding. If necessary, ion cleaning can be used to prevent organic solvents from damaging or leaving residues on the PI adhesive.

[0062] S7 silicone sealant for protection and curing

[0063] A high-viscosity silicone sealant of 6500-10000 cP is evenly applied to the side of the chip. The encapsulated semi-finished product is then placed in an oven. After vacuuming, nitrogen gas is continuously introduced into the oven until the oven temperature is less than or equal to 80°C. The baking process is divided into four temperature zones: the first zone is a 70°C heating phase, which is maintained at a constant temperature for 1 hour, primarily for low-temperature baking and degassing; the second zone is a 150°C pre-baking zone, where the temperature is increased from 70°C to 150°C with precise control of the heating rate, not exceeding 2°C per minute, and then maintained at a constant temperature for 1 hour; the third zone is a high-temperature curing zone, where the temperature is increased from 150°C to the highest temperature. Temperature: The oven temperature is maintained at 200℃~220℃ for at least 5 hours. The fourth zone is the cooling zone. Heating is stopped, but the blower continues normally to gradually lower the temperature. Once the temperature drops to 100℃, the oven door can be opened to accelerate heat dissipation. The nitrogen gas is not turned off. When the temperature drops below 80℃, the nitrogen gas can be turned off. The chip is completely cured by thermal curing. This process makes the leads less susceptible to acid and alkali corrosion. The silicone white glue not only has good adhesion but also further enhances the chip's stress resistance. The silicone white glue can prevent moisture intrusion and also solidify ions, increasing the difficulty of silver ion migration.

[0064] S8 is encapsulated in epoxy resin.

[0065] The chip is surrounded by spherical silicon microparticles with a particle size of 600 mesh or larger, with a filling ratio of no less than 35%, forming a tightly encapsulated structure. This epoxy resin molding compound has high hardness and toughness, can withstand large stress changes, and simultaneously prevents moisture and other harmful substances from entering. The epoxy resin used is a halogen-free, phosphorus-free, and antimony-free formulation, meeting environmental protection requirements.

[0066] In S2, the passivation of the SIN layer and SIPOS layer is performed without separate furnace deposition. After the SIN layer is completed, the product is not removed from the furnace, and the gas is directly replaced to perform the SIPOS layer, thus avoiding oxidation and preventing surface contamination.

[0067] After testing, the packaged sample showed no performance degradation after more than 1000 hours under a high temperature of 85℃, high humidity of 85% and a reverse bias voltage of 160V, verifying the feasibility of this process.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-reliability Schottky axial diode having a chip, both sides of which are provided with leads, characterized in that: The chip adopts a multi-layer protective layer, and the protective layer is sequentially SIN layer, SIPOS layer, SIO2 layer and polyimide glue layer from inside to outside.

2. A production process for a Schottky axial diode for producing the Schottky axial diode according to claim 1, characterized in that: The specific steps are as follows: S1 clean the Schottky axial diode chip, remove the dirt on the surface, and dry after cleaning; S2 internal protection of the chip The chip is sequentially subjected to the following processes: coating photoresist, photoetching, developing, etching, CVD SiN passivation deposition, acid washing before deposition to expand the effective area of the subsequent coating layer, CVD SIPOS deposition, acid washing again before deposition to further expand the coating area, glass coating, glass sintering, LTO, SiO2 formation, third acid washing before film formation to ensure sufficient LTO coverage area, and removing excess photoresist; S3 surface protection of the chip A layer of polyimide (PI) glue is coated on the surface of the chip, the PI thickness is 5um-15um, the width is 300um-500um, the PI glue is solidified, and the excess PI glue is removed to form an initial barrier protection layer; S4 metallization Titanium 0.3-0.5um, nickel 0.5-1um and silver 2-5um are evaporated or sputtered on the surface of the chip as a metal layer; S5 vacuum pre-soldering PUMP tin ball process Printed steel plate is used to align the chip MASK, and the amount of tin is controlled. The amount of tin is mainly controlled by the steel plate hole diameter and the steel plate thickness (30-50N / cm under normal steel plate tension), the hole diameter is 70%-85% of the effective size of the chip window surface, and the steel plate thickness is 0.05mm-0.2mm. The printed wafer is translated into a vacuum welding boat; S6 welding Welding is performed using a cleaning-free and residue-free flux, and ion cleaning can be used if necessary to prevent damage and residue of organic solvents to the PI glue; S7 silicon white glue protection and solidification Uniformly apply 6500-10000cP high-viscosity silicon white glue to the side of the chip, and place the wrapped semi-finished product in an oven. After vacuumizing the oven, nitrogen is introduced, and nitrogen is continuously introduced into the oven throughout the process until the oven temperature is less than or equal to 80℃. The baking process is divided into four temperature zones. The first zone is 70℃ heating, and after reaching 70℃, the temperature is kept constant for 1H. The main purpose is to use low-temperature baking to exhaust the area. The second zone is a 150℃ pre-baking zone, which heats from 70℃ to 150℃. The heating rate is accurately controlled, and the temperature does not rise more than 2℃ per minute. After heating to 150℃, the temperature is kept constant for 1H. The third zone is a high-temperature curing zone, which heats from 150℃ to the highest temperature. The oven temperature is kept constant at 200℃-220℃ for at least 5H. The fourth zone is a cooling zone, where heating is stopped and air blowing is normal to gradually reduce the temperature. The oven door can be opened to speed up heat dissipation when the temperature drops to 100℃. Nitrogen is not turned off until the temperature drops to less than 80℃. S8 epoxy resin wrapping Fill the chip with 400-700 mesh spherical silicon powder particles, and the filling ratio should not be less than 35% to form a tight wrapping structure. The mold (encapsulation) curing time is 120S-200S.

3. The production process for a Schottky axial diode according to claim 2, characterized in that: The electrode heating graphite boat is used in the vacuum pre-welding of S5, inert gas is filled for protection during cooling, and the welding temperature control uses high-precision temperature controller combined with P-TYPE temperature probe to control the temperature change of the graphite boat.

4. The production process for a Schottky axial diode according to claim 2, characterized in that: The non-cleaned and residue-free high-temperature lead-tin-silver solder is used in the vacuum pre-welding of S5, the chip to be sintered is put into the vacuum welding furnace, the vacuum furnace is closed, vacuum is first extracted, then nitrogen is added, vacuum is extracted again, sintering is started, the temperature is between 285-328℃, the high-temperature time lasts for no less than 8 minutes, heating is ended, nitrogen is passed for cooling, when the temperature is lower than 80℃, the nitrogen valve is closed, the chip is taken out.

5. The production process for a Schottky axial diode according to claim 2, characterized in that: The positioning process of the vacuum pre-welding of S5 is as follows: the chip is put at the bottom of the printed steel plate, and is positioned and fixed, a trial printing is performed, the tin paste corresponding point and the chip position difference are checked under the positioning mechanism, the chip positioning workbench is used for adjustment and correction, after the chip position is confirmed to meet the requirements, the chip is printed, and the size and position are detected after printing.

6. The production process for a Schottky axial diode according to claim 5, characterized in that: The double-CCD positioning mechanism is used after trial printing, and a large-size display is combined for chip positioning.

7. The production process for a Schottky axial diode according to claim 2, characterized in that: The epoxy resin wrapping is performed in S8, and the spherical silicon powder particles with particle size of more than 600 meshes are preferably filled.

8. The production process for a Schottky axial diode according to claim 2, characterized in that: The CVDSIN passivation deposition in S2 is to use the silicon nitride (SIN) film to passivate the chip, and the thickness of SIN is 300-500nm.

9. The production process for a Schottky axial diode according to claim 2, characterized in that: The passivation of the SIN layer and the SIPOS layer in S2 uses non-furnace deposition, after the SIN layer is completed, the product is not taken out of the furnace, and the gas is directly replaced to make the SIPOS layer.

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