Optocoupler package receiving end MOS tube soldering process

Abstract

The application provides a kind of optical coupling device package receiving end MOS tube tin soldering process, it is related to receiving end MOS tube connection technical field.The optical coupling device package receiving end MOS tube tin soldering process includes the following steps: MOS tin soldering: fixed optical coupling frame, clean frame welding area, place MOS wafer in preset welding area, preheat, weld 3-5s, form uniform solder layer, after welding, naturally cool to room temperature.The application adopts tin wire welding instead of traditional silver glue welding (MOS die bonding) and first silver glue baking process, realizes the firm connection of MOS wafer and optical coupling DIP7 frame through intermetallic compound (IMC) layer, effectively solves the core problems of poor connection reliability, low heat conduction efficiency, high production cost and insufficient process stability of traditional process, at the same time, avoids the wafer warping problem caused by shrinkage stress generated by silver glue solidification, also reduces the silver glue baking process, simplifies the process flow.

Description

Technical Field

[0001] This invention relates to the field of receiver MOS transistor connection technology, and more specifically to a soldering process for an optocoupler package receiver MOS transistor. Background Technology

[0002] Optocouplers, also known as optocouplers, are semiconductor devices that transmit electrical signals using light as a medium. They offer advantages such as electrical isolation, strong anti-interference capabilities, stable operation, contactless operation, and long service life, and are widely used in industrial control, power electronics, and communication equipment. The packaging process of optocouplers is a core factor determining their performance and reliability. The connection process of the receiving-end MOSFET is particularly critical, directly affecting the electrical conduction, thermal diffusion, and lifespan of the optocoupler. The quality of this connection directly determines the overall reliability of the optocoupler throughout its lifecycle.

[0003] Currently, the connection of the MOSFET at the receiver end of optocoupler devices mainly adopts the silver paste die bonding process. The corresponding traditional process route is: MOSFET die bonding → silver paste baking → thyristor chip die bonding → silver paste baking → IR die bonding → silver paste baking. This process route has many technical pain points, such as cumbersome procedures, long production cycle, high cost, and poor reliability, specifically as follows: First, the connection between the MOSFET and the frame relies on the adhesive effect of the silver paste, which has limited connection strength. The shear strength is usually only 20-30MPa. Long-term use or high temperature and vibration environments can easily lead to delamination and cracking, resulting in poor circuit contact and affecting the stability of the optocoupler device. Second, the thermal conductivity of silver paste is low, with a thermal conductivity of only 1-5W / (m·K). The heat generated by the MOSFET during operation cannot be quickly conducted to the frame, which can easily cause chip overheating and aging, shortening the lifespan of the optocoupler. Third, silver paste is expensive, and the application amount and uniformity of silver paste during die bonding are extremely important, making process control difficult and prone to problems such as overflow and insufficient paste, resulting in a low product qualification rate, usually only 80-85%; Fourth, the old process route includes three silver paste baking processes, each baking time is 15-20 minutes, which greatly extends the production cycle and reduces production efficiency; Fifth, the silver paste has shrinkage stress after curing, which can easily cause MOS wafer warping, affecting the accuracy of subsequent packaging processes and the overall performance of the product, and there are more residues after curing, which may affect the electrical performance of the device.

[0004] Soldering, as a mature metal connection technology, melts the solder through localized heating and forms an intermetallic compound (IMC) layer on the surface of the metal being soldered, achieving a strong electrical and mechanical bond. It offers advantages such as high connection strength, high heat conduction efficiency, low cost, and short process time. However, accurately adapting soldering to optocoupler packaging processes to replace traditional MOS silver paste die bonding and redundant silver paste baking steps, and resolving potential issues like cold solder joints, solder bridging, and chip damage during soldering, while systematically comparing the advantages and disadvantages of solder wire bonding versus silver paste bonding and the performance differences between products produced by the old and new processes, has become a pressing technical challenge in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a soldering process for the MOS transistor of the receiving end of an optocoupler device, which can effectively solve the above-mentioned problems.

[0006] A soldering process for the receiver MOSFET of an optocoupler device includes the following steps: S1, MOS soldering: Fix the optocoupler frame, clean the frame soldering area, place the MOS chip in the preset soldering area, preheat, solder for 3-5 seconds to form a uniform solder layer, and allow it to cool naturally to room temperature after soldering. S2, Thyristor die bonding: The thyristor chip is die bonded to the corresponding area of ​​the optocoupler frame and bonded until there is no warping or offset; S3, One-time silver paste baking; S4, IR die bonding: The optical coupler frame after step S3 is cured by infrared heating. S5. Secondary silver paste baking: After the optical coupler frame has been cured by baking again, the frame is removed and packaged in a conventional manner to obtain the finished optical coupler device.

[0007] Preferably, the positioning deviation of the fixed optocoupler frame in step S1 is ±0.01-±0.03mm. The cleaning is performed by cleaning the welding area of ​​the frame with anhydrous ethanol or plasma cleaning to remove the oxide layer and impurities. After cleaning, there are no visible impurities on the frame surface, and the surface roughness Ra=0.6-0.7μm. The specific preheating operation is as follows: first, preheat the pads at 150°C on the hot plate for 1.5 seconds, then transfer them to the hot plate at 260°C for soldering. The soldering temperature is 260°C, the angle between the solder tip and the pad is maintained at 45-90°, and the solder layer thickness is 0.1-0.2mm.

[0008] Preferably, the die bonding pressure in step S2 is 0.1-0.3 MPa, the die bonding position deviation is ±0.03-±0.05 mm, and the fit between the thyristor chip and the frame after die bonding is 98-99.5%.

[0009] Preferably, the baking temperature in step S3 is 120-140℃, and the baking time is 15-20 minutes.

[0010] Preferably, the infrared heating temperature in step S4 is 150-180℃, and the heat preservation time is 10-15 min.

[0011] Preferably, the baking temperature in step S5 is 120-140℃ and the baking time is 15-19 min.

[0012] This invention provides a soldering process for the receiving MOS transistor in an optocoupler device package, which has the following advantages compared to existing technologies: This invention replaces the traditional silver paste soldering (MOS die bonding) and the first silver paste baking process with tin wire soldering. It achieves a firm connection between the MOS wafer and the DIP7 optocoupler frame through the intermetallic compound (IMC) layer, effectively solving the core problems of poor connection reliability, low heat conduction efficiency, high production cost and insufficient process stability of the traditional process. At the same time, it avoids the wafer warping problem caused by the shrinkage stress generated by the curing of silver paste, and also reduces one silver paste baking process, simplifying the process flow. Attached Figure Description

[0013] Figure 1 This is a flowchart of the soldering process; Figure 2 This is a front view of the solder-bonded package of an optocoupler MOSFET. Figure 3 The image shows the X-ray void ratio of the solder joints of the finished product prepared in Example 3. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] Unless otherwise specified, all reagents used in the following schemes are commercially available products.

[0016] This solution uses a fully automatic soldering and die-mounting equipment with soft solder (260℃ heated guide rail (nitrogen protection), solder tip JAF-TIP-050). The core consumables are optocoupler DIP7 frame, 1.4x1.4mm MOS chip, and 0.5mm diameter Sn:92.35 / Sb:7 / Ni:0.6 / P:0.05 lead-free solder wire.

[0017] Example 1: A soldering process for the receiving MOS transistor in an optocoupler device package: S1, MOS Soldering: Fix the DIP7 optocoupler frame onto the special fixture of the fully automatic soldering and loading equipment. Wipe the welding area of ​​the frame with anhydrous ethanol to remove the oxide layer and impurities. After cleaning, there are no visible impurities on the frame surface, and the surface roughness Ra=0.6μm. Place the 1.4x1.4mm MOS chip into the preset welding area using a high-precision positioning device with a positioning deviation of ±0.02mm. Start the fully automatic soldering and loading equipment and feed a 0.5mm diameter solder wire to the welding point. Control the welding temperature at 260℃ and the welding time at 4s. Maintain a 90° angle between the solder tip and the pad. Preheat the pad at 150℃ on the hot plate for 1.5s, transfer it to the hot plate at 260℃ for welding, and feed the solder wire again to form a uniform solder layer with a thickness of 0.15mm. After welding, allow it to cool naturally to room temperature. S2. Thyristor die bonding: A high-precision die bonding machine is used to bond the thyristor chip to the corresponding area of ​​the optocoupler DIP7 frame. The die bonding pressure is 0.2MPa, the die bonding position deviation is ±0.04mm, and the fit between the thyristor chip and the frame after die bonding is 99%, with no warping or offset. S3, One-time silver paste baking: The frame with completed silicon controlled rectifier die bonding is sent into the baking equipment, the baking temperature is set to 130℃, the baking time is 18min, and the silver paste is baked and cured. S4, IR die bonding: The frame that has been baked with silver paste is sent into the IR die bonding equipment, the infrared heating temperature is set to 165℃, and the holding time is 12min to complete the full curing of the solder layer and the die bonding layer. S5. Secondary silver paste baking: The frame that has completed IR die bonding is sent back into the baking equipment. The baking temperature is set to 130℃ and the baking time is 18 minutes to complete the secondary silver paste baking. After baking, the frame is removed and subjected to routine packaging, electrical performance testing and appearance inspection to obtain a qualified optocoupler device.

[0018] Example 2: A soldering process for the receiving MOS transistor in an optocoupler device package: S1: MOS Soldering: Fix the DIP7 optocoupler frame onto the special fixture of the fully automatic soldering and loading equipment. Clean the frame's soldering area using plasma cleaning to remove oxide layers and impurities. After cleaning, the frame surface is free of visible impurities, with a surface roughness Ra=0.7μm. Place the 1.4x1.4mm MOS chip into the preset soldering area using a high-precision positioning device with a positioning deviation of ±0.03mm. Start the fully automatic soldering and loading equipment and feed a 0.5mm diameter solder wire to the soldering point. Control the soldering temperature at 260℃ and the soldering time at 5s. Maintain a 90° angle between the solder tip and the pad. Preheat the pad at 150℃ on the hot plate for 1.5s, then transfer it to the hot plate at 260℃ for soldering. Feed the solder wire again to form a uniform solder layer with a thickness of 0.2mm. After soldering, allow it to cool naturally to room temperature.

[0019] S2: Thyristor die bonding: A high-precision die bonding machine is used to bond the thyristor chip to the corresponding area of ​​the optocoupler DIP7 frame. The die bonding pressure is 0.1MPa, the die bonding position deviation is ±0.05mm, and the fit between the thyristor chip and the frame after die bonding is 98%, with no warping or offset.

[0020] S3: Silver paste baking: The frame with completed silicon controlled rectifier die bonding is sent into the baking equipment, the baking temperature is set to 120℃, the baking time is 20min, and the silver paste is baked and cured.

[0021] S4: IR die bonding: The frame that has been baked with silver paste is sent into the IR die bonding equipment, the infrared heating temperature is set to 150℃, and the holding time is 15min to complete the full curing of the solder layer and the die bonding layer.

[0022] S5: Silver paste baking: The frame with completed IR die bonding is sent back into the baking equipment. The baking temperature is set to 125℃ and the baking time is 19 minutes to complete the second silver paste baking. After baking, the frame is removed and subjected to routine packaging, electrical performance testing and appearance inspection to obtain a qualified optocoupler device.

[0023] Example 3: A soldering process for the receiving MOS transistor in an optocoupler device package: S1: MOS Soldering: Fix the DIP7 optocoupler frame onto the special fixture of the fully automatic soldering and loading equipment. Wipe the soldering area of ​​the frame with anhydrous ethanol to remove the oxide layer and impurities. After cleaning, there are no visible impurities on the frame surface, and the surface roughness Ra=0.5μm. Place the 1.4x1.4mm MOS chip into the preset soldering area using a high-precision positioning device with a positioning deviation of ±0.01mm. Start the fully automatic soldering and loading equipment and feed a 0.5mm diameter solder wire to the soldering point. Control the soldering temperature at 260℃ and the soldering time at 3s. Maintain a 45° angle between the solder tip and the pad. Preheat the pad at 150℃ on the hot plate for 1.5s, transfer it to the hot plate at 260℃ for soldering, and feed the solder wire again to form a uniform solder layer with a thickness of 0.1mm. After soldering, allow it to cool naturally to room temperature.

[0024] S2: Thyristor die bonding: A high-precision die bonding machine is used to bond the thyristor chip to the corresponding area of ​​the optocoupler DIP7 frame. The die bonding pressure is 0.3MPa, the die bonding position deviation is ±0.03mm, and the fit between the thyristor chip and the frame after die bonding is 99.5%, with no warping or offset.

[0025] S3: Silver paste baking: The frame with completed silicon controlled rectifier die bonding is sent into the baking equipment, the baking temperature is set to 140℃, and the baking time is 15 minutes to complete the silver paste baking and curing.

[0026] S4: IR die bonding: The frame with the silver paste baked is sent into the IR die bonding equipment, the infrared heating temperature is set to 180℃, the holding time is 10min, and the solder layer and die bonding layer are fully cured.

[0027] S5: Silver paste baking: The frame with completed IR die bonding is sent back into the baking equipment. The baking temperature is set to 140℃ and the baking time is 15 minutes to complete the second silver paste baking. After baking, the frame is removed and subjected to routine packaging, electrical performance testing and appearance inspection to obtain a qualified optocoupler device.

[0028] Comparative Example 1: A conventional process for soldering the MOS transistor of an optocoupler device in its packaged receiver: S1, MOS Silver Paste Die Bonding: Clean the DIP7 frame pads with anhydrous ethanol, Ra≤0.8μm, and uniformly apply conductive silver paste to the pad surface using an automatic dispensing device, with a silver paste coating thickness of 0.05mm; place the 1.4×1.4 MOS chip in the paste-coated area, with a die bonding pressure of 0.5MPa and a positioning deviation ≤±0.05mm.

[0029] S2. Initial Silver Paste Baking: Place the frame into the oven at 150℃ for 50 minutes to complete the initial curing of the silver paste on the MOS end.

[0030] S3. Thyristor chip die bonding: Silver paste is applied and the thyristor chip is mounted, and the die bonding parameters are consistent with those of MOS die bonding.

[0031] S4. Secondary silver paste baking: Baking temperature 150℃, baking time 50min.

[0032] S5, IR die bonding: Infrared heating to 165℃, hold for 13 minutes.

[0033] S6. Three-stage silver paste baking: Bake again for 50 minutes to complete the overall curing.

[0034] Comparative Example 2: A soldering process for the receiving MOS transistor of an optocoupler device (existing laser soldering process): S1. Pad cleaning: Plasma cleaning of DIP7 frame pads to remove oxide layer, Ra≤0.8μm.

[0035] S2. Solder paste application: Solder paste is applied to the surface of the pads using an automatic solder paste application device. The solder paste thickness is 0.08mm, and the solder paste material is consistent with the solder wire alloy system of this invention.

[0036] S3, Laser Soldering: Position the 1.4x1.4mm MOS chip; turn on the laser equipment, use non-contact irradiation heating, laser power 35W, single-point soldering time 7s, use laser energy to melt solder paste to form solder joints, and allow it to cool naturally to room temperature after soldering.

[0037] The parameters for subsequent thyristor die bonding, silver paste baking, IR die bonding, and secondary silver baking processes are the same as in Example 1.

[0038] Detection: 1. Weld joint shear strength test: The shear strength of the MOS wafer solder joints was tested using an automatic push-pull force gauge tester, in accordance with the industry standard "Specification for Shear Strength Test of Solder Joints in Semiconductor Packaging" (SJ / T 11389-2009). Operating procedure: Fix the DIP7 optocoupler frame onto the special fixture of the tester, ensuring the frame is stable; adjust the position of the shearing blade to maintain horizontal contact with the side of the MOS wafer; set the test speed to 0.5 mm / s, and apply a horizontal, uniform pushing force until the solder joint breaks; the system automatically records the maximum pushing force value; the shear strength is calculated using formula (1), where the effective area of ​​the solder joint is calculated based on the contact area between the bottom surface of the wafer and the solder. Shear strength (MPa) = Maximum thrust (N) / Effective weld area (mm²) 2 (1) 2. Solder joint heat conduction testing: The thermal conductivity of the solder joint was tested using the laser flash method. According to GB / T 22588-2008 "Measuring Thermal Diffusion Coefficient or Thermal Conductivity by Flash Method", the solder joint was made into a test sample with a thickness of 0.5 mm. One side of the sample was heated with a laser pulse at 25℃. The temperature change curve of the back side of the sample over time was recorded by an infrared detector. The thermal conductivity of the solder joint was calculated. The formula for calculating the thermal conductivity is referred to formula (2): λ = α × ρ × cp (2) Where: λ - thermal conductivity, W / (m·K); A - Thermal diffusivity, m 2 / s (α=(0.1388× d 2 ) / t50), where (d: solder joint sample tin thickness, m; t50: time required for the back side temperature to rise to half of its maximum value, s;) P - Density of solder sample, kg / m³ 3 (This patent uses Sn-Sb lead-free solder with a density of ρ=7200kg / m) 3 ); Cp - Specific heat capacity of solder under constant pressure, J / (kg·K); (For Sn-Sb solder, cp = 210 J / (kg·K)) 3. Product process qualification rate inspection: A batch sampling full inspection method was adopted. Following the sampling standard GB / T 2828.1, 1000 pieces of optocouplers from each process batch were randomly selected for comprehensive inspection of appearance and electrical performance. The formula for calculating the defect rate is shown in formula (3), and the formula for calculating the process pass rate is shown in formula (4). Defect rate = Number of defective products / Total number of samples inspected × 100% (3) Pass rate = Number of qualified products / Total number of samples × 100% (4) 4. 125℃ High Temperature Working Life Test: The average working life test at 125℃ is conducted according to GB / T 24824-2009 standard. A high-temperature accelerated aging test chamber is used to continuously power on the optocoupler device under the conditions of 125℃ and rated working voltage. The electrical performance is tested every 24 hours, and the device failure time is recorded. The average failure time of the batch is used as the indicator.

[0039] 5. Solder joint void rate detection (X-ray non-destructive testing method): According to the IPC-A-610 standard, an X-ray inspection instrument was used to perform tomographic scanning on the solder joints. The detection voltage was set to 100kV and the resolution to 5μm. Images of the inside of the solder joints were acquired, and the software automatically identified void areas and calculated the percentage of void area to the total area of ​​the solder joint.

[0040] Table 1 Performance Testing As can be seen from the data in Table 1 above, the preparation scheme of Example 3 achieved the best results.

[0041] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A soldering process for the receiving MOS transistor in an optocoupler device package, characterized in that, The soldering process includes the following steps: S1, MOS soldering: Fix the optocoupler frame, clean the frame soldering area, place the MOS chip in the preset soldering area, preheat, solder for 3-5 seconds to form a uniform solder layer, and allow it to cool naturally to room temperature after soldering. S2, Thyristor die bonding: The thyristor chip is die bonded to the corresponding area of ​​the optocoupler frame and bonded until there is no warping or offset; S3, One-time silver paste baking; S4, IR die bonding: The optical coupler frame after step S3 is cured by infrared heating. S5. Secondary silver paste baking: After the optical coupler frame has been cured by baking again, the frame is removed and packaged in a conventional manner to obtain the finished optical coupler device.

2. The soldering process according to claim 1, characterized in that, The positioning deviation of the fixed optocoupler frame in step S1 is ±0.01-±0.03mm. The cleaning is done by cleaning the welding area of ​​the frame with anhydrous ethanol or plasma cleaning to remove the oxide layer and impurities. After cleaning, there are no visible impurities on the frame surface and the surface roughness Ra=0.6-0.7μm. The specific preheating operation is as follows: first, preheat the pads at 150°C on the hot plate for 1.5 seconds, then transfer them to the hot plate at 260°C for soldering. The soldering temperature is 260°C, the angle between the solder tip and the pad is maintained at 45-90°, and the solder layer thickness is 0.1-0.2mm.

3. The soldering process according to claim 1, characterized in that, The die bonding pressure mentioned in step S2 is 0.1-0.3MPa, the die bonding position deviation is ±0.03-±0.05mm, and the fit between the thyristor chip and the frame after die bonding is 98-99.5%.

4. The soldering process according to claim 1, characterized in that, The baking temperature in step S3 is 120-140℃, and the baking time is 15-20 minutes.

5. The soldering process according to claim 1, characterized in that, The infrared heating temperature in step S4 is 150-180℃, and the holding time is 10-15 minutes.

6. The soldering process according to claim 1, characterized in that, The baking temperature in step S5 is 120-140℃, and the baking time is 15-19 minutes.

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