What details should be paid attention to when soldering PCB circuit boards

　　PCB circuit board soldering is a crucial step in electronic manufacturing, and details determine success or failure. The following provides a detailed explanation of the details that need to be paid attention to, including manual soldering, reflow soldering, wave soldering, and general precautions:

　　1、 Core preparation work before welding

　　Inspection and pre-processing of PCB and components:

　　PCB inspection: Check if the board surface is clean, free from oxidation, contamination, and scratches; Is the solder mask intact; Whether the solder pads are complete and free from detachment.

　　Component inspection: verify the model, specifications, and polarity; Check for oxidation on the pins (if there is oxidation, gently wipe with rubber or fine sandpaper).

　　Humidity sensitive devices: Devices with higher MSD levels (such as BGA, QFN) should be baked according to specifications to prevent internal moisture expansion during reflow, which can cause "popcorn" phenomenon.

　　Baking of PCB and components: If the storage environment is humid, low-temperature baking (such as 125 ℃, 4-8 hours) should be performed before soldering to remove moisture.

　　Preparation of tools and materials:

　　Soldering iron: Choose the appropriate power and shape of the soldering iron tip. The temperature setting needs to be adjusted according to the melting point of the solder wire and the soldering object (usually 330-380 ℃ for lead tin wire and 350-400 ℃ for lead-free tin wire). Keep the soldering iron tip clean and solder well.

　　Solder material: Select solder wire/paste that matches the surface treatment of the PCB (such as lead-free solder matching lead-free solder on lead-free solder plates). The flux has moderate activity and low residual corrosiveness or requires no cleaning.

　　Auxiliary tools: Prepare solder suction tape, tweezers, soldering flux, solder suction device, magnifying glass/microscope, anti-static wrist strap, etc.

　　Electrostatic protection:

　　Install anti-static mats in the work area, and operators should wear anti-static wrist straps and be reliably grounded to prevent ESD damage to sensitive devices.

　　2、 Key details of manual welding (repair, welding repair, small batch)

　　Temperature and time control:

　　The principle of "first match, then solder": First, use a soldering iron tip to simultaneously touch the solder pad and component pins, allowing them to be evenly heated. After about 1-2 seconds, send the solder wire in.

　　The "Three Three Principles": The entire welding process (heating+tin feeding) should be completed in about 3 seconds to avoid damaging components or causing solder pads to fall off due to prolonged heating.

　　Tin delivery technique:

　　The solder wire should be fed from the opposite side of the soldering iron tip, using the heat of molten solder to melt the solder wire, rather than directly melting and dripping with the soldering iron tip.

　　Moderate dosage is recommended to form full conical solder joints, avoiding excessive short circuits or virtual soldering.

　　Solder joint quality:

　　The ideal solder joint should present a smooth concave crescent shape with a metallic luster, with solder covering the entire pad and wetting the pins.

　　Avoid defects such as cold welding (rough surface, tofu residue like), virtual welding (incomplete wetting of solder), pulling, bridging, etc.

　　Special component handling:

　　SMT component: First fix one pin, then solder the remaining pins. For multi pin ICs, the "drag soldering" technique can be used in conjunction with high-quality soldering flux.

　　Thermal sensitive components: Use heat dissipation pliers or increase welding interval time to prevent overheating and damage.

　　Plug in components: After the pins are formed, they are inserted and soldered from the back. The trimming of the pins should be done after soldering.

　　3、 Key details of reflow soldering (SMT patch)

　　Solder paste printing:

　　The opening size and thickness of the steel mesh are precise. After printing, check whether the amount of solder paste is uniform, full, and whether there is any collapse, bridging, or missing. This is a crucial step in determining the quality of reflow soldering.

　　SMT accuracy:

　　The components are accurately and stably placed on the solder paste, especially for fine pitch devices such as QFP and BGA.

　　Reflux temperature curve:

　　This is the core of the process. Accurately set and verify through actual testing based on the recommended curve, PCB thickness, and component layout by the solder paste manufacturer. The curve usually includes:

　　Preheating zone: evenly heat up the PCB and components, activate the soldering flux.

　　Constant temperature/immersion zone: Thoroughly clean the solder pads with flux to reduce temperature differences.

　　Reflux zone: The temperature reaches its peak, causing the solder paste to completely melt and wet, forming a metallurgical bond. Peak temperature and duration (TAL) are crucial, as being too high or too long can damage components and PCBs, while being too low or too short can result in insufficient melting.

　　Cooling zone: Control the cooling rate to form a reliable crystalline structure.

　　After furnace inspection:

　　Immediately inspect the quality of solder joints with the naked eye or AOI for defects such as monuments, bridging, voids, and virtual soldering.

　　4、 Key details of wave soldering (through-hole components)

　　Fixture design and use:

　　Use appropriate wave soldering fixtures (furnace trays) to protect devices that are not resistant to high temperatures and pre soldered surface mount components, and prevent "shadow effects" from causing poor soldering.

　　Flux spraying:

　　The spraying amount should be uniform and appropriate. Excessive amounts will cause corrosion and residue, while insufficient amounts will result in insufficient soldering effect.

　　Preheating temperature:

　　Adequate preheating can activate flux, reduce thermal shock, prevent PCB deformation and board explosion. Insufficient preheating is one of the main reasons for virtual welding and bridging.

　　Peak parameters:

　　Transmission speed: affects contact time.

　　Peak height: generally controlled at 1/2 to 2/3 of the plate thickness. Too high is prone to bridging, too low is prone to solder leakage.

　　Soldering temperature: typically around 250 ℃ for lead and 260-270 ℃ for lead-free. Need to monitor and maintain stability.

　　Welding angle and direction:

　　The PCB transport direction should be such that the solder joints leaving the peak are located at the end of the component pins, which is conducive to exhaust and reduces bridging. The arrangement direction of components should avoid forming "shadow areas".

　　5、 General and Post weld Processing Details

　　Welding sequence:

　　Following the principle of "low first, high second, small first, large second, inside first, outside first, heat-resistant first, heat-resistant second". First solder the surface mount, then solder the plug-in; Weld short components first, then weld tall components.

　　Residual flux treatment:

　　Determine whether to clean according to product requirements. Thoroughly clean high reliability products. Use cleaning agents compatible with residues (such as water-based, alcohol based) and ensure that they are clean and dry.

　　Post weld inspection and testing:

　　Visual inspection/magnifying glass inspection: Check the appearance quality of all solder joints.

　　Electrical performance testing: Conduct on/off testing and functional testing.

　　X-ray inspection: For hidden solder joints such as BGA, perform X-ray inspection to observe the internal voids, bridging, alignment, and other conditions of the solder joints.

　　Maintenance precautions:

　　When repairing, use appropriate tools (such as a hot air gun with different sizes of nozzles), control the temperature and wind speed well, and avoid damaging surrounding components and PCBs.

　　After removing multi pin components such as BGA and QFN, clean the solder pads and re solder or implant balls to ensure flatness.

　　Summary: Core Safety and Quality Red Line

　　Temperature is both a friend and an enemy: strictly control temperature and time to avoid thermal damage.

　　Cleaning is the foundation: pre weld cleaning ensures weldability, and post weld treatment ensures reliability.

　　Process parameters are the lifeline: machine welding optimization and strict monitoring of curves and parameters.

　　Inspection runs through the entire process: from materials, processes to finished products, layer by layer inspection is the only way to avoid batch defects.

　　Following these details can greatly improve the welding pass rate and ensure the long-term reliability of the product.

　　PCB circuit board soldering is a crucial step in electronic manufacturing, and details determine success or failure. The following provides a detailed explanation of the details that need to be paid attention to, including manual soldering, reflow soldering, wave soldering, and general precautions:

　　1、 Core preparation work before welding

　　Inspection and pre-processing of PCB and components:

　　PCB inspection: Check if the board surface is clean, free from oxidation, contamination, and scratches; Is the solder mask intact; Whether the solder pads are complete and free from detachment.

　　Component inspection: verify the model, specifications, and polarity; Check for oxidation on the pins (if there is oxidation, gently wipe with rubber or fine sandpaper).

　　Humidity sensitive devices: Devices with higher MSD levels (such as BGA, QFN) should be baked according to specifications to prevent internal moisture expansion during reflow, which can cause "popcorn" phenomenon.

　　Baking of PCB and components: If the storage environment is humid, low-temperature baking (such as 125 ℃, 4-8 hours) should be performed before soldering to remove moisture.

　　Preparation of tools and materials:

　　Soldering iron: Choose the appropriate power and shape of the soldering iron tip. The temperature setting needs to be adjusted according to the melting point of the solder wire and the soldering object (usually 330-380 ℃ for lead tin wire and 350-400 ℃ for lead-free tin wire). Keep the soldering iron tip clean and solder well.

　　Solder material: Select solder wire/paste that matches the surface treatment of the PCB (such as lead-free solder matching lead-free solder on lead-free solder plates). The flux has moderate activity and low residual corrosiveness or requires no cleaning.

　　Auxiliary tools: Prepare solder suction tape, tweezers, soldering flux, solder suction device, magnifying glass/microscope, anti-static wrist strap, etc.

　　Electrostatic protection:

　　Install anti-static mats in the work area, and operators should wear anti-static wrist straps and be reliably grounded to prevent ESD damage to sensitive devices.

　　2、 Key details of manual welding (repair, welding repair, small batch)

　　Temperature and time control:

　　The principle of "first match, then solder": First, use a soldering iron tip to simultaneously touch the solder pad and component pins, allowing them to be evenly heated. After about 1-2 seconds, send the solder wire in.

　　The "Three Three Principles": The entire welding process (heating+tin feeding) should be completed in about 3 seconds to avoid damaging components or causing solder pads to fall off due to prolonged heating.

　　Tin delivery technique:

　　The solder wire should be fed from the opposite side of the soldering iron tip, using the heat of molten solder to melt the solder wire, rather than directly melting and dripping with the soldering iron tip.

　　Moderate dosage is recommended to form full conical solder joints, avoiding excessive short circuits or virtual soldering.

　　Solder joint quality:

　　The ideal solder joint should present a smooth concave crescent shape with a metallic luster, with solder covering the entire pad and wetting the pins.

　　Avoid defects such as cold welding (rough surface, tofu residue like), virtual welding (incomplete wetting of solder), pulling, bridging, etc.

　　Special component handling:

　　SMT component: First fix one pin, then solder the remaining pins. For multi pin ICs, the "drag soldering" technique can be used in conjunction with high-quality soldering flux.

　　Thermal sensitive components: Use heat dissipation pliers or increase welding interval time to prevent overheating and damage.

　　Plug in components: After the pins are formed, they are inserted and soldered from the back. The trimming of the pins should be done after soldering.

　　3、 Key details of reflow soldering (SMT patch)

　　Solder paste printing:

　　The opening size and thickness of the steel mesh are precise. After printing, check whether the amount of solder paste is uniform, full, and whether there is any collapse, bridging, or missing. This is a crucial step in determining the quality of reflow soldering.

　　SMT accuracy:

　　The components are accurately and stably placed on the solder paste, especially for fine pitch devices such as QFP and BGA.

　　Reflux temperature curve:

　　This is the core of the process. Accurately set and verify through actual testing based on the recommended curve, PCB thickness, and component layout by the solder paste manufacturer. The curve usually includes:

　　Preheating zone: evenly heat up the PCB and components, activate the soldering flux.

　　Constant temperature/immersion zone: Thoroughly clean the solder pads with flux to reduce temperature differences.

　　Reflux zone: The temperature reaches its peak, causing the solder paste to completely melt and wet, forming a metallurgical bond. Peak temperature and duration (TAL) are crucial, as being too high or too long can damage components and PCBs, while being too low or too short can result in insufficient melting.

　　Cooling zone: Control the cooling rate to form a reliable crystalline structure.

　　After furnace inspection:

　　Immediately inspect the quality of solder joints with the naked eye or AOI for defects such as monuments, bridging, voids, and virtual soldering.

　　4、 Key details of wave soldering (through-hole components)

　　Fixture design and use:

　　Use appropriate wave soldering fixtures (furnace trays) to protect devices that are not resistant to high temperatures and pre soldered surface mount components, and prevent "shadow effects" from causing poor soldering.

　　Flux spraying:

　　The spraying amount should be uniform and appropriate. Excessive amounts will cause corrosion and residue, while insufficient amounts will result in insufficient soldering effect.

　　Preheating temperature:

　　Adequate preheating can activate flux, reduce thermal shock, prevent PCB deformation and board explosion. Insufficient preheating is one of the main reasons for virtual welding and bridging.

　　Peak parameters:

　　Transmission speed: affects contact time.

　　Peak height: generally controlled at 1/2 to 2/3 of the plate thickness. Too high is prone to bridging, too low is prone to solder leakage.

　　Soldering temperature: typically around 250 ℃ for lead and 260-270 ℃ for lead-free. Need to monitor and maintain stability.

　　Welding angle and direction:

　　The PCB transport direction should be such that the solder joints leaving the peak are located at the end of the component pins, which is conducive to exhaust and reduces bridging. The arrangement direction of components should avoid forming "shadow areas".

　　5、 General and Post weld Processing Details

　　Welding sequence:

　　Following the principle of "low first, high second, small first, large second, inside first, outside first, heat-resistant first, heat-resistant second". First solder the surface mount, then solder the plug-in; Weld short components first, then weld tall components.

　　Residual flux treatment:

　　Determine whether to clean according to product requirements. Thoroughly clean high reliability products. Use cleaning agents compatible with residues (such as water-based, alcohol based) and ensure that they are clean and dry.

　　Post weld inspection and testing:

　　Visual inspection/magnifying glass inspection: Check the appearance quality of all solder joints.

　　Electrical performance testing: Conduct on/off testing and functional testing.

　　X-ray inspection: For hidden solder joints such as BGA, perform X-ray inspection to observe the internal voids, bridging, alignment, and other conditions of the solder joints.

　　Maintenance precautions:

　　When repairing, use appropriate tools (such as a hot air gun with different sizes of nozzles), control the temperature and wind speed well, and avoid damaging surrounding components and PCBs.

　　After removing multi pin components such as BGA and QFN, clean the solder pads and re solder or implant balls to ensure flatness.

　　Summary: Core Safety and Quality Red Line

　　Temperature is both a friend and an enemy: strictly control temperature and time to avoid thermal damage.

　　Cleaning is the foundation: pre weld cleaning ensures weldability, and post weld treatment ensures reliability.

　　Process parameters are the lifeline: machine welding optimization and strict monitoring of curves and parameters.

　　Inspection runs through the entire process: from materials, processes to finished products, layer by layer inspection is the only way to avoid batch defects.

　　Following these details can greatly improve the welding pass rate and ensure the long-term reliability of the product.