Introduction
Small reflow soldering machine is mainly used for small batch line soldering and simple electronic products, many small optoelectronic enterprises have more demand for small reflow soldering machine. Compared with large reflow soldering, small reflow soldering cost is much smaller. The temperature profile is the reflow soldering process to control temperature changes in the key parameters, directly affecting the welding quality and product reliability. This article will be a comprehensive analysis of the temperature profile settings and core parameters.
I. Temperature profile basics
1. What is the temperature profile?
Temperature curve is a record of PCB temperature changes in the reflow oven soldering process chart, which reflects the PCB in different heating areas of the temperature change.
2. Four basic stages of temperature profile
Preheating Stage: The beginning stage of the oven temperature profile, where the board gradually enters reflow and the temperature begins to rise slowly. The purpose is to let the circuit board and its components gradually adapt to the high-temperature environment, to avoid sudden temperature changes leading to component damage.
Holding phase: The holding phase is one of the key stages of the reflow oven temperature profile, which determines the quality of the soldering. In this stage, the board is held at a constant temperature for a period of time to ensure that the solder is completely melted and forms a strong connection with the components.
Reflow Stage: The reflow stage is another critical stage in the temperature profile of the reflow oven, which determines the final shape and quality of the solder joint. In this stage, the temperature peaks and begins to gradually decline, the solder begins to solidify and form a strong connection. However, care needs to be taken to avoid excessive cooling rates to prevent soldering defects (e.g. cold welds, cracks, etc.).
Cooling phase: The final stage of the temperature profile of the soldering furnace is also the end of the soldering process. In this stage of the circuit board gradually removed from the high temperature environment and naturally cooled to room temperature.
II. Small reflow oven process
1. The working principle of reflow oven
Reflow oven soldering heating process, the paste will be thermal expansion and contraction, so that the paste pre-coated on the PCB pads can be heated to melt into a liquid state. Subsequently, when the solder paste cools down, it realizes a solid connection between the component pins and the PCB pads.
2. FAQ and Solutions
Solder Balls: An undesirable phenomenon formed during the soldering process where small balls of solder appear on the surface of the solder joint. This is usually due to the welding temperature is too high, the welding time is too long or the welding area design is not reasonable.
Solution: Adjust the welding temperature and time to ensure that the welding parameters meet the requirements; check the design of the welding area to ensure that the welding point of reasonable layout.
Cold welding: means that the welding joints do not reach a sufficient melting state, resulting in a weak connection of the welding joints. This may be caused by insufficient welding temperature, insufficient welding time or improper design of the welding area.
Solution: Increase the soldering temperature and time to ensure that the solder joints are completely melted; check the design of the soldering area to ensure that the solder joints are in good contact with the components.
Continuous tin phenomenon: refers to the formation of melted solder bridging between two or more neighboring solder joints. This is usually caused by too high a welding temperature, welding time is too long or welding area design is not reasonable.
Solution: Reduce the soldering temperature and time to ensure that there is no excessive melting between solder joints; check the design of the soldering area to ensure that the layout of the soldering points is reasonable.
Welding offset: Welding offset refers to a certain error between the welding position and the intended position. This can be caused by problems with the welding equipment or fixtures.
Solution: Check the welding equipment and fixture to ensure its stability and accuracy; adjust the welding parameters and process to ensure the accuracy of the welding position.
III. The core parameters analysis
1. Preheating temperature: The ideal preheating temperature is usually between 150°C and 180°C. This temperature range helps to avoid thermal stress. This temperature range helps to avoid thermal stress, preventing damage to components or defective solder joints due to high temperatures.
Preheating improves solder quality by allowing residual moisture on the PCB to evaporate and reducing bubble formation during soldering. Too low a preheating temperature may lead to insufficient solder joints, while too high a temperature may lead to solder burns or component deformation.
2. Holding time: Holding time is generally set at 60 seconds to 120 seconds, depending on the material and component characteristics. Proper holding time ensures that the solder melts sufficiently to form a strong solder joint.
Factors affecting the hold time include the type of solder, the PCB material, the number of solder joints and the thermal conductivity of the component. If the holding time is too short, the solder joints may not be fully melted, and too long may lead to oxidation of the solder or damage to the board.
3. Peak reflow temperature: Typically between 220°C and 250°C, for most commonly used solders, such as Sn-Pb solders, the peak temperature may be around 210°C, while lead-free solders can reach up to 260°C. The peak reflow temperature is usually between 220°C and 250°C, and can be as high as 260°C for most commonly used solders.
Choosing the right peak reflow temperature is critical because different materials, such as component packages and PCB substrates, have different temperature tolerances. For example, ceramic encapsulated devices can usually withstand higher temperatures, whereas plastic encapsulated devices may require a lower peak temperature to prevent high temperature damage.
4. Cooling rate: Typically set at about 3°C to 6°C per second. Rapid cooling increases the tensile strength of the solder joint, but can also lead to stress concentrations that can cause microcracks.
The proper cooling rate will help create the desired crystalline structure of the joint and improve the overall strength and reliability of the joint. Cooling too fast may result in cracks in the solder, while cooling too slowly may result in a decrease in the physical properties of the joint.
IV. Best practices for temperature profile setting
1. According to the specific conditions of the equipment, such as the length of the heating zone, the material of the heating source, the reflow oven construction and heat conduction method and other factors to set.
2. According to the temperature profile of the solder paste used to set. Different metal content of the solder paste has a different temperature profile, should be in accordance with the temperature profile provided by the supplier of the solder paste to set the temperature profile of the specific product reflow soldering.
3. According to the size of the exhaust air volume to set. General reflow soldering furnace on the exhaust air volume have specific requirements, but the actual exhaust air volume for various reasons will sometimes change, determine the temperature curve of the product, due to consider the exhaust air volume, and regular measurement.
4. According to the actual location of the temperature sensor to determine the set temperature of the temperature zone, if the temperature sensor location in the heat generator inside, set the temperature than the actual temperature is about 30 ℃ higher.
5. According to the PCB board material, thickness, whether multilayer board, size size to set.
6. Setting according to the density of the surface assembly board components, the size of the components and the presence of special components such as BGA and CSP.
V. Tool recommendations
Reflow thermometer is a special instrument used to measure the internal temperature of the reflow soldering, through real-time monitoring of temperature changes in the furnace, to help technicians adjust the furnace temperature parameters to ensure the stability of the soldering process and product quality. Reflow soldering temperature measurement instrument is usually equipped with a temperature measurement board and thermocouples, the temperature measurement board is a special circuit board, which is arranged with a number of thermocouple probes, used to sense the temperature at different locations in the furnace. The thermocouples convert the sensed temperature signals into electrical signals and transmit them via data lines to the tester or computer for data processing and display.
Conclusion
Reasonable setting of parameters is the core to ensure the quality of small reflow soldering machine. Through in-depth understanding and effective adjustment of preheating temperature, holding time, reflow peak temperature and cooling rate, the welding effect and product quality can be significantly improved.
Quick facts about NeoDen
1. Established in 2010, 200+ employees, 8000+ Sq.m. factory.
2. NeoDen products: Smart series PNP machine, NeoDen N10P, NeoDen9, NeoDen K1830, NeoDen4, NeoDen3V, NeoDen7, NeoDen6, TM220A, TM240A, TM245P, reflow oven IN6, IN12, IN12C, Solder paste printer FP2636, PM3040.
3. Successful 10000+ customers across the globe.
4. 30+ Global Agents covered in Asia, Europe, America, Oceania and Africa.
5. R&D Center: 3 R&D departments with 25+ professional R&D engineers.
6. Listed with CE and got 50+ patents.
7. 30+ quality control and technical support engineers, 15+ senior international sales, timely customer responding within 8 hours, professional solutions providing within 24 hours.
