LED Copper PCB Board 3535 LED
Temperature setting techniques for reflow soldering stove:
The reflow soldering stove has 4 zones, which are divided into preheating zone, thermostatic zone, solder melting zone and cooling zone. Most solder pastes can operate in these temperature zones. In order to deepen the understanding of the ideal temperature curve, below is the introduce for temperature, residence time of each zone and variation of solder paste in each zone:
1. preheating zone
The purpose of preheating zone is to heat the PCB board to achieve the preheating effect and to fuse with the solder paste.But at this time, the heating rate should be controlled within the appropriate range to avoid thermal shock and damage to circuit boards and components.Preheat the ramp rate should be less than 3℃/sec, set temperature should be at room temperature to 130℃.The residence time calculation is as follows: set up the environment temperature is 25℃, if the heating rate calculated at 3℃/sec(150-25)/3 it's 42s, if heating rate at 1.5℃ /s, computing (150-25)/1.5 it is the 85s.Usually according to the element size difference degree adjustment time by regulating the heating rate at 2℃/s of the following is the best.
2. Constant temperature area
The main purpose of the thermostatic zone is to stabilize the temperature of components on PCB circuit board and minimize the temperature difference.We hope to achieve the temperature balance of all parts and components in this area and ensure the flux in the solder paste is fully volatilized.It is important to note that the components on the circuit board shall have the same temperature in this section to ensure that there will be no welding defects when they enter the backflow section. Set constant temperature 130℃~160℃, constant temperature time is 60~120 s.
3. Backflow area
The temperature in this range is the highest, causing the component's temperature to rise to the peak temperature.In reflow soldering welding peak temperature is different due to different solder paste used, generally we recommend using solder paste temperature melting point temperature +20~40℃.Peak temperature is 210℃~230℃, keep not too long time to prevent adverse effects on the PCB. Backflow zone heating rate control within 2.5-3℃/s, generally reach the peak temperature within 25s and 30s.Here have a skill is its molten tin temperature is above 183℃,there are two times of molten tin, one is 60~90s above 183℃, another is 20~60s above 200℃, the peak value of temperature is 210℃~230℃.
4. Cooling zone
The lead-tin powder in the solder paste has been melted and sufficiently wetted to the joint surface, and should be cooled as quickly as possible, which helps to create bright solders with good form and no rough solders.The cooling rate of cooling section is commonly 3~4℃/s cooled to 75℃, the cooling slope is less than 4℃/s.
Of course, in mass production, the actual working curve of each product should be obtained according to the SMA size, number of components and variety. From the perspective of time, the whole reflux time is 175s-295s, which is about 3-5 minutes (excluding the time before entering the first temperature zone).