What is the preheating temperature of the constant temperature soldering iron?
The preheating requirement is to ramp up from low temperature (80 degrees) to high temperature (below 130 degrees). Generally, it takes 5-10 minutes to warm up just after starting up, and the warm-up time is generally 120 seconds. The heating temperature of the machine board should be below 180 degrees, and the best temperature of the lead-free peak tin bath is 250-265 degrees. The practice of Guangdong Longren Computer PCB Copy Company has proved that the conveying speed of wave soldering is usually 1500-300mm/min. If it is too fast, it is easy to cause problems such as poor PCB appearance, poor welding contact, virtual soldering, short circuit, less tin, and virtual soldering.
At present, the wave soldering machine basically adopts thermal radiation preheating. Commonly used wave soldering preheating methods include forced hot air convection, electric heating plate convection, electric heating rod heating, infrared heating, etc. Among these methods, forced hot air convection is generally considered to be an effective heat transfer method for wave soldering in most processes. After preheating, the circuit board is welded with single wave (λ wave) or double wave (spoiler wave and λ wave). For perforated elements, a single wave is sufficient. As the board enters the crest, the solder flows in the opposite direction of the board, creating eddy currents around the component leads. This is like washing with water, removing all the residual flux and oxide film on it, and infiltrating when the solder joint reaches the infiltration temperature. Wave soldering preheating temperature control: In the wave soldering preheating zone, the solvent in the flux sprayed on the circuit board volatilizes, which can reduce the gas generated during soldering. At the same time, rosin and activator begin to decompose and activate, remove the oxide layer and other pollutants on the welding surface, and prevent the metal surface from being oxidized again at high temperature.
The printed circuit board and components are fully preheated, which can effectively avoid thermal stress damage caused by rapid temperature rise during the soldering process. The preheating temperature and time of the circuit board should be determined according to the size and thickness of the printed circuit board, the size and number of components, and the number of components to be mounted. The preheat temperature measured on the surface of the PCB should be between 90°C and 130°C. When there are many components in the multi-layer board or patch kit, the preheating temperature should take the upper limit. The warm-up time is controlled by the speed of the conveyor belt.
If the preheating temperature is too low or the preheating time is too short, the solvent in the flux will not volatilize sufficiently, and gas will be generated during welding, causing welding defects such as pores and tin beads. If the preheating temperature is too high or the preheating time is too long, the flux will decompose in advance, the flux will lose its activity, and it will also cause welding defects such as burrs and bridging. In order to properly control the preheating temperature and time to achieve a good preheating temperature, we can also judge whether the flux coated on the bottom of the PCB before wave soldering is sticky.
