The main factor that determines the quality of reflow soldering products is the setting of reflow soldering temperature and reflow soldering speed in the reflow soldering process. The settings of these two key process points determine the quality of the products produced by reflow soldering. Today, I will mainly share the influence and settings of the reflow soldering speed on the soldering quality.
(1) Setting of reflow soldering speed
1. The transportation speed setting is determined according to the time required for the temperature curve provided by the solder paste supplier. Usually, the whole process of welding large boards such as the main board is 5-6.5 minutes, and the whole process of welding small boards is 3.5-5 minutes. The shorter the furnace length, the lower the transport speed setting; the longer the furnace chamber length, the higher the transport speed setting. The setting principle is to ensure that the time required for the PCB to pass through the furnace corresponds to the time required for the temperature curve.
2. The temperature setting of the heating module in each temperature zone is also determined according to the temperature curve of the solder paste supplier. The temperature of the temperature zone is set according to the rising/falling slope of the temperature curve, time requirements and peak temperature. The greater the rising slope, the higher the peak temperature. The higher the temperature, the higher the temperature setting, and vice versa, the maximum temperature setting value cannot exceed the limit value 300 ℃ that the furnace can withstand.
3. For the same temperature curve, the temperature and speed setting values may still be different when producing different PCBs, which is related to the heat absorption of the PCB. The higher the temperature value of , it can also be solved by reducing the transport speed, otherwise, reduce the set temperature or increase the transport speed.
(2) Influence of reflow soldering speed on soldering quality
From a production point of view, the faster the reflow process speed parameters are adjusted, the more products pass through the furnace per unit time, which means the higher the production efficiency. However, considering the thermal shock resistance of components and the thermal compensation capability of each type of reflow soldering, the transport speed parameters of reflow soldering must be improved as much as possible on the premise of meeting the standard solder paste temperature profile. The quality of the decision mainly depends on the thermal compensation capability of the reflow soldering equipment. The combination of transportation and thermal compensation performance can be directly used as an indicator to measure the quality of the reflow soldering performance. Generally speaking, in the case of meeting the normal output of the market, the closer the maximum temperature setting of reflow soldering is to the measured temperature of the circuit board, the better the thermal compensation performance of this reflow soldering machine is.
The cooling section in the reflow soldering process has a very important position. In this section, the lead and tin powder in the solder paste has melted and fully wetted the surface to be connected. It should be cooled as fast as possible, which will help get Bright solder joints with good profile and low contact angle. Slow cooling causes more decomposition of the board into the tin, resulting in dull, rough solder joints. In extreme cases, it can cause poor wetting and weaken solder joint adhesion. The cooling rate of the cooling section is generally 3-10 °C/s, and it can be cooled to 75 °C.
