In the process of using a new reflow oven, the most difficult thing to grasp is how to reasonably set the reflow temperature curve. The temperature setting has a great impact on the quality of the product. Let's take a look at how to set the temperature of the newly purchased reflow oven?
First of all, the temperature setting should be combined with the specific conditions of the equipment, such as the length of the heating zone, materials, structure of the reflow oven, and heat conduction methods.
Determine the temperature of each temperature zone according to the position of the temperature sensor. If the temperature sensor is inside the heating element, the temperature setting should be about 30°C higher than the actual temperature. Also refer to the size of the exhaust air volume to set the temperature.
Generally, reflow ovens have specific requirements for the exhaust air volume, but the actual exhaust air volume sometimes changes.
When determining the temperature curve of the reflow oven, the exhaust air volume should be measured regularly. In addition, according to the temperature curve of the solder paste, different solder pastes have different temperature curves, and the reflow soldering temperature curve of specific products should be set according to the temperature curve provided by the solder paste supplier. The temperature setting is related to the material, thickness, multi-layer board, and size of the PCB board. It also needs to be set according to the density of the surface mount board components, the size of the components, and special components such as BGA and CSP.
As far as the temperature curve of the hot air reflow oven is concerned, we can divide it into four temperature zones: preheating zone, heat preservation zone, reflow zone and cooling zone.
It should be noted that if the time in the constant temperature zone is too long, the active components of the solder paste will volatilize excessively, causing problems such as dull surface and collapse of the solder joints. If the time is too short, the active components will boil when entering the reflow zone, and there will be tombstones. , tin beads, etc. If the constant temperature zone is too short, the material will enter the welding stage under the condition of uneven heating. In addition to poor welding, it will also cause damage to heat-sensitive materials. Long time and high temperature in the welding zone will damage the material, and low temperature will cause defects in the solder joints. If the temperature is high in a short time, the temperature will rise too fast, and the solder paste will boil.
In addition, if the reflow furnace has been used for a long time, it should be adjusted according to the characteristics of the furnace. After the chain speed is increased, the time spent in each temperature zone will be shortened; the temperature of the constant temperature can also be lowered slightly, but pay attention to the coordination before and after; if it is a short furnace, the last temperature zone can be used as the peak temperature zone , that is, directly enter the cooling zone after welding, so that the effect of rapid cooling can be achieved, and the welding time will not be too long.