How much do you know about the temperature curve
Source: Dongguan SMT chip processing factory Yitai Electronics, release date: 2019-09-26, browse:
The temperature curve refers to the curve of the temperature of a certain point on the SMA with time when the SMA passes through the reflow oven. The temperature curve provides an intuitive method to analyze the temperature change of a component during the entire reflow soldering process. This is very useful for obtaining the best solderability, avoiding damage to components due to over-temperature, and ensuring soldering quality. The correct setting of the temperature curve is an important guarantee for welding quality. A typical temperature curve is divided into four stages: preheating, heat preservation (also called activity), reflux and cooling.
<b>SMT patch processing 011</b>
Preheating section: The purpose of this area is to heat the PCB at room temperature as soon as possible to achieve the second specific goal, but the heating rate must be controlled within an appropriate range. If it is too fast, it will produce rrc thermal shock, and both the circuit board and the components may be If it is damaged or too slow, the solvent 183 will not volatilize sufficiently, which will affect the welding quality. Because the heating rate of 160 is faster, the temperature difference in the later SMA of the temperature zone is larger. In order to prevent thermal shock from damaging the components, the maximum speed is generally specified as 4C/s. However, usually the ascent rate is set to lC/s~3C/s. The typical heating rate is 2C/s.
Insulation section: refers to the area where the temperature rises from 120V ~ 150X2 to the melting point of the solder paste. The main purpose of the heat preservation section is to stabilize the temperature of each element in the SMA and minimize the temperature difference. Give enough time in this area to make the temperature of the larger component catch up with the temperature of the smaller component, and to ensure that the flux in the solder paste is fully volatilized. At the end of the heat preservation section, the oxides on the pads, solder balls and component pins are removed, and the temperature of the entire circuit board reaches equilibrium. It should be noted that all components on the SMA should have the same temperature at the end of this section, otherwise, entering the reflow section will cause various bad soldering phenomena due to the uneven temperature of each part.
Reflux section: In this area, the heater temperature is set to the highest, so that the temperature of the component rises to the peak temperature quickly. In the reflow section, the peak soldering temperature varies depending on the solder paste used. Generally, it is recommended that the melting point temperature of the solder paste plus 20C -40X:. For 63Sn/37Pb solder paste with a melting point of 183X3 and Sn62/Pb36/Ag2 solder paste with a melting point of 179X3, the peak temperature is generally 210X: ~2301, and the reflow time should not be too long to prevent adverse effects on SMA. The ideal temperature profile is that the “tip area” that exceeds the melting point of the solder covers the smallest volume.
Cooling section: In this section, the lead-tin powder in the solder paste has melted and fully wets the surface to be connected. It should be cooled as fast as possible, which will help to obtain bright solder joints and have a good shape and Low contact angle. Slow cooling will cause more decomposition of the circuit board into the tin, resulting in dull and rough solder joints. In extreme cases, it can cause poor soldering and weaken the bonding force of solder joints. The cooling rate of the cooling section is generally 3C/s~l(TC/s, cooling to 75X2 is enough.
