Do you know the reflow soldering zone function and something we need to note about it

Reflow soldering is done by re-melting the paste solder pre-allocated to the pcb pad. Implements soldering of mechanical and electrical connections between the soldered ends of the surface-mount components or pins and pcb board pads.

SMT reflow temperature has 4 temperature zones. The functions of 4 temperature zones are different. Among them, attention must be paid to some aspects of temperature zones.

First, the preheat zone of SMT patch

Function: Raise the temperature of the pcb assembly board from the heat preservation room to the usual required activity temperature,

The main points to note here are: from the heat preservation room to 100°C, the heating rate must be controlled at 2-3 deg/s. Otherwise, heating too quickly can lead to the rupture of the thermal components. If the temperature rises too slowly, it will not work. Affects production efficiency and volatilization of flux. Therefore, it is important to pay attention to the temperature and time zone.

Second, SMT patch temperature zone

Function: (1) Make pcb board. Components and pads are evenly heated, reducing the temperature difference between them;

(2) Protection pins and pads will not be oxidized under high temperature conditions;

(3) When the solder paste activity starts, remove the oxides on the pins and pads

Here we must pay attention to the following matters: 1. Must be evenly and steadily warming, not suddenly high, all of a sudden low; 2. Constant temperature zone is too long or the temperature of the constant temperature zone is too high, solder paste activity will complete the work ahead of schedule, prone to cold welding The solder joints are dark with granules or solder balls.

Third, SMT patch reflow area

Function: The function of the recirculation zone is to increase the pcb board temperature from the active temperature to the recommended peak temperature, and then perform welding.

The important things to note here are: 1. The time should not be too short, which will cause the solder joints to be unsaturated; 2. The time is too long will cause oxides and metal oxides, resulting in the solder joints not lasting; 3. The temperature is too high The residue will be scorched.

Fourth, SMT patch cooling area

Function: Can form a good and firm solder joint

Here we need to pay attention to: 1. Cooling too fast, solder joints will become embrittled and not solid; 2. It is best to mirror the reflow curve.