6
5. Temperature wave setting principle
5.1 The reflow soldering theory and the temperature wave
When the PCB goes into heat up area (dry area), the solvent and gas in the solder paste will
evaporate. At the same time, the flux can wet the pad and the component tip and foot. The solder
paste melts, caves in and covers the pad, leading to the pad and component pins insulate the oxygen.
PCB goes into heat preservation area. PCB and components get full preheating. In case of damaging
the PCB and components when it goes into the welding area and the temperature heats up quickly.
When PCB goes into the welding area, the temperature heats up and the solder paste melts. When
PCB goes into cooling area, the liquid solder paste the soldering points solidify. The reflow process
is finished.
The temperature is the key to welding quality. The actual and the setting temperature warming slope
and the peak temperature should be accordant. Before the temperature reaches 160
℃
, please control
the heat up speed in about 1
℃
/S. If heat up too quickly, the PCB and the components will be
damaged, and the PCB may be out of shape. On the other side, the flux volatilizes too fast. And it is
easy to make soldering tin ball. Set the peak temperature 20
℃
-40
℃
higher than the solder paste
melting point. Set the reflow time 10S-60S. If the peak temperature is low or the reflow time is
short, it will affect the welding quality, and serious is causing the solder paste does not melt. If the
peak temperature is high or the reflow time is long, the metal power will be oxidized and affect the
welding quality and serious is causing the component and PCB damaged.
5.2 The set of the temperature wave
Set the wave according to the solder paste and the above foundation. Different solder paste, choose
and set different waves. In addition, the temperature wave has related to the PCB, the density and
size of components. Generally lead-free welding temperature should be higher 40
℃
than melting
point.
6. Details about temperature area setting
♦
Set the temperature and belt speed to initial value, to the cooling oven, should be preheated for 25
minutes.
♦
When the temperature is stable, let PCB pass heat reflow system. If there is no reflow, can
properly reduce the transfer chain rotation speed. Another way is that, do not adjust the speed, and
increase the temperature properly. When adjust the temperature, notice that it cannot exceed the
PCB and component bearing capacity.
♦
Let the PCB pass the reflow system in the new speed or new set temperature. If there is no reflow,
turn to redo the above step. Otherwise, need temperature fine-turning.
♦
The heat temperature wave is adjustable according to the PCB. You can adjust the transfer chain
rotation speed to adjust the temperature. Reduce the transfer chain rotation speed can increase the
product heat temperature. On the contrary, you can reduce the product heat temperature.
Attention
：
♦
If the PCB has been placed components, the PCB pass the reflow and it reflow not very completely,
suggest you adjust then reflow again. Normally, it will not impact the PCB and components.
♦
From low to high when set temperature. If the heat range is over the reflow temperature too high,