The soldering temperature profile consists of four phases. Preheat, soak, reflow and cooling. To set-up a soldering profile (as shown in figure 10-1), parameters like temperature settings for each zone, cooling speed; conveyor speed and fan speed for each zone must be considered.
4.1 Pre-heat
During the pre-heat phase the solvents evaporates from the solder paste. If the temperature rises too rapid during the pre-heat, two problems can occur. Firstly solder balls can be spread when the solvents burst through the flux surface membrane. This is called solder balling. Furthermore the solder paste can slump, because a too rapid temperature rise changes the viscosity of the solder paste. This will result in bridging.

焊接湿度曲线由四部分组成：预热区，恒温区，回流焊区和冷却区。为获得理想的炉温曲线，需在每一区设置温度、冷却速度等参数，并兼顾每一区的传送带速和风扇转速。
在预热区预热时，溶剂会从焊膏中蒸发出来。若温升太快，会带来两方面的问题。一是当溶剂从助焊剂中飞溅出来时，焊锡球将会扩散开来。另外，由于温升过快导致焊膏粘度改变，引起焊膏塌落，出现桥接问题。