*Maximum slope is a time/temperature relationship that measures how fast the temperature on the printed circuit board changes. The ramp�up rate is usually somewhere between 1.0 �C and 3.0 �C per second, often falling between 2.0 �C and 3.0 �C (4 �F to 5 �F) per second. If the rate exceeds the maximum slope, potential damage to components from thermal shock or cracking can occur. Solder paste can also have a spattering effect. The preheat section is where the solvent in the paste begins to evaporate, and if the rise rate (or temperature level) is too low, evaporation of flux volatiles is incomplete.