Reflow soldering temperature
To operate, a thermocouple generates a voltage at the junction of the two wires. Three methods are used to join thermocouple wire together: welding, soldering or twisting. The temperature range will also depend on the type of insulation used. nickel-aluminum) are rated to 760☌ for a 30 AWG wire with a tolerance of ☒.2☌ from 0° to 277☌ (above 277☌, the tolerance is ☐.75 percent). copper-nickel) are rated to 316☌ for a 30 AWG wire with a tolerance of ☒.2☌ from 0° to 277☌ (above 277☌, the tolerance is ☐.75 percent). Two common thermocouples are used: type J and type K. A common wire diameter for reflow profiling is 0.0625" (30 AWG). Insulated, exposed junction thermocouples, used for temperature measurement, consist of solid wires covered with high-temperature insulation. In both cases, these tools range from simple recorders to complex systems that can perform simulation and process monitoring. Many reflow machines have built-in profiling capability mobile profiling systems are also available. Once a time/temperature profile is developed, it must be verified. For example, if the heated length is 183 cm, the conveyor speed range is 45 to 60 cm per minute. Simply divide the heated length of the reflow oven by three (maximum speed) or four (minimum speed). This information can be used to calculate conveyor speed. I have calculated a minimum time of three minutes and a maximum time of four minutes. When the time limits for these various factors are added up, the minimum and maximum time that an assembly should be exposed to reflow soldering can be determined. The time above melting temperature, or dwell time, should be 20 to 70 seconds. The elevated temperature reduces surface tension and promotes wetting. Solder should be heated to a temperature that is 25° to 40☌ above its melting temperature. Activation times range from 30 to 90 seconds. Many fluxes fully activate at approximately 125☌. Ideally, the last of the flux would be consumed just as the solder begins to melt. Using a reflow profile that consumes the flux before the solder melts is a common mistake. It is important to define the flux activation temperature and time. Current literature from several major capacitor suppliers suggests that up to a 4☌ per second change is acceptable.įlux has two attributes that affect the reflow process: It removes contamination and it protects surfaces from further contamination. The traditional rule for capacitors: Do not exceed a 2☌ per second temperature change. Thermal shock, caused by a rapid temperature increase, can also damage components, especially capacitors. Most components can tolerate a peak temperature of 220☌ for 90 seconds. Try to keep the exposure time above Tg to less than two minutes.Ĭomponents may be damaged by excessive heat. The glass-transition (Tg) temperature of common laminated substrate material is between 120° and 130☌. Substrates can be damaged by excessive exposure to heat. Four major factors influence the design of a reflow soldering profile (check with suppliers to obtain exact figures): The cool-down phase helps to control dwell time and cool the substrate back down to room temperature. During the reflow phase, substrate, components and solder particles reach soldering temperature and, as a result, solder joints are formed. During this phase, solvent evaporation commences, flux activation occurs, and the substrate and components are gradually heated. All actions that lead up to proper soldering happen during preheat. Substrate and component cool down.The preheat phase is the preparatory phase. Solder particles melt, solder joints form5. Five specific phases actually take place during reflow soldering:ġ. The reflow process can be described in three basic phases: preheat, reflow and cool down. I have successfully used this approach for more than six years with different equipment and solder pastes. A gradual linear ramp up to the peak temperature and back down again is recommended. The situation changed when convection-dominant equipment was introduced because the user was able to create and achieve the desired reflow soldering profile. The historical reflow soldering profile, "ramp-soak-spike," evolved when infrared reflow equipment dominated the industry (i.e., equipment capability drove the profile).
Numerous factors influence this profile each needs to be carefully studied and understood. Before a reflow soldering method is defined or equipment is selected, a time/temperature reflow soldering profile must be created.