The profile cool-down rate should be controlled within 4☌ per second. The entire profile should last between 3.5 and 4 minutes from 45☌ to a peak temperature of 215☌ (±5☌). After the soak, the assembly will enter the spike area, where the assembly will be reflowed above 183☌ for a target time of 60 (☑5) seconds. Following the ramp, the profile soaks the assembly between 150°to 170☌ within a target time of 90 seconds the assembly should achieve thermal equilibrium by the completion of the soak zone. ![]() The sole purpose of using the RSS profile is to eliminate or reduce a large λT.Īs seen in Figure 1, the RSS profile begins with a steep ramp up to approximately 150☌ within a target time of 90 seconds at a maximum rate of 2° to 3☌ per second. The ramp-soak-spike (RSS)1 profile may be used with RMA or no-clean chemistries, but generally is not recommended for use with water-soluble chemistries, as the RSS soak zone profile may break down the paste activators prematurely and result in inadequate wetting. In fact, using the RTS profile generally will improve wetting. Most solder paste chemistries demonstrate adequate wetting activity when processed in a linear RTS profile. This is a common misconception in the industry, and it bears correcting. It is important to note that the soak zone generally is not needed to activate the solder paste flux chemistry. Because the soak zone is unneeded, the profile may be altered into a linear ramp-to-spike (RTS) profile. The soak should bring the temperature of all parts of the assembly to equilibrium before the assembly reaches the solder reflow temperature so all parts of the assembly reflow simultaneously. The sole intention of the soak zone is to reduce/eliminate a large λT. What they offer is greater zone-to-zone stability, providing a more controlled reflow process. In addition, the maximum temperature and temperature rate of a given profile can be strictly controlled with these ovens. Although the heat absorption may vary slightly because of the varying thickness and component population, forced convection ovens generally provide heat in such a manner that the λT is not significant. One advantage of this type of oven is that they are able to provide heat to an assembly gradually and uniformly, regardless of part color or texture. Most newer-style reflow ovens, known as the forced convection type, blow warm air on and around assemblies. ![]() This could cause a variety of solder defects, including solder balling, non-wetting, damaged devices, voiding and charred residues. With a large λT, some areas of an assembly may receive excessive heat, while other areas may receive insufficient heat. ![]() This temperature variation is referred to as the assembly`s λT. Some areas of an assembly could reach much higher temperatures than other areas. Many older-style ovens were prone to heating different parts of an assembly at varying rates, depending on the color and texture of the parts and substrates being reflowed. The pains often associated with profiling may be reduced greatly if certain guidelines are followed and if there is a strong understanding of the variables that can be encountered during the reflow process.
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