Convection Reflow Oven Detailed Description For an effective soldering process, soldering must be carried out under carefully calibrated conditions in a reflow oven. Solder paste contains a mix of metal, flux, and solvents that aid in the phase change of the paste from semi-solid, to liquid to vapor and the metal from solid to liquid. In soldering, a thermal profile is a complex set of time-temperature values for a variety of process dimensions such as slope, soak, TAL, and peak. By using algorithms such as PWI, engineers can calibrate and customize parameters to achieve minimum process variance and a near zero defect rate. In modern systems, quality management practices in manufacturing industries have produced automatic process algorithms such as PWI, where soldering ovens come preloaded with extensive electronics and programmable inputs to define and refine process specifications. There are two main types of profiles used today: The Ramp-Soak-Spike (RSS) and the Ramp to Spike (RTS). One of the major uses of this method is soldering of electronic assemblies. The method is used in a variety of industrial and laboratory processes, including electronic component assembly, optoelectronics, optics, biochemical engineering, food science, decontamination of hazardous wastes, and geochemical analysis.
For example, if the process mean is set at 200 ☌ with the process window calibrated at 180 ☌ and 220 ☌ respectively, then a measured value of 188 ☌ translates to a process window index of −60%. A PWI of 99% indicates that the profile is within process limitations, but runs at the edge of the process window. A Process Window Index (PWI) greater than or equal to 100% indicates the profile is outside of the process limitations. The center of the process window is defined as zero, and the extreme edges of the process window are ☙9%. Raw temperature values are normalized in terms of a percentage relative to both the process mean and the window limits. The thermal profile is often measured along a variety of dimensions such as slope, soak, time above liquidus (TAL), and peak.Ī thermal profile can be ranked on how it fits in a process window (the specification or tolerance limit).
A graphical representation of the Process Window Index for a thermal profileĪ thermal profile is a complex set of time-temperature data typically associated with the measurement of thermal temperatures in an oven (ex: reflow oven).
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