KIC
Process Window Index™
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A Method for Quantifying Thermal Profile Performance
The Process
Defining, measuring and improving the thermal process is as important to the overall quality and performance of the manufacturing cycle as any other process. There are statistically valid methods for quantifying most manufacturing processes, such as pick and place and screen printer performance. There is no widely accepted method for measuring, analyzing and comparing the performance of thermal profiles, and thus, no quantifiable system of ranking thermal process performance.
The Process Window
Thermal profile specifications are ranges consisting of minimum or maximum values, and most commonly, both. Such ranges typically exist for every single part or component of the product that sees the thermal process as part of the assembly. Additionally, these ranges apply to numerous statistics such as soak time, slope, peak temperature and a variety of others. All of these elements combined as a matrix create a window in which the process must remain or the product will be compromised. Measuring and comparing the thermal profile to its process window is a subjective judgement with no real uniformity or statistically reproducible results; from one engineer or operator to the next; from one product to the next... Until now!
The Process Window Index (PWI™) is a quantifiable, reproducible, statistical measure of how well a profile performs relative to critical process limits. Every thermal profile is ranked on the basis of how it "fits" within the process window. The center of the process window is defined as zero, and the extreme edge of the process window as 99%. A PWI of 100% or more indicates that the profile will not process product within specification. A PWI of 99% indicates that the profile will process product within spec, but it is running at the very edge of the process window. A PWI of 70% indicates a profile is using 70% of the process spec.
The PWI tells you exactly how much of your process window a given profile uses, and thus how robust that profile is. The lower the PWI, the better the profile. The thermal process can now be reliably measured, analyzed, compared and tracked with the same level of SPC and Quality Control available to other manufacturing processes.
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