Process window index

In manufacturing industry, PWI values are used to calibrate the heating and cooling of soldering jobs (known as a thermal profile) while baked in a reflow oven.

Control limits describe what a process is capable of producing (sometimes referred to as the "voice of the process"), while tolerances and specifications describe how the product should perform to meet the customer's expectations (referred to as the "voice of the customer").

One specification outlines that a signal is defined as any single point outside of the control limits.

[5] Each thermal profile is ranked on how it fits in a process window (the specification or tolerance limit).

[6] Raw temperature values are normalized in terms of a percentage relative to both the process mean and the window limits.

[5][6] For maximum efficiency, separate PWI values are computed for peak, slope, reflow, and soak processes of a thermal profile.

In addition, the software also automatically recalibrates the PWI values for the peak, slope, reflow, and soak processes.

By setting PWI values, engineers can ensure that the reflow soldering work does not overheat or cool too quickly.

[5] The PWI is calculated as the worst case (i.e. highest number) in the set of thermal profile data.

In this case, the PWI would be the highest value among the twelve percentages of the respective process windows.