Process Window Index (PWI) is a
statistical measure
In statistics, as opposed to its general use in mathematics, a parameter is any measured quantity of a statistical population that summarises or describes an aspect of the population, such as a mean or a standard deviation. If a population e ...
that quantifies the robustness of a manufacturing process, e.g. one which involves heating and cooling, known as a thermal process. 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
A reflow oven is a machine used primarily for reflow soldering of surface mount electronic components to printed circuit boards (PCBs).
In commercial high-volume use, reflow ovens take the form of a long tunnel containing a conveyor belt along w ...
.
PWI measures how well a process fits into a user-defined process limit known as the specification limit. The specification limit is the tolerance allowed for the process and may be statistically determined. Industrially, these specification limits are known as the ''process window'', and values that a plotted inside or outside this window are known as the process window index.
Using PWI values, processes can be accurately measured, analyzed, compared, and tracked at the same level of
statistical process control
Statistical process control (SPC) or statistical quality control (SQC) is the application of statistical methods to monitor and control the quality of a production process. This helps to ensure that the process operates efficiently, producing ...
and
quality control available to other manufacturing processes.
Statistical process control
Process capability
The process capability is a measurable property of a process to the specification, expressed as a process capability index (e.g., Cpk or Cpm) or as a process performance index (e.g., Ppk or Ppm). The output of this measurement is often illustrated ...
is the ability of a process to produce output within
specified limits.
To help determine whether a manufacturing or business process is in a state of statistical control, process engineers use
control chart
Control charts is a graph used in production control to determine whether quality and manufacturing processes are being controlled under stable conditions. (ISO 7870-1)
The hourly status is arranged on the graph, and the occurrence of abnormalit ...
s, which help to predict the future performance of the process based on the current process.
To help determine the capability of a process, statistically determined upper and lower limits are draw