What and why

Littelfuse expects suppliers to improve quality by systematically reducing variation of key characteristics. Control plans document relevant information about the process followed to address sources of variation until a key characteristic is in statistical control and capable of meeting engineering specifications.

How and when

Key characteristics are typically identified by Littelfuse, and are noted on the design drawings. If Littelfuse has not supplied the key characteristics, the supplier can do so following the process outlined in the "Guide to Reducing Variation in Key Characteristics."

For each of the key characteristics, the supplier identifies:

• Where in the process the characteristic is measured
• Control charts used
• Sample size and frequency of collection
• Maintenance of control charts
• Initial Cpk

A gage variation study is performed and results are documented, potential sources of variation are identified and controls are established to ensure that process parameters and settings don't change. This is documented in the key characteristic control plan.