Special Characteristics (SC)

Introduction

Products have plenty of characteristics, some of them have high impact on conformance, while others not. On top of that, there are many process parameters in the manufacturing that highly affect the outcome, whether our product will satisfy the customer. We always have to ask the same question: what happens if the given characteristic is wrong, or out of specification. This question helps to identify if the given attribute is a special characteristic.

Special characteristics is the most commonly used phrase, however many organization, companies use other naming, such as: key characteristics, significant characteristics, critical characteristics etc. Many companies use different markings for these characteristics, such as shields, diamonds, triangles, special abbreviations, etc.

Source: qMindset.com

TEST ADVERTISEMENT (for temporary testing purposes, source: presse.porsche.de)

Key Features

ISO/TS 16949:2009 uses a very brief and logical explanation for "Special Characteristic" in its 3rd chapter (Terms and definitions): "product characteristic or manufacturing process parameter which can affect safety or compliance with regulations, fit, function, performance or subsequent processing of product". VDA has even released a separate manual about the topic, as the VDA Volume: "Special Characteristics (SC)".

This means the following:

Special characteristics can either be a product characteristic, or a manufacturing process parameter.
Special characteristics can affect functionality (fit, form, function, performance, further processing).
Special characteristics can be safety relevant.
Special characteristics can affect compliance with regulations.

The following table helps to categorize standard - or non-key - characteristics and special characteristics:

Categorization of Characteristics
Standard (Non-key) characteristics	Special characteristics (or Key characteristics / Significant Characteristics)
	Function relevant characteristics (or Significant Characteristics)	Safety relevant / Governmental regulated characteristics (or Critical characteristics)
A product or process characteristic, that does not affect a product’s function, safety or compliance with governmental regulations. No, or very minor impact on customer satisfaction. Low risk	The variation of this characteristic significantly affect fit, form, function, performance or subsequent processing. High impact on customer satisfaction! Moderate / High risk	The variation of this characteristic significantly affects safety, or compliance with governmental regulations. High impact on safety, environment, function or various governmental regulations! Non-conformance of characteristic may cause serious failure! Very high risk
Example: Length of a USB stick. Even though the stick is longer, than specified in the drawing, it still works, and causes no functional failure.	Example: Width of the USB stick’s port (terminal). In case the width of the terminal is not in specification range, the user cannot plug it into the slot. This causes functional failure (non-conformance of fit, form, function)	Example: Pressure in the hydraulic break system. If the pressure is low, it causes the malfunction (functional issue) of the whole breaking system, and on top of that, it may risk injury (safety issue).
Remark: many companies simply do not designate this category.	Remark: some companies use the phrase significant product characteristic, or key characteristics.	Remark: some companies call these critical characteristics.
FMEA severity: 1 – 4	FMEA severity: 5 – 8	FMEA severity: 9 - 10

Source: qMindset.com; ISO/TS 16949; VDA.de

Hints

Some companies use the phrase critical characteristics. Usually, these mean safety or governmental regulation related special characteristics. It is always advisable to harmonize our identifications with our customers' supplier quality manuals, to have a common understanding.

Special characteristics need special treatment. Some of them are regulated by standards, while others are required by the customer, or both:

The management has to designate personnel with the responsibility and authority to select special characteristics together with the customer.
The supplier must prove the conformity to customer-designated special characteristics in terms of documentation and control.
In the frame of design and development planning, the development and monitoring of special characteristics is mandatory.
The organization has to identify, document and review all customer product design inputs, including the special characteristics. The product design outputs have to be verified and validated, including special characteristics.
The Control Plan (CP) must include methods to control special characteristics (with mainly 100% testing, extraordinary SPC, error proofing, etc.)
Process improvement needs to focus on reduction of variation in product characteristics and process parameters. This is particularly relevant for special characteristics.

In practical life, the followings are generally required in the automotive sector:

Special characteristics must be treated with special care during design and manufacturing (e.g. 100% testing, error-proofing, poka-yoke designs, Cpk > 1.67 or even 2.0, full traceability, etc.).
All Special characteristics must be verified and validated during Design Validation (DV test).
Special characteristics must be included / marked in the Control Plan (CP), Design- and Process Failure Mode and Effects Analysis (DFMEA and PFMEA), drawings, specifications, work instructions.
Manufacturing or testing stations that perform a special characteristic relevant process must be labelled.

Source: qMindset.com

Summary

Special characteristics are product characteristics or manufacturing process parameters that have high impact on safety (S), conformance to governmental regulations (G) or fit, form, function, performance, further processing (F).
Special characteristics are also called significant characteristics or key characteristics. Many companies use different markings for these characteristics, such as shields, diamonds, triangles, special abbreviations, etc.
These characteristics need to be treated with special care from design, control and documentation point of view.

Source: qMindset.com

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