IPC-9191 Explained: SPC Implementation Guide for Electronics Manufacturing

If you’ve ever had a customer audit your facility and ask about your SPC program, you know the feeling. They want to see control charts. They want Cpk values. They want evidence that you’re not just inspecting quality into your products—you’re building it in through process control.

That’s where IPC-9191 comes in. This standard, officially titled “General Guidelines for Implementation of Statistical Process Control (SPC),” provides the framework for implementing SPC in electronics manufacturing. It’s referenced in supplier quality agreements, called out in aerospace and defense contracts, and increasingly expected by OEMs who want suppliers that prevent defects rather than just detect them.

I’ve implemented SPC systems in several PCB assembly operations, and IPC-9191 provides a solid foundation. It doesn’t tell you which specific parameters to chart—that depends on your processes—but it establishes the philosophy, organizational requirements, and system elements that make SPC actually work. This guide breaks down what IPC-9191 covers and how to apply it in your electronics manufacturing operation.

What is IPC-9191?

IPC-9191 is the electronics industry’s guideline for implementing Statistical Process Control. Published by IPC (Association Connecting Electronics Industries), it harmonizes with ISO 11462-1, the international standard for SPC elements, while adding electronics-industry-specific interpretation and guidance.

The standard was released in November 1999, superseding the earlier IPC-PC-90. Despite being over two decades old, IPC-9191 remains current because SPC principles haven’t changed—the statistical methods that Walter Shewhart developed in the 1920s still apply today. What has changed is our ability to collect data automatically and analyze it in real time, making SPC more practical than ever.

IPC-9191 Key Information

Attribute	Details
Full Title	General Guidelines for Implementation of Statistical Process Control (SPC)
Document Number	IPC-9191 (ANSI/IPC-9191)
Current Revision	Original (November 1999)
Supersedes	IPC-PC-90 (October 1990)
Harmonized With	ISO 11462-1
Status	ANSI Approved, DoD Adopted
Page Count	Approximately 30 pages

Why IPC-9191 Matters

SPC isn’t just a quality tool—it’s a business strategy. IPC-9191 opens with a clear statement of the financial motive: preventing defects costs less than finding and fixing them. The standard categorizes quality costs into four areas:

External Failures: Warranty claims, returns, field failures, customer complaints. These are the most expensive because they damage customer relationships and brand reputation.

Internal Failures: Scrap, rework, repair, re-inspection. You catch the problem, but you’ve already wasted resources.

Appraisal: Inspection, testing, auditing. Necessary but non-value-added work.

Prevention: SPC, training, process design, capability studies. Investment that pays back through reduced failures.

The philosophy behind IPC-9191 is shifting resources from appraisal and failure costs toward prevention. A properly implemented SPC system catches process drift before it produces defects, reducing scrap and preventing customer escapes.

IPC-9191 Structure and Scope

IPC-9191 is organized into six main sections that build upon each other. Understanding this structure helps you implement SPC systematically rather than jumping straight to control charts without the organizational foundation.

IPC-9191 Section Overview

Section	Title	Focus
Section 1	Scope	Defines what the standard covers and its relationship to ISO 11462-1
Section 2	Normative References	Lists referenced IPC documents
Section 3	Terms and Definitions	SPC terminology aligned with ISO standards
Section 4	SPC Objectives and Organization	Management commitment, financial justification, organizational structure
Section 5	Conditions for Statistical Process Control	Prerequisites for successful SPC implementation
Section 6	Elements of a Statistical Process Control System	The 16 specific elements that comprise an SPC system

The standard uses text formatting to distinguish between ISO 11462-1 content (italicized) and IPC-specific interpretation (normal text). This makes it clear which requirements come from the international standard and which are electronics-industry additions.

What IPC-9191 Covers

The standard addresses SPC implementation at both organizational and process levels:

Organizational Level:

• Management commitment and support
• SPC objectives and communication
• Training programs
• Quality system integration
• Financial tracking of quality costs

Process Level:

• Process documentation and control plans
• Measurement system analysis
• Data collection and recording
• Control charting and monitoring
• Capability assessment
• Corrective action systems

What IPC-9191 Does NOT Cover

IPC-9191 is a guideline, not a specification. It does not:

• Specify which parameters to control for specific processes
• Define acceptable Cpk values (these come from customer requirements)
• Prescribe specific control chart types for specific applications
• Provide detailed statistical formulas (reference ASQ standards for that)
• Cover industry-specific applications (see IPC-9192, 9193, 9194 for those)

IPC-9191 Section 4: SPC Objectives and Organization

Section 4 establishes the management framework for SPC. Without this foundation, SPC becomes a shop-floor exercise that management doesn’t support and eventually abandons.

SPC Objectives

IPC-9191 defines both general and specific SPC objectives:

General Objective: Continuously reduce variation in processes to improve product quality and reduce costs.

Specific Objectives:

• Establish process stability (eliminate special causes of variation)
• Assess process capability relative to specifications
• Maintain process capability over time
• Drive continuous improvement

Financial Motive for SPC

The standard emphasizes that SPC must be justified financially. Track quality costs in the four categories (external failures, internal failures, appraisal, prevention) and demonstrate how SPC shifts spending from reactive to proactive.

Cost Tracking Approach:

Cost Category	Examples in Electronics Manufacturing	SPC Impact
External Failures	Field returns, warranty repairs, customer rejects	Reduced through prevention
Internal Failures	Solder defects, placement errors, test failures	Caught earlier or prevented
Appraisal	AOI, X-ray, ICT, functional test	May decrease as process improves
Prevention	SPC training, capability studies, control charts	Investment increases initially

Organizing for SPC Implementation

IPC-9191 describes the organizational relationships needed for SPC success:

Management Role:

• Set SPC objectives and communicate them
• Provide resources (training, equipment, time)
• Review SPC metrics regularly
• Support corrective action implementation

Technical Role:

• Identify key process parameters
• Establish control plans
• Analyze data and identify trends
• Lead improvement projects

Operator Role:

• Collect data accurately
• Maintain control charts
• React to out-of-control signals
• Participate in problem-solving

Read more IPC Standards:

IPC-9191 Section 5: Conditions for Statistical Process Control

Section 5 defines the prerequisites that must be in place before SPC can succeed. Implementing control charts without these conditions leads to frustration and failure.

Management Support

Management support isn’t just verbal endorsement—it means providing:

• Time for operators to collect data and maintain charts
• Training for all personnel involved in SPC
• Equipment for measurement and data collection
• Authority for operators to stop processes when out of control
• Resources for corrective action

Understanding of SPC Tools and Methods

Everyone involved must understand SPC at their level:

Role	Required Understanding
Management	SPC philosophy, capability metrics, cost benefits
Engineers	Statistical methods, chart selection, capability analysis
Supervisors	Chart interpretation, reaction plans, escalation
Operators	Data collection, plotting, out-of-control recognition

IPC-9191 recommends developing a training plan that addresses each role. Training should be ongoing, not one-time.

Quality System Integration

SPC doesn’t exist in isolation—it must integrate with your quality management system. If you’re ISO 9001 certified, SPC supports several clauses:

• 8.5.1 Control of production (process monitoring)
• 9.1.1 Monitoring, measurement, analysis (data-driven decisions)
• 10.2 Nonconformity and corrective action (reaction to signals)

IPC-9191 Section 6: Elements of a Statistical Process Control System

Section 6 is the core of IPC-9191, defining sixteen elements that comprise a complete SPC system. Not every element applies to every process, but the standard provides a comprehensive framework.

The 16 SPC Elements

Element	Description
6.1 Process Documentation and Control Plan	Document processes and identify what to control
6.2 Definition of Process Targets and Limits	Establish specifications, targets, and control limits
6.3 Measurement System Evaluation and Control	Ensure measurement systems are capable (Gage R&R)
6.4 Documented Work Instructions	Standardize how work is performed
6.5 Employee Training and Involvement	Train personnel and involve them in improvement
6.6 Process Data Recording and Collection	Establish data collection methods and frequency
6.7 Traceability and Production Sequence	Link data to specific lots, batches, or units
6.8 Subcontractor Performance Evaluation	Extend SPC to suppliers
6.9 Process Input Sequencing	Control the sequence of process inputs
6.10 Process Logs	Maintain records of process events
6.11 Process Reliability	Ensure equipment and processes are reliable
6.12 Process Output Monitoring System	Monitor outputs with control charts
6.13 Process Control System	React to out-of-control conditions
6.14 Short-Term Variability Assessment	Assess inherent process variation
6.15 Long-Term Variability Assessment	Assess variation over time (capability)
6.16 Customer Information System	Communicate with customers about process performance

Key Elements Explained

Element 6.1: Process Documentation and Control Plan

The control plan identifies:

• Which process parameters to monitor
• How to measure them
• Sample size and frequency
• Control chart type
• Reaction plan for out-of-control conditions

For PCB assembly, a control plan might include solder paste height, placement accuracy, reflow profile temperatures, and solder joint inspection results.

Element 6.3: Measurement System Evaluation

Before you can control a process, you must ensure your measurement system is capable. IPC-9191 references Gage R&R (Repeatability and Reproducibility) studies to evaluate measurement variation.

Measurement System Acceptance Criteria:

%GRR	Assessment
< 10%	Excellent, acceptable for all applications
10-30%	Acceptable depending on application and cost
> 30%	Unacceptable, measurement system needs improvement

If your measurement variation is large relative to the tolerance, you can’t distinguish process variation from measurement noise.

Element 6.12: Process Output Monitoring System

This is where control charts come in. IPC-9191 doesn’t prescribe specific chart types but references standard options:

Common Control Charts for Electronics Manufacturing:

Chart Type	Application	Example Use
X-bar and R	Variable data, subgroups	Solder paste height by print
X-bar and S	Variable data, larger subgroups	Reflow oven temperature
Individual and Moving Range (I-MR)	Variable data, single measurements	Incoming material properties
p-chart	Proportion defective	Percent boards with defects
np-chart	Number defective	Number of solder defects per lot
c-chart	Count of defects, constant area	Defects per board
u-chart	Count of defects, varying area	Defects per unit area

Element 6.14 and 6.15: Variability Assessment

Process capability compares process variation to specification limits. IPC-9191 addresses both short-term capability (Cp, Cpk) and long-term performance (Pp, Ppk).

Process Capability Metrics:

Metric	Formula Concept	Interpretation
Cp	(USL – LSL) / 6σ	Process potential (spread vs. tolerance)
Cpk	Minimum of (USL – X̄)/3σ or (X̄ – LSL)/3σ	Process capability (accounts for centering)
Pp	Same as Cp but with overall σ	Long-term potential
Ppk	Same as Cpk but with overall σ	Long-term capability

Typical Cpk Requirements:

Application	Minimum Cpk	Notes
General commercial	1.00	Process just capable
Preferred commercial	1.33	Standard automotive requirement
High-reliability	1.67	Aerospace, medical
Critical safety	2.00	Automotive safety-critical

Related IPC-91xx Standards

IPC-9191 is the foundation document, but IPC developed companion standards for specific applications. These provide industry-specific guidance while referencing back to IPC-9191’s structure.

IPC-9191 Family of Standards

Standard	Title	Application
IPC-9191	General Guidelines for Implementation of SPC	Foundation document, all industries
IPC-9192	Implementation of SPC for Base Materials	Laminate and prepreg manufacturing
IPC-9193	Implementation of SPC for Printed Board Fabrication	PCB fabrication processes
IPC-9194	Implementation of SPC for Printed Board Assembly	SMT and through-hole assembly
IPC-9199	SPC Quality Rating	Audit tool for assessing SPC systems

How the Standards Work Together

IPC-9191 establishes what an SPC system must include.

IPC-9192, 9193, 9194 provide examples of applying IPC-9191 to specific processes:

• Which parameters to monitor
• Typical control chart applications
• Industry-specific considerations

IPC-9199 provides an audit checklist for evaluating SPC system implementation against IPC-9191 requirements. It’s useful for:

• Internal audits
• Supplier assessments
• Certification preparation

Each application standard includes an appendix cross-referencing its content to IPC-9191 sections, making it easy to trace requirements.

Implementing IPC-9191 in Your Facility

Implementing SPC isn’t a one-time project—it’s an ongoing program. Here’s a practical approach based on IPC-9191’s framework.

Step 1: Secure Management Commitment

Before launching SPC, ensure management understands:

• The financial benefits (reduced scrap, fewer customer returns)
• The resource requirements (training, time, equipment)
• Their role in supporting the program

Document management commitment in quality policy and objectives.

Step 2: Assess Current State

Evaluate your current process control methods:

• What data are you collecting?
• How is it being analyzed?
• What training exists?
• What measurement systems are in place?

Use IPC-9199 as a baseline assessment tool.

Step 3: Develop Training Plan

Create role-specific training:

• Management overview (2-4 hours)
• Engineer/technician detailed training (16-40 hours)
• Operator training (4-8 hours)

Include both classroom and hands-on components.

Step 4: Select Pilot Processes

Don’t implement SPC everywhere at once. Select pilot processes based on:

• High volume (enough data to chart)
• Known problems (opportunity for improvement)
• Measurable outputs (capable measurement systems)
• Supportive supervision (willing to try new methods)

Step 5: Develop Control Plans

For each pilot process, create a control plan identifying:

• Parameters to monitor
• Measurement methods
• Sampling strategy
• Control chart type
• Reaction plans

Step 6: Implement and Monitor

Roll out control charts, train operators, and monitor results. Expect an adjustment period as people learn the system.

Step 7: Expand and Improve

Based on pilot success, expand SPC to additional processes. Continuously improve based on lessons learned.

Implementation Timeline

Phase	Duration	Activities
Planning	1-2 months	Management commitment, assessment, training development
Pilot	2-3 months	Select processes, develop control plans, initial training
Implementation	3-6 months	Deploy control charts, refine methods, expand training
Expansion	Ongoing	Add processes, continuous improvement, advanced methods

IPC-9191 Resources and Where to Purchase

Where to Buy IPC-9191

Source	URL	Notes
IPC Official Store	shop.ipc.org	PDF and print available
ANSI Webstore	webstore.ansi.org	Electronic format
Accuris (Techstreet)	store.accuristech.com	Standards subscriptions available
Document Center	document-center.com	Authorized dealer
IHS Markit	global.ihs.com	Enterprise subscriptions

Current pricing is approximately $60-100 depending on format and membership status. IPC members receive discounts.

Related Standards to Consider

Standard	Why You Might Need It
IPC-9194	If you do PCB assembly, this provides specific SPC applications
IPC-9199	For auditing your SPC system or suppliers
ASQ B1-B3	Detailed control chart methods and calculations
ISO 11462-1	The international standard IPC-9191 harmonizes with
AIAG SPC Manual	Automotive-specific SPC requirements (if applicable)

Training Resources

IPC Training:

• Check IPC.org for SPC-related courses
• IPC certification programs include SPC content

ASQ (American Society for Quality):

• Certified Quality Engineer (CQE) covers SPC extensively
• Certified Six Sigma certifications include advanced SPC

Software Tools:

• Minitab, JMP, SPC XL for statistical analysis
• InfinityQS, Hertzler, Zontec for real-time SPC systems

Frequently Asked Questions About IPC-9191

Is IPC-9191 certification available?

IPC does not offer a specific IPC-9191 certification program like they do for IPC-A-610 or J-STD-001. However, SPC knowledge is incorporated into other certifications. The American Society for Quality (ASQ) offers certifications that cover SPC extensively, including Certified Quality Engineer (CQE) and Six Sigma certifications. For demonstrating IPC-9191 compliance, use IPC-9199 to conduct internal or third-party assessments of your SPC system.

How does IPC-9191 relate to ISO 11462-1?

IPC-9191 is harmonized with ISO 11462-1, meaning they share the same foundation. ISO 11462-1 content appears in IPC-9191 in italicized text, while IPC-specific interpretation and electronics-industry guidance appears in normal text. If your customer requires ISO 11462-1 compliance, implementing IPC-9191 satisfies that requirement while providing additional industry-specific guidance. The standards are complementary, not competing.

What Cpk values does IPC-9191 require?

IPC-9191 does not specify required Cpk values—those come from customer requirements, industry standards, or your own quality objectives. The standard provides the framework for measuring and reporting capability, but acceptable values depend on application. Common targets are Cpk ≥ 1.33 for general manufacturing and Cpk ≥ 1.67 for high-reliability applications. Automotive customers often reference AIAG requirements, while aerospace may specify values in contracts or specifications like AS9100.

Do I need IPC-9191 if I already have ISO 9001?

ISO 9001 requires process monitoring and measurement but doesn’t prescribe specific methods. IPC-9191 provides detailed guidance on implementing SPC, which satisfies ISO 9001 requirements while going further in methodology. Think of ISO 9001 as requiring “what” (process control) and IPC-9191 as providing “how” (SPC implementation). Many companies use both: ISO 9001 for the quality management system framework and IPC-9191 for the statistical process control methodology within that system.

Which IPC-91xx standard should I start with?

Start with IPC-9191 to understand the foundation and requirements. Then, based on your industry, add the appropriate application standard: IPC-9192 for base materials, IPC-9193 for PCB fabrication, or IPC-9194 for PCB assembly. If you’re in PCB assembly (most common), the combination of IPC-9191 plus IPC-9194 provides comprehensive guidance. Add IPC-9199 when you’re ready to audit your implementation or need to assess supplier SPC systems.

Conclusion

IPC-9191 provides the framework for implementing Statistical Process Control in electronics manufacturing. It’s not just about control charts—it’s about building an organizational culture that prevents defects through process understanding and continuous improvement.

The standard’s strength is its comprehensive approach. It addresses management commitment before diving into technical methods. It requires measurement system validation before process monitoring. It establishes training requirements before expecting operators to maintain control charts. This systematic approach increases the likelihood of sustainable SPC implementation.

For electronics manufacturers facing customer requirements for SPC, IPC-9191 provides defensible, industry-recognized guidance. Combined with application-specific standards like IPC-9194 for assembly operations, it gives you a complete roadmap from “we should do SPC” to “we have a functioning SPC system.”

The investment in SPC pays back through reduced variation, lower defect rates, and fewer customer quality issues. More importantly, it shifts your quality system from reactive (inspecting defects) to proactive (preventing defects). That’s the fundamental philosophy behind IPC-9191, and it’s as relevant today as when the standard was published.

If you’re starting an SPC program or improving an existing one, IPC-9191 is your foundation document. Read it, understand the elements, assess your gaps, and build from there. Your processes—and your customers—will thank you.