4.2 Audits and capability verification

Trust is a very valuable component of any business partnership, but it is not a statistical quality control strategy. Objective verification is always necessary. It is often found that a supplier’s polished quality manual bears little resemblance to the tangible reality on their shop floor. The operational framework is based on a “Go and See” (Gemba) approach. While documentation is certainly necessary, the focus must remain firmly on observing physical processes and verifying actual capability. This chapter defines the audit architecture required to confidently validate that a supplier’s manufacturing capability matches their commercial promises.

The audit hierarchy

Not all audits serve the same purpose, nor are they structured the same way. The Supplier Quality Engineer (SQE) needs to select the correct evaluation tool for the specific objective at hand.

1. System audit (ISO 9001 / IATF 16949)

Objective: Compliance. Does the supplier possess a genuinely functioning Quality Management System (QMS)?
Scope: Reviewing Management Review minutes, Document Control practices, Training Records, and Internal Audit schedules.
Frequency: Typically performed during the Initial Qualification phase (unless a major certification failure occurs later).
Verdict: Generally evaluated as a straightforward Pass or Fail.

2. Process audit (VDA 6.3 style)

Objective: Capability. Is the manufacturing process inherently robust and reproducible over time?
Scope: Analyzing the “Turtle Diagram” of the specific production line. This thoroughly covers the Inputs, Machinery, Manpower, Methods, Environment, and Measurements.
Key Focus Areas:
- ESD Control: Are the operators’ wrist straps tested daily? Are the bench ionizers functional? Are the table grounding points verified?
- MSL Control: Are Moisture Sensitive Devices baked and tracked correctly according to J-STD-033? Are the floor life logs consistently accurate?
- Solder Profile: Is the reflow oven profile validated daily using a physical thermal profiler?
Frequency: Recommended Annually for Class A (preferred) suppliers; Trigger-based (as needed) for Class B/C suppliers.

3. Product audit (VDA 6.5 style)

Objective: Conformance. Does the finished part in the box precisely match the engineering drawing?
Scope: The SQE pulls a random, sealed box directly from “Finished Goods” (parts that are ready to ship) and performs a “Customer Eye” inspection on-site.
Focus Areas: Cosmetic standards, packaging integrity, label accuracy, and basic mechanical fit checks.
Frequency: Highly recommended to be conducted quietly during every single site visit.

Special process validation (the “black box”)

Certain processes simply cannot be verified by inspecting the final output (for example, verifying the shear strength of a wire crimp just by looking at it is impossible). These are known as “Special Processes,” and they require rigid, documented validation parameters.

Requirement: Suppliers must be asked to maintain a clear Validation Master Plan for operations such as:
- Soldering: Reflow Soldering, Wave Soldering, Selective Soldering (Requiring thermal profile validation logs).
- Chemical: Conformal Coating, Potting, Cleaning (Requiring tests like Ionic Contamination).
- Mechanical: Crimping (Pull test data logs), Press-Fit (Force over Distance insertion curves).
Re-Validation Guidelines: This should occur annually, or immediately after any significant equipment repair or line relocation. The SQE should plan to review these specific validation records during the regular Process Audit.

The capability index (cₚₖ)

The goal as an EMS is to procure a “capable process,” not to just pay the supplier to sort out the “good parts” from the bad.

The Expectation: For all Critical to Quality (CTQ) dimensions (such as specific PCB thicknesses or precise connector pitches), the supplier should demonstrate statistical process control.
Suggested Metrics:
- Pₚₖ > 1.67: Desired for New Product Introduction (NPI) or New Tooling validation runs.
- Cₚₖ > 1.33: Expected for ongoing, stable Mass Production.
Data Submission: Require the supplier to submit X-Bar & R Charts alongside every shipment of critical custom parts (like stamped metal shielding or precision milled housings).
Failure Condition: If the Cₚₖ falls visibly below 1.0, the process is deemed incapable. At this point, 100% Inspection generally becomes mandatory at the supplier’s site until the root cause is resolved and control is re-established.

The audit scoring & consequence

An audit is generally ineffective without a clear, objective score that drives corrective action. We recommend a standard Red/Yellow/Green traffic light evaluation system to clearly communicate maturity.

Green (> 90%): Approved. The partner is healthy; standard surveillance scheduling may proceed.
Yellow (80% - 89%): Conditional Approval.
- Action: The supplier must submit a detailed Corrective Action Plan (CAP) within 14 days.
- Guideline: It is wise to place a New Business Hold on the supplier until the CAP is proven complete and effectively closed.
Red (< 80%): Failed.
- Action: Place an Immediate Business Hold on all new orders.
- Containment: Implementing Controlled Shipping Level 2 (CS2) should be strongly considered - where a 3rd Party Inspection is required at the supplier’s expense to protect the active supply chain.

Recap: Audit and Capability Verification Protocols

Audit Type	Objective	Key Requirement / Metric	Frequency / Condition	Consequence / Action
System Audit	Verify functional QMS (ISO 9001/IATF 16949)	Pass/Fail based on documented system review	Initial Qualification; triggered by major failure	Pass/Fail verdict.
Process Audit (VDA 6.3)	Verify robust, reproducible manufacturing process	Validate: Daily ESD strap tests, J-STD-033 MSL control, daily reflow oven thermal profiling.	Annually (Class A suppliers); Trigger-based (Class B/C).	Findings feed audit score and CAP.
Product Audit (VDA 6.5)	Verify finished product conformance to drawing	On-site “Customer Eye” inspection of random sealed box from Finished Goods.	Every site visit.	Direct feedback for immediate correction.
Special Process Validation	Document validation of non-verifiable processes (e.g., soldering, crimping).	Maintain Validation Master Plan with logs (thermal profiles, pull tests).	Annual revalidation; after major equipment/line changes.	Review logs during Process Audit.
Process Capability (Cₚₖ)	Demonstrate statistical control of CTQ dimensions.	Mass Production: Cₚₖ > 1.33. NPI/Validation: Pₚₖ > 1.67. Submit X-Bar & R Charts with shipment.	Ongoing for critical custom parts.	Cₚₖ < 1.0: Process incapable. Mandate 100% inspection until root cause resolved.
Audit Scoring	Drive corrective action via objective maturity score.	Green (>90%): Approved. Yellow (80-89%): Conditional. Red (<80%): Failed.	Applied post-audit.	Yellow: Submit CAP within 14 days; consider New Business Hold. Red: Immediate Business Hold; consider CS2 (3rd Party Inspection).