3.1 APQP & PPAP

As is often said in engineering, quality cannot simply be inspected into a product at the end of the line; it really must be designed directly into the process. Advanced Product Quality Planning (APQP) is a structured framework of prevention. Its purpose is to ensure that the physical reality on the floor matches the original engineering intent before mass production ever begins. The Production Part Approval Process (PPAP) then provides the necessary, documented evidence that this APQP framework actually works at the required production rate. Skipping these critical planning steps usually leads to a stressful launch defined by line stops, heavy rework, and eventual field failures.

APQP: the architecture of prevention

APQP is much more than a simple compliance checklist; it is a phased maturity model. It is best practice not to proceed to the next phase until the major risks of the current phase are thoughtfully mitigated.

The Logic of Phased Gates:

Phase 1 (Plan): The “Voice of the Customer” must be clearly defined.
- If the core requirements are ambiguous, it is usually best to pause. A reliable, compliant product cannot be built against vague or shifting targets.
Phase 2 (Product Design): The underlying schematic and mechanical layouts must be frozen.
- Output: The DFMEA (Design Failure Mode and Effects Analysis). This helps identify exactly what could break in the field.
- Guideline: Critical Characteristics (CC) should be clearly identified here, such as a specific voltage rail tolerance or a critical heatsink gap.
Phase 3 (Process Design): The physical assembly line must be designed to appropriately handle the Product Design.
- Output: The PFMEA (Process FMEA) and the Control Plan. These address how the build process itself might inadvertently fail the design (e.g. insufficient solder paste volume, or incorrect screw torque).
Phase 4 (Validation): The product must be built using the final production tooling and processes.
- Action: The PVT (Production Validation Test) run must be executed. This is where the real-world data for process capability (Cₚ/Cₚₖ) and measurement system reliability (Gauge R&R) is collected.
Phase 5 (Launch): Mass Production (MP) is entered.
- Requirement: An active Safe Launch Plan (Early Production Containment) must be kept running until all the initial exit criteria are confidently met.

PPAP: the evidence of capability

A PPAP is essentially a structured, data-driven agreement between the Supplier and the Customer. It officially states that the manufacturing process is capable of producing parts that meet all specifications, consistently, at the quoted production rate.

When to trigger PPAP

When introducing a New Part or a New Product, a Full PPAP is required.
When an Engineering Change Order (ECO) alters the design or the material, a Delta PPAP focusing only on the affected characteristics is usually sufficient.
When transferring or replacing critical Tooling, a Full PPAP is expected, because a new tool effectively creates a new process.
When a process has been completely stopped or dormant for >12 months, a Re-validation PPAP ensures the process has not drifted.

Submission levels

The specific expected submission level is defined right in the purchase order so expectations are clear from the start.

Level 1: Part Submission Warrant (PSW) only. (Common for low-risk or commercial off-the-shelf items).
Level 3: Full submission, complete with physical samples and all supporting data. (This is the standard default for most custom parts).
Level 5: Includes an on-site review of the process at the supplier’s facility. (Typically reserved for critical safety items).

Critical PPAP elements

While the full AIAG PPAP package typically contains 18 standard documents, the following elements are particularly critical to review:

Part Submission Warrant (PSW): This is the cover sheet. Signing this document confirms accountability that the part is compliant and ready.
Dimensional Results: Every single dimension called out on the drawing must be measured on a randomly selected sample of parts (usually 5 to 30 units).
- Guideline: All general tolerance notes on the drawing must be followed. The title block must be checked: if the drawing says “unless otherwise specified ±0.1mm,” every single un-dimensioned feature must be measured against that standard.
Control Plan: This acts as the operational guide for the production floor. It maps every inspection step to a specific measurement tool and clearly defines the check frequency.
MSA (Measurement System Analysis): This provides the statistical evidence that calipers, fixtures, and optical systems provide reliable, repeatable data.
- If the Gauge R&R is greater than 30%, the measurement system likely needs improvement. It is best to fix the measurement fixture before investigating the manufactured parts.

Recap: APQP & PPAP Phase Requirements

Phase / Trigger	Key Document / Output	Requirement / Criteria	Action / Condition
APQP Phase 2: Product Design	DFMEA	Define Critical Characteristics (CC) per drawing tolerances.	Do not copy DFMEA failure modes into PFMEA.
APQP Phase 4: Validation	PVT Run Data	Calculate process capability indices (Cₚ/Cₚₖ).	Build using final off-tool, off-process setup.
PPAP Submission	Dimensional Results	Measure all drawing dimensions on sample (5-30 units). Respect all global tolerance notes.	Required for New Part, New Product, or Tooling Replacement.
PPAP Submission	MSA Report	Gauge R&R ≤ 30%.	Required for measurement system validation.
PPAP Submission	Part Submission Warrant (PSW)	Signed confirmation of part compliance.	Submission level (e.g., 3) defined in purchase order.