1.6 Engineering Queries, ECO, and Deviation Control

Informal Slack messages, email threads, or casual verbal approvals are insufficient when a warranty dispute arises. Ambiguity in the Golden Data Pack often leads to line-down events, scrapped panels, or silent failures in the field.

The formal Engineering Query (EQ) process is a framework that transforms ambiguous data interpretations into a traceable, binding manufacturing specification. It guarantees that the “As-Built” physical configuration perfectly matches the “As-Approved” engineering intent.

The EQ Workflow

The Engineering Query is the primary mechanism for resolving discrepancies between the engineering documentation (BOM, Gerbers, Fab Drawings) and the physical reality of the factory floor.

1. Initiation and Definition

Submitting open-ended questions is prohibited. An EQ must force a binary, deterministic engineering decision.

• The Problem Statement: The exact discrepancy must be identified clearly. Specific RefDes locators (e.g., C45, R12), exact filenames, and stringent revision levels must be cited.
• The Hard Evidence: High-resolution screenshots, macro photos of physical fitment failures, or conflicting datasheet excerpts must be attached. Forcing engineering resources to hunt for context is unacceptable.
• The Proposed Disposition: The EMS CAM or Process Engineering team must propose a specific technical solution grounded in DFM reality. Asking “What should we do?” is prohibited; instead “Is X acceptable to resolve Y?” must be asked.

2. Disposition Logic

Every EQ disposition must be categorized based on its impact to Form, Fit, Function, and field Reliability.

• Clarification: When the query merely clarifies ambiguous documentation without altering the physical product (e.g., clarifying a smeared silkscreen orientation), the disposition is a Documentation Update.
• Deviation: When a physical material deviates from the spec but is functionally viable for a highly specific batch (e.g., swapping a capacitor brand due to a severe Friday parts shortage), the disposition is a Deviation/Concession.
• Rework: When the physical product requires unauthorized manual processing to meet the spec (e.g., hand-soldering a lifted pad), the disposition is a formal Rework approval.
• ECO: When the core design is fundamentally flawed and demands a permanent change to the Golden Data Pack (e.g., the connector footprint is mirrored), the disposition requires a full Engineering Change Order (ECO).
• Stop-Build: When the defect presents a safety liability or unrecoverable functional failure, the line should be stopped immediately.

Pro-Tip: An “Effectivity Date” or an exact Serial Number range must always be specified on an EQ approval. Open-ended, perpetual EQ approvals risk becoming permanent undocumented design changes—which mandate an ECO, not an EQ.

ECO vs. Deviation Control

Temporary factory concessions must be segregated from permanent engineering design changes to strictly maintain configuration control.

The Deviation (Temporary Concession)

A Deviation constraint is used to authorize a temporary departure from the locked GDP for a defined quantity of units or a rigid timeframe.

• The Scope: Bounded exclusively by a specific Batch ID, PO number, or Date Code.
• The Expiration: The authorization expires as soon as the unit or time limit is reached.
• The Traceability: The exact Deviation Number must be permanently laser-etched or logged in the production history of the affected serialized units.

The Engineering Change Order (ECO)

An Engineering Change Order (ECO) is used to permanently modify the Golden Data Pack.

• The Scope: Applies infinitely to all subsequent manufacturing builds until the next revision is released.
• The Requirement: Requires a revision roll (e.g., Rev A ⭢ Rev B) of the top-level assembly PCBA tracking number.
• The Implementation: The supply chain Cut-In strategy (“Scrap Old Stock”, “Rework Old Stock”, or “Running Change on next PO”) must be explicitly defined.

Final Checkout: Engineering queries (eq), eco, and deviation control

The Control Point	The Critical Requirement
EQ Syntax	Must include: Current State + Hard Evidence + Proposed Binary Disposition.
Approval Channel	Approvals via Slack or Email are invalid. Routing through the PLM/ERP system is required.
Deviation Limits	Maximum unit quantities or a calendar expiration date must be bounded.
ECO Cut-In	The financial disposition of existing physical Work In Progress (WIP) inventory must be explicitly declared.
Closure Loop	The EQ is only closed when the disposition is injected into the live SMT assembly instructions.
SLA Velocity	A strict Service Level Agreement (SLA) (e.g., ≤ 24 hours) must be enforced to prevent line-down events.