1.6 Engineering Queries (EQ), 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

Avoid submitting open-ended questions. An EQ must force a binary, deterministic engineering decision.

• The Problem Statement: Identify the exact discrepancy clearly. Cite specific RefDes locators (e.g., C45, R12), exact filenames, and stringent revision levels.
• The Hard Evidence: Attach high-resolution screenshots, macro photos of physical fitment failures, or the conflicting datasheet excerpts. Do not force the engineer to hunt for the context.
• The Proposed Disposition: The EMS CAM or Process Engineering team must propose a specific technical solution based on DFM reality. Avoid asking “What should we do?”; instead ask “Is X acceptable to resolve Y?“.

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.

Engineering Rule: Always specify a “Effectivity Date” or an exact Serial Number range on an EQ approval. Open-ended, perpetual EQ approvals can turn into permanent undocumented design changes—which requires an ECO, not an EQ.

ECO vs. Deviation Control

You must segregate temporary factory concessions from permanent engineering design changes to maintain configuration control.

The Deviation (Temporary Concession)

Use a Deviation constraint 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)

Use an ECO 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: You must explicitly define the supply chain Cut-In strategy (“Scrap Old Stock”, “Rework Old Stock”, or “Running Change on next PO”).

Final Baseline Checklist

The Control Point	The Critical Requirement
EQ Syntax	Must include: Current State + Hard Evidence + Proposed Binary Disposition.
Approval Channel	Avoid approvals via Slack or Email. Route them through the PLM/ERP system.
Deviation Limits	Bound max unit quantities or a calendar expiration date.
ECO Cut-In	Explicitly declare the financial disposition of existing physical WIP inventory.
Closure Loop	The EQ is only closed when the disposition is injected into the live SMT assembly instructions.
SLA Velocity	Enforce a strict SLA (e.g., ≤ 24 hours) to prevent line-down events.