1.6 Engineering Queries, ECO, and Deviation Control

Relying on informal Slack messages, email threads, or casual verbal approvals creates significant risk, especially if a warranty dispute arises later. Ambiguity within the official documentation—the Golden Data Pack—can lead directly to production stoppages, scrapped panels, or failures that only appear after the product is in the field.

The formal Engineering Query (EQ) process exists to prevent this. It provides a structured framework to transform ambiguous interpretations or discrepancies into a clear, traceable, and binding manufacturing specification. Its core purpose is to guarantee that the physical product being built (“As-Built”) perfectly matches the original engineering intent (“As-Approved”).

The EQ Workflow

An Engineering Query is the primary tool for resolving discrepancies between the engineering documentation—such as the BOM, Gerbers, and fabrication drawings—and the physical reality encountered on the factory floor.

1. Initiation and Definition

To be effective, an EQ must be precise. Submitting vague, open-ended questions is not permitted. Each query should present a clear, binary choice that forces a definitive engineering decision.

The Problem Statement: Clearly identify the exact discrepancy. Cite specific component references (e.g., C45, R12), exact filenames, and stringent revision levels from the documentation.
The Hard Evidence: Attach unambiguous supporting evidence. This could be high-resolution screenshots, macro photographs showing a physical fitment issue, or excerpts from conflicting datasheets. The goal is to provide all necessary context upfront, so engineering resources don’t waste time searching for information.
The Proposed Disposition: The EMS CAM or Process Engineering team must propose a specific, technically sound solution based on Design for Manufacturability (DFM) principles. Instead of asking “What should we do?”, the query should ask “Is implementing solution X an acceptable way to resolve discrepancy Y?“

2. Disposition Logic

Every EQ response, or disposition, must be categorized based on its impact on the product’s Form, Fit, Function, and long-term Reliability.

Clarification: If the query simply clarifies ambiguous documentation without changing the physical product—for example, clarifying the orientation of a smeared silkscreen legend—the disposition is recorded as a Documentation Update.
Deviation: If a physical material must temporarily deviate from the specification but remains functionally viable for a specific batch—such as substituting a capacitor brand due to a critical parts shortage—the disposition is a Deviation or Concession.
Rework: If the physical product requires unauthorized manual processing to meet the original specification—like hand-soldering a lifted pad—the disposition is a formal Rework approval.
ECO: If the discrepancy reveals a fundamental flaw in the core design that requires a permanent change to the Golden Data Pack—such as a connector footprint that is mirrored incorrectly—the disposition must trigger a full Engineering Change Order (ECO).
Stop-Build: If the defect presents a safety hazard or would cause a complete functional failure, production should be halted immediately.

ECO vs. Deviation Control

It is critical to separate temporary factory concessions from permanent engineering changes to maintain strict configuration control over the product.

The Deviation (Temporary Concession)

A Deviation is used to authorize a temporary departure from the locked Golden Data Pack for a strictly defined set of units or a rigid timeframe.

The Scope: It is bounded exclusively by a specific Batch ID, Purchase Order number, or Date Code range.
The Expiration: The authorization expires automatically once the predefined unit quantity or time limit is reached.
The Traceability: The exact Deviation Number must be permanently recorded, either through laser etching or in the production history log, for every affected serialized unit.

The Engineering Change Order (ECO)

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

The Scope: The change applies to all subsequent manufacturing builds indefinitely, until a new revision is released.
The Requirement: Implementing an ECO requires a revision increment (e.g., from Rev A to Rev B) of the top-level assembly PCBA tracking number.
The Implementation: The strategy for introducing the change into the supply chain—often called the Cut-In strategy—must be explicitly defined. Common strategies are “Scrap Old Stock,” “Rework Old Stock,” or a “Running Change” on the next purchase order.

Recap: Engineering Query, ECO, and Deviation Classification

Parameter	Condition / Trigger	Required Action	Constraint / Scope	Documentation / Traceability
Clarification	Ambiguity in documentation, no physical change required (e.g., silkscreen orientation).	Update documentation in Golden Data Pack.	Applies only to clarifying ambiguous documentation.	Recorded as Documentation Update.
Deviation (Concession)	Temporary, functional departure from spec (e.g., component substitution due to shortage).	Formal approval for specific batch/order.	Bounded by Batch ID, PO#, or Date Code range; expires automatically.	Deviation number must be recorded on affected serialized units.
Rework	Unauthorized manual processing required to meet original spec (e.g., hand-soldering lifted pad).	Formal Rework approval.	Authorization for specific, defined rework action.	Approval documented in EQ.
Engineering Change Order (ECO)	Fundamental design flaw requiring permanent change to Golden Data Pack (e.g., incorrect footprint).	Release new revision (e.g., Rev A to Rev B) of PCBA tracking number.	Applies to all subsequent builds indefinitely.	ECO must define Cut-In strategy (Scrap/Rework/Running Change).
Stop-Build	Defect presents safety hazard or causes complete functional failure.	Halt production immediately.	Applies to all affected production.	Initiate formal EQ/ECO process.