Change Order
Understanding Change Order
The Engineering Change Order (ECO) Workflow
During the lifecycle of an RF hardware product, design modifications are inevitable. These changes may be driven by component obsolescence, manufacturing yield improvements, cost reductions, or performance optimizations, such as correcting an impedance mismatch discovered during testing. A Change Order, specifically an Engineering Change Order (ECO), is the formal process used to implement these modifications. It ensures that every change is documented, reviewed for cost and schedule impact, and approved by all stakeholders before fabrication.
The ECO workflow begins with a change request, which identifies a problem or improvement. An engineer then proposes a solution, updating the schematics, PCB layout files, bill of materials (BOM), or assembly drawings. The proposed change package is routed through a review board comprising design engineers, layout designers, purchasing agents, and manufacturing leads. Once approved, the change is assigned a new revision code, and the updated files are released to the production line, preventing the fabrication of obsolete designs.
Implementing Change Orders in RF PCB Fabrication
In high-frequency RF printed circuit boards, even minor layout modifications can have severe electrical consequences. For instance, swapping a decoupling capacitor for one with a different package size or dielectric material can shift self-resonance frequencies, leading to power delivery network (PDN) noise. Similarly, modifying trace widths or spacing to accommodate a different component footprint changes the characteristic impedance, introducing reflections and return loss.
Consequently, RF change orders require rigorous verification compared to standard digital designs. Designers must run post-layout electromagnetic simulations on the modified sections to verify that the change does not violate crosstalk, isolation, or return loss specifications. The BOM must also be checked to ensure that replacement passive components match the original parts in tolerance, temperature coefficient, and high-frequency Q-factor, preventing degradation of the overall circuit performance.
Key Mathematical Relations
Technical Specifications Comparison
| ECO Severity Class | Design Scope Impact | Primary Approval Level | Example RF Change Action | Typical Implementation Delay |
|---|---|---|---|---|
| Class I (Minor) | Non-functional / cosmetic changes | Lead Layout Engineer | Adjusting silverscreen text or component labels | < 24 hours |
| Class II (Moderate) | BOM modifications, same form factor | Project Manager & Quality QA | Substituting an obsolete passive component with equivalent | 1 - 3 days |
| Class III (Major) | Schematic or layout modifications | Engineering Review Board (ERB) | Re-routing a microstrip line to improve return loss | 1 - 2 weeks |
| Class IV (Critical) | System architecture / board fit change | Executive Board / Customer | Changing board substrate material (e.g., FR4 to Rogers) | 2 - 4 weeks |
Frequently Asked Questions
Why are change orders critical in RF PCB manufacturing?
RF circuits are highly sensitive to physical geometries and material properties. A change order ensures that any modification to trace widths, spacing, substrate materials, or passive components is formally reviewed and simulated. This prevents accidental degradation of impedance matching, crosstalk isolation, or thermal performance during fabrication.
What is the difference between a Class I and Class II change order?
A Class I change order represents minor, non-functional edits that do not alter the electrical performance, mechanical fit, or bill of materials, such as correcting silkscreen text. A Class II change order involves functional changes that do not alter the physical board layout, such as substituting a component on the BOM with an equivalent part.
How does PLM software manage change orders?
Product Lifecycle Management (PLM) software centralizes design files, BOMs, and manufacturing documentation. When an ECO is initiated, the PLM system tracks file revisions, routes the ECO package to the appropriate engineers and managers for digital signature approval, and automatically updates the active assembly documentation once approved.