1. Library Development
Required schematic symbols, PCB footprints and component data are created, reviewed and verified before placement begins.
PCB Design Process
A Staged PCB Design Process Helps Control Schedule, Cost and Rework
Reviewing and approving major PCB design stages before downstream work begins can reduce unnecessary rework, clarify project scope and help keep design schedules and costs under control.
Why the Process Matters
PCB design decisions become more expensive to change as the project progresses
PCB design is a dependent engineering process. Placement decisions influence routing, routing depends on the approved stackup and constraints, and final manufacturing files depend on the completed and reviewed layout.
A change made early in the project may affect only a small amount of work. The same change made after placement and routing have been completed can require previously approved work to be modified or repeated.
For example, moving a critical component after routing has started may require traces to be removed and rerouted. The change can also affect differential pairs, length-matched signals, return paths, power distribution, mechanical clearances and other nearby circuitry.
To reduce this risk, 911EDA progresses through PCB design in defined stages and coordinates customer review and approval before advancing into major downstream work.
Staged PCB Design Workflow
Six major stages from library development through deliverables
Each phase establishes information that becomes the foundation for the next stage of the PCB design process.
2. Critical Placement
Connectors, BGAs, major power sections and other mechanically or electrically critical components are placed first so the overall board architecture can be reviewed.
3. Complete Placement
Remaining components are placed and refined around signal flow, mechanical clearances, height restrictions, keepouts, thermal requirements and routing feasibility.
4. Critical Routing
High-speed interfaces, differential pairs, matched-length groups, controlled-impedance signals, BGA escapes and other critical connections are routed and reviewed.
5. Complete Routing
Remaining signal routing, power and ground connections, copper areas, stitching and design-rule verification are completed.
6. Deliverables
After final approval, the native design database and specified fabrication, assembly and documentation outputs are prepared for release.
Customer Review & Approval
Approval checkpoints help prevent avoidable downstream rework
The objective of a staged review process is not to prevent design changes. Changes are sometimes necessary as product requirements develop, components become unavailable, mechanical information changes or engineering decisions evolve.
The purpose of each checkpoint is to make sure the customer has an opportunity to review important design decisions before additional work is built on top of them.
When critical placement is approved, for example, routing can proceed using that placement as an established design foundation. When complete placement is approved, the project can move more confidently into broader routing work.
Typical review checkpoints
- Library verification complete
- Critical placement reviewed
- Complete placement reviewed
- Critical routing reviewed
- Complete routing reviewed
- Final release package approved
Change Impact
The later a major change occurs, the more completed work may be affected
Staged approvals establish clear decision points and help customers understand when a requested change may affect work that has already been completed.
Example
A placement change after routing begins can create significant rework
Consider a board where component placement has been reviewed and approved and the PCB designer has begun routing critical interfaces.
If a component must later be moved to a different area of the board, the existing traces connected to that component may no longer be usable. Nearby routing may also need to move to make room for the revised placement.
On a complex board, the effect may extend beyond those individual nets. Length matching may need to be repeated, differential-pair geometry may change, power and ground connections may require modification and existing routing channels may need to be reorganized.
A late placement change may affect
- Previously completed routing
- Differential-pair geometry
- Matched-length signal groups
- BGA breakout strategy
- Power and ground routing
- Return-current paths
- Mechanical clearances
- Nearby component placement
- Design-rule verification
- Customer review schedule
Scope Changes
Some design changes require an updated schedule or project price
Customer-requested changes are a normal part of many engineering projects. When a change affects work that has not yet begun, the impact may be relatively small.
When the requested change alters previously approved work or expands the original statement of work, additional engineering effort may be required. In those situations, the project schedule and pricing may need to be adjusted.
When 911EDA identifies a change that is likely to affect scope, schedule or cost, the impact is discussed with the customer so the project can proceed with a clear understanding of the revised requirements.
Keeping Projects Moving
How customers can help reduce PCB design schedule changes
Good project preparation and timely technical reviews make the staged process more effective.
Requirements do not always need to be perfect at the beginning of a project, but major electrical, mechanical and manufacturing constraints should be identified as early as practical.
Helpful project practices
- Provide current schematic and mechanical information
- Identify critical components early
- Define connector locations and mechanical restrictions
- Provide stackup and impedance requirements when available
- Identify placement-sensitive circuitry
- Review placement carefully before approval
- Consolidate requested changes when practical
- Provide review feedback promptly
- Communicate requirement changes as soon as they are known
Have a PCB design project ready to discuss?
Send the available design files, project requirements, expected deliverables and target schedule for review.