Achieving routing closure can be one of the most difficult tasks in the PCB design process. User surveys have shown that routing often takes up 50% or more of the PCB design cycle. Space is limited. Signals require special (often conflicting) considerations. Manufacturability must be maintained, and material costs must be controlled. On top of all this the goalposts are typically changing as you design, and the project evolves. Not all is lost though. With the proper strategy and planning these challenges can all be met in stride. Get a chance to learn from the experts at EMA and get the tips and tools you need to help you achieve routing success, even for your most complex designs.

1. Your Route to Design Success:
PCB Routing Tips from the Pros
4/26/2019 PCB Routing Flow 1

2. 4/26/2019 2
Routing is Critical to Success
Over 50% of total design time can
be spent in the routing phase.
- Cadence User Study
PCB Routing Flow

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Define Your Process Upfront
PCB Routing Flow
Placement
Stackup
Constraints/
Criticals
Auto / Interactive
Routing
Cleanup &
Verification

4. 1. Define placement strategy
2. Complete placement
3. Set your boundaries
4. PCB Stack up and impedance requirements
5. Define routing constraints defined for critical nets
– (Diff pair rules, matched length, Impedance control, physical and
spacing rules etc.)
6. Fan out vias established for signal and power connections
7. Define power distribution solution
– (Split planes, pre-poured power islands around regulators, high current
devices, etc.)
8. Route critical nets
– (diff pairs, clocks, matched groups etc.)
9. Bulk routing of remaining nets
10. Final cleanup, DFM checking
Recommended Route Process Flow
PCB Routing Flow4/23/2019 4

5. 5
Mechanical constraints should be evaluated and implemented such as
mechanical mounting holes, mechanical cut outs, route keep-out regions
Connector placements usually have specific X,Y placements and should
be completed first followed by adding fixed properties so they are locked in
Large pin count devices should be placed next, using the signal rats nest
as a guide for orientation to minimize rats nest twisting or crossovers for
better signal flow
Parts should be grouped together by function and rats nest optimized for
routing (Room properties help here)
Decoupling caps should be placed near the device power pins to increase
their effectiveness
Placement
Strategy
PCB Routing Flow4/23/2019

6. 6
Parts should be placed on the coarsest grid based on the pin pitch
of the majority of the parts
Placement grid will be divisible by the routing grid
– example: If most of the parts have a 50 mil pin pitch, then the routing
grid could be 5, 10, 25, or 50 mil
Fan-out of complex parts can be achieved at the library level for
future re-use
Fan-out grid is a multiple of the pin pitch grid
Placement Grid
Tips & Best Practices
PCB Routing Flow4/23/2019

7. 7
Define route keep-ins to manage clearance of
copper planes, vias and trace routing to the
board edge
Make sure to define any required via or route
keep-outs under any connectors. Some
connectors have metal shields etc. that may
short signals
Assembly requirements to be considered
and implemented such as v-scores, break off
tabs, fiducials etc.
Set your Boundaries
Defining Keep-In and Keep-Outs
PCB Routing Flow4/23/2019

8. 8
Take care when defining your stack-up
Stack-up has direct impact on differential
impedance, single ended impedance
Impedance targets should be modeled and
evaluated before moving forward
Results will help you define physical width
and gap spacing rules for differential pairs
PCB Stack-Up
PCB Routing Flow4/23/2019

9. 9
Differential pair parameters defined in the
electrical domain
Length rules defined for clock lines,
matched groups etc.
Physical trace widths, spacing rules, and
via size should be defined based on
board density and current requirements
for any high power devices
Defining Constraints
Why?
PCB Routing Flow4/23/2019

10. 10
Fanout vias are used when designing
multilayer designs
Fanout vias for signal pins allows access
to multiple signal layers for routing.
This provides additional space and routing
channels for designs with increased
density and pin counts
Fanout vias for power must be established
for power distribution and to complete
connectivity to inner plane layers
Fanouts and Power Distribution
PCB Routing Flow4/23/2019

11. 11
Split plane boundaries are established
for separation between copper pours
Saves space/layers for providing power
distribution on less layers
Assigned colors to different power
nets helps to determine split plane
boundary location
Separation widths between planes in
high voltage areas may be increased to
prevent arc-over
Establish Split for PWR Distribution
PCB Routing Flow4/23/2019

12. 12
Critical nets are routed to meet impedance
rules and timing requirements
Common design practices include not
routing high speed signals over plane splits
Why? It causes impedance discontinuities
that impact signal integrity
Segment over void check highlights violations
Routing Critical Nets
PCB Routing Flow4/23/2019

13. 4/26/2019 13PCB Routing Flow
Great, All My Critical
Signals Are Done.
Now What?

14. 14
How do I handle all the rest of the normal ‘boring’ connections?
What is the best use of my time?
Question: What about an auto-router?
Answer: It depends….
What people say about auto-routers…
• It will take too much time to learn the auto-router
• The results are not good (I can do a better job)
• I will spend too much time doing cleanup
• Route quality may impact the performance of the design
Auto-routers often get a bad rap!
‘Bulk’ Routing
PCB Routing Flow4/23/2019

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Bulk Routing
Pros & Cons
PCB Routing Flow
Manual / Interactive Routing
+ More control
+ Less upfront planning required
+ Easier to adjust to changes on the fly
- Can take longer
- Can be error prone (human error)
- Less time to test ‘what-if’ strategies
Autorouting
+ Fast
+ Can try many routing strategies quickly
+ Reusable
- Less granular control
- Can be hard to adjust to design change
- Can be difficult to convey user intent

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Ultimately…
PCB Routing Flow
The goal is to finish the
route effectively, making
the best use of your time
and expertise. Routers are
just tools. Use what works
best for the job at hand.

17. 17
PCB Route Cleanup
PCB Routing Flow4/23/2019
What kind of route defects should I look for?
90-degree corners
Acute Angles
Non-ideal Pad Entry
Here’s a few… Plus some more…
• Parallel line gap
• Uncoupled diff pair segments
• Arc radius
• Non arc corners
• Miter / corner size

18. 18
Manual Inspection is an
option. Often tedious and
error-prone.
Ideally, your CAD tool
provides routines to help
identify problems for you.
Most are easy to fix once
they are found
How to Find and Fix?
PCB Routing Flow4/23/2019

19. 4/26/2019 PCB Routing Flow 19
• Ensuring your design is manufacturable is crucial
• Hopefully your CAD program provides ways to embed DFM rules
and checking into the design process
*Check-out our webinar on Real-Time In-Design DFM for more info
DFM

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Demo Time
PCB Routing Flow

21. 4/26/2019 21PCB Routing Flow
Bonus
Managing/Routing
Large BUS Structures

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Demo Time
PCB Routing Flow

23. 4/26/2019 23PCB Routing Flow
Routing is one of the most critical and time
consuming stages in the design process. With the
proper processes, knowledge, and tools you can
be confident in your ability to achieve routing closure.

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Thank you
Watch the Full Webinar on Demand
https://resources.ema-eda.com/pcb-layout-
routing/your-route-to-design-success-pcb-routing-tips-
from-the-pros
EMA Design Automation
800-813-7494
edc@ema-eda.com
www.ema-eda.com
PCB Routing Flow