1. Designing PCBs Within the Context of a System
Michael Alexander

2. What Is a System? System on a chip (SoC) System in a package (SiP)
Backplane
Silicon
Board
System on a chip (SoC)
System in a package (SiP)
One or more SoCs
PCB system that has ASICs / FPGAs
Mixed analog / digital / RF
Multiple interconnected boards
Rigid-Flex / rigid
Background – definition is many things to many people

3. What Is a System?
Wikipedia defines a system as “A set of interacting or interdependent component parts forming a complex / intricate whole”
A system has structure: it contains parts (or components) that are directly or indirectly related to each other
A system has behavior: it exhibits processes that fulfill its function or purpose
A system has interconnectivity: the parts and processes are connected by structural and / or behavioral relationships
Structure and behavior may be decomposed via subsystems and sub-processes to elementary parts and process steps
A system has behavior that, in relativity to its surroundings, may be categorized as both fast and strong
Surroundings
System
Boundary
Here’s a better view …. Also introduces the possibility of ‘sub-systems’

4. Scope Multi-board PCB system design
Architectural definition
Boards that are connected, integrated, and encapsulated within an enclosure
Interconnection mechanisms
Motherboard / daughtercard
Connectors
Cables
Ribbon cable
Rigid-Flex
Optics
This is often described in many ways and can cover multiple ‘fabrics’

5. System-Level Design Definition to implementation
Focus on
this Area
System Engineering V – the classic design process approach

6. Architectural Definition Process Overview
Let’s start at the ‘top’

7. Architectural Definition Tasks
Capture system structure
Functional blocks
Relationship between functions
Interface details
System architecture
Determine subsystems, based on tradeoff decisions, for example:
Power supply and distribution
Clock diagram
Memory implementation – onboard vs shared
System partitioning
Optimization driven across size, performance, power, interconnects, etc.
System-level timing – budgeted constraints across the system
Isolating mixed technologies – Digital, RF, analog
High level of abstraction
move from idea to reality
Vision to object

8. Architectural Definition System design and development
Tradeoff
Analysis
Early tradeoff analysis enables optimization: Cost, performance, reliability, form factor, and others
Time
Abstraction
Idea
Architectural
Definition
Logical
Detailed
Physical
Release to Manufacture
Prototype / Pre-Production
Production
Collaboration
Management
Throughout development, key decisions need to be made.
The earlier the better!
Reuse

9. Architectural Definition Tradeoffs
Architecture
Ability to partition into multiple PCB’s
Analyze the impacts of partitioning: Cost, power, functional, size, etc.
Correct-by-construction system connectivity
Physical implementation
Link several boards that make up a system
Define interconnecting components (connectors, flex, cables)
Validate connectivity
Manage interconnectivity
Re-target or re-partition as necessary
Retain integrity with logical design
Validate system-level constraints
Manage physical rules, clearance, signal integrity, power delivery, and environmental needs
Tool flow integration
Schematics, FPGAs, cables/harnesses
Support multiple fabrics from silicon to wire
These decisions may involve trading items – performance, cost, power etc.

10. Architectural Definition System design elements
Is performance
to specification?
Is architecture optimized?
Partitioning
Analysis
Cabling
MCAD
Thermal
Data Management
MFG
Key PerformanceIndicators
SYSTEM DESIGN
Are signals transported efficiently?
Is design efficient and conforming to standards?
Will it fit?
BOM and design data up to date?
The trade-offs are also linked to the needs of the whole process ….. Here are a few examples
Are yields acceptable?
Thermal effects on performance?

11. Architectural Definition Partition, analyze… implement?
Collaboration and Management
Analysis
Team-Based
Logical Design
High-Level Architecture
PCB-1
FPGA1
PCB-2
FPGA2
Partitioning
Team-Based
PCB Design
PCB Design
System
Integration
System Integration
and Analysis
System
Design
Re-Partitioning
From Scheme to implementation, designer involvement increases – Electrical Engineers, SI / PI Engineers, MCAD Designers, PCB Designers

12. Architectural Definition Typical flow: Functional blocks
Block representations of main system functions added to architectural design
Each block can be:
Single function
Group of functions
Purely graphical
Represent peripheral objects such as keyboards, monitors, disk drives, etc
Here’s an example of moving from high-level to detail, at the front-end process.

13. Architectural Definition Typical flow: Block relationships
Graphics added to represent relationships
Graphical images to visually indicate:
Functional relationships
Local interconnectivity
As with PCB’s – grouping takes place. Relationships are defined, local interconnectivity considered

14. Architectural Definition Typical flow: Interconnectivity intent
System-level interconnectivity
Graphical representation of:
Interconnectivity between blocks
Guidelines and advisories can be added
Connectivity width can be implied
Needs can be defined as notes or properties to guide informed decisions throughout the flow

15. Architectural Definition Typical flow: Power management
System power delivery needs are listed at top level of architecture
System Power Supplies and Grounding needs defined
System power supplies and grounding needs defined
Power assignment may also influence grouping and division decisions

16. Architectural Definition Typical flow: Subsystem definition
Identify subsystems
Subsystems displayed
Connectors required across subsystems
Multiple blocks assigned to single subsystem
First pass at determining sub-systems – ‘what is located where’

17. Architectural Definition Typical flow: Protocols and interfaces
System Interface connection – automatic or manual assignment
System interface connection – automatic or manual assignment
Interfaces can be physical:
Cable
Flex
Board connectors
PCB traces
Interfaces can be industry standard or user defined
Connectivity reuse – protocols that characterize interfaces can be referenced, such as DDR4, PCI-e, SATA etc. Connectivity reuse.

18. Architectural Definition Typical flow: Reuse design data
Logical
Architectural Definition Typical flow: Reuse design data
Reuse block or design instantiated at system level
Physical
Physical reuse – if a block exists and it works, why not reuse it.
Murphy’s Law may kick in – logic works but layout doesn’t ….. So how do I solve this?
Push into block for logical and/or physical view

19. Detailed Definition Floorplanning
Floor Planning enables physical needs to be explored and evaluated ….. Multiple boards in a multi-board system.

20. Detailed Definition Floorplanning: Early-stage PCB implementation
Physical implementation “discovery” can include:
Function to physical
Component types
Component associations
Physical to function
Re-used layouts
Logical inheritance
Will it fit?
Single board or multi-board?
Re-partitioning needed
System space exploration
Explore connectivity schemes
Determine system-level constraints
Assign constraint budgets to each board
Should physical layout always start with a net list?

21. Detailed Definition Floorplanning: Single or multiple boards
Placement created from list of parts
Reuse blocks
“Scratch pad” placement
Library-driven
No logical information in place
Place from physical library
Footprints
Connectors / mating connectors
Reuse blocks
Temporary symbol support
Place from parts list
Connector selected, mate connector added
Should physical layout always start with a net list?
Temporary components

22. Detailed Definition Floorplanning: Physical to logical mapping
Library-driven placement updated from schematic (cross-probe)
Select on schematic, pick on layout
Check legal matching of schematic symbol to PCB footprint
From scratchpad to layout – reversed engineering
2. Pick on layout
1. Select on schematic
4. Reference designator assigned, connectivity established
3. Compatibility checked

23. Detailed Definition Floorplanning: Multiple boards
User-defined outlines
MCAD imported outlines
“Smart” outlines
Aspect ratio
Edge clearance
Multiple board outlines
Export placement for each board
Outlines known – import and use
Outlines flexible - draw your own or ‘rubberband’

24. Detailed Definition Floorplanning: Connectors
Connector alignment checking
Connector compatibility
2D / 3D views
Connector assignment and mating – library driven / suggested

25. Detailed Definition Floorplanning: Will it fit?
Implementation guidelines
Floorplanned scheme
Actual assembly
Assemble, check, adjust, repeat
- Multiple boards with flexible height restricted areas
Conceptual Idea
Physical Implementation

26. Detailed Definition Floorplanning: System space exploration
System exploration
Signal integrity and power delivery tradeoffs across the system
Develop and explore “the four Cs”
Implementation fabrics across the system
Copper
Connectors
Components
Cables (Harnesses)
Understand and control
Tolerances – minimum, maximum, mismatches
Budgeting constraints across system
Frequency and time domain analysis
Performance is king – two boards with no apparent SI / PI issues fail when joined at the system-level

27. Detailed Definition Floor planning: Tradeoff analysis decisions
Performance vs connection mechanisms
Cable length too long
Signal loss through connector unacceptable
Component / signal coupling across boards
Folded flex – Self-coupling, EMI / EMC
Thermal stress on components
On-board, across-board coupling
Inter-board collisions
Components on two different boards too close in 3D space
Board to enclosure
Board to board
What I want? …
What I get?
What goes in may not match what comes out – it’s the loop I mentioned at the start of the session

28. Detailed Definition Floorplanning: Reuse
Subsystem can be:
Existing logic, existing layout or both
Existing subset of a board – e.g., memory subsystem
Specialized circuit – power supplies, RF circuits, etc.
Reusing subsystems within system design
Qualified, known subsystem
Saves time, reduces risk
Enables tradeoff analysis earlier in the design process
Reuse rather than rebuild ….. Well defined at the board level …. Need to elevate to system

29. Detailed Definition Floorplanning: Productivity aids
Alignment marks
Accurate placement
Guided alignment
Area calculation (head-up display)
Placement may not be a PCB Designer specific activity going forward – so aids are needed
How much space don’t I have
Area Used
Total Area
Subsystem
13.50
14.96
System
21.67
30.36

30. Detailed Definition System validation
Generate connection reports across multiple boards
Manage interconnectivity at system level
Collision detection
System BOM
Others…
Bring it all together – construct, analyze, confirm, release

31. Detailed Definition Floorplanning: Intelligent system diagram
Interconnection management
Interconnection validation during implementation process
Architectural to detailed
Implementation changes from original specification
For example: DDR3 replaced with DDR4
Keeping system design diagram in-sync with the implementation is important
Support top-down and bottom-up approaches
Focus on
this area
Front 2 back just got bigger!
Close the loop: Maintain system integrity throughout development

32. Roadmap Items Related to Capture/Moog
Import Capture
Flat designs with data (5 XXX)
Qir7
Support for External References in case of hierarchical designs
Features Planned for Q4, 2018
Export as Capture Design (Evaluation XXX,XXX)
OEM / ODM collaboration
System Capture working of Capture libraries (XXX)
Native support for existing Capture Library settings
Part Browser support for Capture Libraries and CIS DB
Import Capture (XXX)
Support for Variants(Evaluation)
Features planned for SPB 17.4 release
System Level Design
Multiple board Floor Planning (XXX, XXX)
Component re-assignment across boards
System Netlist
Auto Mapping of connectivity in Detailed Design (XXX, XXX)