1. Printed Circuit Boards
The Design Process

2. What is the Output? Not just a PCB Engineering Drawing Set
Design Specification
Schematics
PCB Artwork
Fab Drawing
Bill of Materials
Part Drawings
Procurement Specifications
Firmware
Assembly Drawings
Test Specifications
Minimum Set to Produce PCB
PCB Artwork
Fab Drawing

3. PCB Artwork Negatives that will be used to produce layers of the PCB
Currently created from Gerber files
Gerber Photoplotter
RS-274X Gerber format is current standard
also known as X-Gerber or Extended Gerber
Produced via EDA (Electronic Design Automation) Software

4. Typical set of RS-274X file names
.GBL - Gerber Bottom Layer
.GTL - Gerber Top Layer
.GBS - Gerber Bottom Solder Resist
.GTS - Gerber Top Solder Resist
.GBO - Gerber Bottom Overlay
.GTO - Gerber Top Overlay
.GBP - Gerber Bottom Paste
.GTP - Gerber Top Paste
.GKO - Gerber Keep-Out Layer
.GM1 - Gerber Mechanical 1
.GM2 - Gerber Mechanical 2
.GPT - Gerber Top Pad Master
.GPB - Gerber Bottom Pad Master

5. NC Drill File The other type of file
NC Drill file provides X and Y locations along with size for all holes
Plated through holes vs uplated holes

6. Eagle Extensions *.cmp Top, Via, Pad Component side
*.ly2 Route2, Via, Pad Inner signal layer
*.ly3 Route3, Via, Pad Inner signal layer
*.ly4 $User Inner supply layer
*.sol Bot, Via, Pad Solder side
*.plc tPl, Dim, tName, Silkscreen comp. side
*.pls bPl, Dim, bName, Silkscreen solder side
*.stc tStop Solder stop mask comp. side
*.sts bStop Solder stop mask sold. side
*.drd Drills, Holes Drill data for NC drill st.

7. Design Process in Practice
Create Parts
Create Schematic
Run ERC (Electrical Rules Check)
Create Board
Place Components
Route Traces
Run DRC (Design Rules Check)
Produce Gerbers and Drill Data

8. Design Rules Manufacturer Specific Advanced Assembly Rules
4 Mil Line Width/Spacing, 1-24 Layers, thick
2-3 Mil Line Width/Spacing, Layers, thick
Minimum Drill Size = 15 to 1 Aspect Ratio
Minimum Pad Size over finished hole Internal .012/External .008
Recommendations (
Component to Component 10mil
Component to Board Edge 125mils
Part Polarity/Pin 1 Markers
Diodes/LEDs mark cathode (-) end with a bar
Capacitors mark positive end – use square hole
Number pins/pads as the manufacturer does

9. Ogres, Onions, and Parfaits
Parts, Schematics, and PCBs are like Ogres
They have layers
Pretty Much Automatic
but Pay Attention to them

10. Creating Parts in Eagle
Parts are created and stored in a library
Difficult to move from one library to another
Parts consist of
Package: The footprint in the layout
Symbol: The drawing for the schematic
Device: Assigns a symbol to a package

11. Symbol Pins Outline “Wires” on 94 Symbols layer
Visible attribute
Pad – Display pad name from Package
Pin – Displays pin name from Symbol
Both – Displays both pin and pad names
Direction should match pin’s function
ERC issue
Outline “Wires” on 94 Symbols layer
Name “>NAME” on 95 Names layer
Value “>VALUE” on 96 Values layer
Instead of “>VALUE” may use name of device
i.e. TSP78514, Teensy++

12. Package Package name should reflect package type
DIP14, TO220-5, LCC20
Pads – type ‘1’ including ‘s in text box then place pads - pads will be numbered sequentially
Pin 1’s pad should be square
or otherwise identified
Package outline on 21 tPlace layer
Name “>NAME” on 25 tNames layer
Value “>VALUE” on 27 tValues layes

13. Package cont. Critical Dimensions Start by placing Pin 1’s pad
Hole to hole spacing
Pad to pad spacing in surface mount devices
Package size is non-critical
Start by placing Pin 1’s pad
Place other pads, holes, and outlines in reference to Pin 1

14. Device
Add a Symbol (Library editor calls this Add a Part) by clicking on two input AND
Add a Package by clicking on the New button
Connect the Symbol’s Pins to the Package’s Pads by clicking on the Connect button
Opens a new dialog box
Click on Pin and Pad to be connected then
Click on Connect
Repeat
Click on Prefix button to assign a prefix
IC, R, C, CONN, J, etc…

15. Save Library
Perhaps you shouldn’t have waited until now to save your work

16. Schematic Entry
Schematic captures the electrical connections of your design
Schematic should flow from left to right
Frames make your schematic look professional
Decoupling Capacitors
Bulk where power connects to board
At least one per IC

17. Schematic Entry Design Flow
Place parts
Define electrical connections
Run ERC

18. Eagle Schematic Tool Bar
Info
Move
Group
Cut
Delete
Name
Smash
Bend a Line
Bus
Place Net Junction
ERC
Copy
Rotate – also right click when moving or placing
Change
Paste
Place Part
Value
Text
Electrical Connection
Label Net or Bus

19. PCB Design Define board outline and other mechanicals Place parts
Mounting holes
Place parts
Use Air Wires/Ratsnest to help place
Autoroute
Add finishing touches
Name of Board
Board Revision
Assembly Revision
Helpful silkscreen legends
DRC

20. PCB Design cont. Edit/Net classes
Allows different widths and hole sizes for named nets

21. Eagle Board Tool Bar
Rip up Route
Autorouter
DRC
Route Manually

22. Eagle Window
Switch to Board
Command Line
CAM Processor
Info Bar

23. Creating Gerbers and Drill File
Create Drill File
File/Run drillcfg.ulp create .drl file
A list of all drill sizes needed
Use CAM Processor to Create more Drill files
File/Open/Job – choose excellon.cam
Click on Process Job button
Creates .dri and .drd files
Use CAM Processor to Create Gerbers
File/Open/Job – choose gerb274x.cam
Check Tabs for proper layer setup
Creates .cmp, .gpi, .plc, .sol, .stc, .sts, .crc, etc…
Might have to add cream component

24. View Gerbers
Before submitting your files to a board house view them in a Gerber file viewer
Viewplot