printed circuit boards the design process. what is the output? not just a pcb engineering drawing...
Post on 22-Dec-2015
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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
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
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
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
Eagle Extensions
*.cmp Top, Via, Pad Component side*.ly2 Route2, Via, Pad Inner signal layer*.ly3 Route3, Via, Pad Inner signal layer*.ly4 $User1 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.
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
Design Rules
• Manufacturer Specific• Advanced Assembly
– Rules• 4 Mil Line Width/Spacing, 1-24 Layers, .02-.15 thick• 2-3 Mil Line Width/Spacing, 25-38 Layers, .01-.25 thick• Minimum Drill Size = 15 to 1 Aspect Ratio• Minimum Pad Size over finished hole Internal .012/External .008
– Recommendations (http://www.aapcb.com/PCBAssemblyTips.asp)• 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
Ogres, Onions, and Parfaits
• Parts, Schematics, and PCBs are like Ogres– They have layers
• Pretty Much Automatic – but Pay Attention to them
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
Symbol• Pins
– 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++
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
Package cont.
• Critical Dimensions– 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
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…
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
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
PCB Design• Define board outline and other mechanicals
– 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
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– Click on Process Job button– Creates .cmp, .gpi, .plc, .sol, .stc, .sts, .crc, etc…– Might have to add cream component
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