Post on 06-Apr-2018
transcript
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ES-HW design
Printed Circuit Boards
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Agenda for today
Basics of PCB Designing
Tools used for designing PCB
OrCAD flow Cadstar flow
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PCB
What are they?
Are they required?
Are they easy to build?
How are they build?
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What are they?
A printed circuit board, or PCB, is used to
mechanically support and electrically
connect electronic components using
conductive pathways, tracks or signal
traces etched from copper sheets laminated
onto a non-conductive substrate
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Are they required?
U need to answer this question for me
If Yes give me the reason
If No give me the reason
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How are they build
Generally three ways
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A practical PCB design flow that is
action-orientedand artifact-focused
Brainstorm
Needs
Evaluate*
Sys arch,block diag
ERC/Sim,Sch/NetlistBOM
ConstraintsCapabilityStandards
DRC,PCB Files,MFG Files
Designconcepts(multiple)
Design(High-level)
*evaluate through models,prototypes, and discussions
Capture(Logical Design)
Layout(Physical Design)
In library,In stock,Standards
Reqs,Budget,Constraints
Figures,Rankings,Tradeoffs
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ORCAD
Oregon + CAD
Its a CADENCE tool, a complete package from
creation of schematic to Gerber generation
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What can we expect from OrCAD
Schematic design.
Convenient drawing capabilities.
Easy creation of new schematic symbols. Automatic design rule checking.
Support for properties such as footprints, manufacturer
part numbers, etc.
Netlist creation from schematics.Access to schematic part database (but can live without it).
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Contd.
Board layout. Multi layer: at least 4 layers, possibly 10 layers or more.
Support for ground and power planes.
Narrow traces: down to 7 mils, possibly down to 4 mils.
Output files in a format suitable for manufacturing: GERBERformat.
Automatic checking design rules, spacing violations, etc.
Good libraries of standard footprints.
Easy creation of new footprints.
Optional: a good AutoRouter can be very useful.
Schematic layout integration (ECO, back and forthannotation).
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Design flow: schematic, layout,
actual board
Software has to manage the consistency between the schematic and the layout.
Photoplotter CAM files are used to manufacture the physical board.
Schematic Capture PCB Layout Actual board
Y
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Schematic symbols are the building blocks
Physical parts are represented by schematic symbols, which have properties. Visible properties: value (e.g., 5 kohms), schematic reference (e.g., R11).
Invisible properties: footprint (1206, 0805, etc), distributor number (P24.9CCT-ND).
Invisible properties are essential both for Layout and for the procurement.
I used to manage invisible properties by hand using the property editor.
Symbols as seen in Capture Managing properties by hand
C t id h ti
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Capture provides many schematic
symbols
Schematic symbols can be picked from libraries.
NB: distributor part numbers of actual parts are not provided in the libraries.
Symbols already placed on a schematic pageList of available libraries
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Often Capture does not provide the symbol that you need
For example, Analog Devices opamp type AD830 is not there. I have to make the symbol for it.
Symbol which was provided: AD829
Here I am constructing
a new symbol AD829_0,
which I will later rename
to AD830 which I need.
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Symbols + connections = schematic
In addition to properties, symbols also have pins.
Pins are connected with wires in order to form a netlist.
The netlist turns a loose collection of parts into the schematic.
The netlist can be written to disk. Layout will read it from there.
The PCB layout program will turn connections into copper traces.
SchematicIndividual symbols
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Before you start: check manufacturing details
Look at the PCB manufacturers website, learntheir specs.
What is the min/max size of holes?
Minimum PCB trace width and separation? Minimum clearances?
Maximum board size?
Limitations concerning the board shape?
Required file format? (Most likely GERBER, but check.)
Etc.
Prepare your board template according to the
specs.
Layout
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Routing
Verifying DRC
Create manufacturing files
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Signal OUT40 MHz * 10 bits
micro
processor
FPGA
ADC 40 MHz * 10 bits
(8 channels)
Analog
signal IN
8 channels
with
digital offset
and gain control
RS-232
Logic connectors NIM
16 lines IN, 8 lines OUT
USB
ECL clock IN
(optional)
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