CPE495 Computer Engineering Design I

Emil JovanovElectrical and Computer Engineering The University of Alabama in Huntsville

Introduction to PCB Design

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Schematic Capture and PCB Design

• ExpressPCB schematic capture and PCB Design http://www.expresspcb.com/ExpressPCB software

• Component selection Through hole SMT

• Design for Test Test points, grounds, etc. Spare components

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ExpressSCH

• ExpressPCB schematic capture Quick Start Guide examples

• New Schematic• Component Manager• Custom Components• Wiring

Standard NET lists ExpressPCB integrated support

• Sheets and Ports• Checking for Errors

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ExpressPCB

• ExpressPCB PCB design Quick Start Guide examples

• Layers• Traces

Linking the Schematic and PCB

• Grid• Rules for Component Placement• Ground plane• Component Manager• Custom components• Ordering boards

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PCB Design

• Component floor plan• Placing components on one side only / both

sides Snap-to-grid

Turn-off for unusual pin spacing Components that need to be in specific locations

Daughter board Minimize trace lengths Component orientation

Polarized part orientation Mark the positive leads / pin#1 (silk or text on the layer)

Leave enough room for traces in the beginning

• Test points and design for test• Print out a copy of the layout and check the

design with real parts

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PCB Design – Power and Ground(s)

• Wide traces to common rails 0.05” - 0.1” (GND) if possible Suggested: Power rail along the front edge, Ground

along the rear edge of the board

• Ground(s) Analog and digital ground Design issues

• System separation Ground problems Optical isolation Double diode Examples

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PCB Design – Signals

• Wide traces for higher current signals 0.01” – 300 mA

Good for low current digital and analog signals 0.05” – 2 A 0.1” – 4 A

• Make at least 10 mils spacing Larger voltages – larger gaps

• Vias (plated-through hole)• Vertical traces on one side, horizontal on the

other Directions: vertical, horizontal, 45 Avoid sharp, right angle turns (use two bends)

• Place text to determine what is the top layer Project, author,etc.

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Analog Ground Example

AnalogGround

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WISE 2.1 Example

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Custom components

• Custom components in SCH and PCB• Libraries

Sharing the same libraries Team work

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Verification

• Print and check component layout• Double check the routing of every signal

Use highlighter

• Check for missing vias Print separate layers

check for traces with dead-ends (not connected) Check for traces that cross each other

• Check for metal components (heat sinks, crystals, etc.) that can cause shorts

• Ordering boards