Printed Circuit Board Design

Transcript Printed Circuit Board Design - IEEE Concordia

IEEE Concordia Electronics Workshop Presented by Marc-Alexandre Chan Concordia University, room EV 2.184 – 19 November 2014 Photo by Christian Taube, CC-BY-SA 2.5.

Workshop Overview

Why PCBs?

– Background Board, components & software 3.

Design Process – Component selection, positioning, routing, power & ground, fabrication – Design your own!

– – – – Positioning Routing Power & Ground Fabrication Design Process – Component Selection – Positioning – Routing Techniques – Ground/Power Planes – Fabrication Restrictions Advanced Design – External Connections – High-Frequency Circuits – Internal Layers

Workshop Overview

Why PCBs?

– Background Board, components & software 3.

Design Process – Component selection, positioning, routing, power & ground, fabrication – Design your own!

Some advanced considerations – External connectors, multi-layer boards, high frequency

PCB Basics

Why PCBs?

Limited alternatives – Breadboard, perfboard, chassis mount Custom designed for each circuit High flexibility Compact (high density) Protective solder mask 20+ layers possible Robots! (or cheap overseas labour) Photo by Christian Taube, CC-BY-SA 2.5.

Technical Background

Board Technologies

Board Materials

Most common: FR4 – Epoxy and fibreglass – Heat resistant, cheap High-frequency boards – Controlled impedance – Usable at 1 GHz or more – Well-known: Rogers Corp.

Layer Structure

Copper layers – Allows traces to cross – More heat dissipation – More compact board Surface Layers – Solder mask – Silkscreen printing

Board Technologies

Components, solder mask, and silkscreen layers on a PCB. Photo by Christian Taube, CC-BY-SA 2.5.

Packages: Through-Hole

Common types of through-hole capacitors (aluminium × 4, ceramic × 4) Axial lead resistor Diodes in DO-41 package TO (transistor outline): TO-220 (left), TO-92 (right), metal can, etc.

Inline packages: SIP and DIP (above); Plastic (PDIP, above), ceramic (CDIP) Photo credits: Abdullah Al Mamun, CC-BY-SA 2.5 Generic / Wikimedia Commons; “Nunikasi”, CC-BY-SA 3.0 Unported / Wikimedia Commons; Adafruit Industries, CC-BY-NC-SA, Flickr; Yves-Laurent Allaert, CC-BY-SA 3.0 Unported / Wikimedia Commons; Kimmo Palosaari, public domain / Wikimedia Commons;

Packages: Surface Mount (1)

SMD capacitors Resistors are similar Sizes in photo: – 1206, 1206, 0603, 0603 – 1210, 1206, 0805, 0805 – 1812, 1812, 1206, 1210 Photo credits: “Shaddack”, public domain / Wikimedia Commons.

Packages: Surface Mount (2)

SOT-23-3 (3-pin small-outline transistor 23) SO-8 (“SOIC” family) (with PDIP for comparison) QFP40 (40-pin quad flat pack) 0.65mm pitch Left to right: SOIC-14, SSOP16, QFN-28 BGA-16 (left, top and bottom of package), with SOT23-6 Photo credits: All images on this slide from Wikimedia Commons.

“Leapfrog”, public domain; “Swift.Hg”, CC-BY-SA3.0 Unported; “SPHL”, CC-BY-SA 3.0 Unported; “NobbiP”, CC-BY-SA 3.0 Unported; “NobbiP”, CC-BY-SA 3.0 Unported.

Design Software

Hobbyist

Eagle (Win) DipTrace (Win/Mac/Lin) KiCad (Win/Mac/Lin) gEDA (Linux) Mfg’s software

Professional

Cadence OrCAD/Allegro Altium Designer Agilent ADS Pulsonix

Design Process

Component Selection

Courses vs. real world – Class: “100nF capacitor” – Real world: What?!

 Material; polarised?

 Maximum voltage  Physical size/package  Heat capacity  Error tolerance  Cost!!

– Digi-Key: 10HV23B104KN – 100nF, 1kV, 10%, $70 ea.

Photo by John Fader. CC-BY-SA 3.0.

Photo by Megger Ltd. CC-BY 3.0.

Component Placement

Balance of objectives – Room for traces – Compactness (cost) – Heat dissipation – Design simplicity – Assembly (soldering) IC pin layouts – Common sense atypical – Dictated by IC structure – Deal with it Photo by Nicholas Wang (modified). CC-BY-SA 2.0.

Component Pinout Example

From the CD4543BE datasheet (Texas Instruments). Used for illustrative purposes.

Yes, you are reading the diagram correctly. The pinout uses order A-D-B-C and A-B-C-D-E-G-F.

Routing Techniques: Traces

Like wires on a PCB Point A to point B Angled lines Can’t cross each other Usually CNC milled – Avoid right angles – Avoid T junctions Classic PCB “look” Photo by Creativity103 (flickr). CC-BY 2.0.

Routing Techniques: Vias

Connect layers – All: Straight through – Some: Buried/blind vias  Difficult and expensive Allows trace “tunnels” – Pass under another trace Tips for vias – Through hole pads = vias!

– Allow for extra space – High current: more vias Photo by Karl-Ludwig G. Poggemann. CC-BY 2.0.

Routing Techniques: Copper Pour

Large area of copper – High thermal capacity – Large current capacity – Obstacle for traces – Obvious light colour Copper pour tips – Might need thermals – Can have vias in them – Island/deadzone removal – Software priority order Photo by t0msk (flickr). CC-BY-NC-SA 2.0.

Practical Strategies

Ground/power planes – Pours cover whole layer – Common in 4+ layer PCB – Lowest priority – Many and/or larger vias Can use several pours – Battery/supply voltage – Regulated voltage – Logic level voltage – Multiple grounds Routing components – Take advantage of mask!

 Traces between pins – Traces under SMD pads Fabrication constraints – DRC limits  Trace-trace clearance  Board edge clearance  Trace-pad clearance – Real-world drill sizes

External Connections

Board-to-Device

Pin Headers Sockets Dedicated Connectors – JST/Servo – Computer Cables – Barrel Connectors Chassis Mounting

Board-to-Board

Slotting – Routing / Fabrication – Gold Fingers – Tab Routing Stacking – Arduino Shields

Connector Examples

Photo credits (clockwise from top left): oomlout (flickr), CC-BY-SA 3.0; Appaloosa, CC-BY-SA 3.0 / Wikimedia Commons; M7, public domain / Wikimedia Commons; Mike1024, public domain / Wikimedia Commons

High-Frequency Considerations

High-Frequency

Board RF Behavior – Transmission line effects – Digital circuit switching – Intentional antennas – Unintentional antennas Controlled Impedance – Simulation / fabrication

Multilayer Design

Problems Alleviated – Ground loops  Traces to ground have impedance in real world!

– Crosstalk Internal Planes – “Free” capacitor – Buried/blind vias

Design Walkthrough Activity

Design a PCB from start to finish!

Link to PCB software: http://ieee.concordia.ca/go/pcb Photo by Windell Oskay. CC-BY 2.0.

Alarm/Buzzer Module

Schematic: Alarm/buzzer module

Alarm/Buzzer Module

How it works: – When TRIG is LO (0V): nothing happens (low power) – When TRIG is HI (5V): buzzer sounds (higher power) – TRIG short circuit to ground same as LOW – TRIG open circuit same as HI (pull-up resistor) Ideas for the module – Plug a switch in between TRIG and GND – Use reed switch on a door frame and a magnet on door!

– Make a microcontroller module to control the alarm – Arm/disarm, intruder detection, alarm patterns, etc.

To Do List

Basic schematic capture – Choose components – Connect with wires Convert to PCB – Create board outline – Target size: 5cm × 8cm – Pre-place components – Verify packages and sizes Custom components – LM555CN  Custom symbol (pins)  Standard DIP8 pattern – Speaker custom symbol and pattern Routing the board – Ground and power planes – Traces for programming – Check drill sizes – Prepare for manufacturing

Board Layout

Sample PCB layout: top layer (left) and bottom layer (right)

Ready for Manufacturing

Sample PCB Gerber file (bottom layer traces)

Ready for Manufacturing

How can you manufacture your design?

Do it yourself with traditional methods – Photosensitive two-sided copper boards – Regular copper board + a laser printer + glossy paper – In all cases: ferric chloride to eat away unwanted copper Get a fab house to do it – Many companies can do prototypes/small orders for cheap – APCircuit (Alberta, http://www.apcircuits.com

) – Advanced Circuits (US, http://www.4pcb.com

) – ITEAD (China, http://iteadstudio.com

) – SeeedStudio (China, http://www.seeedstudio.com

) – OSHPark (US, https://oshpark.com

)

Want to learn more?

More details and “good practices” for PCBs?

– http://alternatezone.com/electronics/files/ PCBDesignTutorialRevA.pdf

Want to start getting into advanced PCB design?

– High power and high current design  Copper thickness (“weight”: standard is 1 oz)  Maximum current through a trace  Isolation slots, circuit isolation – High frequency design (100MHz to many GHz)  Transmission line effects, microstrip design… (ELEC351/353/453)  Cross-talk, resonant circuit layout, etc.

Thank you for participating in this workshop!

Questions? [email protected]

http://ieee.concordia.ca

This work is licensed under the Creative Commons BY-NC-SA 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-sa/3.0/ or send a letter to Creative Commons, 444 Castro Street, Suite 900, Mountain View, California, 94041, USA.