Printed Circuit Board Design 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 1. Why PCBs? Design Process 2. Background – Component Selection – Board, components & software 3. Design Process – Positioning – Routing Techniques – Ground/Power Planes – Fabrication Restrictions Component selection, positioning, routing, power & ground, fabrication Advanced Design – Design your own! – High-Frequency Circuits – Positioning – Internal Layers – Routing – Power & Ground – – External Connections Workshop Overview 1. Why PCBs? 2. Background – Board, components & software 3. Design Process – Component selection, positioning, routing, power & ground, fabrication – Design your own! 4. 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 Layer Structure Most common: FR4 Copper layers – Epoxy and fibreglass – Allows traces to cross – Heat resistant, cheap – More heat dissipation High-frequency boards – More compact board – Controlled impedance Surface Layers – Usable at 1 GHz or more – Solder mask – Well-known: Rogers Corp. – 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) TO (transistor outline): TO-220 (left), TO-92 (right), metal can, etc. Axial lead resistor Diodes in DO-41 package 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) Left to right: SOIC-14, SSOP16, QFN-28 QFP40 (40-pin quad flat pack) 0.65mm pitch 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 Professional Eagle (Win) Cadence OrCAD/Allegro DipTrace (Win/Mac/Lin) Altium Designer KiCad (Win/Mac/Lin) Agilent ADS gEDA (Linux) Pulsonix Mfg’s software Design Process Component Selection Courses vs. real world – Class: “100nF capacitor” – Real world: What?! Material; polarised? Maximum voltage Physical size/package Photo by John Fader. CC-BY-SA 3.0. Heat capacity Error tolerance Cost!! – Digi-Key: 10HV23B104KN – 100nF, 1kV, 10%, $70 ea. 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 Routing components – Pours cover whole layer – Take advantage of mask! – Common in 4+ layer PCB Traces between pins – Lowest priority – Traces under SMD pads – Many and/or larger vias Fabrication constraints Can use several pours – DRC limits – Battery/supply voltage – Regulated voltage – Logic level voltage – Multiple grounds 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 Multilayer Design Board RF Behavior Problems Alleviated – Transmission line effects – Ground loops – Digital circuit switching – Intentional antennas – Unintentional antennas Controlled Impedance – Simulation / fabrication Traces to ground have impedance in real world! – Crosstalk Internal Planes – “Free” capacitor – Buried/blind vias Photo by Windell Oskay. CC-BY 2.0. Design Walkthrough Activity Design a PCB from start to finish! Link to PCB software: http://ieee.concordia.ca/go/pcb 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 Custom components – LM555CN Custom symbol (pins) Standard DIP8 pattern – Speaker custom symbol and pattern Convert to PCB Routing the board – Create board outline – Ground and power planes – Target size: 5cm × 8cm – Traces for programming – Pre-place components – Check drill sizes – Verify packages and 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. Copyright © 2013-2014 the Institute of Electrical and Electronics Engineers, Inc. Contributors: Marc-Alexandre Chan, Ryan Desgroseilliers.