Electronics Systems Design

## ELECTENG 209
# Electronics Systems Design 
### Introduction to Prototyping

.TitleAuthor[Duleepa J Thrimawithana]

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.logo-slide[]
.footer[[Duleepa J Thrimawithana](https://www.linkedin.com/in/duleepajt), Department of Electrical, Computer and Software Engineering (2020)]

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# Learning Objectives

- Understanding the product development life cycle
- Techniques that can be used to develop a quick prototype for design validation
- The evolution of circuit assembly technologies
- Printed circuit board (PCB) terminology 
- PCB development process
 - Schematic symbols
 - Footprints
 - Schematic capture
 - PCB artwork
- PCB design consideration
- PCB manufacturing process
- Testing and validating

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# Lecture Quiz

- The lecture quiz is now available on Canvas
 - Quiz is available for 3 days and allows 3 attempts
 - Best of the 3 attempts taken as the final score

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# Product Development
### Understanding the Product Development Life Cycle

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.logo-slide[]
.footer[[Duleepa J Thrimawithana](https://www.linkedin.com/in/duleepajt), Department of Electrical, Computer and Software Engineering (2020)]

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# Product Development Life Cycle

- Concept and requirements (in EE209 these are given)
 - Starts with an idea which can be turned into a product
 - Requirement gathering, develop specifications and develop a conceptual design 
- Detailed design 
 - Background research to identify applicable prior art, resources and technologies
 - Define the problem, subdivide and then analyse feasible solutions using theory and simulation tools
 - Based on the findings develop a detailed solution for test and validation
- Test and validate solution
 - Through simulations and prototype implementations 
 - Fast tracked using Breadboards, Veroboards, dev kits, PCBs and rapid prototyping tools
- Manufacturing and quality testing
 - Plan manufacturing, setup procurement processes, build, quality test and sell
- After sales support and services to repair faults, maintenance and technical support

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# Circuit Assembly
### A Review of Technologies

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.logo-slide[]
.footer[[Duleepa J Thrimawithana](https://www.linkedin.com/in/duleepajt), Department of Electrical, Computer and Software Engineering (2020)]

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# What to Do After Simulating the Design?

- After proving your electronics design is feasible using theory and simulations, a prototype needs to be built to experimentally validate its functionality 
- In real life you will iterate through many prototypes to refine the design so that it can be manufactured reliably at scale
- How can we interconnect the electronic components needed to build a prototype?
 - For example, in your project, how can we connect the resistors to OpAmp to test functionality?

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# Quick Prototyping

- Breadboards are used to temporarily assemble simple designs for quick testing and validation
 - Could be parts of a design that needs quick validation
 - Only useful when testing low voltage, low current and low frequency designs
- Veroboards are used to permanently assemble simple designs for quick testing and validation
 - Could be parts of a design that needs quick validation
 - Offer better reliability than a breadboard
- Need to ensure components and connections are laid out neatly

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# Circuit Assembly Technology in the '60s

- Rather large through-hole (leaded) components were used
- The components were connected by soldering wires between leads
- Components are mechanically fixed to a non-conducting base plate 
- Bulky designs that are tedious to manufacture 
 - Require manual labour

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name: S6

# Circuit Assembly Technology in the '80s

- Printed circuit boards (PCBs) were used to assemble mainly through-hole devices
 - Surface mount technology starts to gain acceptance 
- Copper tracks laid out on a board, which was made from epoxy, made interconnections between components that were soldered using a Lead alloy
 - These copper tracks were printed on the epoxy mostly using chemical etching techniques 
- Maturing component technology allowed compact components

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name: S7

# Circuit Assembly in Present Day (PI)

- Multilayer printed circuit boards (PCBs) used to assemble mainly surface mount devices (SMD)
 - Dimensions of surface mount devices can be as small as a few hundred micro-meters 
- Surface mount technology (SMT) allows automated manufacturing and compact designs
 - Solder paste dispensing, device placement and soldering done by robots
 - Todays pick-and-place machines can place thousands of components per minute

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name: S8

# Circuit Assembly in Present Day (PII)

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# Printed Circuit Board Design
### Understanding the Fundamentals

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.footer[[Duleepa J Thrimawithana](https://www.linkedin.com/in/duleepajt), Department of Electrical, Computer and Software Engineering (2020)]

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name: S9

# The Terminology

- **Leads (pins)** of through-hole devices are inserted in to **holes** and the copper **pads** around these holes provides a surface to solder the leads
- A **2-layer** PCB consists of an epoxy panel made from **FR4** with copper **traces (tracks)** on both top and bottom sides allowing to make electrical connections between the leads of the devices
- **Plated through-hole (PTH)** technology ensures pads on top and bottom are electrically connected
- **Solder mask** is a non-conducting paint that protects the copper while making soldering easier
- **Silk screen** contains the writing on the board like **designators**, logos, information, etc.

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# PCB Design Step 1 - Component Library

- First, develop a component library containing schematic symbols and footprints for each device
- Schematic symbols are used to represent the devices in a schematic file 
 - Drawn according to international standards such as the IEC60617
- Footprints tell how devices are physical represented on a PCB 
 - Includes information taken from the datasheet regarding the placement and dimensions of holes and pads, association of pads with physical pins of the device, 2D outline, 3D body, etc. 
- Each schematic symbol needs to be associated with a corresponding footprint

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# PCB Design Step 2 - Schematic File

- Once the component library is setup, we can develop the schematic of our circuit showing the electrical connectivity between the devices 
- Layout the schematic a logical manner while observing conventions 
 - Use net labels/ports where needed to reduce clutter
 - Separate functional blocks of your circuit 
- To improve readability add annotations
- Complex designs often spans across multiple schematic sheets

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# PCB Design Step 3 - PCB Artwork

- After drawing the schematic, the PCB artwork can be developed by drawing Cu traces to make electrical connections between devices
 - Planes/pours can also be used to create solid Cu planes for electrical connections
- Before starting the artwork, setup the design rules as per manufacturing and assembly constraints
- Arrangement of devices is very important and is key to doing a good PCB design 
- Traces can be placed using **‘interactive routing tool’** on **top (red)** and **bottom (blue)** layers

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# PCB Design Step 4 - Manufacturing the PCB

- After completing the PCB design check compliance with manufacturing and assembly constraints using **'Design Rule Check'** you should also do a **visual check** by printing it (use 1:1 scale)
- Finally, generate outputs and send for manufacturing
 - PCBs are mainly manufactured through an etching process (and in same cases they are routed)
 - After drilling the PCB, holes are plated with Cu and finally the solder mask and silk screen added

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# Example: PCB Order Through PCBWay

.questions[
Discuss what you will have to specify to the PCB manufacturer if you were to get your PCB design manufactured through [PCBWay](https://www.pcbway.com).
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# PCB Design Considerations

- Arrangement of components is critical
 - MCU pins in use, allocation of Op-Amps, etc. need to be selected to help achieve a good design
 - Arrange in to functional blocks for example digital, power, signal conditioning, etc. 
- Use appropriate track widths and clearances and for your UG projects use
 - Track widths of at least 0.5mm
 - Clearances of at least 0.5mm between tracks and 1mm between tracks and plane
- Minimize parasitic effects 
 - Longer track introduces unwanted inductances and will pickup noise
 - Avoid sharp corners and use shortest path for traces
 - Use effective ground planes
- Allow sufficient clearance between components
 - Allow space for connectors, mountings, heat-sinks, etc.
- Make sure test points are accessible

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# Example: TH vs SMT

.questions[
Discuss the differences between TH and SMT designs. What are **vias** and what are they used for?
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# ECSE Student Designs

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# ECSE Student Designs

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# PCB Assembly (PCBA)
### Assembly, Test & Validation

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.logo-slide[]
.footer[[Duleepa J Thrimawithana](https://www.linkedin.com/in/duleepajt), Department of Electrical, Computer and Software Engineering (2020)]

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name: S19

# Guide to Assembling & Testing

- Devices may be assembled by hand or using semi/fully automated machines
 - In this project you are required to assemble by hand
 - ECSE department has a state of the art SMT prototyping facility (tours can be arranged)
- Before assembling, develop test strategies that can be used to validate the design
- Assemble the circuit in stages while testing as per your test strategies 
 - Assemble, test and validate each functional block independently where possible 
 - After validating each function block of the circuit then interconnecting these to step-by-step while validating each step
- In this course, assemble and test power supply first, then assemble and test level-shifters, afterwards the filters and finally test the entire design
 - Do not ever assemble the entire circuit and expect it to work the first time 
 - Even the most experienced engineers assemble the first prototype in stages while validating each stage before proceeding to the next

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# Soldering Instructions - Getting Ready

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- Health and safety is the first priority
 - Wear safety glasses and clean your hands after soldering
 - Always solder in a well-ventilated and well-lit space
 - Pay full attention when using hot tools 
- Find a suitable soldering iron and select your solder wire
 - Soldering iron tip should be correct size and in good condition
 - If soldering SMT devices, you can use solder paste and a hot air-gun/reflow oven
 - It is recommended to use Leaded solder when performing manual soldering
 - Unleaded solder was introduced to meet requirements of the Removal of Hazardous Substances (ROHS) directive, and is harder to use
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# Soldering Instructions - Prepare PCB

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- Prepare the PCB by making sure pad and hole areas are clean
 - Clean the surface with some isopropyl alcohol (IPA) (or PCB cleaner) to remove any oxidation/debris
 - The use of a brush/toothbrush or cleaning paper is helpful
- Secure the PCB using a vice or masking tape so that it does not move when soldering
 - When soldering ESD sensitive devices use an earthed wrist strap to prevent damage to devices 
- Make sure you have all the devices and tools needed 
- You will need a copy of the schematic and the PCB artwork to identify placement of components
 - Its good practice to 'cross-off' components as you place them
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# Soldering Instructions - Clean Tip

- Set your soldering iron to between **330°C and 370°C** and let it reach this temperature 
 - Solder tip and solder wire should suit the size of pads you will be soldering to
- Once the iron is hot, clean the tip using a damp sponge/bras wool
- Once clean apply a small amount of solder to tin the tip, and wipe again with the sponge/brass wool
 - Solder tip cleaner can also be used if available

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# Soldering Instructions - TH Components (PI)

- Place the device on the PCB by inserting the leads in to the holes
- Briefly apply the soldering tip to the joint to pre-heat one of the leads and the pad 
- After a few seconds of heating (1s-3s), apply the solder wire to the heated joint 
 - Take care not to overheat as it may damage device and/or the traces/pad
- Ensure solder flows and covers the entire pad and lead 
 - It should make a shiny concave shaped solder joint 
 - You may apply flux to help improve the finish of your solder joint as it cleans the surface and avoids oxidization of the metal when heated 
- Check the alignment of device and if not properly aligned heat the solder joint and realign the device 
 - Do note that once you have soldered more than two leads it will be a challenge to realign
- Continue soldering the other leads by repeating steps above

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# Soldering Instructions - TH Components (PII)

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# Soldering Instructions - SMT Components (PI)

- Apply flux on to the pads to help improve the finish of your solder joint as it cleans the surface and avoids oxidization of the metal when heated
- Briefly apply the soldering tip to one of the pads to pre-heat it
- After a few seconds of heating (1s-3s), quickly apply the solder wire making a small solder blob
- Remove the solder wire and place the part while keeping the soldering iron on the pad to keep the solder flowing
- Once device is properly aligned and you have made sure it is flat against the PCB remove the iron making a solder join between the first lead of the device and the corresponding pad 
 - The first solder joint you made is mainly to hold the SMT device in place 
- Solder the next lead by first pre-heating the pad and the lead for a few seconds and then applying the solder wire to ensure solder flows and covers the entire pad and device lead 
 - Should make a shiny concave shaped solder joint
- Once all other leads are soldered, pre-heat the first solder joint and apply solder if needed

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# Soldering Instructions - SMT Components (PII)

- If using hot-air gun set to about 270°C for Leaded solder or to about 320°C for unleaded solder
 - Set the airflow low initially
- You may use a pre-heater to heat the PCB if needed
- Use the syringe to apply solder paste to all the pads you are soldering the devices to
 - Each pad should have enough solder to cover the entire pad in a thin layer
- Place the component on to the pads and ensure component is aligned 
- Hold hot-air gun over component until the solder “flows” and makes shiny concave shaped joints

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# Rework - TH Components

- When prototyping often you have to replace damaged devices or modify already soldered devices
 - If the device is damaged or you do not intend to reuse the device, cut the leads just above the PCB board (on the component side of the board)
- Use a flux pen/syringe to apply flux to the solder joints requiring rework
- Apply the soldering iron to each solder joint until the solder starts to flow 
- Gently pull the component leads from the hole using tweezers
 - If you try to pull the leads forcefully you will damage the pads/traces/through-hole plating
- It may help to add extra solder to act as thermal mass to help keep the solder joint heated
- If you wish to preserve the device, you will have to equally heat all leads (using two soldering irons or a special tip) together before gently pulling the device out
- Alternatively, you may use a vacuum de-soldering station – remember to hold the board in a manner to take advantage of gravity to help remove solder

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# Rework - SMT Components

- If using a hot-air gun, make sure it is set to about 320°C and hold the hot-air gun over the component until the solder starts to flow 
 - This is the recommended option for devices with many legs
- If using a soldering iron, heat all leads equally until the solder starts to flow 
 - It may help to add extra solder to act as thermal mass to help keep the solder joint heated 
- Use a pair of tweezers to gently lift the component off the pads

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# Rework - Cleaning

- Excess solder from the pads/holes can be removed using solder wick
- Alternatively, you may use a vacuum de-soldering station
- Isopropyl alcohol (IPA) or special PCB board cleaner to clean the surface 
 - Use a brush for thorough cleaning

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# Acknowledgments 
#### The latter part of the lecture was drafted together with Travis Scott