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NETTUR TECHNICAL TRAINING FOUNDATION DIPLOMA IN ELECTRONICS – CP04 MASTER FILE FOR PCB DESIGN & FABRICATION SEMESTER III SUBJECT CODE: CP04 03 04Prepared by: Mr.Palani Kumar Approved by: Roopa. P BRevised by: Mrs.Ankitha P (NEC) Course coordinator, CP 04Rev.no. 7 Released: June 2017NTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page1

DETAILED SYLLABUS FOR PCB DESIGN AND FABRICATION SUBJECT CODE CP04 03 04 SEMESTER 3 HOURS PER SEMESTER 40 REV. NO. 7 REV. DATE 22-06-2017 1.0 COURSE OBJECTIVES:At the end of the semester the trainee will be able to 1.1 Trainees will be able to do PCB design using design software. 1.2 Trainees will be able to understand the process for fabrication. 1.3 Trainees will be able to manufacture PCBs.2.0 TOPICSSL.No MAJOR TOPICS TIME ALLOTED1 EAGLE– BASIC CONCEPTS 42 PROPERTIES OF COPPER CLAD LAMINATE(CCL) 33 LAYOUT, GENERAL RULES AND PARAMETERS 6 44 LAYOUT PLANNING 25 BOARD CLEANING BEFORE PATTERN TRANSFER 3 66 PHOTO PRINTING 5 37 PLATING, ELECTRO PLATING, PTH 4 408 ETCHING9 MECHANICAL MACHINING OPERATIONS10 MULTI LAYERED PCB – Important concepts TOTAL HOURSNTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page2

SUBJECT CONTENT:Sl.No Major Topics Time Hrs 1.0 Unit 1 04 1.1 01 1.2 EAGLE – BASIC CONCEPTS 01 1.3 Introduction to PCB softwares 01 1.4 Introduction to EAGLE 01 Sections of Schematic editor 2.0 Constructing schematic 03 PROPERTIES OF COPPER- CLAD LAMINATES (CCL) 01 2.1 Manufacturing of copper clad laminates 012.2 Properties of copper- clad laminates (CCL)2.2.1 Electrical properties 01 062.2.2 Physical properties 2.3 Types of laminates 01 3.0 LAYOUT, GENERAL RULES AND PARAMETERS 01 3.1 Layout general rules &parameters 3.2 History & basics of PCBs 01 3.3 Board types 01 3.4 Single side pcb layout design requirements 01 3.5 Reference designations 01 3.6 Conductor routing practice3.7 General rules for pcb design3.8 Double side pcb layout design requirement3.9 Wave soldering3.10 Reflow soldering3.11 Surface mounted technologyNTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page3

4.0 LAYOUT PLANNING 04 01 4.1 Generation of design 01 4.2 Basic law 01 01 4.3 Via hole 02 4.4 Annular ring 01 03 4.5 Schematic diagram reference designators 01 How to design a pcb without the spikes where to run supply 01 01 4.6 &ground lines on pcb 01 4.7 Micro Via 4.8 Decoupling capacitor 4.9 Transmission line 4.10 Skin effect Solder 4.11 mask 4.12 Legend printing of silk screen 4.13 Grid system 4.14 General rules for pcb design for double side pcb 4.15 Component placement, ground plan 5.0 BOARD CLEANING BEFORE PATTERN TRANSFER 5.1 Pattern transfer 5.2 Organic soils 5.3 Metallic soils 5.4 Particulate matters 5.5 Vapour degreasing 5.6 Mechanical cleaning 5.7 Chemical cleaning 6.0 PHOTO PRINTING 6.1 Liquid photo resist 6.2 Negative acting dry film resist 6.3 Exposing 6.4 Developing 6.5 Rinsing 6.6 Drying 6.7 Plating 6.8 Single sided pcb fabrication by print and etch process 6.9 Single sided pcb fabrication by plate and etch processNTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page4

7.0 PLATING, ELECTROPLATING,PTH 06 7.1 Electroless copper plating process 01 7.2 Immersion plating 01 7.3 Electroless plating 01 7.4 Activator 01 7.5 Electroless bath 7.6 Types of electro plating 01 7.7 Copper plating 01 7.8 Tin plating 05 7.9 Gold plating 01 7.10 Nickel plating 01 8.0 ETCHING 01 8.1 Etchant solutions(etching chemicals) 01 8.2 Equipment & techniques 01 8.3 Types of etching 03 8.4 Ferric chloride etchant 8.5 Cupric chloride etchant 01 8.6 Chromic acid etchant 8.7 Alkali ammonia etchant 01 9.0 MECHANICAL MACHINING OPERATIONS 01 9.1 Introduction 04 9.2 Punching holes 01 9.3 Blanking 01 9.4 Shearing 9.5 Sawing 01 9.6 Routing 01 9.7 Drilling 9.8 CNC drilling 9.9 Laser & system concept 10.0 MULTI LAYERED PCB – Important concepts 10.1 Description 10.2 Needs for multilayer 10.3 Buried via 10.4 Blind via 10.5 Core layer 10.6 Board lay up 10.7 Constructions. 10.8 Multilayer press 10.9 Multilayer laminating processNTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page5

Unit 1 EAGLE – BASIC CONCEPTS 1.1 Introduction to PCB softwares In early days, before the PCB CAD systems even existed, the designers had to manually layout pads, tracks, etc. They also used techniques such as wire-wrap and point to point method for production. These methods needed a lot of patience and time. And if an error occurred, it used to take forever to debug. With the advent of CAD software for PCB designing, those days are gone. Rejoice! These CAD software have simplified the design process beyond any imaginable level. The work which used to take hours previously can now be done in seconds! This has also brought the PCB design process to hobbyists which was earlier limited to professionals. We can now design and fabricate our own PCBs at home. There are industry standards for almost every aspect of PCB design which are set and controlled by IPC (formerly known as Institute for Interconnecting and Packaging Electronic Circuits). There is a standard for everything from designing to manufacturing to testing and to anything else you would need. Many countries also have their own local standards for PCB design, but the ones by IPC are accepted as industry standard around the world.There are many CAD packages available for free as well as for a premium such as Cadsoft EAGLE, Altium Designer, NI Ultiboard, ExpressPCB, Mentor Graphics PADS, etc. 1.2 Introduction to EAGLE EAGLE, an acronym for Easily Applicable Graphical Layout Editor, is a design software by Cad soft Computers. It is widely used by educationalists, students, hobbyists and professionals because of its richNTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page6

yet simple interface with large component library cross-platform support on Windows, Mac and Linux tool. EAGLE Software is the Control Panel. The Control Panel is like the root of every EAGLE operation be it schematic, library or board layout. The control panel consists of the menu bar and the context menu, which is the tree list view of the files on the left namely libraries, design rules, ULP‟s (User Language Programs), scripts, CAM jobs and projects. On the right you will get details about your EAGLE version or description about what. 1.3 Sections of the Schematic Editor Tool Box: The tool box in eagle schematic editor is feature rich. It consists of a number of useful tools for designing schematics. Tool Specific Options: Some tools have their specific settings and options that you can meddle with. These are displayed above the command line once you have selected the tool. Command Line: Since EAGLE also runs on Linux, it can also be operated as a command driven software. In addition to using the GUI, you can also type in commands in this space to select tools, change settings, etc. If you are faster at typing than moving the mouse, you can use this to select tools using specific commands. Once you get used to it, you‟ll realize that it is actually faster than using your mouse. However, for the purposes of this tutorial, we will not deal with this (we have your sympathies :) ) Sheet Display: A schematic file in EAGLE can hold up to 99 schematic sheets. You can summon new sheets by right clicking in the space and clicking on New. You can also right click on sheets to write descriptions. Workspace: This is the area where you will place your components and shape up your schematic. Grid Size and Coordinate Display: Every component in EAGLE has anNTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page7

origin and they can only be placed on a specified grid in the workspace. Grid size refers to the minimum distance apart that you can move/place any component. This is useful to keep your components well placed and organized, otherwise they would be floating around somewhere in the schematic. If it doesn‟t make sense now, wait until you experience it! The current grid size is displayed in this area. The coordinate of the origin of the currently selected object is also displayed in parenthesis. This coordinate is calculate from the origin of the schematic, which is on the bottom left of the workspace.After getting acquainted with the schematic environment, next up is the description of frequently used tools available in the toolbar. Tool Bar Layer Display: This tool displays all the layers which are required in construction of a PCB, namely top, bottom, silkscreen, nets, buses, symbols, names, values, etc. This tool has quite a number of layer options, which will be described as and when required during this tutorial. You can create new layers, edit layers, hide or view layers. Move: The move tool is used to move various objects around in the workspace. You can move the objects by using the move tool on the origin of the objects to be moved. Copy: The copy tool is used to make a copy of various objects in the schematic. Mirror: The mirror tool is used to make a mirror image of any object in the workspace. This tool is used to make the schematic look pretty by adjusting components properly. Rotate: The rotate tool is used to rotate various components inNTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page8

anti-clockwise direction. Group: The group tool is used to make a group of components/objects and to apply specific commands on the group or move them as a block. Delete: The delete tool is used to remove objects from the workspace. Add: The add tool is used to access the component library and add components to the schematics. Replace: The replace tool is used to replace the already present components in the schematic with other device from the library. Name: The name tool is used to change the names of different components. Value: The value tool is used to change the values of different components like resistors, capacitors, ICs etc. Smash: The name and value of any component is attached to it in a specific orientation decided by the component designer. Sometimes these hinder with the connections (net) or buses. The smash tool is used to separate the name and value form the component and allows to move them freely. After smashing, the names and values have their own origin and a translucent line which makes their connection to the related component so that they do not get lost in the schematic. Text: The tool helps you to write supporting text on the schematic (just like you write comments in a code, which is a good thing though). This tool creates text as separate objects.NTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page9

Bus: A collection of parallel wires is known as a bus. For example wire coming out of a connector. The bus tool is used to create bus for various components. Net: To connect components with a single wire, the net tool is used. This tool automatically creates junction where two or more wires are connected. Junction: A junction is a place where two or more wires meet. If the wire or bus tool does not create the junctions automatically, you can use this tool to create them manually. Label: The label tool is used to label the wire or bus connections. This helps you to keep track of the wire names and virtually connected components. The concept of virtual connection will be explained later in this tutorial. ERC: Acronym for Electrical Rule Check, this is a tool which checks for logical errors possibly made by the designer during the construction of the schematic. For example if you ground the VCC pin of an Op-Amp or leave an essential pin open, the error will be flagged when you do the ERC. You can rectify these mistakes and again do a check to see if the problems are solved. Errors: The ERC tool checks the schematic based on a rule set defined by the components in the schematic and also some basic circuit connection logic. Sometimes your circuit might be logically correct but still it is shown as an error. The Errors window lists the errors found by the ERC and displays the location and description of each error. In case the error detected by the ERC is false, you can approve them manually.NTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page10

Now that we are done the description of schematic tools, we will move on to the designing of IR sensor breakout board. This is where things begin to get exciting! Let‟s roll! 1.4 Constructing Schematic Example:IR Sensor circuit Before we begin, we should know what we are going to design. The final schematic that we are going to design will look somewhat like this: IR Sensor Circuit Time and again, you can refer back to this diagram to make the design process easy. The design process in EAGLE is very intricate. We will not be going in depth right away. The level of detail will be increased in subsequent tutorials. To begin with the designing process the first thing that you need to do is to create a new project folder named “IR Sensor Breakout” (of course you can choose any name that you fancy, but we prefer this one!). Then create a new schematic in this project folder. The first thing you want to do is to include all the component libraries, which you can do this by clicking on Library > Use, selecting the component librariesNTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page11

you want to use (or just select) all and pressing Open. In order to design a correct PCB layout, you‟ll need to get the schematics right in the first place since everything depends upon it. EAGLE is a connected software. It links your schematic and board layout. If after designing your PCB layout you make changes in the schematic, it will be reflected back in the layout. So be clear about what you are designing. You can‟t get away with a messed up schematic while secretly hoping that your board layout turns out to be correct. It is an important step in the design process after all. Step 1 – Select and Add your Components The first step is to include all the components required for your product design into your workspace. For the schematic shown above, we need an IR LED, a photodiode, coloured LED, 2 resistors (330Ω, 10kΩ), an op-amp (LM358), a 10kΩ potentiometer and 3 male headers (for Vcc, GND and Signal OUT). The add tool opens a list of components like the one shown below with more or less the same libraries. EAGLE ADD WindowNTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page12

The ADD window includes the component libraries for products from different companies (like Altera, Atmel AVR, Linear, etc.) or IC series (like 40xx, 45xx) or product series from different companies and general categories like battery, connector, etc. You can find the resistors, capacitors, inductors in the RCL library. The schematic symbols are available in US and Europe versions. Different Symbols Many companies update their libraries from time to time. Many major electronic component distributors like Spark Fun or Adafruit have their Own EAGLE libraries for their products that you can download and paste in the lib directory as mentioned in the earlier post. Search! The search box in the ADD window has many features. You can search for your components based on your requirements. It has three check boxes to limit your search queries each of which is explained below. Smds: If you do not require SMD (surface mount devices) in your design you can exclude it to narrow your search query. Description: It will try to find a match of your phrase in the search bar with all the product descriptions. Preview: It is used to toggle the component package preview and description on the right hand side. Many a times you know the IC number but are unable to find the NTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page13

component because the libraries have company prefix or suffix with the IC number (e.g. UA741, LM741, LM741C). This is when you can use wildcards. You can order a search query of the type “**358” (exclude the quotation marks of course), which means it will show all the results having any two letters to replace the asterisk and ending with 358, and “**358**” and so on. Choose your package Once you have found you component you will have to select the right package for your job. Package is how the device is physically available for your use. For example, an LED is available in 3mm, 5mm and 10mm sizes. An IC can be available in DIP, SMD, BGA, TQFP packages. You have to select the right package to suit your needs. For instance, if you plan on hand soldering your components on your board, you would prefer bigger and through hole components rather than in small and surface mount forms. The component preview and the package will be shown in the description on the right hand side. The packages of the components which we are going to use are: IR LED (5mm) Photodiode (5mm) Resistors 1/4Watt (0207) Potentiometer (CA6V) Male Header (MA03-1) LM358 (Dual Inline Package or DIP) If you do not have your required component package listed, or if the Component is itself missing, you can create your own from the Mechanical description given in the data sheet of that component. There will be a separate tutorial for creation of your own component or package. NTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page14

Step 2 – Arrange and Name your Components Arrange the components as shown in the image below by using the move and rotate tool. Arranged Components Tip: While using the move tool if you right click on a component you can simultaneously rotate the component. Now use the value tool to enter the values to the components. For example, enter the value 330E (330Ω) to R1 resistor and so on. You can also use the name tool to change the name of components. Below is an image showing the components with their names and values changed.NTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page15

Components with updated name and value Step 3 – Make Connections To connect the components we are going to use the net tool (not the wiretool). Before making any connections, every schematic must have a voltage supply and ground. So add Vcc and GND from the library. Vcc and GND added to the schematic.The above image shows the schematic with voltage supply (Vcc) and ground (GND) connections. You can have a single Vcc and ground symbol to connect to all the components but it will create too many crossover connections and make the schematic look cluttered. So we can use the copy tool or use the add tool to place Vcc and ground for each circuit block. For instance, create separate Vcc/GND pairs for the IR LED and photodiode, op-amp and potentiometer, and for the male headers. Note: The EAGLE schematic editor virtually connects all the VCCs together and the GNDs together. This is known as virtual connection. Now complete the connections using the net tool to get the schematic as shown below. Be sure to save your work often. You can also turn onNTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page16

the autosave feature from options. Final Schematic Step 4 – Check your Circuit Now check your circuit by running the Electrical Rule Check tool. ERC Check You can see the ERC Errors window on the bottom right. The circuit we designed has encountered two warnings. You can click on the problem and the software will point out the problem area as shown in the image above. The warning states that we have connected the V+ pin of the op-amp to Vcc and V- to the GND. Since we are using the op-amp inNTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page17

single supply mode we can approve both the warnings and save our schematic. Step 5 – Export your Schematic (Optional) To export your schematic as an image you can go to File > Export > Image and save your schematic as an image. This step is optional since EAGLE uses your .sch schematic file to link to your board layout and not your exported image. The exported image is for your reference only.NTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page18

UNIT 2 PROPERTIES OF COPPER- CLAD LAMINATES (CCL) 2.1 Manufacturing of copper clad laminates Electrolytic copper foil:This is manufactured by electroplating method. A thin film of copper metal is deposited on toa slowly rotating corrosion resist metal cylinder which is used as cathode and lower portionimmersed in a copper rich electrolytic plating bath. Pure copper as the anode and immersedinto this solution. As the cylinder slowly rotates in the bath, a thin copper deposit graduallybuilds up into as integral sheet of metal foil which can be gently peeled off from the cylindersurface at the point where the cylinder surface comes out of the plating bath. The rolls of foilas removed from the plating machines are commonly called RAW FOIL. The purity of raw foilis 99.3%. The peeled copper has a very smooth shiny finish on one side and dull finish on theother side. The dull side is again subjected to further process to enhance roughness bychemical oxidation to improve Adhesion. Now, thin copper foils with the thickness of 5µm and9µm are available for manufacturing Multilayer and rigid PCBs. Copper foil thickness tolerances are given below, 1 ounce/ sq.ft. = 0.0014±0.0002 inches (OR) 28.33 gm. / sq.ft. = 35µm±5µm Note: Copper foil can be easily peeled off due to poor adhesion on the polished cylinder to poor adhesion on the polished cylinder. NTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page19

2.2 Properties of copper clad laminatesCopper clad laminates are prepared by pressing layers of filler materialImpregnated with resin under heat and pressure.The main ingredients are: •Filler •Resin •Copper foil 1. Filler These are continuous webs of materials such as paper, glass cloth etc. 2. Resins These are different types. 1. Amino resin 2. Epoxy resin 3. Polyester resin 4. Phenolic resin 5. Silicon resin 6. Telephone resin 7. Polyimide resin 3. Copper foil It is manufactures by the process of electro deposition. After different chemical action, we get the corrosion resistance metal surface of the foil. These are different thickness i.e., 17.5, 35, 70µm Properties of copper clad laminates are 1. Dielectric strength 2. Dielectric constant 3. Dissipation factor 4. Surface & Volume resistance 5. Foil to base bond strength 6. Flexural strength 7. Water absorption 8. Flatness 9. Flame resistance & appearance All electrical and mechanical properties are affected by environmental factors,such as humidity, temperature, corrosive atmosphere etc. 1. Electrical properties 2.Physical properties NTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page20

2.2.1 Electrical properties 1. Dielectric strength It is the ability of an insulating material to resist passage of electric current of a destructive discharge produced by an electric stress, and it depends on a large number of factors such as chemical composition, molecule structure, degree of moisture, voltage applied, thickness of material, ageing etc. 2. Dielectric Constant Dielectric constant is the ratio of capacitance of a capacitor with a given dielectric to the capacitance of the same capacitor with air as dielectric medium. The dielectric constant measured the ability of an insulating material to store electrostatic energy. It varies with temperature, humidity and frequency. 3. Dissipation Factor In an insulating material the dissipation factor is the ratio of total power loss in watts, in the material of the product of the voltage and current in a capacitor in which the material is a dielectric. It varies over a frequency range, moisture and temperature etc. 4. Insulating Resistance This is the ratio of voltage applied to the current flowing in the base laminate. Most test methods use a predetermined DC voltage of 500V. For practical use of this parameter, the measurements are carried out parallel to the surface of the base laminate as well as through the body of the base laminate. 5. Surface Resistance Surface resistivity is the resistance to leakage current along the surface of an insulating material. The surface resistivity depends on factors such as surface humidity, surface cleanliness, surface finish, presence of chemically active agent in the surrounding atmosphere and temperature. 6. Volume Resistivity Volume resistivity is the measured resistance to leakage current through the body of an insulation material 7. Water absorption Laminate absorbs moisture to some extent, when expose to high humidity condition. Thin laminate absorbs moisture adversely affect the ElectricNTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page21

properties. For 1.6mm thick laminate, the approximate water absorptionfigure are as follows:1. Paper Phenolic - 0.75-6%2. Glass Epoxy 0.25% 2.2.2 Physical properties 1. Flexural Strength This is a measure of the force per unit area, which a laminate strip with stand without fracture, when supported at ends and loaded in the center. The values differ in two directions e.g., parallel to the length of filler (length wise) and perpendicular to it (cross wise). The cross wise values are in most cases lower. 2. Water Absorption The amount of water absorbed by a sample of specified size immersed in distilled water for a specified period ( Generally 24 hours) at a specified temperature (e.g., 20 to 25°c), is reported as water absorption in milligrams. The gain in weight can also be expressed as the percentage of increase over the initial weight. 3.Thickness The extent of manufacturing thickness variation and its control within limits is of particular significance when the PCBs are used with edge connector. 4.Warp and Twist Warp or bow is the Warp age along the edge of a sheet and twist is the warp age along the diagonal. Excessive warp age or twist presents problems at various stages of PCB making and assembly. Copper clad laminates are composites of two dissimilar materials such as copper foil and synthetic resin-bonded base laminate with widely different thermal expansion or contraction characteristics as well as moisture resistance. 5. Flame Resistance The electronics industry is becoming concerned with the problem of inflammability of materials used in the equipment. There is a great need to make laminates more flame resistant. When a laminate is in contact with a flame or a spark, it gets hot enough to cause a breakdown of the polymer structure. This develops voids. The rapid oxidation of these free radicalsNTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page22

produces flames. The reaction produce heat, which further degrades the laminate and thus keeps the cycle going on and the laminate burning. 6. Punchability Among all the mechanical properties required for processing of copper clad laminates to printed circuit boards, the most desirable may be punchability at room temperature, punching is the simplest and quickest method of producing complex shapes from the laminate sheets. Good punchability means no cracking, no lifting around the punched holes, smooth edges and smoothness inside holes, combine with a low shrinkage during and after punching especially when laminates are punched at elevated temperature. 2.3 Types of laminates 1. Paper Phenolic Phenolic resin consists of a solution of reaction product of phenol and formaldehyde in a solvent. Phenolic resins are reinforced with paper fillers for copper clad laminates. They are stable enough under a variety of conditions to suit a majority of applications. They definitely have an edge over other types of laminates as regards punchability and the ease of fabrication. Since the phenolic resins are light or dark brown color, the use of a bleached variety of paper is necessary wherever some translucency is desired. Paper phenolic copper clad laminates are attacked by strong alkalis and acids have only a slight or no effect on them, depending on their concentration. 2. Epoxy Laminates Epoxy resin became commercially popular in the 1950s. They are an important rapidly growing class of resins. Generally, Epichlorohydrin and a bivalent phenol are reacted to give the base resin. This again is reacted with suitable hardeners and accelerators to give a cross linked product. None of the other resin has such a good combination of desirable attributes as available with epoxies. Advantages •Low shrinkage •Toughness •High mechanical strengthNTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page23

•Chemical resistance (Acid, Alkali & Solvent) •Water resistance (low water absorption) Commonly used varieties of epoxy laminates as listed in NEMA (National Electrical Manufacturers Association) standards are, FR-3 - Paper Epoxy (Fire Resistance) FR-4 - Glass Epoxy (Fire Resistance) FR-5 - Glass Epoxy (Fire & Temp. Resistance) G-10 - General purpose Glass Epoxy G-11 -Glass Epoxy (Temp. Resistance) 3. Polyester Laminates Polyesters are solutions of unsaturated polyesters resins in co-polymerisable monomers such as styrene, etc. they are exclusively used with glass fiber reinforcement. The resins themselves possess good arc and track resistance, which can be further enhanced by addition of fillers and additives. Their dimensional stability and water resistance are also good. They are not in extensive use in electronics since epoxies can often supply better dielectric properties. Commercially available polyester glass laminates are claimed to comply with FR-6 grade of NEMA. 4. PTFE Laminates Poly Tetra Fluro Ethylene is a thermoplastic, which when reinforced with glass, results in a laminate which has a low dielectric constant and a low dissipation factor under a wide temperature, humidity and frequency range. The Dielectric strength is very high; PTFE laminates are therefore an excellent electrical insulation under severe environmental conditions. PTFE laminates often used for very high frequency and microwave applications but also where high insulation resistance under humid conditions has to be maintained (e.g., input stages for high impedance/low current measuring instruments and amplifiers). However the high costs for PTFE laminates ruled out their widespread use. 4. Silicon Laminates A small portion of copper clad laminates are made of silicon resins with Glass reinforcements. Silicon resins contain silicon, carbon, oxygen and hydrogen and are outstanding in their heat resistance. The glass based laminates haveNTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page24

excellent arc resistance as well as good electrical properties up to 250°C for an extended period and at higher temperature for short periods of time .The silicones are relatively stable under heat. But they do not posses outstanding characteristics of strength at any temperature. Mechanical properties of a laminate containing silicone laminates are not superior compared to the phenolic s and epoxies. It is also difficult to obtain a good copper foil-to-base material bond in the silicone resin system. 5. Melamine Laminates Melamine resins can be combined with a variety of reinforcing fillers but best properties result when glass fabric is used. The most significant property offered by these laminates is a high arc resistance. GM-Glass Melamine variety A major disadvantage of Melamine Glass Laminate is the poor dimensional stability particularly when exposed to alternating cycles of high and low Humidity. It is also difficult to obtain higher mechanical strengths with Melamine resin system. 6. Polyimide Laminates Polyimide is one of the most heat resistant polymers. Reinforced with woven glass fabric, the laminates find use in demanding military and aerospace applications and in special multi-layer circuits. These laminates retain higher copper bond strength at soldering temperatures than the general purpose Epoxy materials.NTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page25

UNIT 3 LAYOUT - GENERAL RULES & PARAMETERS 3.1 Layout general rules & parameters LAYOUT DEFINITION: Layout design is the sketch of outline of components and copper conductor routings, which are interconnected the respective components within the specified area of PCB. 3.2 History and Basics of PCB’s In USA, PCB is call it as “PWB” expansion of PWB is “Printed Wiring Board” Definition of PCB The PCB or PWB provided both the physical structure for mounting & holding electronics components as well as the electrical inter connection between components. A PCB consists of non-conducting substrate (typically fiber glass with epoxy resin) upon which a conductive pattern or circuitry is formed. TOP LEVEL METAL OF THE PCB: Copper is the most prevalent conductor, although, Nickel, silver, tin, tin leads and gold may also used as etch resists or top level metal. 3.3 Board types PCB is invented by Mr. PAUL EISLER in 1937.Only the two most popular PCB types are mentioned here. •Single sided PCB •Double sided PCB •Multi-layer PCBNTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page26

Single sided boards The single sided PCB‟s are mostly used in entertainment electronics where manufacturing costs have to be kept at a minimum. However in industrial electronics also cost factor cannot be neglected and single sided boards should be used wherever a particular circuit can be accommodated on such boards. To jump over conductors tracks, Components have to be utilized. If this case is not feasible, jumper wires can be used. However it is restricted by economic reasons. If this number is more than a few, the use of double sided PCB should be considered. Double sided boards Double sided boards can be made with or without plated through holes. The production of boards with plated through holes is fairly expensive. Therefore plated through holes board are only chosen where the circuit complexity and doesn‟t leave any other choice even such boards the total number of plated through holes in particular of via holes (holes utilized only for through contact and not for component mounting) should be kept to the minimum for the resource of economy and reliability. The cost factors for double sided PCB‟s without plated through holes are considerably lower because plating can be avoided. Through contacts are made by soldering the component leads on both the board side, where required jumped wires may still be added however hand soldering must be applied for soldering of the component side joints. In the layout design ofNTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page27

such boards solder joints on the component sides have to be kept minimum in numbers, because the replacing of such components is extremely difficult. A typical strategy is therefore to realize the conductors as much as possible on the non-component side and to put only the remaining ones on the component side. Such boards are therefore a compromise between serviceability and electrical design optimum on the one hand and the cost factor on the other. 3.4 Single sided PCB layout design requirements All components must be represented pictorially There can be no cross over  Keep point to point conductor runs or straight as short as possible. When unable to use straight lines for conductor runs use 45o bendsNTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page28

• Polarity marks on the layout should be drawn for power terminal, diodes, polarized capacitor • Place all resistors‟ diodes etc… parallel with each other.NTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page29

• Mount resistors capacitors & diode as close together as possible, but enough space should be allowed between components for their servicing & removed The space between conductor paths depends on peak voltage potential across circuit.Components • Multi axis component placement is not accepted.NTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page30

• If the layout consists mainly of IC’s place all IC’s parallel to each other & group them at or near the center of the PCB. • Place or group the transistors & SCR’s in rows & columns Reduce the use of Jumpers to minimumNTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page31

3.5 Reference DesignationsA Assembly PS Power SupplyAT Attenuator isolator Q Transistor, SCRB Fan, Motor R ResistorBT Battery RT ThermistorC Capacitor S SwitchCP Coupler T TransformerCR Diode, Thyristor TB Terminal BoardDC Directional coupler TC Thermo CoupleDL Delay line TP Test PointAmmuncator, Signaling deviceDS (Audible or visual) Lamp : LED U Integrated micro CKTE Miscellaneous Electrical Part V Electron TubeF Fuse VR Voltage RegulatorFL Filter W Cable transmissionG Generator X SocketH Hardware Y Crystal Unit (Piezo Electric or Quarter)J Electrical Connector (Stationery Portion) jack Z Tuned circuitHY Circular Ground SymbolsK RelayL Coil, Inductor EarthLS MeterMG Motor-GeneratorMK Microphone CommonMP Miscellaneous Mech. partsP Electrical Connector (Movable portion) plug ChassisNTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page32

3.6 Conductor Routing Practices3.7 General Rules For PCB Design NTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page33

3.8 Double Sided PCB Design Requirement Double sided copper boards are used when a large no. of components are to be mounted on one printed circuit board. The conductor paths are distributed on both sides of the board and are interconnected by component mounting holes that go through the board (non PTH) and in PTH the conductor paths are interconnected through holes. This is done to avoid cross-over and to reduce the overall size of the PWB package. Because there will be conductor paths on both sides of the PWB. 3.9 Wave Soldering The figure illustrates wave soldering. Component leads are soldered to a printed circuit board by travelling at a predetermined rate of speed through a wave of molten solder. Wave soldering is the most widely used method for soldering components to printed circuit boards. 1) There are cost savings because : 2) Hand soldering is more work. Than wave soldering 3) There is reduced inspection time because of knowledge that every joint is soldered under identical conditions. 4) There is reduced scrap which would result from burning boards with soldering iron. 5) There is the reduced possibility of vapor or flux entrapment. 6) The actual soldering tome per solder joint is extremely short because of the excellent heat transfer conditions, the fast circulation of solder and the pre-heating of the board, as it travels through the solder across the solder wave surface.NTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page34

3.10 Reflow Soldering Screen Printing: In reflow soldering, primarily used for SMO components, solder paste is forced through a metal stencil by either a metallic or polymeric squeeze. The paste contains both solder & flux.NTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page35

Pick and place: After screen printing the boards then proceed to the pick & place machines were they are placed on a conveyor belt. Most SMDs are usually delivered to the production line in either paper or plastic tubes. Some large integrated circuits are delivered in static free trays. Numerical control pick and place machines remove the part from the tapes, tubes or trays and place them on the PCB. Reflow soldering: The boards are then conveyed into the reflow soldering oven. They first enter a pre-heat zone, where the temperature of the board & all the components is gradually, uniformly raised. The boards then enter a zone where the temperature is high enough to melt the solder. 3.11 SMT technology SMT FOR SIMPLER AUTOMATED ASSEMBLY Surface mounting lends itself well to a high degree of automation reducing labour cost and greatly increasing production rates for manufacturers. Look inside any electronic equipment and you‟ll find multiple minute devices. In contrast to the traditional components used for home-brewed kits, these components are mounted onto the surface of the boards. This technology is known as „surface-mount technology‟ (SMT) and the components as „surface mount devices‟ (SMDs).Virtually all of today‟s equipment manufactured commercially use SMT because it offers significant advantages during manufacture, and the use of SMT components enables far more electronics to be packed into a much smaller space.NTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page36

WHY IS SMT PREFERRED? Electronic components can be divided into two categories: Through- hole(TH) and surface-mount(SM). Through-hole components have been used for many years and are designed to be loaded on one side of a printed circuit board (PCB) and soldered on the other. Surface-mount components are loaded and soldered on the same side of the PCB. SMT is preferred by electronics manufactures because if offers several important benefits over through-hole technology: Advantages of SMD 1. It‟s faster for automatic machines to place 2. Has a smaller physical size for the same electrical function. 3. Less parasitic (unwanted) effects. 4. Parts are cheaper. Disadvantages of SMD: 1- Manual prototype assembly or component-level repair is more difficult 2-SMDs cannot be used directly with breadboards 3-SMDs' solder connections may be damaged by potting compounds going through thermal cycling. 4- SMT is unsuitable for large, high-power, or high-voltage parts, for example in power circuitry. 5-SMT is unsuitable as the sole attachment method for components that are subject to frequent mechanical stress SMT COMPONENTS SMT devices (components), or SMDs, are different from their leaded counter parts. Rather than being designed to wire between two points, these are set down on a board and soldered to it. Their leads do not go through holes in the board, as might to be expected for a traditional leaded component. There are different types of packages for different types of components. Broadly, the package styles can be categorized into passive components, transistors and diodes, and integrated circuit. Passive SMT components: These include mainly the RESISTORS and CAPACITORS, which form the bulk of the numbers of components used. The packages for surface mount resistors and capacitors are well standardized. These are rectangular in shape, having metallized contacts at both ends. To provide some degree of uniformity, sizes of most SMT components conform to industry standards, many of which are JEDEC specifications. Obviously, different SMT packagesNTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page37

are used for different types of components, but the fact that there are standards enables activities like PCB design to be simplified. Additionally, the use of standard-size packages simplifies the manufacture because pick-and –place machines can use standard feed for the SMT components, considerably simplifying the manufacturing process and saving costs. SMT packages can be categorized by the types of component, and there are standard packages for each. Several different sizes have been reduced as technology has enabled smaller components to be manufactured and used: 1812 : 4.6mm x 3.0mm (0.18” x 0.12”) 1206 : 3.0mm x 1.5mm (0.12” x 0.06”) 0805 : 2.0mm x 1.3mm (0.08” x 0.05”) 0603 : 1.5mm x 0.8mm (0.06” x 0.03”) 0402 : 1.0mm x 0.5mm (0.04” x 0.02”) 0201 : 0.6mm x 0.3mm (0.02” x 0.01”) RESISTORS TRANSISTORS AND DIODES Diodes and transistors generally use a package are „small outline transistors‟ (SOT). One of the most popular packages is the SOT 23. This package as 3 leads, one on one side and two on the opposite side. The leads from the side of the package are bent in a ‟gull wing‟ shape. This enables them to make contact with the board. Even though diodes have only two connections, these still use the same package. Having two leads on one side and one on the other enables the connections to be differentiated more easily. The SOT23 package can be used only for low-power applications. When high powers are needed, another package designated „SOT223‟, may be used. Thus there is a wide variety of other SOT packages to accommodateNTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page38

different requirements. TRANSISTOR SOT23. This SMT package has three terminals for a diode or a transistor. It can have more pins when it is used for a small integrated circuits such as operational amplifiers. It is 3 x 1.75 x 1.3mm3 in size SOT223. This package is used for higher-power devices. It measures 6.7 x 3.7 x 1.8mm3. There are generally four terminals, one of which is a large heat transfer pad. INTEGRATED CIRCUIT PACKAGES ICs some in following standardized packages: SOIC (small out-line integrated circuits): this package has a dual-in -line configuration and gull-wing leads with a pin spacing of 1.27mm. TSOP (thin small outline package): this package is thinner than the SOIC and has a smaller pin spacing of 0.5mm. SSOP (shrink small outline package): it has a pin spacing of 0.635mm. TSSOP (thin shrink small out-line package): it has a pin spacing of 0.65mm. PLCC (plastic leaded chip carrier): this type of package is square and uses J-lead pins with a spacing of 1.27mm. VSOP (very small outline package): it is a smaller than the QSOP and has pin spacing of 0.4, 0.5 or 0.65mm. LQFP (low-profile quad flat pack): it has a pin on all four sides. Pin spacing varies according to the IC, but the height is 1.4mm. PQFP (plastic quad flat pack): a square plastic package with equal number of gull-wing-style pins on each side: typically narrow spacing and 44 or more pins. Normally used for VLSI circuits. CQFP (ceramic quad flat pack): a ceramic version of the PQFP. TQFP (thin quad flat pack): a thin version of the PQFP. BGA (Ball-Grid Array): a package that uses pads underneath the printed circuit board. Before soldering, the pads appear as solder ball, giving rise to the name. By placing the pads underneath the package there is more room for them, thereby overcoming some of the problems of the very thin leads required for the quad flat packs. The ball spacing on BGAs is typically 1.2mm.NTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page39

UNIT 4 LAYOUT PLANNING 4.1 Generation of design Before starting your layout design, designer should collect the following information from customer Circuit diagram (schematic diagram) Size & Type (S/S,D/S or MLB) Component specification (mechanical size, values codes. etc.) Equipment specification (ventilation, view place for fixing PCB). LAYOUT DESIGN Transition of circuit diagram into the layout design (Task of the designer) Definition Layout design is the sketch of outline of components and copper conductor routings, which are interconnected the respective components within the specified area of PCB. PCB DESIGN In PCB design there are 3 stages • Circuit design (available from customers) • Layout design (layout sketch) • Art work design (output) DIMENSIONS In the United States of America, dimensions for PCB tracks are usually quoted in units of 0.001 in often called „mil‟ and sometimes called THOU. In other countries working in inches, the same unit is normally called „THOU‟ countries working in metric units normally base dimensional specification on micrometers, sometimes called microns;. The unit is 0.000001 meter [ 1/1000 of a millimeter] and may be symbolized variously as u, µ, um or µm. One „mil‟ is equal to approximately 25.4µm TRANSLATING CIRCUIT DIAGRAM INTO LAYOUT • Read and understand the circuit diagram • Make a component list • Find out the IC equivalent and decide the type of board which you are going to do. • Examples: Single sided PWB or double sided PCB etc… • Decide the size of PCBNTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page40

• Take a graph sheet and make a component layout is considering the physical dimensions make a sketch. • Place the pads on the intersection of grid their pads depend on the size & pitch of the components to be mounted. • After placing pads draw the lines where you want to make inter connections. Take care of the size of the conductor thickness while drawing it. • If it is the double sided PCB it has component side and solder use red/blue pencils to draw the conductor. • “RED may be treated as component side and blue as solder side‟ • After making the layout check the layout against the original schematic for circuit continuity and completeness Conductor width • They are based on two factors , • 1.Current carrying capacity • 2.Characteristic of impedance of power interconnecting lines • General Example: If the Power conductor width is 1.0mm, the conductor width for signal is 0.5mm & the ground conductor width is 2.0mm • Example based of current. • Current carrying capacity of 1mm width, 35µm copper thick can carry maximum 3 Amps. For passing 3 Amps: 1. Thickness & Width: 17.5µm & 2.0mm 2. Thickness & width: 70µm & 0.5mm. Standard thickness of copper foil is 17.5µm, 35µm & 70µm. Hybrid or micro circuit copper foil thick is 0.1µm. ultra-thin copper foil thickness is 5-10µm 4.2 Basic law Wgnd line > W supply line > W signal line Wgnd line ≥ 2W supply line W supply line ≥ 2 W signal line a) Current carrying capacity = 1mm = 3Amps ; 35µm thick Cu foilNTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page41

(b)Resistance of 1mm = 35µm Cu Foil ; = 5mΩ/cm length 4.3 Via hole The interconnection between component side & solder side is called as Via hole. It is used in Double sided and Multi layer pcb‟s. 4.4 Annular ring Annular ring is the area around the diameter of hole. It gives electrical connection and mechanical support to the componentNTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page42

CONDUCTOR LENGTH It is based on the voltage drop (resistance) requirements . Ex: Resistance of 1mm WIDTH & 35µm thickness of a copper conductor is 5milli ohm/cm length. (For low current) 4.5 Schematic diagram reference designators Each component is identified by an Alpha numeric reference designator such as: C1, R1,Q1 etc. (C for capacitor, R for resistor, and Q for transistor etc) The number shows the difference between electrical components of the same type (C1, C2, C3 etc.) .The use of reference designators provides an easily recognizable identification for every component part on the schematic. Border Line (size): Border line can be added in mechanical layers and they can be viewed in any layer to provide drill and cut out guides during the manufacturing process. Mounting holes To fix the PCB‟s with the equipment using screws & pins. Every “4‟ we should give mechanical support.NTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page43

HIGH SPEED DESIGN Round the corners to minimize reflections. When a PCB trace turns a corner at a 90o angle a reflection can occur. This is primarily due to the change of width of the trace. At the apex of the turn, the trace width is increased to 1.414times its normal width. This upsets the transmission line characteristic, especially the distributed capacitance and self-inductance of the trace-resulting in the reflection. 4.6 How to design a PCB without the spikes; where to run supply and ground lines on the PCB STIFF Ground means a wider ground conductor back with very low ground resistance which enhances ground capacitor. Impedance: The total opposition offered by a circuit.NTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page44

Single sided PCB Can be applied only a limited cases as cross over of signal lines have to be avoided. Double sided PCB Running Vcc & Gnd lines exactly symmetric on the opposite sides of PCB keeps Zo low between Vcc. UNUSED PCB AREA CAN BE LEFT UNETCHED AND CONNECTED TO GROUNDNTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page45

4.7 Micro via Micro via is used as the interconnects between layers in High Density Interconnect ... Sequential build-up (SBU) technology is used to fabricate HDI boards. 4.8 decoupling capacitor A capacitor which provides a low impedance path to ground for AC and to prevent common coupling between the stages of a circuit. Impedance: The total opposition offered by the circuit.When switching, the noise would be removed from the voltage lines and terminated to the ground line through the aid of the decoupling capacitor. For Fast pulse circuit and high frequency circuits provide one decoupling capacitor (5-50nf) between power supply and ground line . So that fast current spikes can be supplied by this capacitor and do not need to be drawn from the power supply. Can be applied only a limited cases as cross over of signal lines have to be avoided.NTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page46

4.9 Transmission line The PCB techniques can be used to create the special microwave transmission line called Micro strip and strip line. MICRO STRIP: Micro strip is a flat conductor separated from large conducting ground plane by an insulating di-electric as shown in figure STRIP LINE : Strip line is a flat conductor sandwiched between two ground planes 4.10 Skin effect The skin effect is the result of self-inductive effects that force high frequency currents to the surface of a conductor. As the frequency of the signal increases. The thickness of the conducting “Skin” decreases and the DC resistance increases. In the GHZ frequency range, power losses due to the skin effect are important and wide traces are required.NTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page47

4.11 Solder Mask The circuit board are protected from the atmospheric corrosion and he solder bath contamination is prevented by solder resist coating. The coated boards are protected from solder bridge, excess solder uptake, atmospheric corrosion and surface contamination. The solder resistant (liquid resist or dry film resist) coated on the circuit boards after etching by screen printing techniques and photo printing techniques. 4.12 Legend printing or silkscreen The silkscreen layer is also known as “TOP OVER lay”. It is the layer on the top of the PCB (and bottom if needed) that contains component outlines and designators (R1,C1. Etc) and free text which helps in assembly of PCB. The legend can be added to a PCB using a screen printing techniques. White is a standard color Keep all your component designators the same text size and oriented in the same directions. Ensure that all polarized components are marked and that pin 1 is identified 4.13 Grid system A grid is a two dimensional rectangular pattern when reproduced on paper or vinyl glass that can be used as a guide for layout drawing. The designer place the grid under the layout drawing and uses it as a guide for accurate placement or components conductor and pads. Precision grids on glass or polyester films are used in industrial applications. Less accuracy grids are printed on paper and generally used for experiments.NTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page48

4.14 General rules for PCB design for double sided PCB Conductor routing practices In double sided PTH board run the conductor on one side in the y co- ordinate direction. In solder side the conductor density will be more than component side. Distribute max no. of conductors on the solder side and rest of the conductors in the component side. In both sides of the conductors are in same axis, it acts as a dielectric material as a capacitor. Due to soldering, IC‟s like hear sensitive components can be destroyed easily so IC bases are provided. During assembling. It Is very easy to keep and while disordering there is no need of disturbing the base. The sharp internal bending of the conductors should be more than 90o Conductor forming sharp internal angles of 90o must be avoided. If the bending is less than 90o they will act as an electrical spikes.If the angle is less than 90o some chemicals, which are deposited may not get removed while cleaning. So the conductors may get corroded easily. Minimum spacing between the parallel conductors: It is based on the cross talk It is based on the breakdown voltage Cross talk : If complication in PCB design, then there is the problem of signal isolation or cross talk. The need for high lead to finer conductor lines and closer spacing, with the closeness of the conductors and higher signal speeds, the couplings of signals into adjacent conductor lines becomes greater and introduces noise and false signals in to system. The min. spacing between two parallel conductors is 0.5mm.The min spacing between two solder pad is 0.4mm.NTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page49

4.15 Component Placement, Ground Plan 1) Line spacing based on Break down voltage. Less than 45v - 0.3mm 445-80V -0.4mm 80-150v - 0.6mm 150-250v - 1.0mm For AC mains < 250v. - 3mm2) Components placementIn a highly sensitive circuit, the critical components are first placed and alsoin such a manner as to require min. length for the critical conductors. In aless critical circuit distribute the components as per the order of signal flowso as to require the shortest interconnecting length. In some circuits thecomponents are having large no of connecting points. Examples : In LSI circuit these key components should place first ant other components should be grouped around them with respect to the relevant side of the IC‟s. So that the length of the conductors are required less and we will get more space and also easy to route the conductors.3) Components hole diameterIn the PCB any component lead should be fitted only into the hole of aappropriate diameter. Satisfactory soldering results are usually obtained, ifthe diameter of the finalized and plated holes gives about 0.2mm to 0.5mmclearance as compared with the nominal diameter of the component lead.Total Clearance - 0.2 to 0.5mmHole dia = Effective lead dia Total clearance (+) PTH thicknessExample:1) For 0.7mm lead dia0.7mm to 0.2mm to 0.5mm +0.1mm= 1.0mm to 1.3mm2) For 1.4mm lead dia1.4mm to 0.2mm to 0.5mm + 0.1mm= 1.7mm to 2.0mm.NTTF_DIPLOMA IN ELECTRONICS_SEM3_PCB DESIGN AND FABRICATION_REV7_JUNE 2017 Page50