Electronics Manufacturing Processes Manufacture of Electronics Components Manufacture of Printed Circuit Boards (PCB’s) Assembly of components on PCB’s

Electronics Manufacturing Processes Manufacture of Electronics Components Manufacture of Printed Circuit Boards (PCB’s) Assembly of components on PCB’s

Electronics Component Manufacture Electronics Components Mechanical and Electro-mechanical: PCB mounted DIP switches, mains switches, disc drives Passive Solid State Devices: Resistors, Capacitors Active Solid State Devices: Transistors, Diodes, Thermionic valves, FETs and MOSFETs

Passive devices: resistors Carbon Composite Resistor Slug  leads  mold  bake  seal - cheap, poor tolerance, rugged Wire-wound resistor wind wire  leads  mold  seal - high power, low resistance, high frequency apps Film resistor Film is cut by laser  high precision - low frequency applications

Passive devices: capacitors Tabbed tubular paper capacitor Disk-ceramic capacitor Tubular ceramic capacitors

Active devices: Silicon wafer production Quartzite (SiO2) + Carbon (C) + Heat + catalysts  Si + CO2 Raw Si: Si + HCl  SiCl4 + Hydrogen  Fractional distillation  SiCl4 + H2 + catalysts  Si + HCl Pure Si: Pure Monocrystalline Si: Melt pure Si, Seed crystal drawn out slowly Typical Single Crystal Ingot sizes: 1-2m long, 8cm / 15cm / 30 cm diameter  Ingot sliced (Diamond saw)

Active Devices: Doping pure silicon Doping processes: Diffusion (heat wafer in atmosphere with atoms of dopant) Ion implantation (ions of dopant are accelerated, bombard surface) Diode (showing doping)

Active components: Transistors NPN transistor MOSFET Metal-Oxide Silicon Field Effect Transistor

Active components: Integrated Circuits Monolithic IC: Entire circuit made on a single crystal wafer Hybrid IC: Monolithic IC + other components directly assembled into it Hybrid micro-circuit film components

Active components: IC’s.. Depositing films of materials on substrate to make circuits Thin Film Processes: Form components on circuits by vacuum evaporation, sputtering, or anodization Film thickness is ≤ 5 mm Thick Film Processes (silk-screening) Print liquid or paste through a screen (mask) onto substrate  firing (baking) Film thickness is ~ 10 mm Silk-screening

IC’s: Resistive elements deposition vacuum deposition Subtractive process Additive process

Diffused Junction Process - Photolithography is the most commonly used process - Photoresists: positive: more soluble when exposed negative: less soluble when exposed - Feature size = f(wavelength)  small features need low l radiation - Mask = = Artwork - Projection: - Direct: mask scale is 1:1 - Reducing: mask scale is 10:1

Packaging of components - Packaging puts the chip (silicon) into a protective case - Package provides external connections that are spaced conveniently (at distance, arranged in array) for soldering Exploded view of TO package

Packaging of components Structure of a Surface mount component SOIC package Small Outline IC Avoiding possible heat damage to IC during soldering: - Solder a chip carrier to the PCB - Insert chip into carrier

Integrated Circuit (IC) Manufacture - Slicing the Silicon ingot - Fabrication of IC’s (Lithography, Sputtering, diffused junction, …) - Testing each IC on the slice - Dicing (cutting each chip out with a diamond saw) - Packaging

Packaging - Make leadframe - Die attachment (chip bonded to leadframe using epoxy) - Wire bonding (ultrasonic welding) - Encapsulation (moisture resistant coating) - Molding (plastic package) - Marking (chip number, co. name, marked on package [laser, silkscreen]) - DTFS: deflash, trim the leadframe, form the leads, singulate (cut dambars) - Leadfinishing: electroplating the leads

Electronics Manufacturing Processes Manufacture of Electronics Components Manufacture of Printed Circuit Boards (PCB’s) Assembly of components on PCB’s

PCB Manufacture Types of PCB's single-side, double-side and multi-layer Which type to use ? (a) Circuit complexity (b) Available space (c) Cost

Manufacturing glass reinforced epoxy resin copper-clad boards Boards are produced in "clean-rooms" Manufacturing process: hot-pressing • Place copper sheet on the lower plate • Place few layers of glass cloth impregnated with epoxy on top • [IF two-sided PCB's]: Place copper sheet on above • Press between steel plates in a steam-heated hydraulic press (~7,000,000 Pa) • Water cooling to 25º C • Trim to clean out extruded epoxy • Punch/Drill holes for alignment • Make circuit on PCB (lithography) • Drill through holes (for component leads)

Multi-layer PCBs • Similar process as single layer, but takes several steps Schematics and features on Multi-layer PCB’s

Electronics Manufacturing Processes Manufacture of Electronics Components Manufacture of Printed Circuit Boards (PCB’s) Assembly of components on PCB’s

PCB Assembly - Insert leaded component into holes on PCB - Solder - Protective coating Manual electronics assembly Automated electronics assembly

Automated PCB Assembly Component inputs: Leaded Component IC’s, components with no wire leads

PCB Manufacture Surface mount chip assembly: - Silk-screening to apply solder paste on the board - Automated assembly of components (>30,000 components per hour) - IR or Wave soldering

Automatic soldering Step 1. Application of the solder resist Cover PCB with solder resist except Lands Step 2. Flux application Foam fluxing Spray fluxing Ultrasonic Spray fluxing

Automatic soldering.. Step 3. Solder Application Dual wave solder bath

Automatic soldering.. Step 4. Automatic removal of solder bridges: Hot air-jet knives

Types of circuit boards

Special considerations for SMT boards