Building Custom PCBs A PCB is a Printed
Building Custom PCBs
A PCB is a Printed Circuit Board • Early circuits were “Point-to-Point” • Then “Wire Wrapped” • Now PCB – Largely thanks to low cost, high-resolution printing 2
The Board is a Sandwich • Base material (substrate) – Usually fiberglass. (“FR 4”) – Rigidity and thickness – Flexible (e. g. Kapton) • Many different thickness – 1. 6 mm (0. 063") – Most Common – 0. 8 mm like Lily. Pad and Arudino Pro Micro • Cheaper PCBs and perf boards – Epoxies: melt – Phenolics: delaminate, smoke and char when the soldering iron is held too long on the board. – You will know when you solder to it - bad smell 3
The Copper Layer Will Become the Wires • Bonded to the substrate • 1 or 2 sided or more (16+ in layers) – Two-sided is the practical limit for hobby circuits • Different thicknesses available – Specified by ounces per square foot – One ounce per square foot: • about 35 micrometers or 1. 4 thousandths of an inch thick – Most boards have 1 ounce of copper square foot – Some that handle very high power may have 2 or 3 Oz/ft 2 • This is important in predicting when the etching solution is used up! 4
The Soldermask Protects the Circuit • On top of the copper foil is the soldermask • Gives the PCB its green color – Any color really … • Insulate and protects the copper traces and prevent solder jumpers • That is another presentation 5
Silkscreening Adds Labels • Applied on top of the soldermask • Most commonly white but any ink color can be used • I don’t do this … 6
Surface Mount or Through-Hole 7
Motion Sensors on Robot • 4 PIR (Motion) Sensors – HC-SR 505 Mini PIR Motion Sensor – $1. 44 on Ebay (From China) • Technical parameters: – – – DC 4. 5 -20 V <60 u. A Output: High 3. 3 V / Low 0 V Dimensions: 10 mm * 23 mm Angle: <100 degree cone Induction distance: 3 meters Pin 1: V+ Pin 2: Signal Pin 3: Ground 8
Two Options Considered Connect all sensors individually • • 4 Input Pins More wires More Code Easy to expand Cluster the Sensors • • • I 2 C Bus Modular Harder to expand Must build custom PCB Must program the PIC too I 2 C 9
Use the PIC 12 F 1840 & I 2 C Stuff We’ll Use Stuff we won’t • • Purchased from Microchip – http: //www. microchip. com – About $1. 25 each (+ Shipping) • • 31 k. Hz - 32 MHz 125 n. S per instruction @32 MHz 49 Assembly Instruction “C” or Assembly Programmable Operating Voltage: 1. 8 V – 5. 5 V 5 I/O Pins; 1 Input-Only Pin Flash Program Memory with self read/write capability MI 2 C, SPI, EUSART w/auto baud • Comparator with selectable Voltage Reference 4 Channel 10 b ADC with Voltage Reference • • 25 m. A Source/Sink current I/O Two 8 -bit Timers (TMR 0/TMR 2) • One 16 -bit Timer (TMR 1) • • Extended Watchdog Timer (EWDT) Enhanced Power-On/Off-Reset Brown-Out Reset (BOR) In Circuit Serial Programming (ICSP) On Board In-Circuit Debug • Capacitive Sensing Module • • Data Signal Modulator Module Enhanced/Capture Compare PWM (ECCP) • 10
Easy. EDA Schematic https: //easyeda. com • Not the “Best” • Easy • Well supported • Gets the job done • There a lot of other options • Choose the one that suits you the best 11
Get Started … • Demo Easy. EDA 12
Make Registration Marks on Board 1. Make a copy on plain paper 2. Drill mounting holes in board 3. Makes it easier to align stencils top/bottom 13
Cut Out the Board • Leave some room around the edges 14
Remove all Burrs • Iron must rest tight against the board 15
Supplies • Etching Solution – Ferric Chloride • • Etches about 25 in 2 of 1 oz. board per oz. of solution ~$17 for 33 oz. – Copper Chloride in Aqueous Hydrochloric Acid Solution • • • Unlimited use ~$10 http: //www. instructables. com/id/Stopusing-Ferric-Chloride-etchant!--A-betteretc/ – Ammonium Persulfate • ~$8 for 4 oz. dry makes 12 oz. liquid (3: 1 mix) • • • • Copper Clad Board Tape Acetone (Optional) Steel Wool (00 & 000) Soap & Water Isopropyl Alcohol (or water) Clothes Iron (or modified laminator) Water (Distilled optional) Laser Jet Printer or Copy Machine Containers (NO METAL! – Plastic or Glass ONLY!) News Paper Gloves Eye Protection Permanent Marker 16
Print the Stencils • Commercial Product – Print on the dull side • Use Photo Paper – Print on the glossy side • Use a Laser Printer or Photo Copier – NO INK JETS! 17
Transfer Stencil to the Board • Clean with Steel Wool (00 & 000) • Clean with Soap & Water • Rinse with any of these: – Isopropyl Alcohol – Acetone – Water • Tape down the stencils – Align with drilled holes • Iron – – – NO STEAM! Temperature is CRITICAL 275 -325 Deg F (acrylic-polyester) Board should reach same temperature 1. 5 – 4 minutes • Quench the board/film in water 18
Peel Off the Film • For the Blue Film – Gently peel back the film – Blue should stick to circuit – Remove any small “fills” using tape • For Printer Paper – Soak in water until the backing is saturated – Rub the paper away 19
Finish Prep the Board • Trim the board to final size (if necessary) • Wash with Soap & Water (No Solvents!) • Touch up any missing parts – Permanent Marker 20
Etch the Board • Cover the area with • Warm the Solution – 125 Deg F • Put the board in the solution • Agitate constantly – There are machines to do this for you • Check in 5 -6 minutes (warm) or 30 minutes (cold) 21
Finish Up • Scrub with Steel Wool – Under Running Water – Remove the stencil • Silver the board – – – Put the Silvering Solution in a plastic container Put the board in the solution Silvering should be done in 5 -10 seconds Remove the board & Rinse Put the silver back into the bottle • Drill Holes • Apply the Solder Mask – For another day if you are interested … • Stuff & Solder 22
The Practical Side • Find a CAD package – Things to consider: • Community support: are there a lot of people using the package? • Ease-of-use • Capability: limitations on your design – – – number of layers number of components size of board etc. Portability: can you export or convert your designs? • Practice, practice. • Maintain low expectations – Your first board will have problems – Your 20 th board will have fewer • Schematics are important 23
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