Download Building Custom PCBs

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
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The Board is a Sandwich
• Base material (substrate)
– Usually fiberglass. (“FR4”)
– Rigidity and thickness
– Flexible (e.g. Kapton)
• Many different thickness
– 1.6mm (0.063") – Most Common
– 0.8mm like LilyPad 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
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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 per square foot
– Some that handle very high power may have 2 or 3
Oz/ft2
• This is important in predicting when the etching
solution is used up!
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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
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Silkscreening Adds Labels
• Applied on top of the soldermask
• Most commonly white but any ink color
can be used
• I don’t do this …
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Surface Mount or Through-Hole
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Motion Sensors on Robot
• 4 PIR (Motion) Sensors
– HC-SR505 Mini PIR Motion
Sensor
– $1.44 on Ebay (From China)
• Technical parameters:
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DC4.5-20V
<60uA
Output: High 3.3V / Low 0V
Dimensions: 10mm * 23mm
Angle: <100 degree cone
Induction distance: 3 meters
Pin 1: V+
Pin 2: Signal
Pin 3: Ground
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Two Options Considered
Connect all sensors
individually
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4 Input Pins
More wires
More Code
Easy to expand
Cluster the Sensors
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I2C Bus
Modular
Harder to expand
Must build custom PCB
Must program the PIC too
I2 C
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Use the PIC12F1840 & I2C
Stuff We’ll Use
Stuff we won’t
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Purchased from Microchip
– http://www.microchip.com
– About $1.25 each (+ Shipping)
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31kHz - 32MHz
125nS per instruction @32MHz
49 Assembly Instruction
“C” or Assembly Programmable
Operating Voltage: 1.8V – 5.5V
5 I/O Pins; 1 Input-Only Pin
Flash Program Memory with self
read/write capability
MI2C, SPI, EUSART w/auto baud
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Comparator with selectable Voltage
Reference
4 Channel 10b ADC with Voltage Reference
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25mA Source/Sink current I/O
Two 8-bit Timers (TMR0/TMR2)
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One 16-bit Timer (TMR1)
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Extended Watchdog Timer (EWDT)
Enhanced Power-On/Off-Reset
Brown-Out Reset (BOR)
In Circuit Serial Programming (ICSP)
On Board In-Circuit Debug
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Capacitive Sensing Module
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Data Signal Modulator Module
Enhanced/Capture Compare PWM
(ECCP)
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EasyEDA Schematic
https://easyeda.com
• Not the “Best”
• Easy
• Well supported
• Gets the job done
• There are a lot of other
options
• Choose the one that
suits you the best
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Get Started …
• Demo EasyEDA
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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
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Cut Out the Board
• Leave some room around the edges
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Remove all Burrs
• Iron must rest tight against the board
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Supplies
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Etching Solution
– Ferric Chloride
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Etches about 25 in2 of 1 oz. board
per oz. of solution
~$17 for 33 oz.
– Copper Chloride in Aqueous
Hydrochloric Acid Solution
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Unlimited use
~$10
http://www.instructables.com/id/Stop
-using-Ferric-Chloride-etchant!--Abetter-etc/
– Ammonium Persulfate
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~$8 for 4 oz. dry makes 12 oz. liquid
(3:1 mix)
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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
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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!
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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
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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
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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
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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
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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)
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Finish Up
• Scrub with Steel Wool
– Under Running Water
– Remove the stencil
• Silver the board
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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
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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
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number of layers
number of components
size of board
etc.
Portability: can you export or convert your designs?
• Practice, practice, practice.
• Maintain low expectations
– Your first board will have problems
– Your 20th board will have fewer
• Schematics are important
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