Day 3 – PCB Milling Techniques & Fabrication Process

Objective

Students will design a single-sided PCB using KiCad that:

• Uses an ATtiny45 microcontroller
• Controls an LED using a push button
• Can be programmed via a 6-pin ISP header
• Is suitable for PCB milling and hand soldering

Circuit to Design

Functional Description

• ATtiny45 runs at 5V
• LED turns ON when the button is pressed
• Program uploaded via ISP programmer
• Board powered through an external connector
• This is a real microcontroller system, not just a demo circuit.

Block Diagram (Conceptual)

List of Components (Required)

Component	Value / Type	Notes
Microcontroller	ATtiny45 (DIP-8 or SOIC-8)	Beginner-friendly
LED	5mm THT LED	Status indicator
Resistor	220Ω	LED current limiting
Push Button	Tactile switch (THT)	User input
Power Connector	2-pin header or terminal	5V input
ISP Header	2×3 pin (6-pin)	Programming interface
Decoupling Capacitor	0.1 µF	Power stability (important)

Pin Usage (Beginner-Friendly Assignment)

ATtiny45 Pin	Function
VCC	Power (5V)
GND	Ground
PB0	LED output
PB2	Button input
PB5	RESET (ISP)
PB3	MOSI (ISP)
PB4	MISO (ISP)
PB1	SCK (ISP)

Important: PB0–PB5 are reused for both I/O and programming.

KiCad – What Students Must Do

Step 1 – Create the Schematic

Students must:

• Place ATtiny45 symbol
• Add:
  • LED + resistor
  • Push button (with pull-down or pull-up)
  • Power connector
  • 6-pin ISP header
  • 0.1 µF capacitor between VCC & GND
• Label all nets clearly

Rule: Every pin must have a purpose.

Step 2 – Assign Footprints

Through-hole recommended for beginners:

• ATtiny45: DIP-8 footprint
• LED: 5mm THT
• Resistor: Axial THT
• Button: THT tactile
• ISP: PinHeader_2x3
• Power: PinHeader_1x02

Step 3 – Single-Sided PCB Layout

Students must:

• Define board outline (~60 × 40 mm)
• Place components logically:
  • ISP near ATtiny45
  • LED visible on board edge
• Route only one copper layer
• No vias allowed
• Use jumpers only if necessary

Recommended milling rules:

• Trace width: 0.5–0.6 mm
• Clearance: 0.5 mm

Step 4 – Design Rule Check (DFM)

Students must:

• Run DRC
• Fix all errors
• Verify:
  • No unconnected nets
  • No trace overlap
  • Correct clearance for milling

Step 5 – Prepare for Fabrication

• Add text:
  • Board name
  • Student initials
• Export:
  • Gerber files
  • Drill file
• Inspect Gerbers before milling

Deliverables

Students submit:

• KiCad project folder
• Schematic screenshot
• PCB layout screenshot
• Gerber files
• Short reflection:
  • Biggest routing challenge
  • One improvement for next version

Learning Outcomes

Students will learn:

• Microcontroller-based PCB design
• ISP programming concepts
• Single-sided routing strategies
• DFM for PCB milling
• How design decisions affect fabrication