Week 8 : Electronics production - REVIEW

Week 8 assignment could be categorized as follows:

• Group assignment

  • Design rules characterisation (in-house PCB)
  • PCB design submission to a board house

• Individual assignment

  • Fabrication and testing (designed embedded microcontroller system)

For basics of PCB design, please refer to Week 6 : Electronics design

Basics of PCB fabrication

• Methods for PCB fabrication:

  • Chemical: etching, lithography, toner transfer, printing
  • Mechanical (more common for rapid prototyping):
    • PCB milling
      • Bit types:
        • V: Sharp V-shaped tip with straight sides forming an angle. The cutting width depends on the depth the tool cuts into the board—deeper cuts produce wider traces. V-bits are useful for fine traces but can create more vibration.
        • Tapered: A tapered bit has a gradually narrowing body with a small flat or rounded tip. Tapered bits vibrate less and last longer, making them better for consistent milling and deeper cuts.
    • Laser cutting: See week 3 for more details

• PCB materials:

  • FR4 (epoxy glass): Usually used by board houses. Hazardous, fire resistant up to NEMA4.
  • FR1
  • Garolite

• Zeroing: The distance between the tip of the bit and the surface of the PCB. When the bit just touches the board surface, that position is set as Z = 0.

  • Mounting: REVIEW
  • Lowering: Moving the milling bit downward toward the PCB surface until it reaches the correct height for zeroing or cutting. During setup, the operator slowly lowers the bit until it just touches the surface of the board, which is then used to set the Z-axis zero point.

Design rules characterisation

PCBs are generally better than breadboards due to the following reasons :

• Breadboards require through-hole components and therefore a separate inventory is needed for it
• Contacts in breadboards are not very mechanically reliable, which can introduce parasitic resistance and capacitance

Mechanical methods namely PCB milling, laser cutting and vinyl cutting methods were explored. For the latter, please refer to Emily's documentation

PCB milling - REVIEW

say something about usually the distance of the components like 2.54 mm etc

Deburring (removing small copper or board fragments left from milling) can be performed using a steel ruler. Washing with soap and water also removes oils from handling and residues

Laser cutting

The LaserPecker 3 (diode laser) was used; however, it was unable to fully remove the copper layer or would have required a very long time (hours). Chemical etching or other methods may be needed to assist the process, but this is not further explored

Here are some details about the LaserPecker 3 machine based on the official website:

• Laser type : Diode
• Laser wavelength : 1 μm
• Laser spot size : 0.01 mm (the smaller it is, the finer the details could be)

Laser Safety

• The LaserPecker 3 uses a 1 μm infrared laser, which can cause eye injury even if the beam is not visible. Always wear appropriate laser safety glasses rated for 1 μm.
• Operate the device in a well-ventilated area, as engraving metals or plastics can produce harmful fumes.
• Do not leave the laser unattended while it is powered on.
• Maintain a safe distance of at least 50 cm from the laser during operation.

Source: ChatGPT by OpenAI, March 2026

The LaserPecker 3 comes with a mobile app and can theoretically connect via Bluetooth. However, during the test it didn't seem to work and so the alternative - the laptop software called Laser Pecker Design (LSD) Space and connection via USB to the machine - was used and the following documentation focuses on that.

The design must be exported as an SVG file. The laser interprets black areas as material to be removed, while white areas are ignored. This means that the goal when preparing the design is to preserve the traces and pads that should remain on the PCB (white), while marking the areas (e.g. unwanted copper such as the areas for electrical ground) that the laser should remove (black).

Non-Negative PCBNegative PCB

Big rectangle area will be removed and so could lead to longer cutting time

Only the clearance (i.e. the gap between the trace and the rest of the copper area) will be removed; decreasing significantly cutting time

In KiCad, this can be done with the following steps :

• Go to File → Plot.
• Choose SVG as the plot format
• Select the layer of interest (e.g. copper top layer).
• Check the option for “Negative Plot” so that traces will appear white (kept) and the areas to remove will appear black

Further processing can be done in software like Inkscape to reduce the default black areas exported from KiCad.

With processingWithout processing

Design	Result

1 pass = 60 mins cutting time

Design	Result

1 pass = 10 mins cutting time

SVG files exported from KiCad or modified in Inkscape may be interpreted differently by LaserPecker Design Space (LDS)

It was later observed that there can be compatibility issues when reading SVG files from KiCad or Inkscape in the LSD, so converting the design to PNG may be necessary. It is important though to verify that the physical dimensions are correct before starting the laser job because of the difference between raster and vector-based format.

Documentations on setting up the physical machine of the LaserPecker 3 are readily available online (e.g. focal point of the laser). The following settings for the laser cut were used:

• Material : copper
• Passes : 5
• Power : 100
• Depth : 90% (controls the intensity of the laser ablating (removing) the material)

The PCB images shown above are the results of these settings.

Users may try 1 pass at a time and use a multimeter to check if the copper has been fully removed electrically. If there is any slippage or misalignment, refer back to the laser preview before continuing.

It is interesting to note that past documentation suggests that copper removal using fiber lasers can be achieved in just a few passes at similar depth settings (e.g., 4 passes at 90%). In contrast, additional passes were experimented further with using the diode laser (e.g., 7 passes), but the copper was still not fully removed. From this, it can be concluded that the diode laser alone is insufficient for complete copper removal.

PCB design submission to a board house

Designs are typically sent to board houses when producing more than 10 boards or when the minimum trace spacing is around 0.125 mm, finer than what can be reliably achieved with in-house milling (~0.38 mm). For this run, a test is being done to verify the order workflow.

PCB manufacturers require detailed design data to fabricate a board accurately. The key files typically include: :

• Gerber files : Describe the 2D patterns of each PCB layer, including copper traces, pads, silkscreen text, border outline, etc
• Drill files : Lists the location and size of every hole in the PCB. This includes vias, through-hole pads, and mounting holes.

At the time of writing, KiCad version 9 is being used. The screenshot below follows the official website recommendation for exporting the aforementioned files. For full and up-to-date details, please refer to the online documentation.

JLCPCB was selected for this order simply due to its location in Shenzhen, China and no other reason. The PCB was ordered through the manufacturer’s online platform. By uploading the zipped Gerber and drill files, the platform automatically detected the design parameters and pre-filled or suggested appropriate specifications. The remaining options were then selected manually, with notes provided to explain the reasoning.

Parameter	Selected Option	Notes
PCB/PCBA	PCB	PCBA includes components soldered onto the board; only the bare PCB is needed
Surface finish	LeadFreeHASL	More environmentally friendly than HASL (with lead)
Electrical test	Flying Probe Random Test	Free of charge and so nice to have a "four-eye check"

The remaining steps are pretty straightforward and so not further documented here.

Yes, you need a mandarin name for the shipping address details

For the parameters selected above the overall cost is $5.56, with the following breakdown :

• 5 pieces of PCB : $3.20
• Shipping : $2.04
• VAT : $0.32

REVIEW when it arrived

Fabrication and testing - REVIEW

Soldering and Desoldering Techniques: How-To and Tips

Soldering with Lead (Manual)

Add images here (REVIEW)

• Heat & Squish

  • Apply a small amount of flux to the pad or wire.
  • Place solder on the pad.
  • Heat the solder with a soldering iron until it melts.
  • Gently press (“squish”) the component lead or wire into the molten solder.
  • Remove heat and allow the solder to solidify.

• Tin & Heat

  • Heat the wire or PCB pad slightly.
  • Apply a thin layer of solder to tin the surfaces.
  • Place the tinned wire/component onto the pad.
  • Reheat briefly until the solder flows and forms a solid joint.

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• • Apply solder paste to PCB pads using a stencil.
  • Place surface-mount components onto the paste.
  • Heat the board gradually using a hot plate or hot air gun until the solder melts and forms joints.
  • Allow the board to cool naturally.

  Soldering with Solder Paste (Reflow)

  • Note:
    Hot plates are suitable for FR4 boards, while FR1 boards (poor thermal conductors) often require heating from above using a hot air gun (top-down method).

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• Desoldering Techniques

  • Using a Solder Pump

    • Heat the solder joint until the solder melts.
    • Place the solder pump nozzle over the molten solder.
    • Activate the pump to suck up the solder.
    • Repeat if necessary until the component can be removed.

  • Using a Desoldering Wick

    • Heat the solder joint with a soldering iron.
    • Place a desoldering braid (wick) on the joint.
    • Allow the wick to absorb the molten solder.

It is better to prioritise smaller components first, followed by larger components, to ensure accessibility during soldering

Wire jumpers or 0 Ω resistors can be used to connect traces if there were mistakes during the design or to provide bypasses that are sometimes difficult to implement

Which soldering tip to use - REVIEW what is soldering mat