Make Your Own PCBs

This post has its origin from :

Supervisor: “Can you setup a PCB work station for the lab?” ūüôā

There are lots of resources on this topic, which can be found on Google by searching: “Make your own PCB station.” However, the amount of information can be overwhelming. After some trial and error, I found the following components most economical and accessible (in Canada), and that the following steps worked best for me.

For those that don’t know what PCBs are, it stands for Printed Circuit Board. It provides mechanical and electrical support for the electronic components using conductive tracks, pads and other features etched from the copper substrate. The breadboard prototyping wires are replaced by conductive tracks, and the components are connected by soldering. The design of a PCB is all about tradeoffs between factors such as signal integrity, routability, size, cost of manufacturing etc. This post will not go through the design aspects, as a stand alone post dedicated to this topic is required.

step1_a

Lets delve into the physical layers of a PCB:

  • Substrate layer: This provides dielectric isolation. For most low-frequency applications FR-4 substrate is used. This is because FR4 dielectric constant stability varies from PCB to PCB, and over frequency range. Furthermore, FR-4¬†is considered a higher loss board compared to other RF PCB. With that said, signal loss is proportional to trace length. So with short tracks, some HF signals can be designed using FR4 boards without signal integrity issues. The thickness of the¬†substrate is selected based on compactness, connection configuration, impedance matching, flexibility, component compatibility and weight. The connection configuration refers to edge connectors, which may require the right thickness to physically fit the connector. The impedance matching refers to the capacitor behavior between traces on adjacent layers, where the thickness of the board defines the thickness of the dielectric, thus the value of the capacitance. The component compatibility refers to through-hole components. Overall, FR4 boards are the most common for their low cost and durability.
  • Copper layer (top and/or bottom):¬†This provides conductivity for the traces. A thin copper foil is laminated to the PCB with heat and adhesive. The copper thickness can vary and is specified by weight, in ounces per square foot. Most PCB have 1 ounce of copper per square foot, but some PCB handling high power may use up to 2 or 3 ounces of copper per square foot.
  • Soldermask (top and/or bottom): This helps to insulate the copper traces from accidental contact with other metal solder or solder jumpers. This layer gives the PCB its green (most of the time) color. It is overlaid onto most of the PCB covering the tracks, but leaving the pads exposed so the components can be soldered on.
  • Silkscreen (top and/or bottom): This provides labelling of letters, number and symbols on the PCB.

Step1_b.jpg

Popular PCB layout and design software are:

  • Cadsoft Eagle. (Popular and free)
  • Ki-CAD.
  • Altium.

PCB Workstation:

  1. Thin glossy paper (HP Premium presentation laser paper from Staples).
  2. Laser printer (Print with mono color setting).
  3. Isopropyl alcohol 99% or acetone or fine sand paper (SandWet Ultra Fine-600 grit from Home Depot).
  4. Laminator (Swingline Inspire Staples).
  5. Copper board (Rogers).
  6. Ammonia persulfate (NH)4S2O8 (410-1 kg MG-chemicals).
  7. Kitchen scrubs.
  8. Gloves.
  9. Etching system (Circuit specialists ET20).

step2_a

PCB Etching:

  1. Print the board layout on a glossy thin paper using the laser printer. Make sure to mirror the PCB layout for front/back designs. Try not to touch the printed layout as oil from the finger can prevent the transfer of the toner onto the copper board.
  2. Important Step: Clean the copper board with either isopropyl alcohol, acetone or fine sand paper. I find that fine sand paper works best.
  3. Tape the glossy paper (ink face down) to the cleaned copper board.
  4. Turn on the laminator, wait until it has reached its operating temperature. This is usually indicated by a LED. I found laminator works much better than an iron.
  5. Important Step: Continuously feed the board into the laminator for ~10 minutes. This worked well for a ~5×5 cm board. Longer time maybe required for larger and thicker boards.
  6. Gently rinse the board under cold water and wash away the glossy paper. The ink portion with the board layout should stick onto the copper.
  7. Check the ink transfer. Insufficient ink transfer can be applied with an etch resist pen or black sharpie or duct tape (for larger areas). If a ground layer is desired, cover the copper with duct tape to prevent etching.
  8. Set up the etching system in a ventilated area. The tank requires ~2 L of water in order to fully immerse the heater (see the indication line on the immersion heater and this is specific to the tank) to prevent the temperature difference from breaking the heater glass. Then, 440 g of ammonia persulfate with 2 L of water is able to etch 120 g of copper, which translates to a copper area of 1913 cm2 (mass = density * volume). Where the copper density is 8.96 g/cm3, and a copper standard thickness of 35 um is assumed. Therefore, depending on the PCB size and copper thickness, the amount of ammonia persulfate can be varied. The etching solution can be re-used; however, the efficiency of the etching solution degrades as the etching solution slowly decomposes. Therefore, the time required and uniformity of the etch will degrade over time.
  9. Stir the solution. This helps with the uniformity of the etch.
  10. Plug in the water heater, and turn the temperature knob to 40¬†¬įC.¬†This helps to speed up the etching process. Note that if the etching solution is crystallised at the bottom of the tank, lower the temperature.
  11. Plug in the 120 V agitating air pump, and immerse its tube into the solution. This also helps to speed up the etching process and uniformity of the etch.
  12. Let the heater warm for ~5 min.
  13. Clip the PCB onto the copper wire and fully immerse it into the solution, at about mid-way through the tank.
  14. Depending on the size of the board and the quality of the etching solution, the etch can take up to 5 – 15 min. The etching process is exponential. This means at first nothing seems toe be etched, and once a certain time has passed it etches in exponentially fast.
  15. When the copper is removed, it reacts with the ammonia persulfate to create copper sulfate CuSO4, which gives a deep blue color. The more the copper is removed, a deeper blue color appears. This solution is a hazardous waste and needs to be disposed appropriately in a safe manner (NOT down the drain).

Example:

I made an inductance and capacitance measurement circuit to test out the PCB station.

Step 1) Prepare PCB layout.

step4_a

Cadsoft Eagle schematic.

step4_b

CadSoft Eagle PCB layout overall (left), top layer mirrored (mid) and bottom layer (right).

Step 2) Clean the board.

step4_c

Step 3-5) Tape to board and feed through laminator.

step4_d

Step 6-7) Rinse board under water and check ink transfer.

step4_e

Step 8-15) Setup etching station and the etching process.

step4_f

Completed PCB.

step4_g