PCB Making: 8. Etching

There are several kinds of etchants; I am using Ammonium persulfate solution from MG chemicals. It comes as loose powder or crystals. The content releases gasses over time, so you should punch a small hole on the lid of its plastic bottle. These are dangerous and corrosive chemicals, so use a lot of common sense when working with them. There are several variables in the process that you can try to control for the most efficient etching. The goal is to have the shortest etching time and minimal use of etchant chemicals. There is a sweet point in that compromise and you can reach it by experimentation.

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PCB Making: 10. Drilling holes

The best bits to drill holes in your FR-4 board are tungsten carbide bits. They are, however, more expensive. You can also use HSS (high-speed steel) bits, but they will quickly dull. To drill larger holes start with a small bit and then progressively go larger.

Have a good working light shining at the board. This is crucial to get the holes well centered, especially for smaller bits.

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PCB Making: 11. Solder parts

It is time to solder through-hole and surface-mounted components.

I use Chip Quick solder paste for SMT components. When not in use, keep it in the freezer to extend its shelf life (it should not dry up). Chip Quick has a very low melting point and it’s perfect to use for SMT since you can apply tiny drops of it through a syringe it comes with. Apply small drops to pads and then position SMT components on them using tweezers.

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PCB Making: 14. Testing and Troubleshooting

This is general guidance for the initial testing.

Thoroughly examine the board for physical defects: are all traces complete or there are breaks?
Are all pins soldered and is the quality of the solder joints acceptable? The soldering point may be missing (forgot to solder it), may have a bridge or a short, or it may be a poor joint (cold point). Just redo it.
Is any component missing? (Something blunt but may happen!)
You may need a magnifying glass or a loupe with a strong light.

Check again the orientation of components: LED, diodes, connectors, chips – where is pin 1 located. Check the orientation of tantalum and electrolytic caps. On SMT components, this can sometimes be confusing.

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PCB Making: 15. Software

The quality of the tools that we use to write software for projects like this is very important when selecting which MCU we may want to use. Atmel has a very robust IDE based on Microsoft’s Visual Studio (which is arguably the best development environment out there). Coupled with a JTAG interface, writing and debugging firmware with the Atmel toolset becomes a pleasure.

Their ASF (“Atmel Software Framework”) is a good collection of ready-to-use projects and components. Investing time to learn that environment is the best way to become very efficient when using it.

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PCB Making: 16. Conclusion

There are a few things that I did not get to try this time around:

  • Adding a bitmap (for example, a logo) to the board’s layout. I believe you create it as a custom part and use it from your library? Or you somehow download an image.
  • Similarly, it would be useful to make bitmaps for parts like diodes to help orient them as a guide when soldering.
  • How do you remove Eagle layers like Cream, Glue, etc. which are populated? There are also many other tricks to learn with Eagle.

If a project is large enough, one could add a board ID that is readable by the software. That could be done by GPIO pins connected to, or “fused”, to certain voltage levels creating a short ID. This may be overkill for simple boards, but still, it is a known industry practice.

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Etching the PCB: Copper etchant calculator

I really wanted to find out exactly how much etchant would I need for a given board. That would be at least a theoretical minimum to etch all exposed copper, so after some calculation, I made this table. In practice, you would probably want to double that amount to get it to etch faster, but that’s a good starting value to measure.