[Moved again]: Type of Circuit Board for Etching?

[shodai]

Hello. I am trying to add some components to my class and I would like to have my students design and make their own PCB's. I am have never used an etching kit before so I am a little uncertain.

Question 1: I think that given I am in a school environment that the print-paper transfer method would be the best(easiest and cheapest) way to go, but is this right?

Question 2: I have come across a number of different types of board and am wondering which type to look at purchasing; do I want single sided copper board, double sided copper board, POS presensitized copper board, double sided presensitized copper board, copper clad uncoated, or unclad?

 

[betwixt]

Re: Type of Circuit Board for Etching?

1. the print transfer method is cheap and simple but can be difficult to get good results, the print can only be used once. It is not used commercially because it rarely gives consistent results and doesn't lend itself to volume production.

2. It depends on the PCB you want to make:
Single sided means it only has copper on one side, the other is plain fiberglass or cardboard.
Double sided is the same but has copper on both sides.
Pre-sensitized board is available single and double sided but has a special photographic paint covering the copper, you need it if you use a UV light source and resist image.

If the PCB design is simple, you could also consider directly drawing on the board with waterproof ink. The ink will protect the copper it covers from being dissolved by ferric chloride etchant. Obviously, that method is difficult if you want to make several identical copies.

Personally, I use the re-sensitized board and prepare the mask on overhead projector transparency film. You print or copy the original track layout on to the film then lay it over the paint layer of the board then expose it for about 4 minutes to a UV light source. The printed tracks on the film works like a sun shade, it stops the UV reaching the paint, where UV gets through the paint changes chemically so it can be wiped away with developer solution. You are left with an image of the PCB tracks painted on bare copper so when you etch it, the bare areas are dissolved away and the painted areas are left intact. You can get consistent results using this method and it's easy to make tracks as narrow as about 0.2mm, the artwork can be used over and over again too!

Double sided boards are much harder to make so I don't recommend you start with them. The production principle is the same but it is difficult to align the two sides accurately.

Brian.

 

[shodai]

Re: Type of Circuit Board for Etching?

WOW!! That is extremely helpful. Thank you so much. I just have one kind of dumb follow up question. I am assuming that when you say expose it to UV light that there is a specific type of bulb that I would need; what is it and where should I look for one?

 

[betwixt]

Re: Type of Circuit Board for Etching?

You can use sunlight - assuming you are not in the UK where it always rains :-( but getting the exposure time right can be tricky.

The best thing is buy or build a proper UV exposure box. Basically, they are a lightproof box with a glass top and a heavy lid. The UV tube or tubes are inside the box where the wiring is safely out of reach and the light travels up through the glass, through the artwork which you lie on top of the glass and then to the PCB which you lie on the artwork. The heavy lid serves to make sure the artwork and PCB have no gap between them that could allow light creepage to the bits you are trying to keep. There are special UV tubes for the purpose, the look like ordinary white 10" tubes when off and to the eyes look pale blue when lit up. They are typically rated at 8W so they aren't powerful but don't look directly at them for too long because most of the light is invisible but harmful. Be careful to work in subdued or red lighting because the photo resist paint on the PCB is somewhat sensitive to visible light as well as UV.

I made a guide a few years ago that might be helpful to you. It shows a picture of my light box which is still in use after about 25 years!
http://www.atv-projects.com/Making_PCBs.html

Brian.

 

[chemelec]

Re: Type of Circuit Board for Etching?

My Question would be: What is the Circuit you have that you want to make this PCB for?

A really simple circuit board can be made with just a Resist Pen.
A more complex board would be better done with A Positive Artwork and Pre-sensitized PCB Material.
But you need a Computer Drafting Program and a Laser Printer to Create this artwork.

For Etching, Ferric Chloride can be Used.
But a Mixture of 2 Parts of Hydrogen Peroxide and 1 Part of Muriatic Acid (Hydrochloric Acid) is Nicer to work with.
(This Does Not Stain your clothes and other things a Brown Color.)

 

[D.A.(Tony)Stewart]

Re: Type of Circuit Board for Etching?

When we had aprotoype SMT boards, the engineers would use laser print for 20/20 track/gaps and photo develop from a lithography shop to make photo tools for 10/10 resolution. Acid etch , rince and tin dip to prevent oxidation can be messy so careful dipping into plastic tanks with drip hooks into a predrilled holes helps as does a proper drill with 1/4" shaft and short drills for drilling using a vertical axis mini drill setup.

>800 grit wet dry remove oxide pre-etch is necessary for clean etchback. Vibration helps with etch consistancy and heating acid is dangerous but increases etch rate in copper saturated acid. Commercial UV lights are flourescent tubes with the boards flowing directly under the fixed light at a steady rate but other consistent UV light sources are avail. Some use a tiny plastic pump impeller to circulate the acid for consistent etch rates over a area but hard to control without proper design. Even copper fill patterns and hatching for large ground planes can help in some cases for soldering later to prevent large heat sink effects.

THis is one reference,
https://www.instructables.com/id/DIY-Double-Sided-PCBCircuit-Board-Etching/

Predrilled standard corner holes and artwork fiducial marks help align 2x sided etching.
Test patterns like these touch pads in the PCB corners assist with visual feedback on etch rate. and can be used as a ground touch pads for handling ESD sensitive assembled boards.

 

[shodai]

Re: Type of Circuit Board for Etching?

I was just wondering if this would be an appropriate type of bulb to use? https://www.amazon.ca/Eiko-15527-Fluorescent-Blacklight-Length/dp/B000TZWIQK