A Radically Better Fume Extractor

When you're soldering you can notice smoke rising from the solder as the iron melts the metal, as you might have guessed this is not at all good for you or your lungs. There already exists several DIY filtration systems on the internet, but these may only be about 5% effective at reducing the pollutants produced when soldering [1].

Watch the first 14 seconds of the project video to understand the problem.

In this project I'm showing you how to build a much better, still cheap and easy, filtration system. I'll also spend some time explaining the science of how to get rid of the problem in with the solder fumes.

I'm basing this explanation on lead free rosin core solder, which is the type most commonly used at home by hobbyists. All of my sources are available in step 7.

There are a lot of different files needed to complete this project like 3D files, microcontroller code, and PCB design files. I have gathered all the files I developed in this Github repo which acts as the single source for all the files you need, in their latest iteration and update.

Electronics

• 1 x ATTiny85 SOIC-8
• 1 x Linear sliding potentiometer
• 2 x 10k ohm 0806 resistors
• 2 x 100nF 0806 capacitors
• 1 x 10uF SMD ECAP
• 1 x 78L05 SOT89 footprint
• 1 x MOSFET LS44NS
• 1 x Female Barrel Jack
• ICSP helper with pogo pins
• 12V 400mA power supply
• Custom PCB. See github for GERBER files

Mechanical

• 4 x 80mm computer fans. The higher the CFM value the better
• To pull the air and colophony through these tree layers of filters I'm using two computer fans. These hade the highest static pressure I could find for a reasonable price.
• 1 x Miele SF-AH30 HEPA Filter with activated carbon. Like this or this
• Cheap and readily available
• A sheet of cuttable activated carbon filter for kitchen hood extractors. Like this or this
• Also very cheap and readily available
• 2 x M3 nuts
• 2 x M3 16mm screws
• Access to a 3D printer. Everything is mounted inside a sleek looking 3D printed case

The fumes produced when soldering are divided into two categories: We have particulate matter, and chemical gasses. [2]. The main particulates are from the tin, silver, and copper found in most lead free solder [5].

The particulate matter consists of particles so small they are captured by the airstreams around us and starts floating in the air. This happens when particles are of a size of 10 micrometers or smaller [3]. When the particles are less than 2.5 micrometers they not only enter deep into your precious lungs, they can easily enter your bloodstream as well. [3].

The first filter type I'm using is a HEPA filter (High-Efficiency Particulate Arrestance). It is a dense fiber mat that catches 99.9% of all particles at a size of .3μm or larger [1] [7] [8]. And here's an interesting fact for you, this filter is great at stopping particles larger than 0.3μm and smaller than 0.1μm. It's the middle sized particles that are the hardest to stop. 

The larger particles get's stopped easily enough by hitting the filter walls as you would expect. Now the smallest particles are so small they easily collide with tiny water droplets and other stuff floating in the air, which makes their movement random. This is called Brownian motion, and this random movement increases the likelihood of the particles touching the wall of the filter, where it get's stuck due to the filters attraction force [1] [7].

Medium sized particles are so small they don't easily hit the filter walls, and not small enough to move in erratic Brownian motion. They can move with the air flow through the openings in the filter.

The chemical gasses are produced from the intense heat from the soldering iron interacting with the flux inside of the solder, this creates what's known as the pyrolysis products from the solder flux. You may recognize some of the names of these chemicals shown in the picture, and you may also recognize how they really aren't something you want to be breathing. In that case you'd be right. The complete mix of particulate and gases are known as a colophony, and can lead to complications like cancer [4], metal fume fever [5], asthma [5], and other lung damages [6].

To get rid of most of the chemical gasses I will use an activated carbon filter. This is the filter you're most likely to have seen used in other DIY solutions. It may only be about 5% effective at reducing the total volume of the colophony [1], but I still want to add this filter as those 5% constitutes most of the dangerous chemical gasses.

The molecules in the chemical gasses are so small they would pass right through the HEPA filter, which is where the activated carbon comes in. Activated carbon is made from coal which is injected with hot and pressurized gasses. This creates loads and loads of microscopic pores [10]. These pores are fantastic at capturing chemicals by trapping the molecules inside them, in a process called adsorption [11]. 

And here's another mind blowing fun fact for you, 1 gram (.04 ounces) of activated carbon is so riddled with pores it has a total surface area of more than 3000 square meters, or 32 thousand square feet [11]!

The HEPA filter for the vacuum cleaner comes with activated carbon granules. I'm also adding a second layer of activated carbon to increase the total travel distance through the chemical filter, as this is an efficient way of capturing more chemicals.

The 3D files are designed to be printed without supports and at a rough resolution in both layer height and speed.

Print settings

• 0.3mm layer height
• 5 top layers
• 5 bottom layers
• 4 perimeters
• 5% infill

The bottom part of the case took about 8 hours, and the top part took about 6 hours to complete.

The PCB is a regular 1.6mm lead free fiber glass board. JLCPCB were kind enough to sponsor this project. They offer 1-4 layer PCBs for just $2, as well as free PCB Assembly services. Check them out using this link: https://jlcpcb.com/DAA

When receiving the circuit board I started by soldering all parts, except the barrel jack, on the component side while the PCB could lay flat, before soldering the sliding potentiometer on the opposite side. The barrel jack will be soldered when the PCB is mounted inside the case.

To upload the code you can solder temporary wires on the ICSP headers, or use a tool with pogo pins. I used a tool I made in a previous instructable for these kinds of situations, the Combined ISP and FTDI Tool With Pogo Pins.

Before uploading the code you may need to add support for the ATTiny set of microcontrollers in Arduino IDE. Copy the following link into Additional Boards Manager URLs under Preferences in Arduino IDE. https://raw.githubusercontent.com/damellis/attiny/ide-1.6.x-boards-manager/package_damellis_attiny_index.json

Go to Tools -> Board -> Boards Manager, search for "attiny" and install the package.

Please see the attached picture for the settings I used to upload the code to the microcontroller after it was soldered onto the PCB.

When all the building blocks are prepared they come together in a snap:

1. Push the PCB assembly through the fan grills in the case
2. Mount the two fans in the bottom case with the included screws
3. Mount the two fans in the top case with the included screws
4. Solder the fans in the top case to the PCB
5. Push the PCB into its slot on the backside of the case
6. Fasten the PCB with two M3x16mm screws and nuts
7. Push the power wires through the hole for the barrel jack
8. Solder the barrel jack and fasten it with either the included nut or with hot glue
9. Use the HEPA filter to cut a similarly dimensioned square from the activated carbon filter
10. Use knippers to cut the notch on the HEPA filter
11. Slide the HEPA filter into the case
12. Slide the top case into the bottom case
13. Fasten the two case halves together with one continuous strip of electrical tape
14. Attach the activated carbon filter which is held in place with the 3D printed filter grill

You're done!

[1] https://blog.gotopac.com/2020/01/02/soldering-fans-vs-fume-extraction-units-vs-fume-absorbers/#Whats_In_Soldering_Fumes

[2] https://www.weller-tools.com/professional/USA/us/Top-Menu/Know+How+and+FAQ/Know-How+Filtration/Protect+yourself

[3] https://www.epa.gov/pm-pollution/particulate-matter-pm-basics

[4] https://www.cdc.gov/niosh/npg/npgd0547.html

[5] https://www.sentryair.com/blog/industry-applications/electronics-technology/the-hazards-of-solder-fumes/

[6] https://safety.eng.cam.ac.uk/safe-working/copy_of_soldering-safety

[7] https://www.sciencedirect.com/topics/engineering/air-filtration

[8] https://en.wikipedia.org/wiki/Air_filter

[9] https://en.wikipedia.org/wiki/Charcoal

[10] https://molekule.science/activated-carbon-air-filter/#:~:text=Activated%20carbon%20has%20special%20properties,particle%20pollution%20from%20the%20air.

[11] https://en.wikipedia.org/wiki/Activated_carbon

[12] https://www.sentryair.com/activated-carbon-adsorption.htm