Applying Soldermask to PCBs

-

 


I wrote this post in 2022 and it's mostly unfinished, but it's been a year since I've posted anything so I figured I should post this.
 
After much trial and error, I believe I have come up with a method to reliably produce a passable soldermask for THT and SMD circuit boards. The process implements photosensitive resin and a transparent photomask printed on an inkjet printer. I will document the process and some recommending parameters below.

Materials needed:
  • An engraved circuit.
  • Photosensitive UV-curable soldermask resin.
  • A printer with reasonable DPI.
  • Printer-friendly transparent film.
  • A sort of squeegee to spread the resin.
    • A credit card should work well enough.
  • At least 92% isopropyl alcohol.
  • A container large enough to fit the chosen circuit board.




I started with the above engraved circuit. I previously made a post on how to mill circuits using a cheap CNC router so check that out if you'd like to do the same. 

Start by applying resin paste to the board. The distribution has a great affect on how well this circuit will come out, so do your best to lay it out in a pattern that can be squeegee'd evenly.  



Place the transparent film flat atop the resin. Take a credit card and use it to spread the resin as evenly as possible.  I used a Round One card to spread the paste the best I could, but it seems something more rigid would have worked better. 
 
After you expose the film to UV light, you can peel it off and use some alcohol to wipe off the uncured resin.


The board is done! Now you can solder without having to worry about corrosion and short circuits.

Comments

Post a Comment

Popular posts from this blog

Car Chronicles

-
Image
 One of the first real projects I ever completed was an RC car. As a 13 year old with no money, I did not have a 3D printer at the time. I guess cardboard will have to do. This "Mark Zero" iteration was not much more than a breadboard and a few motors taped to a piece of cardboard. Using a salvaged infrared sensor and a TV remote, I was able to communicate with the device from afar. An Arduino Nano set in the breadboard recorded different keypresses so I could associate them with moving the motors in different sequences. A servo motor in the front rotated a set of wheels spinning in a straw, while a small motor in the back drove a gearbox to propel the rear wheels. After this project, I got a 3D printer for Christmas. So I immediately started on the next iteration. This one was 3D-printed. It also used a 2.4GHz nRF24L01 radio module, and an STMF103 dev board. 3D printing opened a huge number of possibilities, though I'll be the first to admit I was...
Read more

Milling circuit boards with a CNC 3018

-
Image
After much frustration, I've managed to mill usuable circuits with my bottom of the line CNC machine. It's a knockoff 3018 I bought off Amazon from VEVOR. It gave me problems for months before one day suddenly deciding to work. To cut circuits I use Candle to control the CNC, FlatCam to create the gcode, and design boards in KiCad.  I originally drilled through hole boards with a home-made drill press, but once I learned to use the CNC for drilling I can't go back. It only requires a separate gcode file and a second z-probe homing and the machine takes care of the rest.    My machine tends to produce nasty burrs on the edges of all my traces, but a quick sanding removes these easily. It's possible sanding the copper reduces its thickness and current-carrying capability, but it works for now. With some tuning, I can manage 0.25mm traces. 0.5mm traces are usually more reliable, though. A 0.5mm pitch QFP-32 footpr...
Read more

Counter Mk1 Prototype

-
Image
 I just finished building this prototype during my free time in class. For now, it's just a STM32F103C8T6 development board connected to a breadboard with an I2C screen, a power supply, and some buttons. You can increment, decrement, or reset the counter using the three buttons, and the small screen will display the current count.  I intend to make this into a finished project with an ergonomic 3D-printed case and some bigger buttons. Its purpose is to help with counting something, while being easily held in an unoccupied hand.
Read more