10 September 2019

DIY PCB making tips - photosensitive dry film

For quite some time I've been struggling with reliable method for making my own PCBs. I tried a few well known methods but none would give consistent results. One of the most reliable was Press-n-Peel blue film. The problem however was its resolution for fine traces and the film shrinking most likely due to temperature. When creating 17cm long board for my power supply I was shocked to find it'd shrunk a few percent. It's not a problem with small boards though.

Another method involving toner heat transfer was fine for thick traces but the fine ones would get flattened when pressed too hard. That would be the case even when using a laminator.

Lately I decided to go for photo sensitive dry film. I ordered some UV led strips and created a lamp that yet has to get its enclosure. I also made a simple timer that was the first board to test the new method.

At first it was great experience but after a while I started noticing imperfections like trapped bubbles or the film not sticking properly. I followed guides I found online. Treated the copper with steel wool, applying the film in water, running through a laminator etc. After closer inspection I found one of the problem was the film itself, which I got one of the cheap ones on Amazon. Here is how it looks:

As you can see the surface is not even and there is lots of thin spots. So it's quite important to find an area free of them. 

Another issue could have been the board preparation. Giving the copper a steel wool treat may not be the best option for the film adhesion. What I did with my last experiment was not to use it. Instead I treated the board only with Brasso polishing solution. It took just slightly longer that the wool but the finish was perfect.

I then applied the dry film directly. I didn't use water or any cleaning solution afterwards. I used some Blu-Tack to hold the board to the desk, peeled a fragment of the protective film and starting from one corner I pressed the film to entire board. The film stuck perfectly.

Initially I used OHP film as the media to print the mask. I had problems with toner sticking evenly to larger areas or even to some thicker tracks. That required me to print 2 copies and use them one on top of another. That in turn caused another issue, which was my printer. The two copies were not identical in size. Probably due to the mechanism imperfection one would always be slightly longer. The same was for tracing paper but at least the paper would absorb more toner and more evenly.

The goal was then to use just one piece of mask and for that the key was proper calibration of the exposure time and the distance between the lamp and the board. A strip of board with repeating pattern did the job. I used 0.2mm tracks with 0.1 & 0.2 mm clearance, and 0.25mm tracks with 0.2 & 0.3 mm clearance. I don't think I would ever go below that.

For the distance of 15cm the perfect exposure time for my lamp was 40 seconds. It shows I can't use the 0.1mm clearance but 0.2 is spot on.

Here is the etched result:

And the last step is to protect the copper and make it easy to solder. For years I'd use dissolved in alcohol organic flux - rosin. It's great and cheap solution but I wanted something more "professional". On one occasion I tried chemical tinning but wasn't happy with the result. Soldering wasn't really easy and the solution itself may pose health risk.

I made a DIY wide soldering tip. I used an old heatsink made of copper and one of unused soldering tips.

This allowed me to tin the board with relatively even layer of solder forming nice ant solid finish:

Soldering the elementals was a breeze and the final component looks quite good:

16 April 2019

Fully Enclosed DIY 3D Printer

I lost my patience and published a "work in progress" version of the video presenting the project. The printer is working fine for over a year now. Here is the video:

31 January 2017

Programmable Power Supply - controlling via iOS (proof of concept)

Testing basic iOS application written in Swift to communicate with my power supply. The supply isn't finished completely yet but the only thing left is its firmware. So now it's a good time for these kinds of tests.

I designed the supply some time ago and have been building it in my spare time. Now it's slowly getting to the final shape. Electronics is completed and some dynamic tests look promising. The only thing left is the firmware. The majority of it works so it's only the extra features, ergonomics, safety and so on. Later I'll do a full teardown/demo of the supply so the video below can act as a sneak peek.

22 August 2015

Logitech Anywhere MX - unbalanced wheel fix

I really like inertial (or momentum) scrolling. Most of the time I use trackpads. OS X uses momentum scrolling by default. Unfortunately, sometimes I have to use 3 button mouse for 3D or graphic design. Besides that, there is coding on a Windows machine so scrolling is quite frequent. Being so used to the way of scrolling, it is hard to switch to just standard wheel in a standard mouse.
Logitech makes mice with a Hyper-Fast scrolling wheel. Works great but there is a fairly annoying glitch. The wheel may, after stopping, move slightly. So when you scroll to the right place in a document, you stop, lift your finger and the document scrolls a few more lines. You scroll back, lift the finger and the screen scrolls again.

So I decided to try and fix it. I used a spring to hold the wheel in place. With very little force it should not stop it from spinning. After straightening an old spring from some broken mechanism, I bent it in a way to fit around the wheel holder. I left one end of it touching the wheel’s ax lightly. Then put a drop of silicone grease and voila!

The wheel does not move anymore after stopping. The time it spins freely has reduced but the documents I work with are not that long to require a few seconds of continuous, high speed scrolling.

28 October 2014

Temporary fix for OneDrive (SkyDrive) invisible icon in OS X Yosemite dark mode [updated]

I’ve had enough of the problem. Just a minute ago the app was updated but still the icon is invisible in dark mode of the Yosemite. It was just a quik dive into the app content and replacing the icon. I’ve changed the original one by replacing the color (black to grey). That’s enough for me as I’m too lazy doing someone elses job. I’m not bothered by the other states of the app. All I need is to see the app is running. The file you’re after is StatusIcon_signedin.tiff. So there you go: 

Update: Skydrive application is updated and fixed the problem.

1 February 2014

Designspark PCB on two machines under Windows 8.1

I use DesignSpark PCB on my main machine for designing schematics and circuit boards. Recently I’ve set up a new, small PC for use just in my workshop. The setup is exactly the same as the main machine, the user, paths, environment and so on. My documents and projects reside inside the SkyDrive folder. As soon as the account was created the entire folder synced. Then I installed the DesignSpark PCB. I also wanted it to use the same paths as the copy on the main PC. For some reason it could not overwrite the existing files. I pressed “Ignore” as the files already existed so it shouldn’t be a problem. The program launched OK but it refused to open my project files presenting an unknown error.

I was just about to give up with the conclusion that DesignSpark doesn’t like such environments when I remebered something what might be the cause.
Integrated with Windows 8.1 Skydrive uses offline files to save space on mobie devices. A file exists on the drive but the content is in the cloud until you open it. Then it gets downloaded. You can also force the download by selecting “Make available offline” option from contextual menu. After performing this step all the problems were gone.

17 January 2014

MPLAB X not launching

While the MPLAB X works great on my home desktop with Windows 7, it won’t launch on my company’s laptop with the same system. The most probable reason is that my account is regulated by my company’s group policies. To fix the problem I’ve found the solution that worked for me. It is to make it to use specified user directory by adding the following parameter to its short-cut target:

“C:\Program Files (x86)\Microchip\MPLABX\mplab_ide\bin\mplab_ide.exe” –userdir C:\Users[your account name]\MPLAB