Saturday, July 6, 2019

Getting Started with SMT

 As my eyesight gets worse, the parts I use for DIY get smaller.  I guess it had to happen?  Pushed into surface mount technology (SMT) and the parts you need to make it go (SMD, "surface mount devices), and perhaps an impending desire to DIY in the Eurorack format, it was time to tool up and solder my first SMT parts.

First off, I needed to be able to see what I was doing, so I bought a microscope used for SMT/SMD work and rework:

There are many scopes to choose so picking one was hard. After some research, I decided to go with AmScope and ultimately the scope recommended by this youtube dude--find it on Amazon here.

(Apparently the YouTube repair dude makes some sort of spiff?  Fine with me. He makes funny, acerbic videos, and has a great NY accent and the NY/NJ screw-you attitude. Someone has to make some money here....)

The microscope it turns out works great....there were no instructions about setting up the stand (I just followed the photos from Amazon but it was still a puzzle at times). I had to wing that. Also, you will need the microscope light (the scope does not come with one; you will need it), a Barlow Lens, and eyepiece eye shields.  And of course: appropriate solder, a good iron, tweezers, flux and most all the rest of the stuff you'd use with through hole. Go to the web page here for links to a lot of what you'll  need.

OK from Tayda I bought the tiny parts, and from JLCPCB I got some Eagle boards fab'd for proof of concept.

Some tiny TL072s.....

Here's the Proof of concept board:

Use 100K resistors for R1-R4 for higher impedance at input.....

So how did it go? Turns out building this board, with the microscope, was easy.  I knew zlich about soldering SMT so I followed the tutorial here. I made a few solder mistakes but as per the tutorial it's easily cleaned out and fixed up with solder wick. 

Let's motorize this pursuit? I whipped up 4 boards:

And then built one out enough to test that a bipolar LED works.  It does!  

Input -5V relative to ground: blue

And 5V relative to ground--red.  Works!

UPDATE 7-13-19: to further shake out this SMT op amp board I modded my trusty Electronotes sample and hold, more in this post.

OK onward!

As with many things in life, this was all much easier than I thought; plunking down the dough for the Microscope helped a lot, although it was a pretty big investment.  But, this would have been hard to do without it.  I am serious: don't breathe the fumes.  See you next time

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