Saturday, July 6, 2019

Getting Started with SMD

 As my eyesight gets worse, the parts I use for DIY get smaller.  

Surface mount devices ("SMD") have become ubiquitous in electronics, along with SMT components (SMT: "surface mount technology), and perhaps an impending desire to DIY in the Eurorack format, meant 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 commission? Fine with me. He makes funny, acerbic videos, and has a great NY accent and I enjoy his New York/New Jersey screw-you attitude).

Also, you will need the microscope light (the scope does not come with one but it's a requirement), a Barlow Lens, and eyepiece eye shields.  And of course: appropriate fine gauge solder, a good soldering 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.

The microscope works great....there were no instructions included about setting up the stand; I followed the photos from Amazon; it was a puzzle but ultimately figured it out. 

OK I had a microscope--and bought extra flux and some fine point tips for my soldering iron. 

What to build?  

From Tayda I bought SOIC op amps, then got some Eagle boards fab'd for proof of concept: a single SMD op amp buffer--can't get much easier than this?

 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 nothing 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. 



In the end 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 using two of these SMD PCB's, more in this post.

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. Update: I have found I don't always need a microscope for SOIC IC's, and/or 1206 sized passive components, but for smaller footprints the tools I bought for SMD work have been a lifesaver. Recommended!

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