Building SMT Hand-Soldering Skills
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Building SMT Hand-Soldering Skills

by HarpDude on Thu Mar 03, 2016 2:59 am

I've learned a lot and enjoyed watching Lady Ada and Collin solder surface mount devices by hand. Using that information, I've taken on a few SMT projects now and am thoroughly enjoying the results. What a huge difference over the through-hole projects I've been doing for the last (ahem) many years.

What troubles me is that it takes good eyesight and a stable hand to accomplish this type of work successfully, two things that are starting to wane for me now that I've been retired for a couple of years. The technique of soldering the first pin while aligning the remainder is working okay for now, but it requires a lot of concentration to get it just right. I've heard of using a bit of poster tack to hold the component, but I didn't have any on-hand to try. Here's how I solved the problem:

1) Use a good LED magnifying lamp with a 3 to 5 diopter lens. The larger the lens the better, especially if you wear glasses.
2) Forget about circuit board vises and such. Put a small, clean scrap of plywood on the table, then tape your PCB to that using painter's tape. I noticed that Collin did this in his SMT video, as well. I use a 6 x 12 x 1/4 -inch scrap of plywood -- it has worked well for all projects so far.
3) Using a small, narrow length of painter's tape, secure half of the component to be soldered, using tweezers to align the component's leads before firmly pressing down the tape. It's pretty easy to get a nearly perfect alignment in this step. Make sure that the tape isn't too close to the component's leads; you don't want to block your view or burn the tape when soldering.
4) With a medium hot soldering iron and a small tip, solder the exposed leads. Use just enough 20mil rosin-core solder to patiently cover each pad and lead, one at a time. If you're careful, you shouldn't have to apply additional flux. I use a Hakko 888D with a TS18-S4 tip set at 600F. To stabilize the soldering iron, rest as much of your hand and arm on the tabletop as is possible.
5) Remove the narrow strip of tape holding the component and finish soldering the remaining leads.

If you're just starting to design and build SMT circuits by hand, choose larger components where possible. I mostly use 1206 resistors, 1210 tantalum capacitors, SMA diodes, and SOIC-8 devices, but have ventured into SOT23-5 and even some 0805 passives with success. I have quite a few more projects in the design phase that will certainly use SMT. Through-hole is great for the breadboard, but I'm completely sold on using SMT now that I know I can successfully and reliably build it by hand.

Oh yeah, the Adafruit ruler (#1554) works great for checking component sizes. Highly recommended.

Again, thanks to Lady Ada, Collin, and especially Trevor and Russ at the local Confluent Maker Space for help and inspiration.

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Use a small strip of painter's tape to align the component while allowing access to half of the leads. When the tape is firmly pressed down, it will resist movement during soldering.
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Close-up of component lead alignment just before soldering.
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End result.
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Last edited by HarpDude on Fri Mar 11, 2016 3:07 am, edited 3 times in total.

Posts: 128
Joined: Mon Dec 07, 2015 2:52 am

Re: Building SMT Hand-Soldering Skills

by adafruit_support_bill on Thu Mar 03, 2016 7:08 am

Nice! Thanks for sharing your technique.

Posts: 61008
Joined: Sat Feb 07, 2009 10:11 am

Re: Building SMT Hand-Soldering Skills

by HarpDude on Sun May 15, 2016 11:26 pm

Update (many SMT PCBs later...) :

1) A small pinch of blue tack (Loctite Fun-Tak) works very well and is a very inexpensive and reusable solution. Appreciate the advice from the makers out there -- thanks!

2) For the smaller SMT ICs, I've also used a small square of heat sink thermal tape (# 1468 https://www.adafruit.com/products/1468) between the component and the PCB to hold it in place for soldering -- and, in some cases, to provide a thermal connection to a PCB heat sink plane. The thermal tape isn't quite as efficient as a solder bond for thermal transfer so don't rely on it for critical applications, but for chips that don't require highly-efficient heat sinking, it works quite well and doesn't seem to break down over time.

Posts: 128
Joined: Mon Dec 07, 2015 2:52 am

Please be positive and constructive with your questions and comments.