Desoldering Components (EE Tip #118)

Every engineer and technician sooner or later faces the challenge of having to desolder a component. Sometimes the component can be a large transformer with 10 pins or a power chip with many connections, and desoldering tools are typically around the $1,000 mark and above.

Chip Quik is a solder-based alloy that stays molten for up to 30 seconds and makes desoldering any component very easy. The only drawback is that the cost of a 2´ length of Chip Quik is around $20. But a little experience can make this go a long way. Having some Chip Quik lying around in the workshop is reassuring for when that urgent job comes in.

Editor’s Note: This EE Tip was written by Fergus Dixon of Sydney, Australia. Dixon, who has written two articles and an essay for Circuit Cellar, runs Electronic System Design, a website set up to promote easy to use and inexpensive development kits. Click here to read his essay “The Future of Open-Source Hardware for Medical Devices.”

CC276: Not a Hockey Fan?

Hockey can be fun, unless you’re building a surface-mount device (SMD) prototype and the “puck” is one of the tiny components getting away from your soldering iron. In an article appearing last month in Circuit Cellar, “DIY?Surface-Mount Circuit Boards: Tips and Tricks for Building SMD Prototypes,” engineer James Lyman inadvertently sparked a bit of debate on the magazine’s website. Readers posted various alternatives to Lyman’s approach to the “SMD hockey” challenge. Here’s how Lyman’s article describes the problem and his solution:

“When I built my first few surface-mount boards, I did what so many amateurs and technicians do. I carefully placed each minute component on the circuit board in its correct position, and then spent several minutes playing ‘SMD hockey.’ With nothing holding the component in place, I’d take my soldering iron and heat the pad component while touching the solder to the junction. Just as the solder was about to melt, that little component would turn into a ‘puck’ and scoot away. Using the soldering iron’s tip as a ‘hockey stick,’ I’d chase the little puck back to its pads and try again, which was maddening…

“It slowly occurred to me that I needed something to hold each part in place while soldering—something that would glue them in place. Commercial houses glue the components down on the boards and then use a wave soldering machine, which does all the soldering at once. That’s exactly what I started doing. I use J-B Weld, a common off-the-shelf epoxy.”

Here is a sampling of alternative solutions readers posted to circuitcellar.com.

  • From Bill: “If you must use epoxy, then the cheapest fast-setting epoxy from Poundland will do the trick.
    “Personally, I’ve always used a tiny spot of cheapo CA superglue, which gives you 20-60 s to position the component. If there are a lot of SMDs on the board, you might want to use an accelerant spray to reduce the CA cure to 5 or 10 s. If you can’t afford proper CA accelerant, then isoprop or a gentle waft above the board with a cloth soaked in a little household ammonia will do the trick.”
  • From Trevor: ”I did a lot of hand soldering of SM parts years ago and agree that it is best to fix the parts before soldering.
    “I used an adhesive made for SM parts from RS Components, which comes in a syringe and is really easy to use. ” (Trevor’s post provides a link to his preferred Electrolube brand.)
  • From Kevin: ”Crikey, epoxying all the components first is a bit brutal. What if you want to change one? Melt the solder and twist, all at the same time?
    “Much easier to tin one pad, then place the part on it with tweezers and touch it with the iron, one end soldered fine, now solder the other end.”

Feel free to visit circuitcellar.com to weigh in or take some of the advice offered there.

DIY Surface-Mount Circuit Boards

James Lyman, an engineer with degrees in Aerospace, Electrical Engineering, and Systems Design, has more than 35 years of design experience but says he was “dragged” over the past decade into using surface-mount devices (SMD) in his prototypes. He had a preference for using through-hole technology whenever possible.

“The reasons are simple,” he says in an article appearing in the June issue of Circuit Cellar magazine. “It’s much easier to use traditional components for building and reworking prototype circuits than it is to use wire to make the connections. Plus, the devices are large and easy to handle. But time and technology don’t leave anyone at peace, so my projects have gradually drifted toward surface-mount design.”

In his article, Lyman shares the techniques he developed for designing prototypes using SMD components. He thought sharing what he learned would make the transition less daunting for other designers.

This accompanying photo shows one of his completed circuit board designs.

Lyman’s techniques developed out of trial and error. One trial involved keeping small components in place during the building of his prototype.

“When I built my first few surface-mount boards, I did what so many amateurs and technicians do. I carefully placed each minute component on the circuit board in its correct position, and then spent several minutes playing ‘SMD hockey,’ ” Lyman says. “With nothing holding the component in place, I’d take my soldering iron and heat the pad component while touching the solder to the junction. Just as the solder was about to melt, that little component would turn into a ‘puck’ and scoot away. Using the soldering iron’s tip as a ‘hockey stick,’ I’d chase the little puck back to its pads and try again, which was maddening. Finally, I’d get a drop of solder holding one end of the puck in place, usually with the other end sticking away from its pad. Then I could reheat the solder joint while holding the puck and position it correctly. I would have to start over with the next component, all the while yearning for that wonderful old through-hole technology.

“It slowly occurred to me that I needed something to hold each part in place while soldering—something that would glue them in place. Commercial houses glue the components down on the boards and then use a wave soldering machine, which does all the soldering at once. That’s exactly what I started doing. I use J-B Weld, a common off-the-shelf epoxy.”

Using an easy-to-get epoxy is just one of the tips in Lyman’s article. For the rest, check out his full article in the June issue of Circuit Cellar.

 

RFI Bypasssing

With GPS technology and audio radio interfaces on his personal fleet of bikes, Circuit Cellar columnist Ed Nisley’s family can communicate to each other while sending GPS location data via an automatic packet reporting system (APRS) network. In his February 2012 article, Ed describes a project for which he used a KG-UV3D radio interface rigged with SMD capacitors to suppress RF energy. He covers topics such as test-fixture measurements on isolated capacitors and bypassing beyond VHF.

Photo 2 from the Febuary article, "RFI Bypassing (Part 1)." A pair of axial-lead resistors isolate the tracking generator and spectrum analyzer from the components under test. The 47-Ω SMD resistor, standing upright just to the right of the resistor lead junction, forms an almost perfect terminator. (Source: Ed Nisley CC259)

Ed writes:

Repeatable and dependable measurements require a solid test fixture. Although the collection of parts in Photo 2 may look like a kludge, it’s an exemplar of the “ugly construction” technique that’s actually a good way to build RF circuits. “Some Thoughts on Breadboarding,” by Wes Hayword, W7ZOI, gives details and suggestions for constructing RF projects above a solid printed circuit board (PCB) ground plane.

You can read this article now in Circuit Cellar 259. If you aren’t a subscriber, you can purchase a copy of the issue here.