Soldering

To get into SDR I needed a radio, and Softrock provides a very cost effective kit.  The radio hardware as it turns out is fairly simple, and Tony Parks is making kits available (in batches) at very reasonable prices.  But , to build a kit, there is that thing about soldering SMT (surface mount technology) components.  There is a lot of SMT advice available – never having done it before I read through a bit of it and decided it is doable.  If you know what a cold solder joint is and how to not make cold solder joints, SMT soldering for softrocks should not be a problem.   See the wb5rvz.com page for links and comment.

Good magnification is necessary while soldering as well as good light.

To remove SMT parts from the packaging use a sharp dental pick and non-magnetic sharp tweezers.  The parts are a couple of milimeters in length.  Work inches from the circuit board to be soldered so you don’t move the tiny parts any kind of distance.

Soldering.    I would not solder SMT without a temperature controlled soldering iron at least as good as the Hakko FX-888.   Without one, soldering is going to be really difficult.  The Hakko is great and SMT is easy.   Use the 1.2 mm tip – it is the right size for this kit.  Also the .015 solder is a must for SMT parts.  This is hair thin solder – use it only for the SMT parts, and other solder for bigger parts.  Melts fast, has a good clear flux built in.

  1. Working conditions. Bright light on the working area. Use magnification.  Keep the pick and tweezers close.  Open the part to be soldered no more than an inch or two from the board which has been clamped firmly in place.  I used a pick to peel off the seal, and invert the part holder and drop the little brick-like component very close to the  board in a clear area.  Work close – very close, and you wont lose the part or worse yet, launch it into space, while handling it.
  2. Soldering iron tip: 1.2 mm chisel tip (for the Hakko the T18-D12).
  3. Temperature: 320 C  seemed to work the best.  I let the iron idle when not using it, then dial up to 320 when ready to solder.
  4. Heat the board pad where the part will be soldered to.  Ideally – position the chisel blade of the iron for maximum contact on the pad to heat, then position solder wire perpendicular to the blade between the pin and the pad if possible.
  5. Resistors and capacitors:  Tin one side of the pad to be soldered, position part, heat and let it drop in place – allign while the solder is liquid.
  6. Transistors:  Tin one of the three pads, heat and align.
  7. ICs:  Tin one pad to tack the part in place with all pins centered on their pads.  Don’t let solder glob – wick off excess liquid solder to ensure solid contact.  ICs are easy but don’t let solder glob.
  8. Don’t let the solder glob into a ball or there will be cold solder joints.  Use copper solder braid to wick excess off the pad/part and ensure the joint is solid.

Additional notes from Jasmine Strong (message 67625) on the softrock40 site on consistency in soldering and resoldering:

Use a damp pad, not a dry one (for cleaning the tip). The steam helps to break down oxide and remove flux residue from the tip.

Use a swab with isopropanol to clean all the flux residue off the “bad” chip, then solder wick to clean all the solder off, then swab it clean again (there’s flux in the braid), then drag fresh solder across it. Don’t be afraid to add more flux; don’t be afraid to clean off spent flux.

The way flux works is that it contains organic peroxides that scavenge oxides and discourage the formation of intermetallic compounds. It has to be heated hot enough to activate it (you get smoke) and once it’s activated it has a limited lifespan of a few seconds; all that’s left after that is sticky goo that needs to be cleaned off.
 

Tools

  • temperature controlled soldering station – Hakko FX-888 with the T18-D12 1.2 mm chisel soldering tip (ordered separately) B+D Enterprises on Ebay.
  • .015 solder – (Ebay – kyle jones – kester .015 63/37 eutectic solder – cheap and fast)
  • roll of copper solder wick – Radio Shack and some comes with the Hakko.
  • dental pick – pointy and sharp
  • tweezers – sharp
  • mountable hands free magnifying lenses and lenses for close inspection of solder joints
  • a jig or something to firmly hold down the board so it doesn’t move while soldering
  • digital multi-meter ( I have a Fluke -77) for testing

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

 
%d bloggers like this: