January 16, 2012

Making an SMD circuit board without specialized equipment (This is a developing story.)

Filed under: To blow your mind — VIP @ 02:58

When you think of soldering an SMD – mounted component on to the circuit board, you are probably thinking of the reflow oven and some other expensive equipment. Not in my case.

But you have to remember that any DIY technology involves some risk taking and some estimation of the economic benefits/losses. I began searching the internet and looking for a cheap solution to make DIY circuit boards at home, and I didn’t find an instruction that would match my goal from the beginning to the end.

What I learned:

  • That this exponential growth but to but with exponential decay function of temperature over time can be obtained by making a control module for the toaster oven with an alarm that will warn you when to open the door. I am still looking for the website I read it at. (Remember the Newton’s Law of Cooling?)
  • There is a way to solder SMDs on the frying pen. I bought a frying pan with low edges for making a French toast.
  • After I tried to solder an SMD onto the breakout board and had the board bend and turn brown from uneven heating, I took some silicone grease that can hold 400˚F (204˚C) and used that to evenly transfer heat. I also tried using sand, but the grease works better.
  • Only if the board is pre-tinned, you can solder the component right on to the board.
  • I bought a laser thermometer. It is not very precise but it is fairly precise when it comes to change in temperatures. (How else would you measure the temperature of the molten solder?)
  • 60/40 solder contains sixty percent tin and forty percent tin. The melting temperature of the solder is 183–190 °C (361–374 °F). Although Tin and Lead have fairly high boiling points, the solder can boil below 300°C and that’s what you don’t want to happen by any means unless you are trying to get lead poisoning.
  • I bought a portable range so I could experiment with solder boiling outdoors.
  • Lead is a known toxic metal but more expensive ROHS-compliant solder has a number of other neurotoxic heavy metals to replace lead. Antimony is one of them.

Fluxes are the trickiest part: there are too many options on the market to try in a lifetime.

  • Plumbing paste is not recommended because it is acidic and will corrode the solder spot after the assembly is finished, because the moisture in the atmosphere will make the remains of the solder into electrolyte. (Can it be washed away with alkali? Not sure yet. Experiment is on the way.)
  • Old-school chunks of brown rosin can be dissolved in rubbing alcohol to make a very good flux for precision soldering. Store it in the bottle and use a linen brush to apply the flux onto the solder joint. The rosin can hold your SMD component.
  • Modern organic solvent rosins are more expensive, but superior to rosin flux. They have a limited shelf life. Some of them can glue the component on to the spot the way rosin solution can.
  • A rare and a more expensive industrial product – the solder paste has a mixture of both, flux and powdered metals. As the heat is applied, the paste melts, burns out the flux and forms a strong solder joint. Similar to brazing.
An example of a successfully soldered SMD negative voltage generator. This silicone grease makes an ideal medium to transfer heat from the frying pan to the circuit board.


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