Iffy's Soldering Info

Iffy;14016744 said:

It was requested that I post this info in this thread...

Bigger da Blob, Better da Job...NOT!


Having taught USAF High Reliability Soldering based on NASA curriculum standards, I’d like to share some critical soldering guidelines for ya'll. It's not rocket science; just a lil' physics, common sense and 'touch' (more on that in a bit).

BTW, there was a study that determined that there was, on average, 200 lbs of excess solder on a typical B-52 at the time. Ergo, the soldering course!

Here we go:

- Use 60Sn40Pb rosin-core solder (most common). 63Sn40Pb is ideal due to no plasticity stage, but hard to find locally and not cheap.
- Only use rosin flux for electronics.
- Prep all wires and the soldering tip by using a rosin paste flux and a small amount of solder.
- Dip tip in flux, apply solder, then thermal shock the tip by lightly wiping tip on a water dampened sponge or cotton cloth. This will ‘blow off’/shed tip contaminates.
- Apply a small amount of solder twix the fluxed lead(s) and the tip to build a heat transfer bridge.
- When solder flows, move the solder away from the lead tip to within 1-1½ lead diameter of the stripped wire insulation. Minimal solder with 100% coverage = 'touch'.
- Remove all flux residue from the lead(s)/connection with Denatured Alcohol (DA) using a lint free cloth/wipe. DA does not leave a residue. Rubbing alcohol will suffice, but can leave a slight haze.
- When attaching tinned leads to a circuit board/component, repeat the above steps.
- Add solder to the soldering tip while it’s resting. This minimizes oxidation/erosion of the tip. When you’re finished soldering, just let the blob harden as the tip cools. You will re-prep the tip prior to your next project.

For de-soldering (i.e. circuit boards, speaker lugs), use de-soldering wick to remove old solder. Remember to flux the wicking prior to applying the prepped soldering tip. Also remember to clean the contact point(s) to remove the flux residue. In an emergency de-soldering situation, if ya don't have any de-soldering (wicking) braid, pull some ol' braided shielding off a coax cable (guitar/speaker/TV), stretch it taunt, flux it and suck 'er up.

Do not abrade/scrape the soldering tip to remove solder. You'll be shortening it's life and doing more harm than good.

Do not cut your solder. Use your soldering iron/gun. This seals the solder and prevents rosin 'weeping' and evaporation.

In high vibration and/or stress environments, take extreme care in stripping the insulation. Any nicks that scrape strands and/or removes pre-tinning can be a 'weak link' and a possible failure point.

NEVER reapply heat to a joint without following the steps above. Failing to do so is a common cause for a cold and hazy solder joint. All proper joints should be shiny when using 60/40 solder.

Use an appropriate wattage iron/gun for the job. For cabling, you can use higher wattagse. If you use a very low wattage iron on cabling, you may not have enough heat to melt the solder before contamination occurs, especially for grounding braids. For circuit boards and small leads, use a low wattage iron. The larger ones can, and will fry smaller components.

I have 15W, 25W, 40W irons, a dual 100/140 wattage gun, plus a resistive temp control station. The 25W iron is my go-to for 90% of my soldering. A 15W iron should be just right for your mod circuit board assemblies.

Assuming you follow the guidelines, timing (aka 'touch') is the 'holy grail' if 'saddled' with just one iron. Just establish a good heat bridge and watch for clean solder flow.

I just rewired two mics that had 24 gauge wires (re very small). Had to use the 15 watt pencil iron to prevent insulation burn off.

For circuit board connections, follow the same basic steps outlined above. When de-soldering a circuit board pad that has a hole for component mounting, don't forget to wick both sides of the board.

In critical heat sensitive areas, you can use clip-on heat sinks to protect adjacent micro-circuitry.

In the absence of good ventilation, aim a fan to blow over, not on, your work to remove fumes/smoke.
Do not blow on molten solder! That's another common way to get a cold solder joint. The solder must cool at its own rate for the best connection and maximum integrity.
Cleanliness and proper heat transfer using minimal solder is the key for the best connection! It’s all in the physics, preparations, cleanup and ‘touch’.

Hopefully these guidelines will lead you to zero resistance and reliable connections.

If ya have any questions, corrections or suggestions, please LMK!

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