Zoso!, via

If we listened to most crusty engineers, we’d never stop using leaded solder. My crustiness, on the other hand, is leading to greater health-related conservatism. Lead free solder melts at a higher temperature, and is therefor harder to work with; the benefit, however, is keeping this dangerous chemical out of your personal environment. Here’s the Materials Safety Datasheet if you want the details.

Kester NGX1, via

For my first test, I used Kester NXG1 (the stuff that OSH Park ships as an add-on product). I was shipped a minimally-labeled syringe, so I’m grabbed the general NXG1 specs from the manufacturer’s website:

1. Alloy:
   1. Mostly tin, with a little bit of silver and copper
2. Powder size:
   1. Smaller particles can be printed through smaller screen apertures
3. Type: No-Clean
   1. Flux is incorporated into solder in order to remove oxides and promote adhesion/wetting
   2. No-clean doesn’t require post-processing with flux remover (though some people still do it due to potential problems with sensitive boards)
4. Halogen: Yes
   1. Fluxes that contain halides leave the most residue and are easier to clean.
   2. The presence of halogen or halides (synonymous for our purposes) can pose environmental and even technical issues.
   3. Like the no-clean conversation, I’m assuming any potential technical problem created by halides is an edge-case.
5. Lead: No
6. Application: Screen/stencil
   1. I assume the alternative would be a more freely flowing formulation that’s better for syringe application.

Reflow profile, via

Once you’ve picked your solder formulation, the next step involves setting up a custom reflow profile. This information is found on the product’s datasheet, and is a total rabbit hole! Should I review the specs of every one of my project components to verify they can withstand my intended profile? I think we both know I didn’t do that. Parts are cheap, so I just waded in with a test. My main questions were as follows:

1. Will the solder wet the parts/pads and get good adhesion/conductivity?
2. Will any of the parts fail when cooked at that temp and for that duration?

Shaving the yak, via

After setting up a custom profile to match my solder, I populated a board and gave it a go. Unfortunately, it seemed that the Reflowr (previously discussed here) just wasn’t getting up to the right temps. Perhaps my device needed recalibration?

Calibration with IR gun

Initial tests returned wonky results; it seemed that my reflower was not getting as hot as its internal sensors were reporting. My IR readings of the plate surface seemed to confirm this, but a conversation with the manufacturer revealed that I should be pulling my readings from the non-metallic surface of a PCB resting on top of the plate. After adjusting my measuring technique, I was still getting low readings. What the heck was going on?

This issue has gone on for so long I’m just going to post this as-is. Stay tuned for the solution (I hope).