Chip Quik SMD291AX Solder Paste no clean 63Sn/37Pb in 5cc syringe 15g

Not going to pretend this is a discovery — Chip Quik SMD291AX has a reputation in the hobby electronics community for a reason and that reputation is earned. Been running this through a stencil on leaded paste reflow work for a limited board run and the results have been consistently clean across the whole batch. Paste consistency is exactly where it needs to be. Extrudes smoothly through a stencil without bridging on fine pitch pads, holds its shape between application and reflow without slumping, and the tack is strong enough that components stay put through handling without shifting before heat is applied. These sound like baseline requirements but cheaper pastes fail at least one of them reliably. 63/37 eutectic alloy means a sharp liquidus transition at 183°C with no plastic phase — you get a clean reflow without having to babysit the thermal profile as carefully as you do with non-eutectic alloys. The joints come out shiny and well formed consistently. No clean flux residue lives up to its name. Left the boards as-is after reflow and the residue is minimal, non-corrosive, and doesn't cause any issues with continuity or appearance. When I do clean it IPA takes it off without any effort. 5cc syringe format is practical for stencil work and hand application on rework. Keep it refrigerated between sessions and it stays workable for a long time without drying out or separating. If you're doing any volume of SMD assembly and still experimenting with paste brands stop experimenting. This is the one.

Perfect for dealing with computer elements and for tight places.

Heats up and flows more or less as expected, with the odd bit of solder flying off. Make sure to clean up with isopropyl alcohol after use.

As the old saying goes, "a little goes a long way". I practiced soldering using an old SMD based VGA card, removing components, solder wicking the pads, applying this paste, setting the component in place and heating it with my hot air workstation. It's satisfying to see the grey pasted suddenly flash into a silvery mercury--like liquid, and seeing it pull into the pads to form a perfect solder joint. Just a tiny pin dot of the stuff on each solder pad is all you need. Any more than that and you'll need to wick away the excess as it forms solder bridges. After I made several successful chip replacements on the test board, I tackled my expensive audio analyzer relay replacement. This paste made short work of it. Highly recommended.

I've been able to use the same syringe of this flux for years, storing it in the refrigerator. I've had better results with this flux than others when stenciling. The solder seems to reflow more easily and the components stay put when using a hot air iron at low air velocity. Throw it in the refrigerator for a bit, or it will tend to stencil into small puddles instead of well-formed shapes. In my opinion, it's the best.