Thermaltronics TMT-FP-1 Rosin Flux Paste, 2.0 oz (57 g)

Works great. Just needed some flux for some projects and this works great. No issues and definitely worth it. Quality stuff.

I use this whenever I need to tin the tips of magnet wire. That's the main purpose, being able to dip something before applying solder to it. Works like it should.

The Thermaltronics TMT-FP-1 Rosin Flux Paste is a dependable, high-quality flux designed to improve solder flow, enhance wetting, and reduce common soldering issues like cold joints or bridging. Compact, easy to apply, and formulated for electronics work, this rosin paste is a reliable choice for hobbyists and professionals alike. 🔥 Flux Performance & Chemistry Rosin flux plays a critical role in soldering by cleaning metal surfaces and promoting better solder adhesion. The TMT-FP-1 excels in this core function: Improves wetting: Encourages solder to flow smoothly into joints Cleans oxide layers: Helps remove stubborn oxidation on pads and leads Reduces defects: Minimizes cold joints, incomplete flows, and bridging when used properly 📌 Verdict: A solid rosin paste that noticeably enhances solder performance compared to “no flux” or generic alternatives. 🧴 Ease of Application One of the strengths of this product is its user-friendly paste form. The consistency makes it easy to place exactly where it’s needed — especially useful for fine-pitch work or dense boards. Paste format: More controllable than liquid flux Application tool: Often used with a small brush, toothpick, or applicator Non-messy: Clean paste that doesn’t run or drip excessively 📌 Verdict: Very approachable for beginners and convenient for seasoned technicians. 🛠️ Use Cases & Compatibility The TMT-FP-1 Rosin Flux Paste works well in a variety of soldering scenarios: ✔ Through-hole and surface-mount components ✔ Repair and rework projects ✔ Leaded and lead-free soldering (with appropriate temperature adjustments) ✔ Circuit boards with minor oxidation 📌 Verdict: Versatile enough for most hobby, repair, and light professional soldering tasks. 💡 Thermal & Residue Behavior Rosin flux tends to leave behind slight residues — but this formulation maintains a low-residue profile that is less likely to cause issues in finished assemblies (though cleaning might be recommended for sensitive electronics or optical circuits). Residue: Light and non-corrosive Temperature range: Performs well within typical soldering ranges 📌 Verdict: Good balance of activity and cleanliness. 📦 Packaging & Size The paste comes in a small, sturdy tube or jar that’s easy to store on a workbench. The size is convenient for occasional use, but frequent solderers may find themselves returning for refills sooner than with larger bottles. Package: Compact and bench-friendly Storage: No leakage; resealable 📌 Verdict: Practical packaging, though larger size options would be nice for heavy users. 🔎 Pros Encourages improved solder flow and wetting Easy to control thanks to paste form Works well for both leaded and lead-free solder Low-residue rosin formula Great for detailed PCB work and component reflow ⚠️ Cons Smaller quantity — may require frequent replenishment for heavy users Rosin flux residue still exists — cleaning recommended for certain sensitive applications Not as active as some high-activity no-clean flux pastes (but remains safer for general use) ⭐ Final Verdict The Thermaltronics TMT-FP-1 Rosin Flux Paste is a solid, reliable flux that enhances soldering performance by improving wetting, cleaning oxidation, and reducing common joint problems. Its paste format makes it easy to use precisely where needed, and the low-residue rosin formulation is appropriate for a wide variety of boards, components, and skill levels. Whether you’re a hobbyist stepping up to more complex projects or a technician focused on cleaner joints and better consistency, this flux paste is a practical bench companion that delivers noticeable results.

Excellent no nonsense flux. The design of the cap makes it impossible to remove and it pisses me off

This is seriously a great rosin, the consistency is like a thick whipped honey... Can get a little messy with stringers but it does stick where you want it, unlike many competitors. The downside is the that can they package it in. It is next to impossible to pry open and when you do finally crack it... The rosin has stuck to the lid and you end up with it all over the place. If they'd just put a little release swivel on the can like is done with shoe polish there would be no problem. Seriously though.... It takes 5 minutes of sweat and cursing to get that lid off. I repackaged mine in a baby food jar. Now I get all the love and none of the hate!

This flux paste does its job perfectly and performs just as expected. Great product for a very reasonable price.

Makes the solder flow, good cost

From the MSDS obtained online from the manufacturer, this is 40-60% petrolatum (vaseline) and only 35-45% rosin (originally pine tree sap; often a synthetic blend of chems these days). By comparison, High quality Radio Shack rosin is minimum 65% rosin and works like a dream. "Flux" comes from the Latin for "to flow". A mild acid in melted rosin removes the oxidation layer from the surface of exposed metals (wire strands for my purposes) and coats them so that solder can flow freely between the strands and form a sound joint. Without a flux like rosin, you end up getting a "cold solder" where the surfaces of the joint are coated with blobs of solder but it doesn't penetrate the wire strand bundle to the center. That is a weak solder joint and prone to failure. Vaseline does nothing to deoxidize metal, though it can help molten solder flow more easily, so that's kind of a mediocre way to "extend" the rosin. And it's cheaper to manufacture. Like many things, with rosin flux you get what you pay for. Next time it'll be Radio Shack flux... Next time I'll buy a different brand that's all rosin or at least mostly rosin, but this time I needed it in a hurry and this petrolatum-based rosin flux was the only reasonably priced product that shipped by prime as fast as I needed. I use this to assist soldering with cheap crummy Chinese rosin-core flux solder that barely has any flux in it (decent, more expensive domestic solder contains sufficient good quality rosin flux inside), and tend to slather it on my connections with a flat toothpick, so there ends up being enough rosin in the vicinity to get the job done. Keep in mind that soldering makes a tough physical connection; though tin/lead solder will conduct electricity, it does not do so as well as copper wire. Soldering is for durability, not to conduct electricity. Rosin core solder/flux is only for electronics work, not plumbing (acid flux that would destroy electronics) or making stained glass (expensive silver solder). Different solders and different fluxes for those applications. For a hobbyist electrician, a few ounces of flux will probably last for years; decades for the rare tinkerer. At least you know the vaseline won't evaporate in that time, argh!