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Suzy's super rosin paste flux


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We're in a no-clean, water-based, lead-free world, and that sucks. Decent rosin paste flux is getting harder to find every time I go looking, and with the secrecy around formulations who knows what's in that stuff.

 

Here's a recipe for paste flux just like your grandma made when you were a kid. Nothing but the finest free-range organic ingredients, and made with love. Cook some up and gift it to that special engineer in your life, or just make a batch for your own use.

 

Seriously, this doesn't just resemble paste flux. It's the actual thing. It's not activated, which means that there are no acids added besides the naturally occurring abietic acid in the rosin. You can add additional acids if that suits your process, but go easy.

 

This recipe makes enough to last a typical engineer a good few months. The ratio of rosin to vaseline yields a flux that's just right for syringe dispensing, with good tack.

 

Ingredients:

 

15g of gum rosin, in chunks.

10g vaseline.

 

Method:

 

Combine the rosin and vaseline in a 48ml Kilner hexagonal preserve jar. Break up the rosin if necessary to get it into the mouth of the jar.

 

IMG_1513.jpg

 

Heat the mixture in the oven at 120˚C for about 20 minutes. The rosin will melt and form a thick treacle layer under the vaseline, which will go perfectly clear.


IMG_1514.thumb.jpg.e2d8f7cc7ed310dbc3394510d6d901d9.jpg

 

Pull it out and stir to combine layers with a paddle-pop stick.

 

Pop it back in the oven for another few minutes, to encourage any trapped air bubbles to rise to the surface.

 

Take it out of the oven and let it cool for ten minutes or so before sucking into syringes, if that's your preferred dispense method. I find if I leave it too long it thickens up and is hard to draw into the syringe

 

IMG_1518.thumb.jpg.ab6a7023994c6981fe4ed5051da797a4.jpg

 

Edited by Suzyj
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That is amazing, @Suzyj.  :thumb:

 

But I'm wondering when does one have to use flux?  Both the (not lead-free!) solders I use:

* Loctite 0.7mm 362 SN62 5C, and

* TRT Wonder Solder (1.5mm diam)

 

... seem to include their own flux - as they flow easily?

 

Regards,

Andy

 

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Additional flux is needed when you’re reflowing solder. A typical SMD process is to tin a pad, then bring the component into contact with the pad and reflow. If you don’t use additional flux then this doesn’t work. The flux in the solder wire is (barely) enough for the initial wetting of the pad. There’s none left for the subsequent melting.

 

I do piles of SMD, and use a lot of flux. It’s the secret sauce for perfect solder joins.

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51 minutes ago, Suzyj said:

Additional flux is needed when you’re reflowing solder. A typical SMD process is to tin a pad, then bring the component into contact with the pad and reflow. If you don’t use additional flux then this doesn’t work. The flux in the solder wire is (barely) enough for the initial wetting of the pad. There’s none left for the subsequent melting.

 

I do piles of SMD, and use a lot of flux. It’s the secret sauce for perfect solder joins.

 

Aah, OK - for SMD soldering.  Thanks.  :thumb:

 

(I recently went through a build process that involved a total of 24 SMD devices - plus lots of through-hole devices.  I didn't enjoy the SMD work!  :o )

 

Andy

 

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Extra flux helps with through hole reworking as well, any reworking really, nice thread, Suzy :thumb:

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There’s nothing wrong with SMD! I quite like building surface mount boards. I like to do an unholy mix of surface mount and through-hole, with plenty of MELF resistors and diodes.

 

 

C8E01A48-843C-479F-945D-C1CE201AFA4B.jpeg

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Normally I clean my boards before I take photos, as showing my flux is a bit like going out in my PJs. This thread, however, is about flux.

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It’s very soluble in isopropyl alcohol, so cotton buds dipped in iso to mop the majority up straight after soldering.

 

Once the board is assembled I do a thorough scrub in hot (like 80 degree) water with some safe wash detergent in it, then rinse with deionised water.

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