How to Make DIY Solder Paste for Tinning PCBs at Home





Introduction: How to Make DIY Solder Paste for Tinning PCBs at Home

I was looking for a solution for pre-tinning my DIY PCB boards. One way to do this is by reflowing solder paste. Another very cool use is repairing brass instruments - like trumpets, trombones and tubas, because all you need to do is heat up a joint with the paste in place and it magically bonds at the right temperature.

If you go on EBay and search for solder paste - the pro stuff costs an arm and a leg for small amounts, so I was wondering if it is possible to make entry grade solder paste at home. After looking at several forums, I found a forum conversation in which someone used shavings from a filed block of solder mixed with solder flux to create paste, and reported it as success. I decided to recreate this, and in the process discovered that it is much easier than i thought. And the bonus is that working with the pre-tinned pcbs is so much easier, soldering times are now significantly reduced. 

Also read this:

What you will need:
1)  Solid Solder - 50-50 or 60-40. You can use solder that has flux in it - as long at it is NOT acid based flux which will corrode your components
2) A medium to fine file - the finer the file - more work but better quality paste
3) Solder Flux - also called "solder paste" but do not confuse this with real solder paste. Make sure it is not acid based for intended for soldering! Radio shack sell some of this stuff. 
4) a toaster oven, fire, or oven. 

This instructable has 12 steps.

Step 1: Prepare Solder Bits for Melting

1) Cut the solder into strips or pieces
2) Put in aluminium foil. fold the foil a few layers thick so no solder will leak out and mess up your nice toaster oven or stove or leak on something important like your foot
3) Form a makeshift "pan" or "boat"  

Step 2: Bake, Cook, Grill or Toast

You want to melt the solder into a nice big blob.

I used the toaster at the highest heat (broil setting) for 40 minutes.
You can also place the boat on a metal plate over a counter top stove. WARNING:  Do not put the makeshift boat/pan directly on a fire, as it will eat through the aluminium, and you will have a nice solder puddle to clean up. You do not want to get in trouble with the local home management team. 

Once the solder melts, take it out/off and let it cool down into a bar of solder, the shape does not really matter. 

Step 3: Cooling and Prepping

Discard the aluminium wrapping. 


Step 4: File/Grind the Solder Bar

Simple really: File or grind the solder bar into a fine powder. Note if you go fast you will get bigger pieces and eventually the bar will heat up, so you want to rotate the bar from time to time to prevent it from melting due to the friction heat!


Step 5: Mix the Powder Into the Flux

In this picture i added too much powder to the flux and it became chunky - I will need to add more flux to this paste. Nevertheless, this is sufficient for the next demonstration.

Step 6: A First Test

After a few test boards - I decided to try this out on a real project. For the purpose I revamped a classic NEVE based preamp that will be transplanted inside a classic RCA Varacoustic ribbon microphone, and will give it the gift of a super sound, phantom power and real world versatility. 

I was in a rush to show off, so unforunately I didnt strip off all the photoresist (the blue residue on some of the pads and leads. This is where the solder will not catch on properly. Lesson learned. Next time let the board sit in the resist remover (baking soda)  instead of trying to quickly scrape it off. 

Step 7: Add THIN Later of Paste

I put what i though was a little bit of paste on board. When you see the results you will see I should have put less. and spread it around. It really doesnt matter where the gray solder is. once the flux melts and the solder melts - the solder will magically be pulled onto the traces and coat the copper. 

TIP: One nice thing I discovered is that if you want to get really good results in etching, exposing, and tinning - you can clean off the board with Comet kitchen cleaner and it works better/safer/quicker/far-better than acetone. 

Step 8: Heat the Board - Part 1

For this demo I used a hot air rework gun so you can see it in operation. You can also use the "toaster reflow" method if you can get your toaster to 500F or try the broiler - also might work!

Step 9: Heat the Board - Part 2

Here i stopped half way - just so you can see how the paste magically flows onto the traces

Step 10: Almost Finished

After the board is completely flowed - it will be covered with flux which you will need to clean using (yes again) Comet - or dish soap and water. You can use scotch brite to get rid of the flux. 

Step 11: Final Reflowed Board

As you can see for a first try its not bad - no solder bridges!  Assembling a PCB becomes a piece of cake. You can also use it for SMD components (yes I tried - there are a few SMD Caps on the board that were easy to assemble).

Step 12: Final Result

The final results are a cost effective way to produce enough solder paste to last you a lifetime, at home with minimal effort!

Hope you enjoyed this instructable!



    • Water Contest

      Water Contest
    • Creative Misuse Contest

      Creative Misuse Contest
    • Oil Contest

      Oil Contest

    26 Discussions

    can you tell me the name of flux ?

    Are there any issues with tracks accidently joining to one another with small melted 'bridges' ? I have been trying to find some solution to this for ages, thanks!

    2 replies

    Before you make the circuit you can use a solder paste stencil, which helps to avoid briding. A simple tutorial could be found here :

    1) Solder sucker (or desoldering iron). (Which is an iron with a built-in sucker.)

    2) Solder Removal Braid (or just use ordinary stripped multi-strand wire).

    Wow awesome idea, never thought about sanding it.

    Wow, that is so cool! I love your creative use of what you had around you to accomplish a goal! I think I will try this in my test etch board.

    I wonder if anyone has tried to do this in a ball mill? Skip the first remelt and throw the chunks into a rock tumbler with some good steel bolts. Do you think that would work?

    4 replies

    Ok tested it in (now defunct) coffee grinder. Thinking blender. Also make sure you use the shredded pieces and not chunks of solder, or the spindle will jam.

    I think perhaps a small 12 coffee grinder might work better. Just need to be careful it doesnt overheat the solder into the meting point....

    Nice experiment and thanks for posting this. I have a small collection of soft gray metal but still haven't done a single trial.

    Thanks for solving my problem!
    I love these kind of simple creative innovations which make our life simple :)

    Thanks for solving my problem!
    I love these kind of simple creative innovations which make our life simple :)

    Thank you very much! This tutorial saved me a few bucks :)

    Just as an addendum: Indeed - well ventilated area and wear a mask... lead is poison.

    I use the final paste also as a quick dip for coating the tip of my soldering iron.

    Or, to minimize the risk of aerosolizing and subsequently breathing in the solder:

    the file under water and, while wearing gloves, run the solder across
    the file. Drain the water, collect the filings, and in a draft-free
    space, let the particles dry. Once dry, mix the filings INTO the flux
    (to minimize agitating the filings into the air).

    Yes, this method
    is more time consuming, but it virtually (IMHO) eliminates any health
    exposure, Until you forget to look before crossing the street and get
    run down by the motorist engaged in a text exchange.

    @masterpj I faced the same problem and I tried with a 95/5 (lead free) and 80/20 leaded.
    I was going to try it with 60/40 as its got a smaller plastic range, but seeing your post I think best option would be to go for 63/37 as it has no plastic range at all and solder melts exactly at 191degree Celsius. Though I do still think that I'll have to make my own flux (with 80~85% Rosin powder with 20~15% isopropyl alcohol by weight) the market version is made for the newer solders (95/5) usually.

    I tried this.
    But the solder didn't melt.
    The flux did flow though!
    I even cranked up my hot air station to the max, the solder still didn't melt or attach to the board. (only a reallllllllllllly tiny bit did).
    It's 60/40 solder.

    The flux is a rosin paste (the fake amtech one found on ebay)
    What might I be doing wrong?

    I use a $10 electric griddle for reflow soldering. That would probably work quite nicely. You can pick them up for next to nothing at thrift stores sometimes.