Solder flux uses and solder

Solder paste uses and solder

I recently received this and am learning about what applications it is good for.

https://imgur.com/3pGTm0a

I put a small amount on a project board and the solder seemed to adhere better.

I am using up some old RS solder that has the paste already in it, though it may have dried out quite a bit.

Later I plan to buy some Kester 44 Rosin Core Solder 60/40 .031"

What situations would be good to use the paste in?

When I solder it's usually small work and stranded wires. Frequently the tiny wires are tarnished and resist taking solder (flux or no flux). I've seen times when only a few wires take solder. If I left those few to hold the join together then it's a sloppy job, prone to fail quickly.

So I remove tarnish by scraping or sanding. I apply a dab of flux with a toothpick. Often a blob of solder is already on the gun. I tin all strands. My aim is to do the job quickly before excessive heat causes insulation to melt and distort.

I look with a magnifying glass to make sure all strands are tinned. And then when I make the join I don't need a third hand to hold the solder.

Re: Solder paste uses and solder

I put a small amount on a project board and the solder seemed to adhere better...

Click to expand...

This is strictly a flux and not a solder paste.

These are gums and resins- they are purified and mildly activated rosin.

These are soluble in organic solvent but insoluble in water. You can thin the paste with a little alcohol.

If the surface to be soldered is slightly dirty, solder will not stick. Common solder is an eutectic of lead and tin and they form an alloy with copper. That makes a strong bond.

Copper surface oxidises easily when exposed to air and that makes soldering difficult. The flux is a reducing agent and cleans the surface and helps the liquid solder to wet the surface.

Excess flux does no harm. You can also remove the excess left over on the board with ethanol or isopropyl alcohol.

Personally I feel that the solder present within the core is too little. You should use the paste every time you feel that the solder is not sticking well (within 2-3 secs after melting).

Apply solder flux directly on the board and then use the iron and the solder wire.

Usually it works well (unless the corrosion is extensive: it is clearly visible).

BradtheRad said:

When I solder it's usually small work and stranded wires. Frequently the tiny wires are tarnished and resist taking solder (flux or no flux). I've seen times when only a few wires take solder. If I left those few to hold the join together then it's a sloppy job, prone to fail quickly.

So I remove tarnish by scraping or sanding. I apply a dab of flux with a toothpick. Often a blob of solder is already on the gun. I tin all strands. My aim is to do the job quickly before excessive heat causes insulation to melt and distort.

I look with a magnifying glass to make sure all strands are tinned. And then when I make the join I don't need a third hand to hold the solder.

Click to expand...

Thanks, I use a magnifying glass as well, especially with circuit boards. I am looking for a 10x as 4x is sometimes not strong enough.

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c_mitra said:

This is strictly a flux and not a solder paste.

These are gums and resins- they are purified and mildly activated rosin.

These are soluble in organic solvent but insoluble in water. You can thin the paste with a little alcohol.

If the surface to be soldered is slightly dirty, solder will not stick. Common solder is an eutectic of lead and tin and they form an alloy with copper. That makes a strong bond.

Copper surface oxidises easily when exposed to air and that makes soldering difficult. The flux is a reducing agent and cleans the surface and helps the liquid solder to wet the surface.

Excess flux does no harm. You can also remove the excess left over on the board with ethanol or isopropyl alcohol.

Personally I feel that the solder present within the core is too little. You should use the paste every time you feel that the solder is not sticking well (within 2-3 secs after melting).

Apply solder flux directly on the board and then use the iron and the solder wire.

Usually it works well (unless the corrosion is extensive: it is clearly visible).

Click to expand...

Thanks.

I also have found that using a flux improves the solderability.

On corrosion.

I have bought 12 gauge automotive wire with very black strands, even when 4 inches are cut off. ?

I returned it and made sure the new wire was corrosion free.

fixit7 said:

I have bought 12 gauge automotive wire with very black strands, even when 4 inches are cut off. ?

Click to expand...

Was that wire pulled from an old Triumph TR6 from the late 60's with cloth insulated wiring or something? That certainly doesn't appear to be new wire.

No, it was wire bought from a O'Reilleys auto parts store.

Maybe it was stored next to car batteries where so H2SO4 vapors were around?

fixit7 said:

No, it was wire bought from a O'Reilleys auto parts store.

Maybe it was stored next to car batteries where so H2SO4 vapors were around?

Click to expand...

Either that or they are really really really old wires to oxidize that much, but your probably more likely to be right, that they were stored near batteries. Some of the stuff you find in auto parts stores are extremely old.

H2SO4 vapors were around?

Click to expand...

H2SO4 does not produce much vapor at room temperature. If the copper were corroded by the acid, the color would have been green/blue.

Black color suggests simple oxidation (copper oxide is black; there is another oxide that is red). The common flux cannot remove the black oxide (but it works with the curpous - the red variant- oxide).

The interesting part is that the oxidation has penetrated deep inside (you will find it even after cutting off 12 inches).

Strange but true, cotton covered copper wires corrode less (they do not use the plasticizers) compared to the common PVC insulated ones.

"Copper oxide is black"
'Another copper oxide is red".

Seriously? While the colours are correct, the explanation is not. These are not basic oxides.

Here copper corrosion colors...
https://www.worldcoppersmith.com/copper-patina-guide/

While the colours are correct, the explanation is not.

Click to expand...

I am somewhat amused to see your comment and no other explanation. If there are mistakes you should point out explicitly and also provide the corrected version.

These are not basic oxides.

Click to expand...

Your chemistry knowledge is corroded; both cupric and cuprous oxides are basic.

Any regular text book will help.