Simple Trick For Solder Paste In Storage

Hello there,

As many of you probably know, solder paste is good for doing SMD packages and so it helps to purchase a tube. The downside is that it isnt cheap, and to make things worse it does not store for a very long time because of chemical interaction between the rosin and the suspended lead (and other metals) over time. The solution degrades over time and causes some problems with soldering after a certain age.

To help get around the long term storage problem, it is kept in the refrigerator. That allows the longest storage life. The downside to this is that it is supposed to be left out of the fridge for 3 hours before use so it can reach room temperature. The heat however is what accelerates the degradation of the product however, so repeatedly leaving out in room temperature means the life is more limited than if it was just left in the fridge the whole time.

The simple trick works when you only have to solder a few chips at a time and you dont want to leave the tube out just for those few. Simply squeezing out a small portion of the product onto a clean, dry surface means that amount will be subject to room temperature while the rest can be put back into the fridge. A toothpick can then be used to spread some of the product out across the pins for soldering later after the small portion has had time to settle to room temperature.

I just did a small SMD 8 pin package a little while ago and it worked pretty well. The bulk of the product in the tube should last longer that way.

After using solder paste now i almost dont ever want to use regular solder anymore for anything

Thanks Mr. Al
A few hours ago I posted my comment lamenting the fact that expensive solder paste has a very limited shelf life. Your trick will bring a few extra weeks of that valuable paste.

Would it be possible to freeze it for even longer life?

crutschow said:

Would it be possible to freeze it for even longer life?

Click to expand...

Hi,

Good question, and what i found on the web doesnt help much.

What the sites all say is DONT freeze solder paste, but they NEVER say why not or what happens if you do.

Solution? I'll have to test some myself, since no site i found actually tested this idea out.
I'll freeze a few small samples in a little while and let them stay in there over night, then test one sample for solderability after say 24 hours then another sample after a week. Of course i will allow plenty of time for each sample to come back up to room temperature before trying to solder with it.
That's unless someone else can find some good information about this idea first.

LATER:
Two samples in the freezer now (see pic).
Those two small samples could be used to solder maybe four 8 pin SMD packages.

I understood that the reason to wait for the solder paste to warm up before using it was to avoid condensation forming on the paste. I'm not sure how important that is, but I don't think that squeezing a bit out to let it warm up will avoid condensation.

Hi,

Well i have two ideas on this.

First, in my case, i would be using it fast enough anyway so that condensation would not have much time to form.

Second, in the case of the small sample squeezed out, then perhaps it could be covered with plastic wrap while it warms up.
Also, the plastic wrap can then be inserted into a glass of warm water to help heat it up faster.
Since i already have the two samples in plastic wrap, i'll just cut one sample away from the other and let it warm up naturally at room temperature. I'll see how it works after that.
I probably wont try the first sample as soon as i though but wait a bit longer, maybe a couple days depending on what else is happening around here this week.

You reminded me of on other thing i should mention though is that i dont have any way to test possible secondary effects such as the effect of having more than usual moisture in the paste mix. The effects with some tests may not show up short term but may takes months to find out. For example, excessive moisture in the mix, excessive air bubbles, etc. All i can do is solder something and then see if it worked by a simple test of that device or connection. I dont have any way to examine the internal structure of the solder mass that might be available in a good lab.

MrAl:

This may be a "related aside"
I had lots of trouble with Sta-Silv silver solder flux. It's a water based flux for brazing basically.
The lifetime was crap.

Bottles such as these https://www.sciencecompany.com/HDPE-Plastic-Bottles-C2626.aspx did the trick. Basically, they seal tight.

A reminder, that you can load it into a dispensing syringe too. e.g. https://www.amazon.com/Syringe-Luer-Slip-Sterile-Pack/dp/B000FMYDLU/ref=cm_cr_pr_product_top?ie=UTF8 i/e/ Pull the plunger out and load from the backside.

I realize your method does the "quick thaw". I have some of the bottles. Maybe I should store the last syringe I got in one of them rather than a small zip lock.

Hi,

Thanks for the links.

When i got my solder paste i discovered that the needle that dispenses the product was quite large in diameter and so would dispense too much at a time, so i became very adept at using a toothpick to distribute the stuff across the pins instead of using the needle. This means it basically doesnt matter what kind of package it comes in because i can always just scoop some up and use the toothpick or similar instrument to spread it across the pins.
Since your post i've thought about squeezing it all into another container, maybe a small jar or something, like the type with the snap on lid like those used for storing mixed color oil paints. Still thinking about this

Here's a trial pack of dispensing needles: https://www.proto-advantage.com/store/product_info.php?products_id=1200013

Hi,

That looks interesting too. Are they implying that all solder paste tubes have the same threads for the needle attachment? That would be good. The stuff i have is a little thick though, i wonder if it would push through say a #22 gauge needle. Right now what i do is push some out on a flat surface, then toothpick it into place on the PCB and chip pins. I had to do that because if i use the present needle i have it would dispense enough paste on four pins to solder ten 8 pin dip packages.

That's another thing i like about this stuff...i dont need much to solder one or two ic chips. If i can get it to last long i'll never have to buy it again. Otherwise i'll have to hurry up and order and solder all the SMD chips i think i'll ever need to DIP breakout boards

From the pictures, they look like standard Luer taper with lockng hubs (https://en.wikipedia.org/wiki/Luer_taper), so should be interchangeable. A 22 gauge is pretty small. Have you considered 19 gauge?

John

PS: If you cut the end of the needle off (assuming it has a point) to give a blunt end, you may be able to get smaller dots of paste. There is a small trick to cutting the needles.

MrAl said:

Hi,
Are they implying that all solder paste tubes have the same threads for the needle attachment? That would be good.

Click to expand...

Dispensing needles are blunt. I actually have the assortment from proto-advantage, Solder paste comes in either Luer-lock or Luer taper. I have both. The larger tubes seem to be Luer-Lock (Threaded).

The needle tips fit both. I checked.

KeepItSimpleStupid said:

Dispensing needles are blunt. I actually have the assortment from proto-advantage, Solder paste comes in either Luer-lock or Luer taper. I have both. The larger tubes seem to be Luer-Lock (Threaded).

The needle tips fit both. I checked.

Click to expand...

Hi,

That sounds good. Mine is threaded. I also thought about squashing the end of the needle, but not sure what kind of metal it is made of. stainless might crack, not sure.

jpanhalt said:

From the pictures, they look like standard Luer taper with lockng hubs (https://en.wikipedia.org/wiki/Luer_taper), so should be interchangeable. A 22 gauge is pretty small. Have you considered 19 gauge?

John

PS: If you cut the end of the needle off (assuming it has a point) to give a blunt end, you may be able to get smaller dots of paste. There is a small trick to cutting the needles.

Click to expand...

Hi there John,

Oh i did not realize they took their design from the medical profession.

Do you mean that if you cut off the end the end gets partially closed because of the way the metal burrs over a little?
What do you think about squashing the end a little, think that would work (i dont want to ruin it either)?

I was thinking small gauge because i realize i need very very little on the pins when i go to solder an SMD package. I dont really know what gauge would be best or even work for that matter, but if squashing the end works then i could do that i guess.

Imagine squeezing out a 1/4 inch long strip of the stuff through a 1/16 inch ID needle. That's about how much is used for my SMD 8 pin packages. That's how small the quantity is, so imagine trying to squeeze that out from a smaller needle, going across the row of pins at the very end of each pin. That's why i thought a small dia would work, but then again i dont even know if the stuff is liquid enough to be pushed through a 22 gauge or even larger like 20 gauge. Never tried it. This is still very new to me yet. Basically to date i have soldered just 2 packages using the solder paste, and all i really konw so far is that it is not the thinnest stuff on earth, meaning it takes a good amount of force to push it through the needle i already have which is around 1/16 inch diameter, so i imagine it would take even more to push through a 20 gauge.

There are quite a few variables with this stuff i guess. Mine came in a syringe tube so it's not in a jar like some are, so it would be harder to mix with more flux unless i cut open the tube and squeezed it all into a new jar. Not sure if i want to do that either yet

MrAl said:

Do you mean that if you cut off the end the end gets partially closed because of the way the metal burrs over a little?

Click to expand...

Yes, that is what happens, even when you use an abrasive cut-off. The solution is simply to put a piece of wire inside the needle, then cut it. The fit needs to be good, but not too tight. Wires of all sizes are available. I usually use a steel wire, but I suspect copper might also work. The needles I have worked with are stainless and weakly magnetic (400 series?). You can also file a notch and snap them. However I cut them, I remove the burr on the outside with a polishing wheel. A sharpening stone will also work.

Your material is already in a syringe. If you need additional syringes, there is a brand called "Air Tite" (https://www.air-tite-shop.com/c-3-syringes.aspx) that I use for models and such. They are distinguished by not having a rubber tip on the plunger, so they can be used with a variety of solvents and adhesives without contaminating them. AirTite used to sell direct, but now I think it only sells through distributors.

What do you think about squashing the end a little, think that would work (i dont want to ruin it either)?

Click to expand...

Like all stainless, needles work harden, but I think you can collapse the end a little. I would put a small wire inside the needle and squeeze against it to keep from getting the hole too small.

I was thinking small gauge because i realize i need very very little on the pins when i go to solder an SMD package. I dont really know what gauge would be best or even work for that matter, but if squashing the end works then i could do that i guess.

Click to expand...

I have not looked up the particle size in solder paste. I assume it is pretty small, but the viscosity of the paste is high. Too small a needle, say a 25 gauge, might require a lot of pressure to apply and might even cause separation of flux from solder -- don't know, haven't tried it.

Most of the needles I use for adhesives and such are in the 19 to 22 gauge range. I still use fine solder (0.015") for hand soldering and have not used solder paste, because it has such a short shelf life. For applying small dots of whatever or for holding parts, I use "tooth picks" made of music wire. I simply deburr and slightly round the cut end. The wire I use is about 0.035" diameter.

There are quite a few variables with this stuff i guess. Mine came in a syringe tube so it's not in a jar like some are, so it would be harder to mix with more flux unless i cut open the tube and squeezed it all into a new jar. Not sure if i want to do that either yet

Click to expand...

From what I have read from every manufacturer, I would keep the paste in the syringe, as that minimizes exposure to air. Also, every manufacturer advises against freezing. I could not find a technical reason for that with data, but there are many things that are could happen, such as aggregation of particles, changes in the gel properties of the flux, and so forth. In the biological sciences, it is not unusual to find things that are more stable when cold, but destroyed by freezing. Whole blood is just one of many such things.

John

EDIT: Just browsed the AirTite site. It is now selling many syringes with elastomeric tips on the plunger. Here is a direct link to the model of AirTite syringe I use a lot:
https://www.fishersci.com/shop/prod...-sterile-graduations-0-2cc/1481728?tab=access

Note: It is not Luer lock, so you want to be sure the needle is on tight to avoid accidents.

Hi again,

Yes i read that too, that freezing is not a good idea, but i have samples in the freezer now that i intend to test soon.

I also read now about people making their own solder paste by grinding up used solder (splashes, etc.) and mixing the grit with flux. Would be interesting to try.

MrAl said:

Hi again,

Yes i read that too, that freezing is not a good idea, but i have samples in the freezer now that i intend to test soon.

I also read now about people making their own solder paste by grinding up used solder (splashes, etc.) and mixing the grit with flux. Would be interesting to try.

Click to expand...

Well I've done that, and it works fine. But you have to make a powder via filing a solder oval made by remelting solder [from a desoldering pump] in a s/s teaspoon over the stove top. But lead powder spreading around your work area ain't a great thing. Do it outside and wear gloves.
It is good for the environment though, significant reduction in lead waste generated by you.

BTW chilling opened Krazy glue is the bomb, it lasts for years.

Hello Mosaic,

Oh yes, good point, something to think about and be careful about (tiny ground lead particles).

About the crazy glue though, that's got to be the number 1 best idea of the year that i have heard !
I DEFINITELY have to try that right away!
So many frustrating dried up tubes of super glue now, i almost gave up on it completely.
I had one tube that had a special closing mechanism, and that lasted for about a year i think, but i dont even know where to get that package anymore.
I will be trying this as soon as tonight.

BTW, how long do you leave the super glue out before using again, or do you even leave it out at all before using after removing from the freezer?

As a rule of thumb, organic chemical reaction rates double or halve for each 10°C change in temperature. I use a standard canning jar with a rubber-lipped seal (Ball brand) to store cyanoacrylate (CA) adhesives in the freezer. I usually get small plastic bottles, rather than tubes as it is easier to apply in small amounts from the bottles. I also insert a small-bore Teflon tube into the tip to get even finer control.

If I am storing unopened bottles, I will put several in the same jar. However, with bottles that have been opened, it is best to store only one bottle per jar -- maybe two if I am working on an active project. I even store the CA bottles in the jars at room temperature to protect from moisture. The reason for that precaution about multiple bottles in the same jar is that occasionally one bottle will "set off" and that can cause the others stored in the same jar to degrade as well.

Thirty minutes at room temperature is generally sufficient to warm the bottles past the point that water will condensate on them. Adjust that time according to your humidity.

As a final hint, some metals such as aluminum will set off CA easily. Copper is much less reactive. You can put a puddle of CA on a scrap piece of PCB and it will stay for an hour. I sometimes do that when I am using the CA to fix very small SMD's to the PCB before soldering. A microdot of CA applied with a wire toothpick will hold resistors and capacitors in place nicely.

John

MrAl said:

Hello Mosaic,


BTW, how long do you leave the super glue out before using again, or do you even leave it out at all before using after removing from the freezer?

Click to expand...

I don't freeze em....they're in the butter compartment. I can use it anytime at that temp. 2 years running since being opened!