Solder paste handling info needed

[Gunga]

Hey all. I finally bit the bullet and bought some solder paste (in a syringe). Can anyone share tips on use and storage?

- refrigeration?

- warming before use, refrigeration after?

- how much to use?

- surface prep (cleaning, flux?)

• how to best use a gas range and frying pan? I’ve seen some guides. I usually use an old soldering iron but want to switch to a range to do triples.

Any other tips? I did look at the reflow video above and it didn’t work well for me.

I’ve done a lot of reflow but wanted to improve my techniques.

[BlueSwordM]

- REFRIGERATION

Always keep your solder paste refrigerated when not in use. That way, you can keep in tip top shape as long as possible.

- USAGE

Take it out of the refrigerator 3-4 hours before you use it optimally speaking. Once you’re finished, put it back in. We’re obviously not manufacturers, so we don’t use the whole tube, and we have to compromise with that.

Use what you need to use. A bit more is better than a bit less.

- TIME FOR BEST USE

Ideally, you’d use the solder paste within a year, but if you can use other stuff to help you out, you can use solder paste up to 5 years(personal anecdotal experience) within any trouble.

- HOW TO GET THE BEST SOLDERING JOB POSSIBLE WITH FLUX

Flux, flux, flux! Flux is your best friend. The older solder paste you have, the more it helps. I’ve managed to save a lot of old solder paste just by using any kind of flux. Using it prevents oxidation and removes oxidation as well.

- SURFACE PREPARATION

Just cleaning with isopropanol is good.

- SOLDERING

I personally use a hotplate for soldering, but an oven with iron frying pan that has a lot of thermal mass is best for this kind of thing, as it mimics the initial style of heating in commercial soldering. If you have plates with time based temperature control, that would be best.

As for a natural gas oven, it is fine, but make sure to stop the heat completely when the SMD part is soldered(like an LED).

[Gunga]

Thanks so much! I’m talking about stove top vs oven though right? What is your work flow when doing multiple reflows?

[Vegas_LED_Fan]

That advice is interesting. I have in my hand a 2 ounce can of Alpha metals brand soldering paste that must be more than a decade old and it still functions flawlessly. I live in the Mojave Desert so the garage where this can is stored certainly reaches 120 degrees F (maybe more) in the summertime. The active ingredient, according to the label, is zinc chloride. It is an inorganic salt and therefore is not degradable. I apply small amounts of it using the end of an artist’s paint brush. The one I generally use is about 1/8” wide but I could use a pointed brush for more precise work. Nothing on the can mentions any special storage requirements.

[bobvoeh]

@Vegas LED Fan

That advice is interesting. I have in my hand a 2 ounce can of Alpha metals brand soldering paste that must be more than a decade old and it still functions flawlessly. I live in the Mojave Desert so the garage where this can is stored certainly reaches 120 degrees F (maybe more) in the summertime. The active ingredient, according to the label, is zinc chloride. It is an inorganic salt and therefore is not degradable. I apply small amounts of it using the end of an artist’s paint brush. The one I generally use is about 1/8” wide but I could use a pointed brush for more precise work. Nothing on the can mentions any special storage requirements.

Its a Dry Heat

[BlueSwordM]

@Vegas LED Fan, the trick is the flux inside of the solder paste as well as the little solder balls.

If you can keep the solder bass together and have some nice flux, it can work very well

[BlueSwordM]

@Gunga, I only have experience on stove top, not inside of the oven.

I will never dare to use an oven, as that is far too expensive, energy intensive, and risky for food if I use the same oven.

That’s why I just use a time temperature controlled hotplate for reflowing now.
It was 100% worth the time investment, and even the money investment if I were to buy it new

[Gunga]

Can you send a link? I’m in Canada too.

[BlueSwordM]

I actually bought this one used a few years ago, it was a super lucky buy, and I even outfitted something near it with a relay timer to be able to control when to shut it off and run a fan at low RPM to cool it down a bit more quickly to get close to the ideal soldering profile:
https://www.aliexpress.com/item/1005002584173802.html

Absolute overkill, but it nicely beat the scientific hotplate I was using in the past

[Gunga]

Ah ok. I’m not that much into it…

I’ll just practice on the stove

[Marc_E]

I used a cheap IR thermometer to measure the temp increase of the pan i use on the hob, i monitored each power setting to see which one increased the temp closest to the rate the LED manufacturers recommend (basically took a reading every 5 seconds) and worked out when to turn off the power so that the pan temp peaks at the right temp.
In my case the hob needs to be on for 80 seconds at max heat, 30 seconds after this is reflow time. All rough measurements but the temp vs graph time is close to the manufacturers recommendations.

[SammysHP]

A well seasoned cast iron pan works best! Don’t forget the oil. /s

[Gunga]

@Marc E

I used a cheap IR thermometer to measure the temp increase of the pan i use on the hob, i monitored each power setting to see which one increased the temp closest to the rate the LED manufacturers recommend (basically took a reading every 5 seconds) and worked out when to turn off the power so that the pan temp peaks at the right temp.
In my case the hob needs to be on for 80 seconds at max heat, 30 seconds after this is reflow time. All rough measurements but the temp vs graph time is close to the manufacturers recommendations.

That’s funny. I just ordered an ir thermometer yesterday. How much time and effort is it to do multiple LEDs this way?

[Bob_McBob]

Solder paste intended for electronics usually has quite specific performance characteristics, particularly with respect to stenciling. Older or poorly stored paste can have issues with viscosity (thinning) or coalescence (the individual balls don’t come together as well). This stuff is very important on a production line where you need the paste to behave predictably at all times, and following the manufacturer’s refrigerated storage guidelines ensures it will behave exactly as expected for the intended shelf life. For a lot of hobbyist use it doesn’t matter as much, and I doubt many flashlight modders store their paste in the fridge unless they regularly build drivers from scratch and need reliable stenciling.

[Gunga]

This is also good to read. When I look up solder paste handling info, it’s usually telling me to refrigerate and discard after warming up for use. Which is a non starter for me.

[Gunga]

Btw. Does anyone have the data for recommended pan temperature again? And 80 seconds is good to ramp to that? I like this plan. Would a tiny cast iron pan work? I got a tiny 4” one for chocolate I’ve never used (and will never use) so no worries about food contamination.

[Marc_E]

@Gunga

Btw. Does anyone have the data for recommended pan temperature again? And 80 seconds is good to ramp to that? I like this plan. Would a tiny cast iron pan work? I got a tiny 4” one for chocolate I’ve never used (and will never use) so no worries about food contamination.

80 seconds is specific to my hob so not a generic thing, could be quite a difference on yours. And i’m going from memory from what i was doing a couple of years ago, i have it written down somewhere but that 80 seconds well may actually be 120 seconds instead of the 1min 20 seconds i’ve remembered it as

The cast iron pan would be fine, if you measure the temp in the pan it doesn’t matter what it’s made of really.

My hob is an old electrical one that has a lot of residual heat, hence having to allow for the temp still increasing once it’s been turned off. I use a 4” aluminium camping pan, it makes little difference to the temp because of the hob. I would guess a 4” cast iron one wouldn’t make too much difference but a large cast iron skillet would likely slow down the rate of temp increase and as my hob is on max i couldn’t increase it, which wouldn’t be ideal i can’t see it making much difference to me as a hobbyist.

If you have a more instant hob, such as infrared or induction, the cast iron may help control and maintain the heat slightly better that alu, and take a bit longer to cool down afterwards which would be better for the LED.

The soldering temperature recommendations are in LED spec sheets, for example a standard XP-G2 spec sheet: https://cree-led.com/media/documents/XLampXPG2.pdf

If you look at p32 in this one it shows a graph of the temp/time recommended for reflowing, takes a bit of time to match the numbers to the markers on the graph but once done it makes sense.

As for multi reflows, it depends on your speed and preperation but i’ve done triple boards comfortably without rushing. I miiight be able to do a board with 6 LEDs but i would need to work out how to prolong the pan staying at reflow temp, mine cools off too quickly.

My main focal points were on keeping the LED’s temp shock to a minimum by not heating it too quickly, and staying below it’s max recommended temp, which is why i used a thermometer rather than guesswork. I just wanted to know i hadn’t cooked the LED so i didn’t have to factor it in as possibility when troubleshooting a build.

Remember, folks on here do reflows with butane torches and soldering irons heating the MCPCB directly which would indicate a lot tolerance in the process, so anything even close the manufacturers specs should be fine.

I also remember one reflow (i purposely ignore the other couple :person_facepalming: ) where i forgot to heat the LED with the MCPCB so flowed a cold LED straight onto a hot MCPCB, it’s still working fine.

[Gunga]

It’s funny. I used a soldering iron on mcpcb and have had good results. I used to use an aluminum pan. That was generally fine. I was never successful with triples and occasionally cook a mcpcb. I had a disaster that ended up working (we shall see for how long) the other day trying to adjust my techniques. I’m planning on using the small pan, ir thermometer, gas stove, and solder paste from now on. I’ve rarely had issues but my last mod has prompted me to clean up my technique (got a shipment of 519s to play with).

[Marc_E]

I can see that, if you’re doing a single LED it’s easy to take temperature cues from when the solder starts and stops flowing, and once it starts flowing it’s generally that way for long enough to do the reflow without having to heat it again, and if not you can give it a quick hit with the iron to get it flowing again.

With a triple you want to keep the solder flowing for a longer period of time and there are no clues as to how hot things are actually getting so it’s very easy to overheat things.

If you weren’t getting a thermometer you could mitigate this by just letting the solder cool down enough to stop flowing between each LED on a triple so you know you’re not getting too hot with each hit of the soldering iron. Not ideal but better than disaster.

Oh, and as gas is instant the cast iron should act as a bit of a heat buffer to smooth the heat transference to the MCPCB. Nice.

[jon_slider]

here is a nice little hotplate option for $16
https://www.amazon.com/Remover-Heating-Soldering-Welding-Station/dp/B07W1ZZH8T

I store my solder paste at room temp, the flux tends to separate out after about a year (I think thats what the expiration date is based on)… makes it harder to squeeze out, and spread thin, but it still works