Solder paste handling info needed

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

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.

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.

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 :smiley:

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.

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).

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.

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

Thsnks Jon. I’m in Canada so different selection and prices.

this “PTC Heater” is 110V and 220C,
a good temperature for a reflow plate:

https://www.amazon.ca/Thermostat-Constant-Temperature-Heating-Element/dp/B08LK7VN54/

not a full kit … needs legs and a plug…
hope you find something you like

the Bob_McBob approved model (lol) is this one for $50 https://www.aliexpress.com/item/33022471796.html

the main difference is the temperature is adjustable. I use 200C for reflows, but I also use 100C for softening stubborn loctite… works nicely!

Thanks for the links Jon. The second one looks interesting but it’s $25 shipping on a $50 item.

oh, shipping to canada is higher…

this link comes out to $58 with shipping to Canada:
https://www.aliexpress.com/item/33022471796.html

good luck w your options… I hope you end up with a setup you like

Still says $25 but I’ll check Amazon too.

That would be plumber’s solder paste. The ZnCl will continue to be active after a reflow.
I don’t know of a solvent specific to neutralize, but experience says don’t electronically solder with acid paste. Things get corroded with time, especially with moisture. Perhaps your region is too dry for such, so tops for your location.

As I would occasionally re-flow, I’d use a 1” wide x 3” long 1/8” thick aluminum plate held in a table vice with a 2” overhang. Placed the MCPCB and heat it from underneath with a micro-torch. Much success on single emitters. Quick and no kitchen set-up.

Wanted to buy one of those UYUE hotplates (link) as Jon pointed out, but the shipping killed the deal. Then one winter storm day I found some random parts and made my own (which was more of an undertaking than I had expected) (link).

try reloading the page?

this is what I see:
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FYI $19USD -> $25 CAD (approx.)

Edit: exchange rate 1 USD = 1.30 CAD

aha! thanks
$58 US to Canada
$50 US to USA

How about Vaseline?

I took over an old electric skillet that the family no longer used. It maxes out at 425F which is perfect for reflowing LEDs with MECHANIC Sn63/Pb37 soldering paste. And it smell like pancakes when it heats up!

It’s not hot enough to remove non-leaded reflowed LEDs, so I used my soldering iron to do that instead.

I don’t store my soldering paste in the fridge and it’s been working fine for many years. But it’s also down in the basement so it doesn’t get that warm.