Which solder paste for LED reflow?

JasonWW · 2019-03-10T09:45:15.000Z

staticx57:

JasonWW:

I don’t even use solder paste. I use the same solder that I use with my iron, Kester 44.

I clean the old solder off the pad then add flux and solder with my iron. Then more flux and put the led on top and heat the mcpcb up again.

The thing about pastes is they go bad over time and then don’t work well. I’d rather have the reliable spool and do the extra step. Just my opinion.

How do you reflow? If you are using hot air for a PCB or hot plate for MCPCB paste is really helpful. I have been using the same cheap syringes of paste for a few years now without issues.

Hot air.

A lot of pastes technically expire like 6-9 months after date of manufacture. I rarely reflow stuff, so that paste just goes to waste with me. I’m also not real comfortable using it after the expire date. It’s probably okay, but eh.

mattjk · 2019-03-10T13:24:22.000Z

You can revive expired paste by mixing some IPA in. Its just the carrier fluid for the flux that evaporates

Muto · 2019-03-10T13:42:42.000Z

You guys rock.
Ordered the MG

Figured there would be plenty of choices and just like when I first visited here, I have no clue what a lot of the terms used in the above posts mean and don’t need to know just need what works all around best for an amateur hobbyist and it looks like this stuff will do well.
Thanks again

Keith

DB_Custom · 2019-03-10T13:49:59.000Z

Kester EP256, nothing else. To me the MG Chemicals sucks.Kester EP256

nsl18 · 2019-03-17T04:10:03.000Z

clemence:

SnBi based solder paste has very BAAAAD thermal properties and very brittle. EDIT: I only use it for [wire pads] on hard to solder MCPCB, mixed with approximately 30% Sn60Pb40 to make it slightly flexible. Never use it for LED or anything requires good thermal conductivity.
AFAIK, Sn52Bi48 only has 19W/MK TC. For comparison: copper ~400W/MK, Aluminum ~200W/MK, Brass ~100W/MK, Stainless steel ~16W/MK, Sn63Pb37 51W/MK, SAC307 62W/MK.

[Clemence]

The thickness of alloy is very small to have a significant effect on final heat dissipation. An more narrowed space- the p-n junction to thermal pad. You was compare the junction themperature with different alloy, with infrared thermometr?

clemence · 2019-03-17T04:50:58.000Z

nsl18:

clemence:

SnBi based solder paste has very BAAAAD thermal properties and very brittle. EDIT: I only use it for [wire pads] on hard to solder MCPCB, mixed with approximately 30% Sn60Pb40 to make it slightly flexible. Never use it for LED or anything requires good thermal conductivity.
AFAIK, Sn52Bi48 only has 19W/MK TC. For comparison: copper ~400W/MK, Aluminum ~200W/MK, Brass ~100W/MK, Stainless steel ~16W/MK, Sn63Pb37 51W/MK, SAC307 62W/MK.

[Clemence]

The thickness of alloy is very small to have a significant effect on final heat dissipation. An more narrowed space- the p-n junction to thermal pad. You was compare the junction themperature with different alloy, with infrared thermometr?

It is significant. 50W/MK vs 86W/MK TC made huge difference in output. Haven’t tested 19W/MK vs 50W/MK but I suspect the difference would be much greater.

[Clemence]

Chatika_vas_Paus · 2019-04-12T09:02:12.000Z

Someone used this Good for leds?

clemence · 2019-04-16T19:04:00.000Z

Chatika vas Paus:

Someone used this Good for leds?

It’s works good but not my favourite. Keep it in cool in an air tight container, gets dry fast when left open overnight. I prefer higher oily flux content. Get the syringe container for longer shelf life.

[Clemence]

Overload · 2020-08-16T14:25:19.000Z

I’m new with soldering paste and bought this paste from ali:

soldering paste

When heating it with hot air it doesn’t realy melt and the structure stays the same(tried temperatures from 150-450°C), also the color of the paste stays grey and I assume it should get silver when melting(like tin)?
It doesn’t get realy hard when cooled down, I can scratch it of with my fingernails
I stored it in the fridge(4°C) as soon as it arrived here, but it did 2 weeks from China till here, maybe the higher temperature within shipping time did something with the paste?

alpg88 · 2020-08-16T14:36:48.000Z

i get mine from digikey, they ship in cold container like medicine, or perishable food, if the paste requires it. i usually buy small quantity, and i do not buy a lead free, i do not believe a lead solder under the led, in a sealed light is a cause to be concerned, but it makes more reliable joints. to be honest i never even look at brand, i used several different brands i got from them, not one gave me an issue.

moderator007 · 2020-08-16T15:10:36.000Z

Reflowing really is a area in which good quality paste can save you alot of headaches. If you happen to find some cheap stuff that works good then that’s great.
In my opinion you will save time and money spending a little more and buying good paste to start with.
This is what I use and has worked super, I have had no reason to try anything else.
https://www.digikey.be/product-detail/en/chip-quik-inc/SMD291AX50T3/SMD291AX50T3-ND/5130159
Others might have more recommendations that work great too, but this one is all that I have ever needed.
.
Edit: Didn’t realize I had already commented in this thread, double post.

forsh · 2021-01-06T12:06:04.000Z

In reflowed my first led today and it stuck

Happened to have a triple mcpcb with one led that died a horrible death , so reflowed another one in its place !! With a soldering iron , heated up the sides , and under the pcb

It came off in time

Cleaned and tinned the pads and under the new led going on

Fluxed the pads popped on the new led and heated up the sides with a soldering iron

But if a get to fix but it took and works

Maybe I’ll heat the mcpcb board under when I’ve got time

But for a ghetto fix it worked
I used lead solder

Sari33 · 2021-01-07T20:29:09.000Z

How possible solder past Sn63/Pb37 melt at 148 degree?
www.aliexpress.com/item/1005001640757014.html

JasonWW · 2021-01-08T00:13:45.000Z

Sari33:

How possible solder past Sn63/Pb37 melt at 148 degree?
Page Not Found - Aliexpress.com

I don’t know. That mixture should be closer to 180*C. It’s possible they are listing it at a lower temperature in order to boost sales when it’s really going to melt at a higher temperature. If it really does melt at 148 maybe it’s because of the flux they are using? Hopefully somebody here can tell us more.

As a side note, I personally stick to name brand products from stores I trust. There are some shady products out on the market.

Edit: I just noticed that the description says it is lead-free while the picture says that it is 37% lead. So something seems pretty fishy.

Lightbringer · 2021-01-08T00:21:20.000Z

Sari33:

How possible solder past Sn63/Pb37 melt at 148 degree?

Same reason why you can get a 9990lm light that runs off 3 AAA cells.

Sari33 · 2021-01-08T09:31:26.000Z

JasonWW:

Sari33:

How possible solder past Sn63/Pb37 melt at 148 degree?
Page Not Found - Aliexpress.com

I don’t know. That mixture should be closer to 180*C. It’s possible they are listing it at a lower temperature in order to boost sales when it’s really going to melt at a higher temperature. If it really does melt at 148 maybe it’s because of the flux they are using? Hopefully somebody here can tell us more.

As a side note, I personally stick to name brand products from stores I trust. There are some shady products out on the market.

Edit: I just noticed that the description says it is lead-free while the picture says that it is 37% lead. So something seems pretty fishy.

And this is the standard type,183°melt Microns: 20-38um
https://www.aliexpress.com/item/4000341198680.html?spm=a2g0s.8937460.0.0.10212e0eXDaK5v

It’s the syringe version better for long storage than jar?
Both sealed but once jar opened air will enter.
Hope there aren’t clones for this brand

https://www.aliexpress.com/item/33045181014.html?spm=a2g0o.cart.0.0.331c3c00Hcdujp&mp=1

Agro · 2021-01-08T10:18:06.000Z

Does anyone want some free solder paste?
Order this.
Make a video of a regulated iron set to 170 degrees, unable to melt it.
Ask for a refund.

I got some free solder this way twice while seeking a legit SnBi brand. Though TBH quality was really low, not worth the hassle in my case. In my videos I actually compared to regular Sn60Pb40 solder which melted earlier than the fake SnBi.

Sari33 · 2021-01-08T11:06:19.000Z

www.aliexpress.com/item/4001224951324.html?
Number 4 should be Sn/Bi,but who know.

Agro · 2021-01-08T12:53:34.000Z

I got a Mechanic SnBi solder wire that turned out to be fake.
QY-309Bi seems real.

BTW, I would NOT recommend it for LED reflow.
Thermal conductivity is worse than SnPb and I remember how Led4Power expressed concerns that low temperature joints were mechanically much weaker.

c_malc · 2021-01-31T13:49:10.000Z

Sari33:

How possible solder past Sn63/Pb37 melt at 148 degree? Page Not Found - Aliexpress.com

Sometimes the translation is SHOCKINGLY bad (and wrong).

I mean, this is ridiculous:

Lead-free Low Tin

and