Which solder paste for LED reflow?

clemence · 2019-03-10T04:12:43.000Z

Useful information:

[Reference] Physical and Mechanical Properties of Solder Alloys Flashlight Modding and DIY Parts

Physical and Mechanical Properties of Solder Alloys Original source: http://alasir.com/reference/solder_alloys/ Solder Alloy Melting Point, °C solidus / liquidus Density, g/cm³ Electrical Resistivity, µΩ⋅m Thermal Conductivity, W/m⋅K Tensile Strength at Break, kgf/cm² Tensile Elongation at Break, % Brinell Hardness, HB alloys of tin (Sn) with silver (Ag) and / or copper (Cu) Sn96.5Ag3.5 (alloy #121) 221 / 221 7.37 0.123 55 580 35 15 Sn95Ag05 (alloy #13…

[Clemence]

BlueSwordM · 2019-03-10T04:13:12.000Z

@Muto, do not use SnBi thermal paste for anything other than soldering springs.

It does not work well for LEDs and connections at all.

amars7 · 2019-03-10T04:14:24.000Z

Awesome info, thanks!

clemence · 2019-03-10T04:16:52.000Z

BlueSwordM:

@Muto, do not use SnBi thermal paste for anything other than soldering springs.

It does not work well for LEDs and connections at all.

Except mixed. I mixed it with ~30% Sn60/Pb40. But don’t forget to heat it first to temp slightly above 60/40 melting point. Otherwise the 60/40 granules will stays unmixed. You still get around 150C combined melting point

[Clemence]

moderator007 · 2019-03-10T05:12:08.000Z

I use this stuff SMD291AX50T3 Chip Quik Inc. | Soldering, Desoldering, Rework Products | DigiKey
Works really well for me.

All the resistor’s plus cap’s (size 0402) and other components are reflowed with the Chipquik and a hot air.
I use this same stuff for all my led reflows too, I haven’t found a need to try anything else, if it’s not broken why fix it.

.

Lexel:

sn62pb36ag2 is still the best leaded solder compond

I agree 100%. I haven’t found anything better. The added silver also helps improve conductance.

WillyD · 2019-03-10T05:13:04.000Z

I know Micro Center has locations in PA, so if you have one near I’d suggest checking out their soldering supplies. I used to order everything after Radio Shack went away until I finally realized Micro Center has just about everything you’ll ever need.

JasonWW · 2019-03-10T08:28:58.000Z

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.

staticx57 · 2019-03-10T09:26:58.000Z

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.

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