very useful, thank you!

Can you send me a 250g sample of the AU88GE12

So to maximize thermal conductivity for overdriving emitters one should use pure Indium or Tin?
I suspect using pure Silver, Copper or Gold will fry the emitter

clemence wrote:

Bort wrote:

So to maximize thermal conductivity for overdriving emitters one should use pure Indium or Tin? I suspect using pure Silver, Copper or Gold will fry the emitter

The question will be: is it worth the money spend/lumen gain?
Depends on intended applications. Pure Indium fluxless wire price is very expensive USD 95/3 ft.

Sorry to “necro” this thread, but I am hoping to find some information.

This week I bought a seringe of solder paste: Sn96,5Ag3Cu0,5 . This is the paste I bought:
https://www.tme.eu/gb/details/esac305_40/solders-other-lead-free/ag-term...

This my first time using solder paste, and I am no expert on this (or anything else!).

I will use this paste mainly to reflow some emitters that I will get soon.
I started practising on some older MCPCBs and with some old leds (just to test the “melting point”), and I noticed that it didn’t “melt” as good as my solder wire.

It started melting but then it became a sort of past with lots of tiny blobs that didn’t melt and that were a bit sticky

As I don’t have any tool or appropriate platform to make the reflow, I used my electrical stove, put the MCPCBs with the solder and waited for it to melt with time. It never reached that point and what happened was just what I described above…

So, my questions are,
How do we use this solder paste to get it to melt well to reflow the emitters?
How long does it normally take to melt?
What precautions must be taken?
What temperature should the stove reach to make it melt?

Last but not least, should I buy/use other type of solder to reflow, given the conditions I have (stove / lighter / soldering iron)?

I am sorry these are some questions I would like to see answered if possible.

Also, if anyone can point me to a video reflowing with this specific paste, that would be nice, as I searched but couldn’t find one.

BTW, here are the photos of the sh**y work I did

Thanks in advance!!

Either you need more heat or the flux is shit burning up before it bonds the solder balls together

Never seen such bad stuff, even with the cheap Chinese paste
You may try some more flux that does not burn, but I guess that paste does not work

To keep the LEDs in safe max temp go for leaded solder paste it behaves a lot better

Lexel wrote:

Either you need more heat or the flux is shit burning up before it bonds the solder balls together

Never seen such bad stuff, even with the cheap Chinese paste
You may try some more flux that does not burn, but I guess that paste does not work

To keep the LEDs in safe max temp go for leaded solder paste it behaves a lot better

Solder paste is hard to find in national stores, and those that have them are sold out Ali and Ebay are full of fake stuff.
What could be a “good” product to use for reflowing leaded or non leaded?

MascaratumB,

While looking for Mechanic “XG-50” solder paste jars, it happens that I found this Karmor Tools store advertisement where Sn42Bi58, Sn63Pb37 and Sn96.5Ag3Cu0.5 solder pastes are sold. Nothing really wrong there, except that…

… a whopping 260 °C is claimed as Sn96.5Ag3Cu0.5's melting point. You need to raise the MCPCB temp above the melting point figure, and keep it above while you reflow. As a rule I manage to get any job done without exceeding +35 °C above solder melting point, which is less than 220 °C for Sn63Pb37 (183 °C melting point).

SN96.5Ag3Cu0.5 is probably a paste with too high melting point for reflowing leds. Standard Sn63Pb37 is cheap, good and beautiful:

• https://www.ebay.com/itm/MCN-Phone-Repairing-Solder-Soldering-Paste-Flux-XG-50-Sn63-Pb37-Alloy-20-38um/253660705741
• https://www.ebay.com/itm/60g-Welding-Flux-Mechanic-Soldering-Solder-Welding-Paste-Flux-XG-80-Tool/254292863718 Bigger jar.
• https://www.aliexpress.com/item/32965550021.html XG-50 in AliExpress.

I myself am very happy with “Mechanic” Sn63Pb37 solder paste.

Hope this is of help.

Sun, 03/29/2020 - 05:39; Sun, 03/29/2020 - 08:10

MascaratumB wrote:

Lexel wrote:

Either you need more heat or the flux is shit burning up before it bonds the solder balls together

Never seen such bad stuff, even with the cheap Chinese paste
You may try some more flux that does not burn, but I guess that paste does not work

To keep the LEDs in safe max temp go for leaded solder paste it behaves a lot better

Thanks for your reply Lexel!
Hum, I just tried different approaches (heating the stove before putting the plate, progressively heating the stove, using some piece of copper below the pcb to maintain the heat so that it didn’t have a break…) and all failed. I guess that adding flux wouldn’t be any good too in this case
The blobs never cease to exist in any situation…
It seems that this is indeed a bad solder paste Or, the fact that I don’t have the appropriate tools is what leads to those images

Solder paste is hard to find in national stores, and those that have them are sold out Ali and Ebay are full of fake stuff.
What could be a “good” product to use for reflowing leaded or non leaded?

I have used some good paste in the beginning I had from an old work
Since 2 years I use the cheap leaded Chinese paste, it has its flaws not liking any pressure like in a syringe with small hole or repeatedly used over a stencil in small quantity, it gets harder fast

Its so cheap I don’t hesitate to likely have to trash half of it, just put used in an old 50g container
Always pushing small fresh amounts out of the syringe with no tip or needle

Anyways unless you use a stencil I would always apply solder wire and some Amtech flux, the Chinese Amtech copy is as good as the original
Then moving the emitter around to make sure it wets everywhere
Then give dome a light tap to push out uneven/too much solder

I made a video here, those LEDs were scrap that someone soldered with lead free solder too hot, problem is they did not soak themselves to the pads as the lead free was not at its melting point before mixing with leaded one
usually when flux added new LEDs pretty much jump to a center position as they wet then very good

generally I top off at about 200°C with solder wire, above 195°C it flows very good

thank you for posting the video, that is a great camera arrangement to show both views.

i’ve never used paste or lead-free solder so have a question about the process.

Usually when soldering i first apply flux to the surfaces, then heat and touch the solder wire to “tin” the items, or to make the joint to connect a part to a pad.

It appears that flux was added as the final step in the paste/floating process. Is this due to mixing leaded and lead-free solder, or is this typically the way it is done?

Lexel wrote:

I have used some good paste in the beginning I had from an old work
Since 2 years I use the cheap leaded Chinese paste, it has its flaws not liking any pressure like in a syringe with small hole or repeatedly used over a stencil in small quantity, it gets harder fast

Its so cheap I don’t hesitate to likely have to trash half of it, just put used in an old 50g container
Always pushing small fresh amounts out of the syringe with no tip or needle

Anyways unless you use a stencil I would always apply solder wire and some Amtech flux, the Chinese Amtech copy is as good as the original
Then moving the emitter around to make sure it wets everywhere
Then give dome a light tap to push out uneven/too much solder

Lexel wrote:

I made a video here, those LEDs were scrap that someone soldered with lead free solder too hot, problem is they did not soak themselves to the pads as the lead free was not at its melting point before mixing with leaded one
usually when flux added new LEDs pretty much jump to a center position as they wet then very good

generally I top off at about 200°C with solder wire, above 195°C it flows very good

Thanks very much for your reply and help and for your video Lexel, it was really helpful!
I normally don’t use solder flux because the wire I have melts well, but for the reflows I guess I will have to get some.

About the paste, I’ve been reading and receiving some other suggestions about the quality of the paste, and as I am not soldering so frequently, I will probably try to get some better paste that can last for a while, so that I don’t waste many.

One thing I noticed was that your plate was slowly heating and the solder went melting evenly.
Seeing that, I and not sure if the process/method I did was the ideal one. I will have to try again to see how it works if I heat it slowly (with lower temperatures).

I am also takiung note of the solder composition to see what I can get locally. Some stores are pretty expensive in terms of shipping and many of them either don’t have the produts I am looking for, or ther are, eventually, fake!

Again, thank you very much for the help!

Barkuti wrote:

SN96.5Ag3Cu0.5 is probably a “too hot” thermal paste for reflowing leds.

Thanks you too

…..

A noob like me surelly has a lot to learn from you folks!!!

LoL I wrote SN96.5Ag3Cu0.5 is probably a “too hot” thermal paste… 

Edited it, paste with too high melting point for reflowing leds sounds better.

MascaratumB, I recommend you to get some standard “Mechanic” Sn63Pb37 solder paste besides any other stuff. True, tried and tested classic recipe, works pretty good imho. It is cheap, so you can practice plenty with the paste thing. Best if stored in some fridge, and take proper care of it.

MascaratumB wrote:

About the paste, I’ve been reading and receiving some other suggestions about the quality of the paste, and as I am not soldering so frequently, I will probably try to get some better paste that can last for a while, so that I don’t waste many.

Solder paste has a shelf life of like 6-12 months at 7°C, if you use not it often go ahead and buy cheap Chinese mechanic paste, if it gets worse buy new one for like 2 pounds

kennybobby wrote:

thank you for posting the video, that is a great camera arrangement to show both views.

i’ve never used paste or lead-free solder so have a question about the process.

Usually when soldering i first apply flux to the surfaces, then heat and touch the solder wire to “tin” the items, or to make the joint to connect a part to a pad.

It appears that flux was added as the final step in the paste/floating process. Is this due to mixing leaded and lead-free solder, or is this typically the way it is done?

Rosin core flux tends to oxidase when it’s a longer time hot
The Amtech (fake) flux not, but adding it as final step likely gives the best result

As I wrote the LEds were used and full of lead free solder on the pads, so they behaved not like new LEDs which would likely soak themselves easily on the pads even without additional flux added
Basically adding flux always makes the result better, so you cant overdo it

Lexel wrote:

MascaratumB wrote:

Lexel wrote:

Either you need more heat or the flux is shit burning up before it bonds the solder balls together

Never seen such bad stuff, even with the cheap Chinese paste
You may try some more flux that does not burn, but I guess that paste does not work

To keep the LEDs in safe max temp go for leaded solder paste it behaves a lot better

Thanks for your reply Lexel!
Hum, I just tried different approaches (heating the stove before putting the plate, progressively heating the stove, using some piece of copper below the pcb to maintain the heat so that it didn’t have a break…) and all failed. I guess that adding flux wouldn’t be any good too in this case
The blobs never cease to exist in any situation…
It seems that this is indeed a bad solder paste Or, the fact that I don’t have the appropriate tools is what leads to those images

Solder paste is hard to find in national stores, and those that have them are sold out Ali and Ebay are full of fake stuff.
What could be a “good” product to use for reflowing leaded or non leaded?

I have used some good paste in the beginning I had from an old work
Since 2 years I use the cheap leaded Chinese paste, it has its flaws not liking any pressure like in a syringe with small hole or repeatedly used over a stencil in small quantity, it gets harder fast

Its so cheap I don’t hesitate to likely have to trash half of it, just put used in an old 50g container
Always pushing small fresh amounts out of the syringe with no tip or needle

Anyways unless you use a stencil I would always apply solder wire and some Amtech flux, the Chinese Amtech copy is as good as the original
Then moving the emitter around to make sure it wets everywhere
Then give dome a light tap to push out uneven/too much solder