Best method for attaching LED to star?

[dnlwthrn]

So I've ordered an MC-E (from Endeavor) and since it doesn't come mounted to a star, I ordered a series-wired star for it from DX. I also have an XR-E that I got as a sample from Cree (gotta love working for an engineering firm) that needs to be mounted to a star.

What's the best method? I'm assuming they're soldered when they come mounted alread, but there's a LOT of material to heat up on the star before you could get a good solder connection. Can someone point me to a reference/tutorial? I've done quite a bit of soldering, but not on anything with that much mass to heat up...

Thx!

 

[R33E8]

I assume you can use a bit of solder paste? Just mount the star on a hotplate or something and carefully place the LED on..

 

[dnlwthrn]

That's kind of what I figured. I'll probably give it a go with the XR-E (since it was a freebie) and see what I find. I'm guessing you need to use as little heat as possible for this...

 

[Oznog]

Yeah you need solder paste. Actually this is hard to find in the US, you can get it cheap from DealExtreme BUT be careful to get the lead solder paste not the solder flux paste without the solder in it. DX is often unclear on that but look at the comments.

I've used a heatgun but you have to be careful not to overheat the board. There's an insulating later between the aluminum and top traces (which needs the heat) and that insulator can be damaged by high temps. I kind of wonder if the toaster oven isn't a better choice since it circulates heat to the top, except for the problem that the LED package can't tolerate extremely high temps either.

 

[dnlwthrn]

Yeah you need solder paste. Actually this is hard to find in the US, you can get it cheap from DealExtreme BUT be careful to get the lead solder paste not the solder flux paste without the solder in it.

So I checked DigiKey, a supplier we often use at work for electronics stuff, and was shocked. Most of the solder paste they carry is non-stock, special order. The one they did have as a stocked item was for 500g and was over $50!

DX is now sending me some, at a measly $3.73 for 50g.

Since I have some extra stars for the XR-E, I may play around with heating them to see what's going to work the best while I wait for my solder paste.

 

[odessit]

What is the number for the paste and the star? I am in the same situation as you.

 

[Nake]

I use this paste with good results.

http://www.solder-it.com/solderpaste.asp

 

[dnlwthrn]

The soldering paste I ordered is SKU 04711, and the stars (5 pack) are SKU 16544.

I may get some of the stuff Nake listed as well... I like the idea of a syringe-like applicator.

 

[Cemoi]

I use this paste with good results.
http://www.solder-it.com/solderpaste.asp

Thanks for the advice.
Can it be used to solder electronic components, especially tiny ICs otherwise hard to solder by hand with a soldering iron?
Is it available in retail stores?

 

[LED Boatguy]

I've had good luck with a heat gun and DX's solder paste. Probably done it fifty times and not a failure yet, and that includes some pretty small SMD chips. Heat slowly from the bottom. When you see the paste kick off, give it about 5 seconds more heat then back the heat gun away. Let it cool naturally. At least this works for me.

I just got a syringe and an assortment of needles from Zephpaste. Have not used it yet though. $$$! Ouch.

http://www.zeph.com/zephpaste.htm

Also have a new IR toaster oven and PID controller on order so I can do controlled temp reflow.

 

[Nake]

Thanks for the advice.
Can it be used to solder electronic components, especially tiny ICs otherwise hard to solder by hand with a soldering iron?
Is it available in retail stores?

Can't say about the components, I've only done Cree emitters to boards.

I don't see any mention of retail sales locations on their site. I ordered directly.

 

[evilc66]

Solder paste like that is perfect for smd work. I have built many prototype boards by hand using a syringe filled with paste (very tiring on the hands after a while) and a butane heat gun. Very easy to use. Try and get one with a water soluble or no-clean flux. Makes life a little easier on cleanup.

 

[mds82]

I did this myself once just using silver solder and a hot plate

I heated the hot plate and then melted some silver solder right onto the MCB ( the star) . after that lowered the temp a bit and placed the LED right into place - i havent had any problems with it at all. it was very easy.

 

[dnlwthrn]

If I get some time at work tomorrow, I'll try that... I thought maybe it would work, and the solder I have melts at a fairly low temp. Time is the issue right now...

 

[Cemoi]

I don't see any mention of retail sales locations on their site

I contacted them, and they answered:

1. This product is available at Lowes
2. Their minimum shipping fee (which I haven't found on their website) is $10

 

[Cemoi]

I did this myself once just using silver solder and a hot plate

What do you mean by a hot plate?
A few pictures or the URL of a tutorial would be welcome for a nube like me.

 

[mds82]

Well not really a hot plate, i just used the stove top burner on my oven. I help the MCPCB Star with tweezers and kept turning up the heat until it was hot enough to melt the solder. I ended up putting the burner somewhere around medium, and that was hot enough to melt the solder onto the star. After that i dropped the LED into place, gave it a little push to make sure it stuck, and then took it off and let it cool down.

 

[dnlwthrn]

I actually have ceramic hot plates here at work. Similar in idea to an electric range, but with a smooth ceramic top. It has a dial for controlling the surface temp. If I get around to trying things this week (looking unlikely at the moment) I'll take a few photos...

 

[Oznog]

I've had good luck with a heat gun and DX's solder paste. Probably done it fifty times and not a failure yet, and that includes some pretty small SMD chips. Heat slowly from the bottom. When you see the paste kick off, give it about 5 seconds more heat then back the heat gun away. Let it cool naturally. At least this works for me.

That's a little off though. Pastes have 2 phases, one where the solvent bubbles off and the second where the solder reflows. If you do it too fast, the larger bits of solder still have a lot of evaporative cooling going on. And it's a little violent.

Ideally, you'd watch for the paste to bubble lightly and you can see it dry out and take on a dull appearance. When I do this with a heat gun I back off on the heating as soon as I see this to let it finish without getting any hotter. Then when it all settles in a few seconds put the heat close again and the solder joints flash over into reflow.

The cooling period is also an important 3rd stage, which affects the strength of the joint.

Though for the most part just heating it until it melts is "good enough".

 

[dnlwthrn]

Well, I tried it... A couple of thoughts. I used traditional rosin-core solder, and this may be part of the issue, but it took quite a bit of heat from the hotplate to get the solder to melt. I actually cut off a small length of solder, coiled it up, and set it on the center pad. When it started to melt, I added solder to the + and - tabs as well. When setting the LED onto the puddle of solder, you have to have REALLY steady hands, or you'll put things on crooked. I need to double check continuity, as I'm afraid the solder from the center pad may have run over onto the electrical connections when I put the LED on. Also, be careful not to get the LED too hot! Duh. I'm just glad I practiced on the free sample that I got, as I'd hate to damage my new MC-E...