# best way to solder leads to stars ?



## RustyShackleford1 (Jan 16, 2016)

I'm new to working with these surface-mount LEDs. After they're reflowed to a "star", what is the easiest way to solder leads to the '+' and '-' terminals on the star ? I'm using solid wire, probably 20ga I'd guess. I have tried tinning the pad (on the star) and the wire first, and that seems to help, but I'm still not getting very good joints. Thanks.


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## peter yetman (Jan 16, 2016)

Are you using flux, or have you rosin core solder? One or the other is good. I had trouble too until I used a 45W Weller Iron with a flat tip. You need to heat the pad area for aboutt 15 secs before attaching the wire, as the heatsink pulls a lot of heat away. I've been soldering since before I could walk, and still have trouble with these. I'm impressed you did the reflow - too scared.
P


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## Steve K (Jan 16, 2016)

I think you'll need to provide more info. Pictures, perhaps?

You might also want to tell us what you don't like about these solder joints.


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## lucca brassi (Jan 16, 2016)

you have to work with proper soldering iron - normally i work with head with 80W and flat tip (ERSA-i-CON ) good it is also to preheat a star a little to cca 60°C)

solid wire ? you need a wire with flux inside http://www.amazon.com/dp/B00ARBEMCE/?tag=cpf0b6-20 or attach liquid flux on http://www.amazon.com/dp/B016G4DHRG/?tag=cpf0b6-20


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## peter yetman (Jan 16, 2016)

How do you manage to get a nice shiny dome over the joint?
P


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## FRITZHID (Jan 16, 2016)

Flux flux flux! Make sure you heat thoroughly and then don't move the joint until solder has hardened. Remember RoHOS solder will often look gray or foggy compared to lead based solder.


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## DIWdiver (Jan 16, 2016)

The problem with stars is that they are designed to suck heat away from whatever is hot. Thus it is very difficult to get the joints hot enough to solder properly. Everyone mentions flux, and that's important, but if you can't get the joint hot enough, you'll never get a good joint no matter how much flux you use. If you can solder other things well but have trouble with stars, the problem is heat not flux. It helps to have a big beefy soldering iron with a fat tip in good condition. It also helps a lot if the star is not yet connected to the heatsink.

Lucca mentioned wire with flux inside. He was referring to the solder wire, not the copper wire you are trying to solder. Most (not all) solder for electronics has flux in the core. Plumbing solder never has flux inside, AFAIK.


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## Illum (Jan 16, 2016)

flux, flux, flux.... that and isolate the star from any other metal. Have a 50+ watt iron, use the broad side of the chisel tip. Avoid silver bearing solder [higher melting point]

I use Kester 951, but any flux should work.


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## Steve K (Jan 17, 2016)

to echo DIWdiver, you'll never be able to properly solder wires to a star that is mounted to a suitable heatsink. That was one reason I suggested providing photos... it would provide us with a lot of incidental info that could provide hints to what was wrong. 
In case it's not clear, always solder wires to the stars *before* attaching the star to the heatsink.

and speaking of what is wrong, my suggestion to the OP to describe what is perceived as being wrong with the solder joint still applies.


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## peter yetman (Jan 17, 2016)

Illum said:


> flux, flux, flux.... that and isolate the star from any other metal. Have a 50+ watt iron, use the broad side of the chisel tip.


I think that's where I've been going wrong, I always rest the star on a metal table to solder it as I was worried that the heat from the iron would damage the emitter. Wrong?
P


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## FRITZHID (Jan 17, 2016)

The emitter was reflowed at a temperature that's was much higher than your soldering iron will provide while soldering the contact pads. I solder my star leads on a rubberized anti-static mat, never had a failure.


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## peter yetman (Jan 17, 2016)

Thanks for that Fritz.
Looks like I'm filling in for the Op on this one!.
P


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## RustyShackleford1 (Jan 17, 2016)

Sorry, I tuned out for awhile...

I have a lot of experience soldering. I am using rosin-core solder (Tenma 21-1045) and a nice soldering station (Tenma 21-7930). I have epoxied the star to a small piece of FR4 (making some home-made wedge-base bulbs) at right-angle, and holding that in a vise; so I don't think much heat is getting sucked away.

The thing I don't like about my joints is I don't see a nice solder fillet. It's more like the wire is just kind of stuck to the pad on the star.

I think I'm starting to get the hang of it though. I first solder the wire to the FR4, then bend it so spring tension holds it against the star. That seems to be working better. As opposed to first soldering it to the star, and having to try holding it in place using pliers.


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## NoNotAgain (Jan 17, 2016)

A small drop of RMA flux on the pad, pre-tinned wire, and a 80 watt or higher iron with chisel tip. 

I hold the wire down with a Teflon tool, wet the iron tip, make contact for 2-3 seconds and wait another 10 seconds for the solder to solidify. 

You need mass for the solder tip, otherwise the heat sink of the Star will suck all the heat away. 

The Weller iron I'm using is sold for lead stained glass work.


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## FRITZHID (Jan 17, 2016)

RustyShackleford1 said:


> Sorry, I tuned out for awhile...
> 
> I have a lot of experience soldering. I am using rosin-core solder (Tenma 21-1045) and a nice soldering station (Tenma 21-7930). I have epoxied the star to a small piece of FR4 (making some home-made wedge-base bulbs) at right-angle, and holding that in a vise; so I don't think much heat is getting sucked away.
> 
> ...



My guess would be you were causing mechanical fault in the joint when holding it with pliers. This can cause both ugly and "cold" solder joints.
Often enough a "third hand" tool works well to prevent this but in the future you may want to solder the leads before mounting the star.


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## m4a1usr (Jan 17, 2016)

Like Don said. HEAT your work prior to applying the soldering iron. Makes things so much easier. You'd be surprised to see how well you can solder by elevating the item temp by just a 20 or 30 degrees C. 

I.E. break out the GF hair dryer or get yourself that belated X-mas gift. A heat shrink gun!


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## FRITZHID (Jan 17, 2016)

m4a1usr said:


> Like Don said. HEAT your work prior to applying the soldering iron. Makes things so much easier. You'd be surprised to see how well you can solder by elevating the item temp by just a 20 or 30 degrees C.
> 
> I.E. break out the GF hair dryer or get yourself that belated X-mas gift. A heat shrink gun!



I've personally never needed to preheat a LED star, unless it's a specific job where it's already mounted on a heatsink. With proper soldering technique and tools it's not necessary. Just use proper wattage iron, flux OR flux core solder and do it off a heatsink and you'll be fine. Just make sure everything is tinned, apply heat for 10-15 seconds and then hit it with solder.


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## nbp (Jan 17, 2016)

Great tips guys, this is a super thread. Subscribed!


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## lucca brassi (Jan 22, 2016)

as i have previously said ... solder on small regulated stowe with temp around 60-70°C . But all soldering have to be done in few seconds 










PS : that is nothing special -rework machines have preheating plates


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## uk_caver (Jan 24, 2016)

I've soldered to a lot of stars, with lead-free solder, and I've rarely had any difficulties even when they're fixed to decent heatsinks. No added flux, no pre-heating.

I use a temperature-controlled iron, with a reasonable-sized bit (2.3mm wide oval). Usually I tin the pad first, then solder the wire later in a quick action.
I normally use PTFE-coated wire, since though it's a bit harder to strip, it gives a neat result with fine wires with no insulation melt-back, and the wire I use has silver-coated copper inside which solders really nicely and very quickly.

That said, having used Luxeon/Seoul/Crees for the last 12 years, I recently had to solder to some LEDEngin stars for a UV project, and they were all a real pain - it was far harder to solder to those stars resting on a soldering mat than to other stars well-fixed to big heatsinks.


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## lucca brassi (Jan 25, 2016)

oxide on surface .....

http://www.robotroom.com/PCBTarnishEraser.html

https://www.jprelec.co.uk/store.asp/c=703/PCB-Eraser-Cleaner

P.S. : if you use blue pencil rubber , after cleaning press surface with some insulating tape (leaves no adhesive on the surface ) to remove the remains of eraser


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## uk_caver (Jan 25, 2016)

I don't clean normal stars before soldering these days, and I solder with SnAgCu solder with a fairly mild no-clean flux inside. That said, the stars I tend to use these days are from Cutter, and the pads are gold plated. I do remember some older stars having tinned pads which did sometimes need a scrape from a knife or a subtle pass from a Dremel cutting disc at low speed to clean off an oxide layer - it's surprising just how delicate a Dremel can be at doing that kind of thing.

Having a clean soldering iron bit really helps heat the transfer rate, and hence ease of soldering when soldering to anything with a meaningful thermal mass.
I've found a brass wool tip cleaner really helps keeping a clean bit, maybe particularly when using lead-free solder and hence running the iron at a higher temperature.

I don't know what it is about the LEDEngin stars that makes them such a pain to solder - maybe they have a much better thermal path from the pads to the star body.
In the end, I did all the things I don't normally need to do: very gently Dremel-scuffing the surface; giving a touch from a flux pen; and finally using the non-tapering bit on my soldering iron, which is essentially a 6.5mm diameter bar with a slope-cut end.


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## DIWdiver (Jan 25, 2016)

Are the LEDEngine stars copper and the others aluminum? That would make a big difference.

Another thing that could make a difference is the thickness (and possibly the material) of the insulating layer. Typically this is essentially a very thin printed circuit board, about 0.007" thick IIRC. On the cheapest ones, this layer covers the entire star. On the best ones, there's an opening so the LED's thermal slug can solder directly to the metal substrate, which has a small 'pedestal' so the metal substrate is level with the top of the insulation in this area. Perhaps LEDEngine went with no opening, but used a thinner and/or more thermally conductive material.


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## uk_caver (Jan 26, 2016)

They're aluminium.

If better conduction to the star body is the main source of the difference, it would seem to point to regular stars having meaningful room for improvement in that area.
These things weren't just a bit harder to solder than typical stars, but seemed to be in a different league, though I suppose that some of that may come down to relatively few degrees out of a couple of hundred making the difference between melting solder and not melting it.


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