How Can You Efficiently Solder Wires to LED Chips?

[kolleamm]

Hi,
We are currently working on a project that uses LED chips. Each chip has 4 contacts that need wires soldered onto them. The chip is about 1" x 1", with the contacts being fairly small.
What would be the most practical way to accomplish this? Does anybody know any reliable companies that could do this for us?
I'm considering converting my 3d printer into an automatic soldering machine but perhaps someone here can offer a better solution.

Thanks in advance

 

[berkeman]

You are soldering wires onto the SMT pads? Why not just make simple adapter PCBs and use SMT reflow soldering?

Can you say more about the application? Where do the "wires" in your current design go?

 

[kolleamm]

You are soldering wires onto the SMT pads?

That's correct, could you tell me more about the PCB and SMT reflow? That sounds very interesting.

The wires go to the power supply, 2 for brightness, 2 for color shifting.
The power supply has 7 wires :
Output wires (3) : 2 positive, 1 ground
Input wires (4) : 2 sets of positive and negative that determine the output intensity

 

[hutchphd]

Can you say more about the application? Where do the "wires" in your current design go?

When you said "chips" I was thinking 0402 SMD parts. These things are an inch square?? Do they need heat sink? What is the application please?

 

[kolleamm]

The chips look similar to the 3rd one from the left (the square one next to the big square).
The SMT pads are only on one side.

 

[kolleamm]

When you said "chips" I was thinking 0402 SMD parts. These things are an inch square?? Do they need heat sink? What is the application please?

The application is for a high power lamp, the case will be aluminum to help absorb the heat.
About 8 chips per lamp so far.

 

[hutchphd]

You will need thermal contact to the case if you run these COB (chip on board) units anywhere near limit. What are the heat sink specs and does the manufacturer suggest a soldering protocol?

 

[berkeman]

Do they need heat sink?

This ^^^^

High power LED applications require careful heat sinking, so there are special ways to mount them to the metal. @hutchphd makes a good point that the manufacturer probably has recommended mounting techniques...

I'll look to see what I can find. A traditional PCB does not thermally conduct well...

 

[kolleamm]

You will need thermal contact to the case if you run these COB (chip on board) units anywhere near limit. What are the heat sink specs and does the manufacturer suggest a soldering protocol?

They will definitely generate a lot of heat so a heat sink is essential. I don't have the documentation at the moment but I will request it.

 

[hutchphd]

Often for individual LED the board has thick copper both sides with many thruhole vias for heat conduction. There are also thick film techniques that incorporate aluminum heat sinks directly: I have not used them.

 

[kolleamm]

Often for individual LED the board has thick copper both sides with many thruhole vias for heat conduction. There are also thick film techniques that incorporate aluminum heat sinks directly: I have not used them.

I wish these had a thruhole contact, sadly its just on the front where the LED is.

 

[berkeman]

Often for individual LED the board has thick copper both sides with many thruhole vias for heat conduction.

Yeah, that's similar to what I was thinking. make a small 2-sided PCB with the 4 SMT pads connecting to the LED(s), and a ground pad under the LED body that has vias stitched to a ground pad on the other side (without soldermask). Use heat sink grease between the LED and the top side pad, and between the bottom side pad and the metal heatsink. That may be how they make LED PCBAs like the ones below, that I've seen mounted to metal heat sinks...

https://en.wikipedia.org/wiki/Thermal_management_of_high-power_LEDs

https://www.instructables.com/High-Power-RGB-mount/

 

[berkeman]

The wires go to the power supply, 2 for brightness, 2 for color shifting.
The power supply has 7 wires :
Output wires (3) : 2 positive, 1 ground
Input wires (4) : 2 sets of positive and negative that determine the output intensity

BTW, if some of those SMT pads for the LED can be considered "Ground", you may be able to tie those to your PCBA heat sink directly (through wide traces and quick vias to the bottom side of the PCB for thermal contact to the metal chassis.

 

[hutchphd]

Destructively take a look at an LED lightbulb. Nontrivial technology of conductors laid onto aluminum plates. Why are you building your own lightbulbs?
The COB lights are very good (My basement lab is lit using one old PC power supply and COBs everywhere). I back them onto my steel air ducts. I am not sure they make sense for this. The heatsinks need to be good, copper is not cheap, and then you have to build them! But I will do what I can to help.

 

[berkeman]

I don't have the documentation at the moment but I will request it.

Can you post a link to the datasheet? (sorry if you already did and I missed it)

 

[kolleamm]

Can you post a link to the datasheet? (sorry if you already did and I missed it)

I just requested it, hopefully I can get it soon.

 

[berkeman]

Did you buy them from Digikey/Mouser? They usually post datasheets. What is the Mfg and Part Number -- a Google search usually gets you to the datasheet...

 

[kolleamm]

Did you buy them from Digikey/Mouser? They usually post datasheets. What is the Mfg and Part Number -- a Google search usually gets you to the datasheet...

Nah these were custom made by Samsung.

 

[Tom.G]

Nah these were custom made by Samsung.

Especially for you?
As surplus?
Rejects?

If you can not get a datasheet and factory support, you might consider either hiring an engineer that has done this before, or cutting your losses.

I once worked at a company that used small solid state LASER assemblies. The owner was always looking for a "Good Deal."

He found a low cost source for some product made in the Far East. What a headache!

After we finally decided to do 100% inspection and burn-in we were running 8% to 15% failure rate per batch, with a few more fails after product assembly and final test. Of course the parts were all paid for by then.

Hopefully your story has a happier ending. That company no longer exists.

 

[DaveE]

Have you asked the manufacturer how they think their parts should be mounted and cooled? I'd bet they know better than us.

 

[kolleamm]

You guys make good points. I'm merely working together with the guy who ordered the chips and had them custom made for him. I asked him to request the datasheet, and am still waiting on his response. We tested the chips and they do work as expected, and yes they do generate a lot of heat.

I'm pretty sure we could find a heat-sink solution just by testing different setups if we don't get the datasheet.
We just haven't found the most practical way yet to attach wires to these chips since soldering is fairly tedious and time consuming especially for many units.

 

[hutchphd]

We just haven't found the most practical way yet to attach wires to these chips since soldering is fairly tedious and time consuming especially for many units.

Also soldering an otherwise unsupported wire is never a good idea. The stress point at the solder/wire interface is a disaster particularly for stranded wire. What is the vibration environment? Someone needs to rethink this.
Good money after bad.

 

[kolleamm]

Also soldering an otherwise unsupported wire is never a good idea. The stress point at the solder/wire interface is a disaster particularly for stranded wire. What is the vibration environment? Someone needs to rethink this.
Good money after bad.

90% of the time the lamps will be stationary so vibration shouldn't be much of an issue. We can further secure the wires if necessary.

 

[berkeman]

I'm pretty sure we could find a heat-sink solution just by testing different setups if we don't get the datasheet.
We just haven't found the most practical way yet to attach wires to these chips since soldering is fairly tedious and time consuming especially for many units.

You may know this already, but one of the big problems with inadequate heat sinking of high-power LED lights is a shortened lifetime. So if you just solder wires to isolated LEDs without heat sinking, the lamps will probably dim and fail withing just a few years.

 

[kolleamm]

You may know this already, but one of the big problems with inadequate heat sinking of high-power LED lights is a shortened lifetime. So if you just solder wires to isolated LEDs without heat sinking, the lamps will probably dim and fail withing just a few years.

Yes, the heatsink has been a part of the lamp from day 1. We just need a practical way of attaching the wires.

 

[Tom.G]

Here is an off-the wall idea: Is there a thick enough contact pad on the LEDs that you can spot weld a ribbon of metal to the pad and then to the power source?

Spot welding is commonly used to make battery packs and is a LOT faster than soldering. Typically Nickel ribbon is used, Copper mostly doesn't spot weld.

Another maybe is pressure contacts to the LEDs. Depends a lot on the environment though, both chemical and mechanical, to find compatible contact material. This approach could be enhanced for better contact by using Silver or Copper paste at the interface, as is done with high current (several thousand Amps) busbars.

Cheers,
Tom

 

[Rive]

We just need a practical way of attaching the wires.

Sorry, but for this size of batch it's usually (hand)soldering

Considering the type of the carrier (IMS), it'll be a really painful job. You may need a preheater.

Or you can try to find a company with matching profile.

...spot weld...

Difficult to say if IMS can tolerate that or not. But spot weld would require solid wires and flat surfaces as far as I know? Not sure that would work out well.

 

[Tom.G]

Then there is also Wire Bonding, which I failed to mention in an earlier post. It has been in use in transistor and integrated circuit production for over half a century.

The process for I.C.s usually uses Gold wire of 1mil diameter (0.001in, or 25microns) that is friction welded to the chip and to the package leads. I have heard of, but not seen, the use of Aluminum wire instead of Gold. For high current, multiple wires would be bonded to the same pads.

I understand that these days it is done automatically using machine vision, back then there were humans operating the machines. Anyhow, it is a well characterized and in-use method.

You may be able to find a contract house that does wire bonding that ends up cheaper than soldering. It is certainly a LOT faster.

Cheers,
Tom

 

[shjacks45]

I worked in a PCB shop. Soldering is done to protect physically joined parts/wires. If I ask "what is supporting the LED?" please don't say the wires.
Also, what is the solder specified? Is it ROHS or Tin-Lead?
Most newer electronics is surface mount, non-lead solder. Higher Power LEDs require the board they are attached to dissipated heat. These LEDs are attached with thermal epoxy or physically.
The maker of your chip may offer a "development kit" which saves a lot of time.
There are tutorials on YT for making your own surface mount boards. I previously used a frying pan to melt the solder paste on surface mount boards I made, but now use a heat gun ("blow dryer") to melt it as I can keep a constant temp.

 

[kolleamm]

what is supporting the LED?

The chips sit on top of an aluminum heat sink at this stage in the development.
The contacts are fairly thin on the surface as far as I can tell so I don't think spot welding would work. I don't know a lot about wire bonding but I will certainly do some research on it.
We may just have to find a company to do this for us regardless since it would be highly impractical for us to even build/buy machinery that could accomplish this.
The question now is what type of service do we need.