LED MCPCB Stars and other shapes General Information Thread

HarryN · Jun 8, 2011

Hi, At various times, people look for information on LED mounting, in particular on MCPCBs and often in star or other formats.

I thought it might be a good idea to have one thread that concentrated this accumulation of information, links, properties, and experiences with various MCPCBs and stars.

This is intended to be more of an information accumulation thread, not a detailed discussion about whether or not stars and MCPCBs are the optimum way to mount an LED.

Nonetheless, I have had some mixed experiences with commerical stars and will post this learning curve here for people to see. Perhaps others will as well.

HarryN · Jun 8, 2011

Opulent Stars

I needed to solder some high CRI 400K Rebels onto stars for a project, and Future carried these stars so I bought them at the same time. The price is quite low - I think something like $ 0.50 / each, so I bought them for practice work.

I reflowed them using a frying pan and professional grade Sn/Pb/ Ag solder paste, at just a high enough temperature to flow the solder, plus boil off the flux. I did not measure the actualy soldering temperature, instead, I slowly heated up the pan until a small dab of solder paste in the pan melted.

Results
- Of course, my technique improved over time, so the yield improved as well
- The boards have a nasty habit of delaminating, and the surface insulator literally chars during use
- A second reflow / rework is nearly impossible
- I cannot imagine that these boards would hold up to no-lead soldering

Thermal results
- No real technical data
- I am only driving the Rebels at 500ma for this application, so the heat generation is low
- Nonetheless, I expected the star to get a bit warmer than it did under use, rather than virtually no warming
- The stars were connected to a rather large heat spreader setup, but still - seemed like the heat was not moving much

Wiring
- I tried various methods to connect wires to the star connections
- Direct soldering wires, soldering on crimp connections, etc.
- On a significant number of the stars, the pad lifted either during soldering, or from relatively minor wire induced stress
- Result - I am quite sure that this will be the main reliability limitation of the light I built with this star. Fortuneately, it was just a 4 LED desk lamp for my daughter, so it is not that demanding of an application

I will reiterate that my soldering skills are not perfect, and I probably had too high of a temperature ramp rate on these. I am still not sure of an ideal method to attach wires to the pads though, as this seems like a weak area.

Suggestions are welcome.

Harry

HarryN · Jun 9, 2011

Hi, found a few historical threads, some went into depth, some not.

06c8e3c0f90a5a76722ef6870f9c1e05

HarryN · Jun 9, 2011

Hi, found a few historical threads, some went into depth, some not. I searched around and found prior threads on bergquist material:

http://www.candlepowerforums.com/vb...ED-Star-board-(Bergquist)&highlight=bergquist

http://www.candlepowerforums.com/vb...mal-transfer-calculations&highlight=bergquist

Not exactly a conventional MCPCB but an interesting custom variation:

http://www.candlepowerforums.com/vb...at-home-interior-lighting&highlight=bergquist

And of course this interesting thread from archer on his quest to design / buy MCPCBs, and related discussions and inputs:

http://www.candlepowerforums.com/vb...m-copper-MCPCB-for-an-XML&highlight=bergquist

HarryN · Jun 11, 2011

Hi, I would like to get some feedback on experiences using the bergquist star boards. In particular:
- soldering experiences
- delamination or not
- methods used to make very solid wiring connections such as:

a) I just soldering on wire and I am happy
b) It peeled
c) I soldered on a crimp connector first
d) I had a heck of a time
e) It is so easy, why are you asking

Feel free to comment on other brands as well. Reflow soldering an LED onto a star is (hopefully) rather LED brand agnostic.

Thanks

Harry

SemiMan · Jun 11, 2011

I have done perhaps 100 Rebels onto Opulent stars and have not had the issues you have described. I have had no issues with delamination at all. That is using lead free solder.

I do use a temperature controlled heat plate.

If you are using a frying pan, I hope it is a high quality pan with a thick aluminum plate. Otherwise the temp variations are likely large across it. I expect your star may be getting way too hot.

Semiman

HarryN said:
Opulent Stars

I needed to solder some high CRI 400K Rebels onto stars for a project, and Future carried these stars so I bought them at the same time. The price is quite low - I think something like $ 0.50 / each, so I bought them for practice work.

I reflowed them using a frying pan and professional grade Sn/Pb/ Ag solder paste, at just a high enough temperature to flow the solder, plus boil off the flux. I did not measure the actualy soldering temperature, instead, I slowly heated up the pan until a small dab of solder paste in the pan melted.

Results
- Of course, my technique improved over time, so the yield improved as well
- The boards have a nasty habit of delaminating, and the surface insulator literally chars during use
- A second reflow / rework is nearly impossible
- I cannot imagine that these boards would hold up to no-lead soldering

Thermal results
- No real technical data
- I am only driving the Rebels at 500ma for this application, so the heat generation is low
- Nonetheless, I expected the star to get a bit warmer than it did under use, rather than virtually no warming
- The stars were connected to a rather large heat spreader setup, but still - seemed like the heat was not moving much

Wiring
- I tried various methods to connect wires to the star connections
- Direct soldering wires, soldering on crimp connections, etc.
- On a significant number of the stars, the pad lifted either during soldering, or from relatively minor wire induced stress
- Result - I am quite sure that this will be the main reliability limitation of the light I built with this star. Fortuneately, it was just a 4 LED desk lamp for my daughter, so it is not that demanding of an application

I will reiterate that my soldering skills are not perfect, and I probably had too high of a temperature ramp rate on these. I am still not sure of an ideal method to attach wires to the pads though, as this seems like a weak area.

Suggestions are welcome.

Harry

HarryN · Jun 11, 2011

Hi, Thanks for the reply.

The frying pan is very thick aluminum on a large electric burner. I preheat the pan very slowly warming it up until a thin layer of solder paste just melts. It is not hot enough to remelt a solder blob in the bottom of the pan, so perhaps that gives you some indication of temperature. I am planning to try a thermocouple next. The hot plate idea is good, the only thing is that if I put the money into that, I would rather have one with programmable temperatures, so I can run a "real" reflow cycle.

The opulents are listed as being capable of Pb free soldering conditions, but it must be Indium solder because the test I did with Sn based Pb free solder paste on these guys was even worse.

I experimented with reflow time under two different conditions:
a) Until it just melted everywhere
b) Until the flux stopped smoking

The star is then pulled out and placed on a metal grid to cool.

In the "no LED test run", the solder on the stars melted all across the star at virtually the same time, indicating that the temperature is not all that uneven. Even if it were somewhat non even, the Al in the star would tend to smooth that out.

What I suspect is that the star cannot handle the shock of going from room temperature to being in the hot pan, but that is just conjecture on my part.

Questions:

a) how are you attaching wires to the stars ? Clips / crimp connectors, or just soldering on the wires later ?
b) Are you still using these stars or a different brand ?

I mostly have my own LED MCPCBs made, but these were easy to obtain and I just needed some simple stars for a home project.

I am getting ready to buy another batch of stars - it certainly won't be this brand, but I am not sure what it will be.

HarryN · Jun 15, 2011

A few more links for interesting stars:

A custom 8mm dia. board for sale:

http://www.cpfmarketplace.com/mp/showthread.php?247689-8mm-XM-L-MCPCB

And some general info on comparing a few brands of stars (in German)

http://www.messerforum.net/showthread.php?t=95912

panicmechanic · Jun 15, 2011

HarryN said:
A few more links for interesting stars:
http://www.messerforum.net/showthread.php?t=95912

Thanks for this link! I was only suspecting that the amount of copper has a lot to do with the XM-L's ability to cope with higher current. Several disappointed users reported in another forum, claiming not to have profited from driving it harder. Some of them used "LT" stars.

HarryN · Jun 16, 2011

I am glad this thread and the links are useful. Here is one more (discussion about wire attachment to stars)

http://www.candlepowerforums.com/vb...D-Star-wire-connections&p=3671183#post3671183

HarryN · Jun 16, 2011

An old thread (2006) on stars and some experiments.

http://www.candlepowerforums.com/vb/showthread.php?140996-Cree-XR-E-Thermal-Concerns&p=1687859

LED MCPCB Stars and other shapes General Information Thread

HarryN

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HarryN

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HarryN

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HarryN

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HarryN

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SemiMan

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