New VirEnce MCPCB for E17/E21/119/144/233U

Thanks Bark,
Even without super material CDTP can be designed to surpass neutral DTP approach as long as you have the required surface area. The idea is to lower the heat potential difference (does anyone know shorter terms for this?) thus less thermal resistance. This is pretty much why Nichia still manufacture 2 pads design.
In theory two pads design can achieve lower Tj compared to three pads design (ignoring the surface area required) since copper used in cathode/anode has much better thermal conductance than the dielectric material commonly used in LED. Combined together with very high conductance and thin solder joint such as Indium solder, the result should be even better.

Upstream just at the heat source, heat flux intensity is higher that downstream where the surface area is cooler and larger.

For example: If a 119 has to pass 10 watt of power through two tiny solder pads. The heat intensity is roughly 10 watt/11,9 mm^2 (0,84 W/mm^2). After heat flux passing the solder pads, the intensity lowers down to 10 watt/201 mm^2 (0,05 W/mm^2) using a circular 16mm MCPCB.

My simple logics:

- Upstream:
common Sn60Pb40 thermal conductance ~50 W/M.K
heat intensity ~ 0,84 W/mm^2

- Downstream
Thermal pad material with X thermal conductance
heat intensity ~0,05 W/mm^2
To get the same state, thus X= ~2,9 W/M.K

I still don’t have any valid data to stand up for this one yet. I rather make some and then test it based on that logic. The universal VirEnce board test result was higher than expected. And I think (emphasizing the: I think), solder choice is one of the most important thing in CDTP design, it’s where the bottleneck occurs (not downstream at the MCPCB’s thermal pad). As long as we use MCPCB with surface area reasonably LARGER than the footprint of the LED’s solder pads.

I’m using Sn96,5Ag3Cu0,5 for most of my newer project now. It’s harder on the boards (218C liquidus) than 60/40 and requires extra effort to get a good reflowed boards. The thermal conductance is ~58-60 W/M.K.
I have a spool of SnxxAgxx (lost the label) solder wire rated at 70W/M.K but requires 240C to a flowable liquidus. Much harder and stronger joint very useful for aluminum soldering.

The larger the MCPCB surface/mating area to the heatsink, the less sophisticated the thermal pad required.

That’s the ideas behind my idea….

Indalloy #290, 97In3Ag, is eutectic, melts at 143°C/289.4°F, and provides a 73W/m×K thermal conductivity figure. Sources:

Cheers ^:)

Very nice, must be expensive though

“melts at 143°C”

would be too low for my liking

Best thermal protection….when it gets hot the LED would just dropping run off the board :smiley:
Good for “normal” applications, not for you Matthias

Well, I think the opposite is the case. That stuff is for special applications. For normal application, just go with normal solder paste. Or go with SnAg (96.5/3.5) if you really want good thermal properties. 221°C reflow temperature shouldn’t be a problem at all and that stuff is quite affordable.

Yup, for example soldering over soldered joint. I have many PVC backed waterproof cable connector joiner with very low melting temp solder. Just apply moderate heat using heat gun.
Hey, I think that Sn96,5Ag3,5 is very similar to my spool. Mine rated at 221C but in practice I had to set my hotplate to 240C for it to reflow properly. That’s the solder wire I used when I sent Djozz the samples. 240C reflow temp really turned those white S30 VirEnce board dark yellow. I also used wrong flux to worsen the looks.

chouster, the thermal conductivity figure you provide for Sn96.5Ag3.5 is not supported by the guys at Indium Corporation. They claim a 33W/m×K for it (Indalloy #121). Check it out in the table link above, and here: Alloy Thermal Conductivity @ Indium Corporation.

Cheers ^:)

@ clemence

But I think you made a very valid point. It’s the solder joint that has to pull away the heat from the LED at first and using Sn96,5Ag3,5 instead of standard Sn63Pb37 should give an increase of 56% in thermal conductivity. Just use solder paste with less agressive flux.

clemence, you slipped in while I was still editing my post.

So, you reflowed those Nichias with 96.5Sn3.5Ag? Ooops! You may had created a heat transfer bottleneck, so Djozz's tests may not resemble the results most of us would get with Sn63Pb37/Sn60Pb40/Sn99.3Cu0.7…
Time for a little retest?

Cheers ^:)

That was accidental….
I dipped the solder wire to a super aggressive ALUMINUM flux. If you see those boards in Maukka’s spectrum test thread, some were extremely “burnt” by the flux.

I don’t know if the move to SA35 (Sn96,5Sn3,5) would really make measurable end result difference (higher lumen) with thin solder line. With proper soldering (very thin bond line) the difference would be minimal. In the case of thicker joint then solder choice should be more critical.
I usually just put a small blob of solder paste and heat until the LED soldered, then remove excess solder using fluxed solder wick to create the thinnest possible joint. LED pre-centering is critical with this method. Less solder between LED and solder pads give less self centering effect.

Heat transfer bottleneck? Of course, just like all of us. Until there’s a solder with thermal conductivity same/higher than cathode/anode material, there will be bottleneck at the solder joints. You can achieve that though. Just “weld” your LED pads to the MCPCB using the same technique as those copper electroforming - 100% pure copper joint! Hahahaha

As I wrote earlier, with such a thin joint the difference in the solder’s thermal conductivity would be not that obvious anymore. But we need an expert to validate my thoughts here.

It is a bit of a gut feeling, but in the course of testing quite a few leds and ledboards I did not notice obvious performance effects of using thick or thin solder layers under the led, so my working conclusion is that once you use a DTP board and thus the connection from the thermal pad to the core is all-metal, then the thickness of the solder layer is not the thermal bottleneck anymore. In this reasoning, using a solder type with 1.5 times the thermal conductivity of common solder will not change much either.

But again, I do not have hard data from a clean test on this.

Well, indeed it’s time for a re-test. I’m not an expert in metallurgy science. A real life test should be enough. But this time only the new 16mm and 20mm. Are you ready Djozz? :wink:

@Barkuti,

you refer to some company selling special Indium solders. Now, do they at least give us the temperature at which the thermal conductivity is that bad as they state? Thermal conductivity of such an alloy decreases with rising temperature. If they want to provide facts, they should at least tell the whole story. A thermal conductivity without corresponding temperature is useless.

That’s at 25°C. —-> 78 W/m⋅K

That’s at 85°C. ——> 55 W/m⋅K

Fact is, 96.5Sn3.5Ag is superior to most standard solder compositions, regarding thermal conductivity. Maybe that’s why the VirEnce board tested even better as expected, maybe not that much of an impact, but certainly no disadvantage.

EDIT: Well, maybe “superior to most” isn’t the right way to say it, but it’s certainly no slouch in that regard.

Anyways, I think we should rather be talking about the best ways to isolate the board, if we don’t go the way of having cathode across the entire housing of our lights. Aluminum nitride can be bought cheaper at some chinese suppliers at alibaba for example, but the thing is, you’d have to have two additional layers of thermal compound. With some pad or thermal foil (both insulating type of course), you wouldn’t have to use any thermal compound in between and such a foil usually comes in much thinner as a disc or sheet of ALN.

That's what I was talking about earlier. An MCPCB manufacturer could assemble emitter boards with a foily layer of Aluminium Nitride as dielectric. That's it.

Cheers ^:)

Yeah, or diamond PVD coating. But with this board, as it is, what would be the best, affordable way to put it to a good use? What’s the best foil for this application?

Guys, please remember that AIN coated MCPCB can’t conform to irregular rough surface as good as soft thermal pad. This fact offset its benefit. Unless, you always have to lap your heatsink/pill to near perfect FLAT mirror like finish.

Thermal pad/adhesives is the way to go for our application and my current budget.

Clemence

16mm board

- 1,6 - 1,8mm thick

- 2 x 3mm dia. wire slots

  • with/without thermal pad (0,5/1 mm thick)

20mm Board

- 1,6 - 1,8mm thick

- standard screw slots

- 2 x 3mm dia. wire slots

  • with/without thermal pad (0,5/1 mm thick)

Thermal pad info:

- Thermal conductivity 12 W/M.K

- Thermal resistance 0,18 C/W at 50 psi

  • Compressible down to 30% original thickness at 100 psi

What about optics holes? Ledil / Carclo / Gaggione / else?
Feel free to add more suggestions