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

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

More wire slots please, makes cable routing/balancing easier. Example:

Cheers ^:)

I have to reserve as large as possible surface area hence only critical slots/holes will be added

clemence, I only said slots, not holes. Two holes, and 2 slots at each hole's sides. This allows routing two thinner wires per slot, resulting in a flatter profile, handy when you have a retaining ring screwing down over the board (I think Noctigons suck because of only 2 slots). :-)

Cheers ^:)

Question,

For the 20mm:
Do you need the screws to be completely flush with the board surface (countersunk).
OR…
Is it OK to just let the head protruded (normal M3 x 0,5 screw head)?

Thank you,
Clemence

A 16mm board, if screw holes are added, must have them countersunk or the scews will mess with many reflectors. =less needed for 20mm

No screw holes for the 16mm only the 20mm has it.
How do you usually secure the 16mm and 20mm boards?

In many flashlights they are just pressed down by the reflector, or adhesive is used under the board, this is especially common for 16mm boards. 20mm boards are sometimes screwed down. The holes in the board may best be somewhat wider than the used screw, to have some wiggle room to center it under the reflector. Thinking of that, it may be a good idea to not make countersink holes.

I thought so too. With countersunk holes, the free play is limited. It’s also easier to isolate the screws from the board (CDTP limitation).
You know what Djozz? “CDTP” is popularized by you! You were the first to use that term, AFAIK :wink:

Screws in general might be a problem. They might create an electrical connection between mpcb and the heatsink.