A Deceptive Thermal Question for PCB Layout?
Alas ... I was never strong in thermodynamics.
This is for you Printed Circuit Wizards
Here is my problem in a White LED layout, See first picture
What or how do I find the OPTIMUM VIA Diameter for Heat TRANSFER ??
This is for you Printed Circuit Wizards
Here is my problem in a White LED layout, See first picture
- Trying to pass excess LED heat to back side copper through VIAs
- I know the larger the VIA Dia the lower the thermal impedance.
- Intuitively as the hole grows it will eventually make heat transfer much worse
What or how do I find the OPTIMUM VIA Diameter for Heat TRANSFER ??
Discussions
Best Answer 6 years ago
I'd think, as long as the hole in the via is filled with a metal (i.e lead, tin, whatever) it would benefit the thermal conductivity. Once the hole is big enough t be a hole (i.e. has air inside) thermal conductivity would get worse. The diameter would depend on the process(es) used. So, you should contact the manufacturer for detailed information.
Without further ado, I'd just put some 0.5mm holes/vias in a 1mm grid. - As long as you don't have to pay for every single hole separately,
Answer 6 years ago
The wire in hole is an excellent suggestion,
but would not survive the production expense requirement.
I particularly like the wire in the holes as then they could be placed in radially alignment.
Answer 6 years ago
I did not mean to put a wire into the hole. I meant to make the via small enough that it will be filled with copper during the plating process that normally only plates the sides of vias and through holes. Or let the via get filled during soldering. If you use a wave soldering process, just keep the vias free of solder stop lacquer so they can suck up the tin. If you use SMD make a separate stencil and fill the vias with soldering paste before the reflow process. If you have a lot of money to spend, look for a PCB manufacturer that can produce copper inlays. The perfect way to transport heat away from the LED (and money away from you :-)
Answer 6 years ago
You are quite correct about the general lack of money.
My client is a capable scientist and good friend that may change my direction
at the rise and fall of a new factoid.
There are SMD LEDs on one side and through hole components with SMD 317s
on the other side with room for 2oz copper cooling surfaces.
Low volumes and manual assembly only profitable in a military setting,
makes for a can of worms rules for production arrangements.
I greatly appreciate the most excellent proffered suggestions from this great
community but I have my exact answer in that Nichia application note PDF
that I shared with you..
A
6 years ago
I got a D in thermo.
I suppose you have visited this site: http://www.powerguru.org/thermal-impedance-and-thermal-resistance/
Answer 6 years ago
Thanks Bill
Yes ..... but only hours ago from a previous comment.
A
6 years ago
A client brought this super Nichia application note PDF to my attention today.
Optimal Thermal Design with Through Holes
I take it to mean, that the experimental data suggest a 1mm to 1.2mm hole as a best VIA LED heat transfer construct.Answer 6 years ago
Nice link. Saved for future reference.
6 years ago
Use aluminium PCB material.....
Answer 6 years ago
Ill bring it up.......
However this is a Re_Grade => Buyer wants Lamp with LED stock is no longer available.
A New LED start to discontinued product cycle is under three years !!
Which is faster then gov purchasing reaction cycle.
Improved efficiency causes consternation because the current is lower and DIFFERENT then the spec.
Answer 6 years ago
Put some 1W power resistors on the board ;-)
Answer 6 years ago
It was a serious option for a short one time meeting.
Answer 6 years ago
PS running white LEDs cooler and below continuous design current significantly
extends Life and color of the phosphors being used.
6 years ago
What does the data sheet for the LED say. That's the kind of information that will be on the data sheet. Especially if additional cooling is required.
Answer 6 years ago
it's a white XL CREE LED... see the PDF
Most thermal management involves many mini VIAs directly under the LED.
My client supplies military lights and there are a mixture of conflicting product specifications
that were probably developed early in the LED white conception cycle,
Color being very high on the ranking order.