Tag Archives: Light-emitting diode

PCB layout tips for thermal vias

I came across an article on PCB layout in Electronic Design magazine. It’s a pretty good article and I am glad to see the trade magazines realize we care as much about PCB layout as the bus-caching architecture of some DSP chip. The article talks about using vias to take heat away from the die-attach-paddle (DAP) of integrated circuits:

“To reduce operating temperatures easily, use more layers of solid ground or power planes connected directly to heat sources with multiple vias. Establishing effective heat and high-current routes will optimize heat transfer by means of convection. The use of thermally conductive planes to spread the heat evenly dramatically lowers the temperature by maximizing the area used for heat transfer to the atmosphere (Fig. 4).”

No there is a lot of caution you need to exercise when trying to get the heat out of a part just using a circuit board. You have to realize the guidelines in the datasheet are usually based on one part making heat, sitting on a standard board of a certain dimensions. If you have a lot of hot components you can’t expect the same die temperatures for the part in question. Same goes if you have the board covered with some tight enclosure.


WEBENCH can estimate thermal performance of a switching regulator, but it is just an estimate, highly dependent on your particular layout and application. Note the buck regulator catch diode is the hottest thing on the board, and how little heat is radiated out the bottom, despite the thermal vias.

Texas Instruments WEBENCH is a neat program, especially because it has Mentor Graphic’s FloTherm built in to help you see the hot spots in switching regulators. This is what taught me that a modern buck regulator will have more heat coming out of the catch diode than the pass FET. It made perfect sense once I saw the heat diagram. After all, a diode has 0.6 to 0.9 volts across it, while a modern FET has such low on-resistance it hardly drops any voltage at all.

But realize a simulation is just that, for both electrical and thermal designs. You have to rely on my brother’s maxim from Bell Labs: “An ounce of trial is worth a pound of opinion.” And any simulation is just that, a computer’s opinion on what your circuit will do. So I and several pals have learned a few things with real-world experience. One is that vias rarely work as well as you need them to. The first problem is that the amount of copper in the “barrel” is dependent on the circuit board fabricator. Thin plating means low heat transfer.


Here is a nice side-view of some thermal vias in a PCB. Note the thicker copper on the top and bottom helps to dissipate the heat, and the bigger the area, the better.

The best thing is to fill the vias, which really gets the heat out, but is an extra-cost option. Other than that, plan on a lot of vias under the part. The article excerpt above talks about using inner layers to get heat out, but in my experience that has limited usefulness. Do top-side and bottom-side copper pours. If you can get several square inches, that is great, but if you have a top-side pour, which you should, and a bottom-side pour, well there is not a lot of heat that can radiate from the inner layers unless you can dump heat into an entire ground plane. Remember you have to stop the CAD program from putting thermal reliefs in all the vias. And realize that without thermal reliefs, to de-solder the part you will need a Metcal hot-air rework station or a Hakko hot air gun, (or two). You will need a good iron to solder the part as well, and you have to tell the assembly house that they may have to modify the thermal profiles of their IR reflow ovens so that the parts get soldered correctly.

As far as heat transfer to the atmosphere, it’s something like 100 times worse than getting the heat out of the leadframe. Even if the part does not have a die-attach paddle, you can figure out what pins are connected to the substrate of the die and make sure those pins have a lot of copper area. All the same tricks apply, you can pour topside copper from the pin and be sure to pave over any thermal reliefs the CAD program puts around the pin pad. Vias down through the board to copper pours on the bottom side will get more heat out. Raw copper, or copper with nickel or gold will dissipate more heat than copper covered with soldermask.

I sent the article to my pal Wayne Yamaguchi, who has worked on getting the heat out of LED flashlights for a decade. He learned that not all “rules of thumb” you read in datasheets will accurately forecast the heat you can dissipate into a circuit board. Regarding the article, Yamaguchi wisely notes: “Everything said is correct, but, practically speaking and implementing is something else.” Wayne then sent a link to a thermal calculator for vias that he likes. Wayne notes: “Playing with the via calculator you can determine that FR4 is some pretty awful stuff and also you will find out that 1 oz copper foil is not a good thermal conductor.” He notes the same site has some other great tools. Wayne also pointed me to a Cree technical article (pdf) about thermal vias for high-power LEDs.

Super Mario question mark lamp lights up Maker Faire

The light of nostalgia was burning bright at Maker Faire last week, thanks to product designer Adam Ellsworth of 8bitlit and his Super Mario question mark block lamp.

The custom-made, touch-activated lamp brings your room one step closer to Mushroom Kingdom, not just with its funky yellow aesthetics, but also its classic Mario Bros. sounds.


Every time you touch (or punch) the lamp on, it rewards you with the classic coin “ding” sound, while every eighth punch triggers the extra life “1-UP” sound for added happiness.

The lamp is made from laser-cut plexiglass and uses four energy efficient LED lights. It comes attached to an 11 foot power cord, but can also double as a bedside lamp with the additional purchase of a custom acrylic stand. Best of all? It runs on Atmel’s AT Tiny Chip.


Atmel-powered Lumapad is an open-source LED project

The Lumapad can best be described as an open source, high intensity, 8000 lumen LED lighting system built around a user-programmable Arduino (Atmel) compatible micro-controller and an (optional) electric IMP.

According to project designer Richard Haberkern, 32 ultra-bright LEDs are positioned in a landscape array to provide bright, even and controllable lighting, drawing only 88 watts. Meanwhile, a built in electronic dimmer makes the light intensity adjustable to fit just about any environment.

“This is no ordinary bright light,” Haberkern explained. “With your own custom software, you can control the light intensity, flash effects and even the color temperature via your iPhone, Android device or any computer with an internet connection. An Arduino compatible controller along with the newly available Electric IMP WiFi SD card are both built in, [so you can] control the Lumapad any way you can imagine.”

As noted above, the Lumapad is powered by an Arduino compatible ATmega 328P micro- computer and is pin-for-pin compatible with most open source Arduino boards on the market. The ATmega328P – an 8-bit AVR RISC-based microcontroller – combines 32KB ISP flash memory with read-while-write capabilities, 1024B EEPROM, 2KB SRAM, 23 general purpose I/O lines, 32 general purpose working registers, three flexible timer/counters with compare modes, as well as internal and external interrupts.

Additional specs include a serial programmable USART, a byte-oriented 2-wire serial interface, SPI serial port, a 6-channel 10-bit A/D converter (8-channels in TQFP and QFN/MLF packages), programmable watchdog timer with internal oscillator, and five software selectable power saving modes. By executing powerful instructions in a single clock cycle, the ATmega achieves throughputs approaching 1 MIPS per MHz, balancing power consumption and processing speed.

On the software side, developing for the IMP is unlike your typical embedded development environment, as there are no SDKs to install, JTAG pods, or long download time. Rather, you develop your code in a browser-based IDE, compile it and run on the IMP in under a second. And, using the Arduino compatible micro-computer, you can write multiple programs to control a scene or room lighting.

The Arduino-powered Lumapad has already reached its funding goals on Kickstarter, with 225 backers and $94,482 pledged. Additional information can be found here on Kickstarter, or the official Lumapad website.