I've got myself a high power SMD 850 nm LED, 650 mW radiant power. I need to use this non-stop for hours at a time. So I need to solder this to a heatsink to manage the heat. I've got 4 them, actually -- to account for the vast potential for me destroying one or two of these before I get it right. It looks like this (screen shot from its spec sheet, the link is below).

enter image description here

Are there any standard adapters that I could use to make the soldering easier? My previous version (3x less heat dissipation) was on a star adapter which, in turn, was mounted to a finned sink with thermal paste, so I was planning to recycle the heat sink. That sink is also threaded, to which a glass lens is neatly attached. However, this time I am worried if that thermal paste+star won't be dissipate the heat. If it helps, I have an endmill, and I can modify standard Al or Cu pieces (Al is easier) to make this work. I've got eye protection for the IR as well.


Thank you in advance!

  • 1
    \$\begingroup\$ The datasheet clearly shows you need a temperature controlled SMT station to be successful at soldering these to a board. I'd suggest that you may be better simply loading these on a simple PCB with some sizeable copper area thickness, then use cold air to provide thermal control. If you are in a factory environment you can generate cold air from compressed air very easily, and it works super well. You can then use very small or even no heat transfer areas. I've tested high power cpus in an environment like this with no heatsink attached. \$\endgroup\$ Aug 2, 2017 at 0:01
  • 1
    \$\begingroup\$ Thank you, Jack, for the comment! I suppose the key statement in the specs is: " to be reflow soldered on to a PCB" the meaning of which I did not know until now. Dip-soldering (which is I guess what I am doing) is mentioned, but performance is not guaranteed. Regarding blowing air on these: I was hoping to avoid this as this may cause vibrations. The LED is used to provide illumination to particles imaged under a microscope; I will then track the particles with ~5 nm resolution in a feedback loop, and any variation in illumination/position due to vibrations throws the tracking off. \$\endgroup\$ Aug 2, 2017 at 1:24
  • 1
    \$\begingroup\$ You could use standard 2 oz FR4 laminate as a single sided (no holes, only use SMT components) pcb and simply bond this to an Aluminum or copper plate/heatsink for rigidity. amitroncorp.com/printed-circuit-boards/aluminum.html ... you could equally front mount heatsinks using Berylium Oxide TO3 washers which are readily available and cheap: aavid.com/product-group/interface/insulators/beryllium amazon.com/ABL-HEATSINKS-510AB0500MB-TO3-HEAT/dp/B00DK84ZMI \$\endgroup\$ Aug 2, 2017 at 3:36
  • 1
    \$\begingroup\$ Jack -- great hint on Be Oxide as insulator. I was thinking to use glass coverglasses which I have in abundance, but Be Ox sounds better. Is the thickness of the Cu foil on the PCB enough? How wide of a piece in area of Cu foil does one need for 5W dissipation before thermal paste can take over? I am also thinking to use a fly-cut-flattenned Cu coin with a machined elevated pillar the size of the heat sink pad... heat it up on a temp controlled hot plate, drop the solder, drop the LED on it, immediately transfer on ice/larger plate. \$\endgroup\$ Aug 2, 2017 at 12:46
  • 1
    \$\begingroup\$ Jack -- may I ask what your opinion on using a silver disk to mount the LED, say, penny-shaped? I would pass it on an endmil to make a pillar in the middle, say about 0.5 mm high, and 2x4 mm W/L. Surround it with an insulator (a coverglass or BeOx washer). This way I would avoid oxidation during heating before soldering, and won't need to use nitrogen flow to prevent oxidation (as copper would do). The heat sink pad on the LED claims to be silver, so, that matches well. Place the LED, place the whol assembly on ice/large metal block to cool it. Touch-solder 2 wires once cooled. \$\endgroup\$ Aug 2, 2017 at 13:54


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.