Mike S
Newly Enlightened
- Joined
- Apr 29, 2011
- Messages
- 132
Hopefully this isn't in the wrong place. If it is, I apologize.
There's a graph online that shows the different values for various types of solder. When the unit is given in watts per meter per kelvin (W/m-K), is it better to have a solder with a higher or lower value? The solder paste I use is the lowest on the graph and thought this would be best when reflow soldering the LED's. Now I'm wondering if this may have been a poor choice.
Lately I've been buying bare emitters and making my own version of a MCPCB by using ultra thin copper clad boards and reflow soldering the LED directly to copper. The copper board is 0.13 mm thick before it's been etched. I usually remove the all the copper from the back side to make it as thin as possible. With the copper removed from one side, it's now only 0.09 mm thick.
Since there's a small void created by the PCB layer that the solder must fill, is the transfer of heat now much worse because of it, or is it negligible?
To keep the void as small as possble, a drinking straw is used to press down on the LED while it's being reflow soldered. The hole in the center of the straw fits perfectly over the dome so that it's only pressing down on the flat substrate. Different straws work for different LED's. For example, a coffee stir fits nicely over an XP-G.
I've done some side by side comparisons between MCPCB's with LED's already mounted and the homemade version using XM-L's, XP-G's, MC-E's, ML-B's and Rebel's. The homemade version heats up a little faster, but the copper is also thinner at 1.55 mm. The aluminum MCPCB's are between 1.75 mm and 1.95 mm. Once I use up the thin stuff, I plan to order something a little thicker and test again.
I believe it is working well, but wanted to get some feedback. I've used it on everything from 13 mm "stars" on up to 100 mm x 100 mm arrays which have the linear SMT drivers mounted on board and sharing the same heat sink. Sometimes the outer edges of the PCB will slightly lift up, so I found that instead of removing all the copper from the back side of the PCB, I'll leave an isolated copper trace along the entire edge and reflow solder it to the heat sink. That will hold it down nice and tight and make the whole thing more sturdy.
If this continues to work, I plan on adding an opaque layer of "solder mask" (I think that's what it is called) over the top of the PCB to seal in the traces and make it look a little more professional.
There's a graph online that shows the different values for various types of solder. When the unit is given in watts per meter per kelvin (W/m-K), is it better to have a solder with a higher or lower value? The solder paste I use is the lowest on the graph and thought this would be best when reflow soldering the LED's. Now I'm wondering if this may have been a poor choice.
Lately I've been buying bare emitters and making my own version of a MCPCB by using ultra thin copper clad boards and reflow soldering the LED directly to copper. The copper board is 0.13 mm thick before it's been etched. I usually remove the all the copper from the back side to make it as thin as possible. With the copper removed from one side, it's now only 0.09 mm thick.
Since there's a small void created by the PCB layer that the solder must fill, is the transfer of heat now much worse because of it, or is it negligible?
To keep the void as small as possble, a drinking straw is used to press down on the LED while it's being reflow soldered. The hole in the center of the straw fits perfectly over the dome so that it's only pressing down on the flat substrate. Different straws work for different LED's. For example, a coffee stir fits nicely over an XP-G.
I've done some side by side comparisons between MCPCB's with LED's already mounted and the homemade version using XM-L's, XP-G's, MC-E's, ML-B's and Rebel's. The homemade version heats up a little faster, but the copper is also thinner at 1.55 mm. The aluminum MCPCB's are between 1.75 mm and 1.95 mm. Once I use up the thin stuff, I plan to order something a little thicker and test again.
I believe it is working well, but wanted to get some feedback. I've used it on everything from 13 mm "stars" on up to 100 mm x 100 mm arrays which have the linear SMT drivers mounted on board and sharing the same heat sink. Sometimes the outer edges of the PCB will slightly lift up, so I found that instead of removing all the copper from the back side of the PCB, I'll leave an isolated copper trace along the entire edge and reflow solder it to the heat sink. That will hold it down nice and tight and make the whole thing more sturdy.
If this continues to work, I plan on adding an opaque layer of "solder mask" (I think that's what it is called) over the top of the PCB to seal in the traces and make it look a little more professional.