The patterns for the XML and XPG are what CREE recommends. I believe that paste on the nubs helps wet them and enhances their ability to wick out excess solder. These stencils are 0.0035 inches thick… you will be getting a MUCH thiner and more consistent layer of solder than any manual technique.
The XRE and MTG are a bit different. Mine have the full area under the the thermal pad pasted. CREE’s have a smaller area pasted on the XRE and four blobs under the MTG. They also have the overflow nubs. That should work better for the way we tend to use them… heavily overdriven and manually pasted and reflowed.
Probably won’t do the color XML and MCE any time soon… I might do a “weirdo LED” one later for other models.
Plus, you can’t get a nice, even, controlled amount of paste using eyeball techniques. Even worse is trying to tin the pads with solder. Most people don’t realize just how little solder it takes to do it right… 3.5 mils is about the thickness of a sheet of paper. Hopefully the Sinkpad/Noctigon stars are planar enough to be able to handle it.
I almost always get too much paste on there, and have to press down on the emitter with tweezers o squeeze it out. I’m in for two. Can you get a price on Stainless ones?
OK, I’ll stick with the $3 option and get a backup one.
Oh, any way to add duplicate XM-L and XP-G stencils on the same sheet without driving up the cost much? Those are the ones to get used the most, and therefore get worn out first. Just a thought. I’d still order two.
Based upon the size of the stencil sheet, it works out best with the four patterns on it. They are cheap, just buy more. With a little care, they should last longer than you…
The test run of stencils are here! They work well… with a little practice. My first attempt at applying paste took around 6 tries to get it right. The next took two. The next two went without a hitch.
What I do is stick the star down to a table with a small piece of double sided tape… smaller than the star so the tape does not stick out past the edge and snag the stencil. I stick my finger on the tape a few times so the top is less sticky than the bottom. Keeps the tape on the table when you remove the star.
I put a couple of strips of masking tape across the stencil, align the pattern to the star, and stick the stencil down to the table with the masking tape. It takes a bit of practice to get the tension right so the the pattern stays aligned. A little stabilization with one hand can help keep the stencil aligned.
I put a little dab of paste on the edge of a strip of credit card material (You say you are a wise man that doesn’t have credit cards? Go to Kinkos/Fedex store and get a free payment card from the machine). Hold the strip of card at a 45 degree angle and swipe it across the stencil.
Carefully lift the stencil. If all went well you will have the pads covered properly with no bleed between them. You will be amazed at just how little paste is used. If you got bleed, misalignment, etc, wipe off the star, clean the stencil with alcohol, try again.
Lift the star off the double sided tape. You may have to scrape the tape off of the star.
Drop the LED onto the solder paste. I was able to test the LED with a meter before reflowing the star. There was no shorts between the power connections and the thermal pad and the LED lit up.
Reflow the star… I use a small butane torch. One thing is that I got no excess solder oozing onto the overflows to indicate that the solder flowed. Also the LED was perfectly aligned to start with and did not do the “floaty rotatey dance”. I looked for a tiny amount of flux bubbling out of the edges and a shiny edge of solder at the edge of the LED.
