first try at reflow soldering

Well Im about to give reflow soldering a try for the first time. I have my solder paste, hot plate and components ready to sizzle.


any last words of advice???? Med or med well

My advice is to follow the manufacturer's recommendations as much as possible. I recently had great success by using two hotplates. The first was set to 150C and the second was set to 250C. I set the star on the 150C hotplate for 2 minutes to preheat it and then quickly transferred it to the 250C hotplate. It only took 5-10 seconds before the solder melted and I could remove the LED with forceps.

I used a thermocouple to determine the temperature of the hotplates, but you could also use some oil in a pan and a thermometer.

I wanted to reflow solder a MC-E emitter onto my own copper star, but didnt have any form of hotplate. Where would you get something like that?

I ended up drilling an conical shape into a 1.5" x 1.5" x 0.25" aluminum plate I had around, and was able to fit the tip of my trusty digital Weller soldering iron tip into the hole. I attached a thermocouple to the end of the aluminum plate (farthest from the iron tip) to make sure the coolest part was up to temperature. I adjusted the temp on the soldering iron to the lowest point that would melt solder (which was way below the peak temp on the recommended reflow curve). All I needed to do was set the MCPCB star against the flat surface of the Al plate and within 5 seconds, the solder was molten and I removed the emitter with tweezers. When I soldered the emitter to the copper star, it was just as simple. I placed a little bit of that cheap solder paste (found at DX for a low price) in the center of the copper part, and let it melt. I then set the MC-E into place and carefully picked up the copper part so the emitter did not shift.

I did not use a pre-heat or cool down cycle. How will that hurt my LED emitters? Thanks.

One more thing. I seen in a post by Holzleim where he used an iron (for clothes) and turned it upside down. I wonder if the cheaper ones would get as hot. Just run it without any water for steam of course. I may have to check my local OddLots for a cheap, but full sized and adjustable iron, and mount the heating element and hotplate to some fixture I can put on my work bench.

-Tony

Well, I don't know if anyone can really authoritatively say which methods are fine and which ones are a problem since as a community we have already come up with a myriad of ways and are likely to come up with ways that have not yet been tried or even though of yet. Things that could happen to an LED from getting too hot would include reduced output or none at all. Even heating too rapidly could result in the disconnection of a lead due to thermal expansion mismatch of interfaces. And then there is the whole business of drying the LED before soldering - but that only applies to new LEDs the first time they are reflow soldered.

I have even seen video of someone using an electric range burner to reflow solder by placing the LED star directly on the burner soon after it had been glowing red. He got the LED off and it still produced light afterwards, so it seems that the manufacturer recommendations are conservative. But this is what we should expect given a society in which everyone tries to CYA.

I like the idea of using an iron to make your own reflow station. That can give you a stable selectable temperature for better results. In addition to a soldering iron attached to a metal plate, one could also use a metal plate placed on an electric range burner or preheated in an oven. Everybody be careful out there. :wave: P.S. - Ovegloves are great!

well i attempted and succeeded at reflow soldering my cree leds to my home made flexible circuit board.

Now here is my issue,

How can you make this process a little faster. The cree leds have those extremly small pads on each side of the bottem of the led that you must solder to. If you etch the circuit just a hair bit smaller than the dimension of the led it makes placement difficult. However if you make it too big you take the chance of the solder flowing into the thermal pad and shorting out the led.

am I missing something or is reflow soldering a cree a pita.....

So far I like the cree over my old luxeons. However the luxeons have those very convient little leads sticking out of each side to solder to... that makes life much easier

Well one of the functions of the ramp-up is to heat the solvents out of the flux. If you go too fast, the solvent boils violently, may spatter the solder or throw parts off their intended pads.

I know what you mean Axkiker. I prefer to use thermally conductive adhesive to attach the emitters. If you clip the corners of the ceramic substrate off using a pair of fairly heavy duty cutters (like diagonal cutters), then you cut through the electrical connections that lead to the pads on the bottom and you don't have to worry about them at all. That leaves you with the pads on the top to solder to.

hey that's pretty cool that you tried soldering the leds to a homemade flex pcb. I thought about doing that but haven't gotten around to it yet. would be great to see some more details about the diy flex pcb and how that worked out for you.

personally i have soldered many boards using the clothes iron technique, and find it to be immensely useful. my ex-girlfriend's cheap clothes iron seems to be optimized for exactly this application, with a stable and accurate thermostat, good for nicely preheating the board. the only problem i've had with it so far has been uneven heating when i tried to reflow a board 6 inches long with something like 120 components on it. for some reason the center got too hot without the ends heating up much at all and I killed an MCU.

came across this detailed post a few days ago of a more elaborate setup. lots of good info though:
http://www.instructables.com/id/Extreme_Surface_Mount_Soldering/