1st time doing reflow

Hi all,

I just tried reflowing of bare emitters on a triple MCPCB (from Illumination Supply) for the first time & I think I failed terribly.
So I have a few questions to ask before I try again:

1) Before reflowing the emitters, do I need to apply solder/flux on the positive & negative contact point on the MCPCB?

2) Will the emitters or triple MCPCB be damaged from high temp?
I placed the bare board on a hot plate before placing the emitters but I am not sure what the temperature is.

3) I kinda screwed up with one of the emitters, shorting the whole emitter totally & tried to run it.
I saw a spark at the wires & I knew something was wrong.
What will be the damage level here?

Will the MCPCB be damaged or just the emitter that is placed wrongly?
How about the other 2 emitters that is placed in the correct polarity?

Thank you so much...

- JonK

Hey Jon,

Dont be discouraged, these things happen to use all from time to time. I commend you on making the effort to advance your craft.

1. The flux thing depends on if your using regular solder and an iron, or if you have a good solder paste.

When I have to use regular solder and an iron, I put on just enough to glass over the 3 contact points. Then flux them and put down the emitters. With the kester no clean solder paste, I have no need of additional flux.

2. It is certainly possible to damage the emitters and the board if the heat gets too high. I have seen boards get so hot they came apart.

Using an electric skillet is a good way to control the temp when your reflowing. I personally put down my soldered paste, place the LEDs, set the boards in the cold skillet and then turn the heat on. This lets the whole thing heat up evenly. On my skillet the temp needs to be set to about 360 F to wet the solder. Once its done I shut off the heat and let thinks cool in the skillet at the very least until the solder hardens.

3. There is no way to tell how extensive the damage is without taking it apart. If you unsolder the LEDs you can test them individually with your DMM. Just turn it to the continuity setting ( when you touch the leads together it makes a ringing noise). Touch the leads to the + and - terminals of each LED. If the LED is still good it will light up about 1 lumen.

If your going to reuse that board after you get the LEDS off I would take some solder wick and remove all the old solder and start over. Its very easy to get too much solder on these, which can cause a short or cause the LED to be raised up. Both are very bad.

I know this stuff can be frustrating, but once you get a couple of em done it gets a lot easier.

Good lux.

Hi,

Thank you for your comprehensive reply!

When you say damaged the board, does it mean that the internal circuits will be damaged?
Because right now, the MCPCB looks fine on the outside.
I've yet to remove all the emitters to check the continuity.
So I'm actually bracing myself that the PCB might be damaged as well.

JonK

Sent from my Awesome phone from somewhere in the mountains

From my experience, the solder mask will usually turn brown and start peeling off before any damage to the underlying copper traces occurs.

Ok, seem like my board is still doing fine if ita based on the outlook of it.
Thanks man.

JonK

Sent from my Awesome phone from somewhere in the mountains

Oh gosh, I reflowed the emitters in the wrong polarity!
I thought that the anode for the emitter was to the positive of the PCB.

After I made the changes of direction, the LEDs were still able to light up.
Does that mean that they are still okie? Or will they be unable to run at the max capability due to the damage?

BTW vestureofblood, thanks for the DMM tip to check if the emitter is still working.
I was able to salvage 2 emitters out of the 3.

If they light up, they should be good to go.