Yep, the thing got tanned. That's what happens when you're a n00b in these matters and try to dissolve/spread some solder onto the base “the way of the tiger” (i.e. no rosin/flux). :FACEPALM:
Good video! You got your hand/fingers in the way a few times when it gets interesting but hey… no problem
There is one thing I was always very curious about: the LED and pad have 3 connection points, two for + and - connections and one large pad that is resposible only for heat transfer from the LED to the sinkpad, right? Now you took A LOT of that solder paste on that first pad. now what happens if you take so much that the solder under the LED creates a electric connection between + and headpad, or - and heatpad, or even between all 3 of them? When connecting this to power it should create a short and destroy the LED, right?
How do you make sure this does not happen? You seem to be very tolerant and even move the LED around on the pad when the hot solder is fluid, I don´t get why it works anyway.
EDIT: those DTP boards like the sinkpad also have some kind of “cavity” or pit where the solder can “flow in”, while cheap aluminium stars like this don´t. Does this affect the process?
Of course, whatever is in between the contact pads and the thermal one “repels” the solder.
When converting a non-DTP copper board to DTP via milling the thermal/central pad even to the very edge of the contact ones, the same behaviour can be observed: it's the dielectric layer, of course.
I bet you my kingdom they come from the same OEM, but the Sinkpads undergo custom tailoring.
By the way, just had some more reflowing practice:
This time it went really shiny. That small heatsink (which once cooled the northbridge of an 8KHA+) is my new reflowing pan, thanks to it I've been able to carefully monitor the reflowing temp.
Yes, your correct. 3 pads one for + and - and one for heat. I do put extra solder in the center, and then move the LED from side to side to make sure all pads are covered. When you tap on the top of the dome fast like shown in the video the extra solder will eject from under the LED. Pushing down on the emitter like that to get rid of the extra will ensure there are no shorts. Its very very rare that you will ever get a short doing it this way.
You are correct about the cavity in the center of a sinkpad. The reason that cheap LED stars do not have that cavity is because they fill it with substrate material. This material is a very poor conductor of heat. In the sinkpad that little gap is filled with solder which is a much better conductor of heat.
The process for re flowing will be the same on either type of board.
Though one should be careful doing this and without shaky hand. When I reflowed Photo Red XP-Es to a 3XP board (and soldering it to the triple spacer and stock pill) over a hot plate while being ill, I ripped off the silicone dome when trying to adjust the LED. It did survive the experience though I harbour suspicions that its light output is worse than its brethren.
Hot de-dome is a method used by several around here. I don’t know about XP-E, but the XP-E2 R3 that I have are very easy to de-dome with heat. Any time you de-dome an LED, you will lose lumens, but I doubt there was any damage done. Maybe you should de-dome the brethren so that they are all the same. :smiling_imp:
Good luck on the reflow sac. Quality solder paste goes along way to a perfect job if your going that way and dont forget to get the + and - in the correct orientation.