This is the first thing that came to my mind. I use a regulated iron which I set at 300C and when I kept it attached to the PCB for some time, the blob of solder did attach to the plate and looked like a normal blob. But then it just snapped off as if there was dirt underneath. Which was not since I used soldering acid that had worked every time before that.
I am not sure what wattage is this iron, but I used it with an attached aluminum plate for reflowing an LED on another board and it did it easily.
But OK, I’ll try higher temp. I think the iron can go up to 450C.
So far I am very happy with that single 3K. It does have some tint shift, but for a warm tint this is irrelevant.
The specific 5K I tried was a benchmark mule emitter. On par with my trusty 083 but with the potential for a much higher output. Just need to confirm the observation with the other three 5K LEDs on the board.
The one 4K I tried (out of four on the board) had bad tint shift, that nasty green corona which I hate in 219B/C. Not that much of it, but still unacceptable. This was so strikingly different from the 5K that I was really puzzled. But it looked like the tint shift was different in different directions, which may have to do with the remaining three unlit LEDs, reprocessing the light of the lit LED.
Regardless of the tint shift, the on-axis tint was excellent in all the CCTs. No green, no magenta, but I’ll need to double check this in a well illuminated ambient light conditions. My little workshop was not like that today.
So next thing will be to test the consistency of the tint shift patterns across the samples.
These are all on-axis measurements for both bare leds and with a reflector, right?
What I find interesting is that with the reflector, the LEDs up to 4K keep their CCT while for the 5K and 6.5K LEDs the spot is ~500K cooler than the spill, which means that the tint shift in cooler LEDs is different from that of the warmer ones.
EDIT: what kind of sensor do you use? I have an x-bright i1, that came as part of my display calibration bundle, do you think is it the right tool for your kind of measurements?
It’s an x-rite i1pro. You can measure tint (cct and duv, xy coordinates) with the i1 display (pro) colorimeter, but not the CRI, which requires spectral data from a spectrometer. I recommend using the Argyll tools, especially spotread.exe.
For manual reflow we strongly suggest Pb63Sn37 solder paste. Poorer wetting of leadfree solder paste requires precise dispensing and LEDs placement.
The ultra thin solder mask/solder resist is somewhat fragile, especially in hot temperature during reflow process. Avoid any hard and sharp objects on it.
Solder mask is rated to survive multiple reflows up to 300°C only for a brief moment (< 30 seconds). Prolonged high temperature exposure above 240°C will make it less white while still functional
Soldering LED wire can be difficult because the board is very thermally conductive.
Fixes: Use more powerful solder iron with as big as possible tip, pre-heat the base (or the case/host), use intermediate wire (solder a short slave wire to the pad first).
Note: I successfuly solder all the boards using 30 watt solder iron with board temperature of 150C or...
200 watt solder iron at base temp of 100C. I use cheap Dekko 30 - 200 watt iron with big pointy (blunt) tip. My more expensive 20 - 130 watt Hakko Presto is too weak after I modified it to finer tip.
Just to add to the soldering discussion:
For soldering wires to the MCPCB pads, I use a faulty 60W soldering iron.
It doesn’t stop heating, keeps going hotter and hotter, until it glows dark red (you can see it when you turn the lights off). When you then touch some solder wire, the solder evaporates or something, at least it’s not on the soldering tip.
But holding the tip on the mcpcb, and then adding solder works perfectly, like working on a normal pcb.
