Anyone else noticed that Cree changed their datasheets on many LEDs for the reflow characteristics
including XPL, XML, XPG2, XPG3 and XHP35
before they were 3K/s now they are 1.2K/s like XHP50/XHP70 were in the past
No, I did not notice that. Would that matter if my reflows are more like 30K/s? :innocent:
what is K/s? I search in google but nothing…
oC/second ,or how fast temperature rises.
the more thermal stress a reflow does the higher is that you reduce lifetime or even destroy the diode
XHP70.2 with 30K/s would destroy it
Since I never noticed performance problems and I can obviously not easily measure lifetime effects, I never bothered taking the official reflow profile into account, but it may be a good idea if I want to make a flashlight that is intended to really last without upgrading the led all the time (which is rare being a BLF addict).
Thinking of how I do reflows now, there is an easy way to make the profile much better. After heating up my small heatblock to 220 degC, instead of placing the ledboard directly on the block, I can place a cold block of aluminium in between. With the extra metal,the heating up is way slower but the end-temperature is about the same.
I may do a wee test and measure with the IR-thermometer how close I get to 1K/s.
Ok, thanks for the explanation
My first ever reflow was on a gas stove and that happened to be disaster. I killed emitter because of of too long exposure on high heat. I learned my lesson then. Now am always heating boards with blowing hot air under board just enough to reflow emitters perfectly and quickly cooling down board with ice cold water soaked spounge. I found it very reliable and fast procedure.