semi OT- removing plastic lens from LED

That was our regular PCB cleaning brew.

We make a board with 24 bicolor LEDs, and we had a few intermittent LED failures. One thing we tried was soaking the LEDs in the solvent for an hour, instead of the usual ~~ 1 minute. That did the thing in the pic. Seems to bust wire bonds.

We won't wash them in the future.

This is a Bivar part, "The robust package is ideal for harsh working environments..."

Other LEDs seem fine.

--

John Larkin         Highland Technology, Inc 

jlarkin at highlandtechnology dot com 
http://www.highlandtechnology.com 

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom laser drivers and controllers 
Photonics and fiberoptic TTL data links 
VME thermocouple, LVDT, synchro   acquisition and simulation

Light Sensor ??

What does hacking an LED do that a regular "light sensor" won't do ??

h

Well this is a bit embarrasing since it's written by my boss.

But basically it detects single photons. Which is way cool for ~$0.10.

This is all old news, but there's been a redesign to the elecronics box.. a dding a voltage source (lm317) some series resistors and an LED light sourc e. Yellow led's are great and greens stink.. visible light led's seem OK.. so the spectral response is mostly unknown.* (I need a monochrometer... W ell maybe just a wideband light source.)

George H.

*like being mostly harmless.

Got it, I mostly found chemistry to be confusing.

George H.

180C? RoHS reflow solder processes go up to 260C. Yeah, a lot of LEDs melt there, but...

RFNA is rocket fuel (specifically an oxidizer). It's truly nasty stuff.

I've seen stress corrosion cracking in acrylic when PCBs were cleaned with certain solvents. Nothing like the visible crazing but where there were stress risers (eg. threads) cracks would gradually propagate. This was in some very nice clear acrylic moldings we had made for instrument faces. The problem was solved by baking off the boards to remove small amounts of residual volatiles before assembly.

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward" 
speff@interlog.com             Info for manufacturers: http://www.trexon.com 
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

It takes some pretty nasty stuff to remove epoxy. I think most folks who want a part decapped send it out, unless they're in the business of reverse engineering or similar stuff.

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward" 
speff@interlog.com             Info for manufacturers: http://www.trexon.com 
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

If you are close, use something more like emory cloth or other fine sandpaper...

5 mm LEDs use epoxy and anything that removes it chemically will be toxic. Fumes from burning epoxy are also known to be carcinogenic.

Although we know LEDs work as detectors, the efficacy is poor and spectral bandwidth is not flat.

If it is optical sensitivity you wish to measure, ie. CIE weighted eye resp onse, then I strong recommend the Panasonic photo sensors with CIE correcti on. they are buffered internally and work well as current sources into res istive load to ground from a 5 V supply. You can change sensitivity with re sistor load values and measure from < 1 LUX to greater than 150kLux on dire ct sunlight. They have a wide beamwidth , so a stepped black aperture is n eeded if you want to make narrow angular measurements from a distance. I have successfully used these to make an LED tester for a Goniophotometric m eter for testing at 1 meter distance with stray light being blocked in the fixture design.

If you need more details, let me know what you are testing.

Tony Stewart

A lot of them are polycarbonate. You can cut it with dikes.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 USA 
+1 845 480 2058 

hobbs at electrooptical dot net 
http://electrooptical.net