Please deduct one point for spelling my name wrong.
No. I thought you said your flashlight was bright and possibly 1
watt. Those are common 5mm LED's with 0.5 watts maximum.
These photos look very much like what I would expect to be hiding
under what I believe to be a lens of some sorts:
This looks a bit closer:
That data sheet is also slightly insane, specifying the luminous flux
as:
Lumen typ.: 19 mcd
Lumens are measured in umm.... lumens, not millicandelas. It is
possible to convert between lumens and mcd's using the viewing angle:
Anyway, 19 lumens is not very bright but probably good enough for a
pocket flashlight.
And I tried so hard to get the ?Lei/Lie? bit right! (c; 2 steps forward,
1 step back...
One of those images (located here):
formatting link
looks exactly like the one in my light. It?s squat, with very (relatively)
large yellow die(?) in the center. I don?t think there?s a separate lens.
Maybe it?s molded to focus the light (integral lens)?
Wish I could find that LED other than @ Alibaba...
Ah-HAH! From that Alibaba image page: ?strawhat LED?. Search turns up
similar-looking LEDs. Searching on the terms ?strawhat? and ?dimple?
tells me that this form-factor is for radial distribution of the light, not
throwing a beam. Which means the flashlight designer wanted the reflector to
shape the beam, not the LED.
So I?m looking for one of these types.
Thanks.
(Why are my search skills so crap? Google keeps returning Manga images and
cartoon faces...)
Really, before I got my pick and place machine, I hand-soldered about 25,000
.1uF 0805 capacitors. NEVER ONCE had a bad one. I still hand-solder a fair
number of low production boards and prototypes, and have never seen a
problem with MLCCs.
Jon
Sorry for the delay but I missed the followups to my comment.
Thermal shock easily cracks MLCC caps. I learned that the hard way
while fixing several Apple Mac Mini computahs, which feature a
collection of MLCC on the bottom of the main board.
The original failure mode was shorted MLCC caps caused by either
thermal shock or board flex. The bad ones were easy to find with an
ESR meter. However, when I tried to install replacements (and
guessing the part value because Apple doesn't supply service
information to non-authorized repair shops), I managed to crack and
short several known good MLCC caps with a soldering iron. Having
learned the lesson, I used some solder paste and a hot air SMT reflow
gun to do the soldering. I also pre-heated the PCB and let the caps
cool down slowly. I don't know if that was necessary, but it worked
every time. I'm told that two solding irons used as a tweezer also
works, but I haven't tried that yet.
You'll find some more details under:
Lots of articles and guidelines on handling and soldering these caps,
some of which warn about using a soldering iron. For example:
6. Soldering with a Solder Iron
Attachment by soldering iron is not recommended. A
heat shock may cause a crack in the MLCC chip capacitors,
however, if solder iron is used, the following precautions
should be taken: ... (etc)
Damage Prevention When Soldering Ceramic Chip Capacitors
Hand Soldering
- A pencil type soldering of 30 watts
maximum and with a diameter of 3 mm
maximum should be used.
- The soldering iron tip temperature should
be less than 300C [572F] and maximum
contact time should be 5 seconds.
- The soldering iron tip should never come in
contact with the component body.
Ever try to solder a small MLCC cap without touching the body with the
soldering iron tip? Good luck.
In order to prevent damage (cracks) to the component that
can be caused by localized rapid heating and heat shock, preheat
the chip, for example, to prevent it from being subjected to
heat shock.
I've heard these stories a number of times. And, yes, maybe some people use
insanely hot irons or in some other way cause this problem. And, some
really large caps are prone to this damage. But, as I say, I have hand-
soldered over 25,000 0805 MLCC caps of modest value without seeing this
problem. I use a very good Weller temperature-controlled iron, and run it
at a modest temperature. Much better to use an iron with really good
thermal conductivity at a lower temperature than one with poor conductivity
at a very high temperature.
Jon
Well, I must admit that I didn't take any special precautions.
Methinks that the relative humidity in my office runs between 40% and
60% but is not monitored or recorded. Occasionally, it gets low
enough to where static electricity becomes a problem, or high enough
to where I'm rather uncomfortable, but those are rare. The caps a mix
of cut tape and loose bags stored in Ziploc bags (mostly pink
anti-static) and in paper coin envelopes. Nothing in hard plastic or
metal drawers that might chip or crack them. Although I know that
these caps make tolerable hydrometers (and microphones), I don't think
they can absorb enough moisture from the air to where a steam
explosion would be a problem.
I did some digging to see if humidity might be a problem in storage
conditions. There were plenty of notes on how a cracked capacitor
might allow water to enter the dielectric. Soft (solder) termination
is the recommended fix. Some suggests pre-heating the capacitors
before soldering to drive off any moisture. One demands that the caps
be used within 12 months. I didn't see humidity as being a problem
until AFTER the capacitors had cracked. It would take some time for
the moisture to alter the capacitor characteristics. With my hand
soldering technique, I managed to instantly produce shorted
capacitors, which methinks was more likely due to uneven thermal
expansion, than to moisture incursion.
I haven't had any problems with cracking but I used to have problems
with end caps falling off. I haven't seen the issue for some time,
though perhaps it was a problem with the manufacturer. Our purchasing
group prefers Murata, so that's what I use (GRM series).
We pre baked some boards and other components before assembly and
reflow. That eliminated cracked multilayer SMD capacitors, tombstoning
of two lead components and losing end caps. That was in N Central
Florida which has plenty of humidity problems. The so called HVAC
'engineers' were clueless about how to control the humidity, so we had
to resort to baking. LSI SMD ICs were backed and heat sealed into
antistatic bags with moisture adsorbing packets.
We had a high failure rate on hand soldered FIR chips, before we
started baking them. The bottom of the packaging was the thinnest, and
it would bow out as it released steam during hand soldering. No one in
EE or ME believed me, until I finally got them to try it for themselves.
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