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Wiring our Micro LEDs
If you've wired up some of our 2x3
LEDs, you've gained the general techniques required to wire up our Micro (or
LEDs. The solder pads are much smaller (as are the LEDs), but with good
magnification (here we go again...), all of the same steps apply. If you need to
review wiring procedures for our 2x3's, direct links are
Our RED Micro, Nano and
Subminiature LEDs are wired
differently than all of our other LEDs. The polarity mark on the LED is for the
ANODE (+) connection, not the CATHODE (-) connection.
Let's wire up a Micro LED
Following is a graphic step-by-step wiring of a Micro LED using
our NT301 Holding Tool. The
wire routing method shown, we refer to as "back wiring" (for lack of a better
term). The wires are routed directly away from the back of the LED. This is a
useful wiring method, for example, if we were going to build a streetlight or
building light and want the LED facing down from the inside of a lampshade, or
to face down from the ceiling of a building interior.
Our LEDs are packaged
in a black conductive plastic carrier strip. This strip contains pockets, or
cavities that contain the individual LEDs and are held in place by a clear
plastic cover-strip that can be pealed back to remove the LEDs. The reason that
the carrier strip is conductive is that the LEDs are static electrically
sensitive devices. Therefore, before removal or
handling of the LEDs, precautions to prevent static discharge should be taken
(good grounding, anti-static mat or wrist strap, etc). Please review the
packaging and handling procedure here.
Once an LED has been removed from its protective carrier and placed in some
temporary receptacle, orient the LED so it is "face up" (solder pads and
circuit board side facing down) in the receptacle. we are now ready to
carefully grasp the part with tweezers and position it for wiring. Since we
will be using our Holding Tool, we will transfer the LED from its temporary
receptacle to a riser block as shown in Figure 1 below.
This riser block is used to space the LED above the
workbench so our Holding Tool can properly grasp the sides of the part.
This "riser block" can be any small smooth block that is at least 1/4"
in height. We use a piece of 1/4" thick white styrene and it seems to
work very well. As you will see in Figure 2, this block is necessary to
provide clearance for the side of the Tool that has the longer padded
clip. Position the LED "long ways" from left to right and closer to the
right side of the riser as shown by the arrows in Figure 1 above.
Now, grasp the Holding Tool by the un-padded clip and
invert the Tool upside down with the unpadded clip held in the open
position. See Figure 2 below.
Lower the open clip over the LED and gently release
the clip so it grasps the LED by the "sides". Very important:
Grasp the LED slightly right-of-center as shown above so that
the left side of the LED will be exposed past the left side of the clip
as shown by the arrow positions above. This is to ensure the solder pad
on the left side of the LED will be exposed for easy soldering when the
Tool is turned over. See Figure 3 below.
Turn the Holding Tool over and clamp its
brass sheet base in your bench vise or whatever you will be using to
secure it while it is on your workbench surface. If you use a bench
vise, note that the bottom of the brass sheet is square and straight for
easy alignment in a small vise. Note that the LED is offset slightly in
the clip allowing the solder pad on the right to be totally exposed.
This will make soldering to the pad much easier.
Since the LEDs are polarity
sensitive devices, we use color-coded wiring to differentiate between the
positive (+), and negative (-) electrical connections. In keeping with standard
electrical conventions, we will connect the RED
wire to the positive (+), or Anode solder pad of the LED (the electrically “hot”
connection), and the GREEN wire to the
negative (-), or Cathode solder pad (electrical “ground” connection). Remember
that in the case of Red LEDs, the polarity mark points to the Anode
(+) connection. For all other LEDs, the polarity mark points to the Cathode (-)
connection. For all LEDs, the RED wire
should be connected to the Anode solder pad.
Figure 3, above shows
view of a typical Micro LED. Note the fat “T” shaped opening between the solder
pads on each end of the LED. The base of the “T” points at the polarity mark. In
this example, it points to the solder pad that is the Cathode, or negative (-)
electrical connection. Another reminder is that (except for Red LEDs) the
Cathode solder pad is shaped like a "C" (for cathode). Since the
cathode solder pad is on the right, we will solder the
GREEN wire first.
Figure 4 below, shows a tinned
segment of green #38 magnet wire positioned over the cathode (-) solder pad of the
LED. This is performed by gently holding open the padded clip while sliding the
green wire into position over the solder pad, then releasing the padded
clip to grip the wire. Center the wire over the pad and align the wire so that the insulated
portion begins at the inside edge of the solder pad, as shown. This is easily
done by opening and closing the padded clip with the right hand while
adjusting the wire with the left hand. Position the wire so it lays flat
against the pad. If necessary, a sharpened toothpick can be used to
gently move the tinned portion front to back for best position.
In the next step, the wire
will be soldered to the solder pad of the LED. Remember, these LEDs are very
sensitive to thermal shock and excessive heat. Manufacture’s recommendations for
soldering of these devices limits solder temperature to a maximum of 260ºC
(500ºF), and a maximum contact time (soldering iron contact) of 2 seconds. In
reality, since the wire has been pre-tinned and the solder pad is gold plated,
actual contact time for acceptable solder flow should be much less that ½
second. A quick “touch” with a properly tinned iron having a tiny amount of
low-temperature solder is all that will be required to complete the solder
joint. As mentioned in the 2x3 LED wiring procedure, as an aid to the quick and
even flow of the solder joint, we recommend placing a tiny (very tiny) amount of
liquid flux at the point where the tinned wire and solder pad touch each other.
Too much liquid flux will require cleanup.
Figure 5 below is an end view of two LEDs. The left view shows a good solder joint
which has a low, smooth profile. The LED on the right has a solder joint with
too much solder, which also contains peaks and a general irregular surface.
Again a tiny bit of liquid flux will assist the quick and even flow of
solder. An additional technique that will assist in getting a nice low-profile
solder joint is shown in step 12 and Figure 6 below.
When positioning you iron tip over the part a technique
that will help minimize the size of the solder "blob" that occurs at the
solder pad & wire junction, is to contact the tinned portion of the wire
with the molten solder just off the pad and allow it to "wick" onto the
pad. The tinned wire will readily accept the molten solder and act like
a wick drawing it up the wire. This method will give you much better
control of the amount of solder that actually flows onto the solder pad.
See Figure 6 below.
below shows the green wire soldered to the cathode (-) solder pad of the LED.
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