For LED lighting, SMD & COB which one is better

Issuing time:2017-08-09 16:45

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LED as a lightemitting diode, is often used in a variety of lighting systems, from a certain circuit board to a large lamp, so far there are   patch beads, COB integrated beads, and so on, different types of LED will be used in different occasions.  


Then for LED light source, which one is better, the SMT bead or the COB bead? What's the difference?


Firstly, the leds used to be called 5 beads, which are about the size of soybeans and mung beans, and the part of the LED bead that actually lights up is the black, sesame-sized dot in the center.


When we zoom in on the black dot, we see that there is a plate under it, and on the plate is a small sesame seed, which is divided into several layers like a cloud cake.

Zooming in on these layers, the top layer is called the ptype semiconductor layer, the middle layer is the luminous layer, and the bottom layer is called the n-type semiconductor layer.


How did the light come from? In fact, the electrons and the holes in the p-type semiconductor collide violently in the luminous layer, resulting in photons, which emit light. This is the most basic principle of LED luminescence, which is why LED is called luminous semiconductor.


It is composed of electrons and holes in two kinds of semiconductor to produce photons, but sesame is too small and fragile to be used directly, so we will put it into a plate, connect the wire, and finally seal it with a rubber sleeve, this is a usable LED lamp bead.

One might ask, what semiconductor material gives off white light? In fact, so far, no semiconductor material has been able to emit white light. Then we usually use the white lamp bead, is how to produce?


Nobel Prize winner shuji nakamura, is he the one who invented the white LED? In fact, what he invented was not the white LED, but the blue LED. Because of the blue LED, he created a convenient system for the white LED, and he was awarded the Nobel Prize for his great contribution.


So let's see, how do blue leds become white? This is the mille layer cake, again, P layers, light layers and N layers, but on top of the mille layer cake, there is an extra layer of phosphor.


Two layers of semiconductors, electrons and holes combine to produce blue photons in the glowing layer.

This blue light, some of it comes directly from the black layer, and some of it hits the phosphor, and interacts with the phosphor to give off yellow light, and mixes to produce white light.


Of course, a little more blue light is white with a high temperature, and a little more yellow light is white with a low temperature. We usually see LED, although many are not the size and shape of mung beans, but the principle is actually the same.



1. Pin insertion (DIP)
Like there is an LED chip in the middle, the bottom is installed with a launch bowl, the shelf shade, anode pole, the next lead frame is inserted in the circuit board, outside the epoxy resin package, this is called pin insert (DIP).
-1. Common shapes: DIP comes in many shapes, round, oval, square and shaped.
-2. Luminescence types: monochromatic luminescence, two-color luminescence and multi-color luminescence.
-3. Common type: 3mm, 5mm, 8mm, 10mm...

-4. Application: this kind of bead is almost not used in the field of lighting, but more used in car lights, indicator lights, display screens, mini torches, etc.


2. Low power surface mount (SMD)
-1. Common models: there are many models of low-power surface mount, but there are no special specifications, so we have used them. Finally, we found that there are several types that we use more, so they become the standard.

-2 application fields: there are many application fields of low-power surface mount. Due to its small size, it can be used anywhere, so it is applicable in all fields. There are bulb lights, flat panel lights, down lights, tubes, PAR lights, tape lights, ultra-thin light boxes, etc.


3. High-power surface mount (SMD)

Application: the lamp bead is usually used with a lens. Can make shoot light, cast light, can apply in a lot of places.


4. Integrated package COB
-1. Common shapes: COB has round, long and square shapes.
-2. Common models: SOLERIQ ® S9, SOLERIQ ® S13, XUAN1313, XUAN1919.

-3. Application: replace bulb, indoor lighting, outdoor lighting, etc.


5. CSP (Chip Scale Package)

CSP is the latest technology and refers to a package that is about the size of a chip.



Patch bead and COB integrated bead which is good?


Different kinds of lamp beads, its use is not the same. The light source of chip kind has pin type, have tabular stick type, also have COB type, different lamp bead has different use.


Let's take a look at the following LED beads. Take the soybean to do the contrast, insert the foot type is a little bit smaller than the soybean; Some cobs are large and the high-power ones are about the same size as soybeans. Many of them are very small.


There are many kinds of small power table sticker package, their advantages are small size, small power, can be stuffed in a lot of very small place. For example, the common model has 3528, referring to the size of its side. Generally it is a rectangle, 3528 is 3.5mm×2.8mm.


It is often used in various places such as lamp tube, bulb, lamp belt, anyhow want small want thin word, use this kind of lamp bead basically.


COB is an integrated package, which seals a number of small chips on a substrate and coats them with phosphors.

It's about the size of a coin, but there are bigger ones, like half a book. The advantage is that you can put a lot of points together to make a concentrated light, or a little bit more power.


Common model basically is the diameter that according to its circle, also have square of course package, this model of each manufacturer is different, but it is chip + phosphor combination actually, just combination form is different just.


In addition, there are a lot of new packaging methods, such as some are called CSP, it is a chip level packaging, its phosphor powder made into a piece, so it is the whole lamp bead is very small, you can put this kind of bead on a board to combine arbitrarily.

There is also a linear COB, for example, we often see a filament lamp, it is a yellow filament, in fact, is a COB.


Linear COB has a longer length, the following is a meter long COB light source, the substrate is densely arranged with a lot of chips, and then coated with a layer of phosphor, is a COB light source.


How does this work? It can be made into a hard light bar. Such a thin and uniform glowing hard lamp bar, compared with the hard lamp bar stuck in the aluminum profile, cheap and convenient, but its cutting and welding line is not very convenient, anyway, there is a choice between the two.


Finally, to sum up, whether the patch or the COB, each has its own use, not to say who is good or bad, the difference between them is that the patch is scattered, you can use it flexibly, and the COB is to help you integrate, it is good to think of the application method and way, you choose it.


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