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Technical Overviews


Learn more about:

Overview of LED Array Methods
About Chip-on-Board
About COBRA™
Laser Safety


Overview of LED Array Methods

LED arrays can be built using several methods. Each method hinges on the manner in which the chips themselves are packaged by the LED semiconductor manufacturer. Examples of packaged, lensed LEDs are shown in Figures 1, 2 and 3.



 

Figure 1: T-Pack LED


 


Figure 2: Surface mount colored LED







Figure 3: Surface mount white-emitting


These packages can be affixed to a heat-sinking substrate using either "through hole" mounting or surface mounting. The through-hole mounted devices are often referred to as t-pack LEDs (with designations T1, T3, T5, etc.). Arrays built of t-packs are shown in Figures 4.


Figure 4: LED Array comprised of t-packs

 
Importantly, it is also possible to procure wafers of bare, unpackaged chips, alsocalled "dice". See Figures 5 and 6.



Figure 5: Semiconductor LED wafer


 

Figure 6: Chip-on-board array. In this example, blue and red LEDs are interleaved

 


Using automated pick-and-place equipment, ProPhotonix takes such individual chips and affixes them to printed circuit boards, creating so-called "chip-on-board" LED arrays. Close-up microscopic photographs of chip-on-board arrays are shown in Figures 7 and 8.
Figure 6: Chip-on-board array. In this example, blue and red LEDs are interleaved


Using automated pick-and-place equipment, ProPhotonix takes such individual chips and affixes them to printed circuit boards, creating so-called "chip-on-board" LED arrays. Close-up microscopic photographs of chip-on-board arrays are shown in Figures 7 and 8.

 

 

Figure 7: Microscopic photograph of chip-on-board LED array.

Figure 8: Microscopic photograph of chip-on-board LED array. Close-up.



Figures 9 and 10 show larger regions of chip-on-board arrays.



 

 

Figure 9: Chip-on-board LED array. The LED chips are the dark dice in the gold-colored horizontal stripe at the top of the board.

Figure 10: Chip-on-board LED array

An LED array is generally built up on a printed circuit board. The pins or pads or actual surfaces of the LED chips are attached to conductive tracks on the PCB. PCB materials may include fiberglass-filled epoxy, ceramics or metals, depending on thermal and mechanical requirements.

With the LED chips or LED packages attached directly to a printed circuit board, LED arrays are perfectly amenable to electronic control. Indeed, many of the LED arrays produced by ProPhotonix involve a good deal of electronics, beyond the LED chips themselves.

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About Chip-on-Board

Assemblies built from t-pack LEDs are often unsatisfactory, in that they do not always provide sufficiently uniform lighting, and are not well heat-sinked, and they are bulky due to the size (several millimeters) of each t-pack device. Nonetheless, for some applications, t-packs do actually prove to be the most appropriate, cost-effective solution.

In cases in which t-packs cannot provide the required performance however, chip-on-board emerges as the answer. The obvious advantages of chip-on-board LED arrays are:

Compactness

  • High intensity due to tight packing density
  • High uniformity, even at close working distances

 

A further - and very important - advantage of chip-on-board LED arrays is that they are amenable to superior heatsinking during continuous, moderate-power operation. They key to efficient design is to ensure that LED PN junction temperatures are as low as possible, which leads to long lifetime as well as wavelength and intensity stability. While the heat from a t-pack LED can only be directed away from the PN junction via the electrodes, the situation is much better when, as in the case of chip-on-board, the chips are placed in intimate contact with a properly designed, thermally efficient substrate structure. See Figure 11. The red arros indicate the flow of heat.


 

Figure 11: Superior thermal performance of Chip-on-board.



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About COBRA™

A bore competency of ProPhotonix' LED division revolves around its state-of-the art automated pick-and-place and wire bonding equipment. These capabilities, combine eith the company's close relationships with various PCB manufacturers and semiconductor houses, enable ProPhotonix to undertake a program of research on LED chip-on-board methods. ProPhotonix has recently developed a new proprietary LED array method, dubbed chip-on-board reflective array (COBRA™). This patent pending technology combines the thermal advantages of chip-on-board with the optical efficiency of a reflective cup. The advantages of COBRA are illustrated in Figure 12. In applications requiring particularly high brightness and directional illumination, ProPhotonix implements the COBRA approach for the construction of the LED array.



Figure 12: the optical efficency of a reflective cup is combined with superior thermals of C.O.B. in the new proprietary COBRA™ array method.

For more about COBRA™, click here.

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Laser Safety

The light emitted from these devices has been set in accordance with IEC60825. However, staring into the beam, whether directly or indirectly, must be avoided. IEC60825 classifies laser products into three categories depending on light emitted, wavelength and eye safety.

 

 

Class II
"Caution", visible laser light less than 1.0mW. Considered eye safe, normal exposure to this type of beam will not cause permanent damage to the retina.

 


Class IIIR
"Danger", visible laser light between 1.0mW and 5.0mW. Considered eye safe with caution. Focusing of this light into the eye could cause some damage.

Class IIIB
"Danger", infrared (IIIR), and high power visible laser considered dangerous to the retina if exposed.

NB: It is important to note that while complying with the above classifications, unless otherwise stated, our laser diode products may alter its original design classification, and it is the responsibility of the OEM to ensure compliance with the relevant standards.


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