The present application relates to light emitting diode device (LED), and more particularly to thin flat solid state lighting that is cost effective to manufacture, has prolonged life span and better lighting.
Note that the points discussed below may reflect the hindsight gained from the disclosed inventions, and are not necessarily admitted to be prior art.
Being environment friendly, smaller in sizes, and longer lifetimes, and also having lower power consumption, high efficiency for lighting, less heat radiation, Light emitting diodes (LEDs) lamps have been replacing filament bulbs, halogen or fluorescent lamps for general illumination indoor and outdoors. LED lamps also are especially useful in large screen displays, back light for liquid crystal displays (LCD), the indication lights for electronic apparatus, traffic signal lights, decoration lights or illuminators.
To be more robotic and easy to use, LED packages have been developed so that they can be directly plugged into an existing socket intended to receive a conventional filament light bulb.
A typical LED package structure is the “spot” type as shown in FIG. 1. This package structure includes, from bottom up, a metal substrate-electrical insulator layer or adhesive layer, LED chip layer with reflect cups, electrode layer for wire connection, and a epoxy or silicone gel lens with phosphor layer inside. In FIG. 1a, a typical LED package shows to include an LED chip 1, an adhesive layer 2, a substrate 3, an electrode layer 4, an electrode wire 5, a base frame 6, a phosphor layer 7 and transparency lens 8.
Generally, to increase the light output efficiency from LED chip 1, the back side of substrate 3 may be configured as a heat sink, and the surface of substrate 3 may be configured as a reflective cup, and LED chip 1 is then mounted on substrate 3 by using insulate adhesive gel 2, which is usually silver paste or transparent insulating paste. LED chip 1 is connected with the electrode layer 4 by Au or Al wire 5, and the electrode layer 4 and the LED circuit 1 is then set on base frame 6.
A phosphor mixed silicone gel may be used between LED chip 1 and the reflection cup of substrate 3, forming emission layer 7. Epoxy or silicone may be injected onto phosphor layer 7 and covers substrate 3, LED chip 1 and wires 5, forming optical lens 8.
During the packaging process, insulator material (silver past or transparent insulating paste) as the adhesive layer is dropped onto substrate 3; then LED chip 1 is attached on substrate 3 by die bonding. The electrodes 4 in LED PN junction pad and the circuit board are connected by wire bonding. Then transparent epoxy or silicone gel is dropped to the surface of packaged LED unit, forming optical lens 8 on the LED chip surface (encapsulating). Lens 8 conducts light from the chip to the air as well as isolates the chip from the air. In a white LED, a phosphor layer may be coated onto the LED chip surface before the transparency epoxy or silicone lens is formed.
This typical LED package structure and packaging process is widely used, and a single LED package can generate 0.05-5 W power depending on the chip size. Many LED units are usually arrayed together on a printed circuit board (PCB) to form a lamp module, and making a lamp, as shown in FIG. 1b. 
The multiple packaged LEDs are mounted to a PCB substrate 9 by a thermal conductive adhesive layer 10. Due to such “spot” light from each LEDs, the emitted light distribution is not uniform. In practical application, a diffuser transparent plate 12 is normally used by controlling the distance 11 between the plate and LEDs to obtain a uniform illumination.
This typical LED package structure sees challenges in increasing illumination efficiency, being cost effective in manufacturing.
The thermal conductive efficiency of silver paste or transparent insulating paste is about 1-5 W/m·K, the heat generated from the LED chip therefore cannot be dissipated sufficiently quickly through such material, and causing elevated temperature of the chip, which in turn will decrease the light emission efficiency and shorten the life time of the LED, or even cause LED failure. The several intermediate layers that consist of insulator materials such as epoxy insulator, Ag paste, transparent gel, between the LED chip and the substrate, are thermal resistance materials that also contribute to the poor heat dissipation.
The “spot” structure generates high light intensity around the center of the LED chip and lens, weaker light intensity around the edges, thus producing a “glazing” effect which can be harmful to the eyes. For an LED lamp that has many arrayed LED package units, the distribution of light will not be uniform. In order to achieve uniform light distribution, usually a diffuser film or structure of certain thickness is used above the LEDs, however, resulting in decreased light efficiency.
Moreover, the epoxy or silicone gel lens which seals the LED chip from moist and dust, generally has poor thermal conductivity, the heat generated from the chip is mainly dissipated through the backside to the substrate.
The reflect layer generally uses metals such as Ag, Al thin films, the fabrication process involves sophisticated vacuum or chemical deposition which is highly costly.
Further, for “spot” structure LED lamp fabrication, multiple steps are involved. LED chips are first packaged as “spot” tube with the electrodes and lens; then the package LED tubes are arrayed by connecting in parallel or series and mounting on a PCB; a diffuser layer is then placed on top of the LED lenses; finally power supply and driver are connected.
This process is relatively complex and time consuming, and needs significant man power in the production line.
To overcome some of the above mentioned problems, a highly thermal conductive materials and transparency material with refraction index changing is described in USPTO Patent Application 2009/0026484 and a flat type LED using high thermal conductive substrate is described in USPTO Application No. 2009/0010009.