1 . The latest products and developments of LED backlights reported in November 2006 that Samsung's LCD monitors produced in 2008 will all use LED backlights. Samsung Electronics will also apply LED backlight technology to LCD TVs. It launched a 40-inch LCD TV product in September 2006.
In November 2006, DELL and HP began shipping next year (2007) LED backlight notebooks (NB). It is expected that 25% of NBs will use LED backlights in 2008. In addition to DELL, Japanese manufacturers such as SONY and TOSHIBA have introduced NBs with LED backlights. LED backlights in NB have gradually become the mainstream in the market.
In November 2006, Song Hengyi, chairman of Shenzhen Diguang Electronics Co., Ltd., said, “Since 2005, various TFT-LCD manufacturers around the world have increased the output of LED and LCD TV panels. It is expected that the LED backlight LCD TV panel will be in 2008. More than 30%."
In September 2006, Li Bingjie, general manager of Taiwan's Jingdian, pointed out that the largest business opportunity in the 7-inch LED panel is the automotive product segment. In 2007, it is expected to officially enter the Design in phase, and LED will begin to be widely used in notebooks in 2007. On the panel backlight of the computer, Xinjingdian is ready to actively strive for this huge business opportunity.
2. Background
(A) A trend in the semiconductor industry (including IC and solid- state lighting SSL) is a trend in the semiconductor industry (including IC and solid-state lighting SSL): the design of the chip's structure is to improve its performance, at the same time, The structural design of the next process (package) is matched to the needs of the final application.
The trends in the semiconductor IC packaging industry and LED backlights are: (1) packaging "known good die"; (2) reducing or not hitting gold wires; (3) electronic products moving toward thin and light directions development of.
In the LED packaging process, the LEDs need to be connected to an external power supply via a gold wire. The inadequacies of the gold wire are as follows: (1) is one of the reasons for the decrease in yield and reliability; (2) usually after the LED chip is packaged, and then aging, which brings disadvantages to the packaged product that cannot determine the performance of the chip. Factor, once the chip of the packaged product is unqualified, the packaged product will be unqualified, and it is very important to age the LED chip before packaging; (3) the gold wire increases the thickness of the packaged product of the LED, hindering the product to the thin and light direction development of.
(B) Vertical structure LED
LED chips have two basic structures, a lateral structure (Lateral) and a vertical structure (Vertical). The two electrodes of the lateral structure LED chip are on the same side of the LED chip, and the current flows laterally in unequal distances in the n- and p-type confinement layers. The two electrodes of the vertically-structured LED chip are respectively on both sides of the epitaxial layer of the LED. Since the patterned electrode and the entire p-type confinement layer serve as the second electrode, the current flows almost entirely vertically through the epitaxial layer of the LED, and there is little lateral flow. Current ["Vertical Structure of Gallium Nitride Based LEDs", 2006-6-1, China Semiconductor Lighting Network].
Vertically structured GaP-based LED chips have been on the market for several years, and sapphire-based vertical structure GaN-based LED chips have been on the market since November 2005 (SemiLeds).
There are two basic methods for fabricating vertical structure LED chips: stripping the growth substrate and not stripping the growth substrate.
1. A vertical structure GaP-based LED chip grown on a gallium arsenide growth substrate has two structures:
• Do not strip conductive GaAs growth substrate [13th Research Institute of China Electronics Technology Group, etc.]: Conduct a conductive DBR reflective layer on a conductive gallium arsenide growth substrate, and grow a GaP-based LED epitaxial layer on the conductive DBR reflective layer on.
figure 1
• Stripping gallium arsenide growth substrates [Lumileds, wafers, etc.]: Figure 1 shows the vertical gallium arsenide-based LEDs and process flow of the wafer [2006 China (Shenzhen) International Semiconductor Lighting Forum]: laminated reflective layer in GaP-based LED On the epitaxial layer, the conductive support substrate is bonded and the gallium arsenide substrate is stripped. The conductive support substrate includes a gallium arsenide substrate, a gallium phosphide substrate, a silicon substrate, a metal and an alloy, and the like.
2. The structure of a vertical structure gallium nitride (GaN)-based LED grown on sapphire is shown in Figure 2 [2006 China (Shenzhen) International Semiconductor Lighting Forum]:
Manufacturing a vertical gallium nitride-based LED process: laminating a reflective layer on a gallium nitride-based LED epitaxial layer, bonding a conductive support substrate on the reflective layer, and stripping the sapphire growth substrate. The conductive support substrate includes a metal and alloy substrate (SemiLeds), a silicon substrate, and the like.
figure 2
3. Vertical GaN-based LEDs grown on silicon wafers have two structures [2006 China (Shenzhen) International Semiconductor Lighting Forum]:
• Do not strip the silicon growth substrate: A metal reflective layer or a conductive DBR reflective layer is laminated on the conductive silicon growth substrate, and the gallium nitride-based LED epitaxial layer is grown on the metal reflective layer or the conductive DBR reflective layer.
• stripping the silicon growth substrate: a metal reflective layer stacked on a GaN-based LED epitaxial layer, a metal reflective layer on the conductive support substrate bonding, peeling off the silicon growth substrate (LatticePower, Shimei).
Both the horizontal structure and the vertical structure LEDs need to be connected to the external power source through the gold wire. The horizontal structure LED requires at least two gold wires, and the vertical structure LED needs at least one gold wire to connect with the external power source, each gold The wire itself and its two solder joints are one of the reasons for the decrease in yield and reliability. The space occupied by the gold wire increases the thickness of the package product of the vertical gallium phosphide-based or vertical gallium nitride-based LED. Moreover, since the gold pad is extremely small (usually around 100 microns), it is difficult to directly age the LED chip. Usually, after encapsulation, aging is performed, which brings disadvantages to the package that cannot determine the performance of the chip. Once the packaged chip fails, the package product will be unqualified and difficult to repair, increasing production costs. Especially for applications with multiple LED chips, such as LED backlights (usually including hundreds of chips) and RGB LED display devices, it is especially important to age the LED chips before packaging, which can greatly improve yield and reduce costs. .
(C) Through-hole flip-chip soldering lateral structure GaN-based LED
image 3
In order to solve the problem of gold wire, a flip-chip lateral structure GaN-based LED with a metallized silicon support substrate has been proposed, and Figure 3 is a schematic diagram of the structure [second ultra-high brightness light-emitting diode (LED) and Semiconductor Lighting Industry Development and Application Forum, November 2005, Shanghai].
Figure 4 is a schematic diagram showing the structure of a flip-chip solder lateral structure GaN-based LED with a metallized silicon support substrate with an antistatic diode.
Figure 4
However, the above method has two characteristics: (1) are for horizontal structure LEDs; (2) are for GaN-based LEDs.
Therefore, for RGB LED devices, if only the blue and green LED chips do not need to be gold wire, the red LED chip still needs to be gold wire, or, as long as one color LED chip needs gold wire, the whole package The thickness of the product does not drop to the bottom, and it is not possible to age all of the LED chips before packaging. The problem mentioned above still exists.
(D) Through-hole vertical structure LED
This paper describes a via-hole vertical structure GaP-based LED, a via vertical structure GaN-based LE D, and a via vertical structure ZnO-based LED without gold wire.
The through-hole vertical structure LEDs described in this article are suitable for vertical structure LEDs that need to be stripped of the growth substrate. The structure and production process of the via vertical structure LEDs are for GaP-based LEDs, GaN-based LEDs (polarized and non-polar) The ZnO-based LEDs are identical, except that the method of stripping the growth substrate is performed. Therefore, the GaP-based LED, the GaN-based LED, and the ZnO-based LED are not further distinguished below, which is generally referred to as a via vertical structure LED.
3 . Advantages of through-hole vertical structure LEDs
The advantages of the through-hole vertical structure LED are as follows.
• All types of vertical structure LEDs available (including vertical structure GaP-based LEDs, vertical structure GaN-based LE D, and vertical structure ZnO-based LEDs, ie, existing vertical LEDs of all colors: red (R) light LEDs The green (G) light LED, the blue (B) light LED and the ultraviolet light LED can be made into the vertical through-hole LEDs. Therefore, the through-hole vertical structure LED has a great application market.
• All manufacturing processes are performed at the wafer level.
• Since there is no need to connect the gold wire to the external power supply, the thickness of the package of the LED chip with the vertical structure of the through hole is reduced. Therefore, it can be used to manufacture ultra-thin devices such as backlights and the like.
• Increased yield and reliability due to the elimination of gold wire.
• Aging before packaging, packaging qualified chips after aging, reducing production costs. Especially for chip-on-board (COB) devices, it can greatly improve yield and reduce production costs.
• High antistatic capability, especially for vertical through-hole LEDs with anti-static diodes.
• The use of larger diameter via/metal fill plugs and multiple via/metal fill plugs further enhances the heat dissipation efficiency of the metallized support substrate. This feature is especially important for high power LEDs.
• For blue LEDs, it is easy to apply phosphors and avoid halos.
4. Through-hole vertical structure LED: with anti-static diode
(A) A structure of an LED with a through-hole vertical structure with an antistatic diode.
Figure 5 shows the first example of an LED with a through-hole vertical structure with an antistatic diode.
The direction of flow of the LED current in the vertical structure of the via is as follows: the second pole of the external power supply —— the second electrode ------ the via hole / the metal filled plug 2 ------ metal layer 2 ----- Reflection / Ohm / Bonding Layer ------ GaP or GaN or ZnO based epitaxial layer ------ Optimized graphic electrode ------ Half via hole / metal filled plug - ----- Metal layer 1------- Through hole / metal filling plug 1 ------ First electrode ------ The first pole of the external power supply.
Figure 5
There may be more than one semi-via/metal filled plug electrically coupled to the patterned electrode, particularly for high power, large size LEDs.
The method of connecting with the external power source: after the LED chip of the vertical structure of the through hole is aged, the first electrode and the second electrode of the LED chip with the vertical structure of the through hole are reflowed or eutectic (eutectic) and the package tube Seats or heat sinks or PCB boards are soldered together. The external power source is directly electrically coupled to the first electrode and the second electrode of the LED chip of the vertical structure of the through hole through a packaged socket or a heat sink or a PCB. The advantages of the through-hole vertical structure of the LED chip are as follows: (1) reflow or eutectic soldering improves the thermal conductivity of the through-hole vertical structure of the LED chip; (2) reflow or eutectic solder buffer due to the LED chip and the packaged header or Stress caused by the difference in heat expansion coefficient of heat sink or PCB; (3) Reduce contact resistance.
(B) Production process of an LED for manufacturing a through-hole vertical structure with an antistatic diode
LEDs with through-hole vertical structures with anti-static diodes can be fabricated using different manufacturing processes.
Figure a: Preparing an LED epitaxial wafer and a metallized silicon support substrate with an antistatic diode. LED epitaxial wafers: include GaP-based LED epitaxial wafers, GaN-based LED epitaxial wafers (polarized and non-polarized), ZnO-based LED epitaxial wafers, or epitaxial wafers of other semiconductor devices. Growth Substrate Material: For GaP-based LEDs, GaN-based LEDs, ZnO-based LEDs, or other semiconductor devices, different growth substrates are used, for example, GaAs growth substrates, GaP growth substrates, sapphire growth substrates, silicon carbide growth. Substrate, ZnO growth substrate, silicon growth substrate, composite GaN-based growth substrate, composite ZnO-based growth substrate, and the like.
Figure b: Epitaxial wafers bonded to LEDs (or other semiconductor devices) and metallized silicon support substrates with antistatic diodes. Bonding methods include conductive paste, metal melting, metal diffusion, etc. [LumiLeds, wafer photoelectric, etc.].
Figure c: Peeling the growth substrate until the first type of confinement layer is exposed. The method of peeling varies depending on the growth substrate. For example, a GaAs growth substrate, a GaP growth substrate, a ZnO growth substrate, a silicon growth substrate, a composite GaN-based growth substrate, a composite ZnO-based growth substrate, or the like can be used, and different methods can be employed.
The semiconductor epitaxial layer and the reflective/ohmic/bonding layer are etched at predetermined locations until the first electrode on the metallized silicon support substrate is exposed to form a first half via.
Figure d: A protective layer is formed in the first half via.
Figure e: The protective layer is etched until the first electrode on the metallized silicon support substrate is exposed, forming a second half via.
Figure f: A metal plug is formed in the second half via, the metal plug being electrically connected to the first electrode on the silicon support substrate. A patterned electrode is formed on the first type of confinement layer, and the patterned electrode is electrically connected to the metal plug.
(C) Other structures of LEDs with through-hole vertical structure with anti-static diodes
Figure 6 shows a second example of an LED with a through-hole vertical structure with an anti-static diode. The second example shown in Figure 6 differs from the first example shown in Figure 5 in that the semi-via/metal filled plug is laminated on the via/metal fill plug 1 in the support substrate with a slight production process. different.
Figure 6 shows the flow direction of the LED current in the vertical structure of the via as follows: the second pole of the external power supply —— the second electrode ------ the via hole / the metal filled plug 2 ------ Metal layer ------ reflection / ohmic / bonding layer ------ GaP or GaN or ZnO based epitaxial layer ------ optimized pattern of electrodes ------ semi-via / metal Filling plug ------- Through hole / metal filling plug 1 ------ First electrode ------ The first pole of the external power supply.
When the LED with the vertical structure of the through-hole with the anti-static diode is connected to the external power supply, there are two options: (1) the first electrode and the second electrode are respectively connected to the two poles of the external power source by reflow soldering or eutectic soldering. The connection, therefore, does not require a gold wire; (2) can also be connected to one pole of the external power source by the gold wire on the optimized pattern electrode, and the second electrode is connected to the other pole of the external power source.
5. Through-hole vertical structure LED: no anti-static diode
Figure 7 shows an example of an LED with a through-hole vertical structure.
Figure 7 shows the through-hole vertical structure of the LED as shown in Figure 5-6. The metallized support substrate has no built-in antistatic diode. Since there is no built-in antistatic diode, the material of the metallization support substrate includes an aluminum nitride substrate, a ceramic substrate, a silicon substrate, and the like. The LED epitaxial layer 10 is grown on a growth substrate and bonded to the metallization support substrate 11 via a reflective/ohmic/bonding layer 12. Peeling the growth substrate and the buffer layer (the growth substrate and the buffer layer are not shown in FIG. 7 because the growth substrate and the buffer layer have been peeled off), and the method of peeling is different for different growth substrates, and the first type of restriction layer is exposed. The electrodes of the current diffusion layer and the optimized pattern are respectively stacked thereon.
6. Through-hole vertical structure of LED chip package
(A) LED chip with aging through-hole vertical structure before packaging
The through-hole vertical structure of the LED, especially the high-power through-hole vertical structure of the LED, the area of ​​the first electrode and the second electrode is much larger than the size of the conventional wire-bonding pad of 100 micrometers, for example, for a 1 mm x 1 mm The through-hole vertical structure of the LED, the first electrode and the second electrode can be 1 mm x 0.5 mm and 1 mm x 0.45 mm, respectively, so that it is easy to age before packaging.
(B) Heat dissipation of the LED chip with a vertical structure of the through hole
The heat generated by the through-hole vertical structure of the LED is conducted through the high thermal conductivity reflection/ohmic/bonding layer, the metal layer, the silicon support substrate/via/metal filled plug, and the first and second electrodes. It is not difficult to calculate The thermal resistance of the through-hole vertical structure of the LED chip is small. In the calculation, the protective layer (purple area in Figure 7-8) is 75x75 microns, omitting the thermal resistance of the silver layer in the reflective/ohmic/bonded layer, the metal-filled plug is copper and occupies 60% of the silicon-supported substrate The area and total thermal resistance are shown in Table 1.
In order to compare the thermal resistance of different structures of the chip, in the following Table 1-3, only the thermal resistance of the chip and the solid crystal layer are considered, and the thermal resistance of the heat sink, the PCB, and the circuit board are not considered. Because different LED chips can use the same heat sink, PCB, and circuit board.
For comparison, Figure 9 and Table 2 show the thermal resistance of LEDs with a vertical structure supported by silicon.
The thermal resistance of the via vertical LED is only 71% of the thermal resistance of the vertical structure LED with silicon as the supporting substrate.
For comparison, Figure 10 and Table 3 show the thermal resistance of LEDs mounted in LED/eutectic solder.
The thermal resistance of the through-hole vertical LED is only 33% of the thermal resistance of the LED/eutectic LED.
(C) Through-hole vertical structure of LED chip package
(1) packaged in an SMD type bracket
One or more through-hole vertical structure LEDs are packaged in SMD type brackets by reflow or eutectic soldering. For example, each SMD type bracket is packaged with a through-hole vertical structure LED (Figure 11), or red, green, and blue through-hole vertical structure LEDs are packaged in the same SMD type bracket (Figure 12 ),Wait.
The red, green, and blue rectangles in Figures 11 and 12 represent the vertical, vertical, red, green, and blue through-hole LEDs, respectively, which represent the positive and negative electrodes, respectively. The distance between the positive and negative electrodes can be as small as 40-50 microns. The other ends of the positive and negative electrodes may be on the side or bottom side of the SMD type of stent (not shown).
(2) packaged in a heat sink or PCB or circuit board (COB)
(2.1) Through-hole vertical structure of LED package on heat sink or PCB or circuit board
Figure 13-14 shows the through-hole vertical structure of the LED packaged directly on the heat sink or PCB or board by reflow or eutectic soldering. Figure 13 shows the positive and negative LEDs (in red and black, respectively) of a vertical through-hole LED electrically connected to the heat sink or the positive and negative poles (represented in red and black, respectively) on the PCB or board. The external power supply is connected to the "+" and "-" poles on the board.
It is also possible that a plurality of through-hole vertical structure LEDs are directly packaged on the same heat sink or PCB or circuit board.
Figure 14 shows an LED with two via vertical structures connected in series on the surface of the board. The external power supply is connected to the "+" and "-" poles on the board.
Multiple (or even hundreds or more, depending on the needs of the application) through-hole vertical structure LEDs are directly packaged on boards with circuits (or heat sinks or PCBs, etc.) by reflow or eutectic soldering, which can be Series, parallel or serial/parallel mixing. Alternatively, the circuit can be laminated on the inside or the back of the heat sink or PCB or board.
(2.2) The through-hole vertical structure of the LED is packaged in a heat sink or a recess in the PCB or board.
Figure 15-17 shows an LED package with multiple via vertical structures in a heat sink or a recess in a PCB or board. The grooves can have different shapes (such as circles and squares) and depths. The thickness of the board depends on the application (for example, as small as several hundred microns, as large as a few millimeters). The material of the circuit board may be metal/alloy, PC B, silicon wafer, ceramic chip, and combinations thereof.
(2.3) RGB LEDs with through-hole vertical structures are packaged in heat sinks or recesses on the PCB or board.
Figure 18-20 shows an RGBLED package with multiple via vertical structures in a heat sink or recess in a PCB or board. In Figure 18, the red, green, and blue rectangles represent the vertical, red, green, and blue through-hole LEDs, and the white rectangles with "+" and "-" represent the positive and negative poles, respectively. Red, green, and blue through-hole vertical LEDs are stacked in a single groove, and the LEDs of each color are separately controlled. The electrode circuit can be laminated on the back side of the board or on the surface or inside of the board (not shown in Figure 18).
In Figure 19, the red, green, and blue LEDs are common anode controlled (also common cathode control). The white rectangles represent the positive and negative electrodes, respectively. The electrode circuit is laminated on the inside or the back of the board.
Figure 20 shows an LED package with a vertical structure for each via in a recess. Multiple LEDs on the board are serial/parallel to form another example of RGB display.
The red, green, and blue rectangles represent red, green, and blue LEDs, respectively. An LED with a vertical structure of through holes is stacked in each groove. The white rectangles represent the positive and negative electrodes, respectively. The electrode circuit is laminated on the inside or the back of the board.
3G Mobile Phone，3G GSM Smart Phone，3G WCDMA Smart Phone
Bluetooth Headphone Co., Ltd. , http://www.nssmartphone.com