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Future LEDs will be packaged with DPC ceramic substrates

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With the input power of the LED chip from time to time, the large heat generated by the large dissipated power has proposed an updated and higher demand for the LED packaging material. In the LED heat dissipation channel, the package substrate is the key link connecting the heat dissipation path in the watch, and has the functions of heat dissipation channel, circuit connection and physical support for the chip to stop. For high-power LED products, the package substrate is characterized by high electrical insulation, high thermal conductivity, and thermal shortening coefficient matched with the chip.
Resin-based package substrate: it is difficult to match the cost of the high
EMC and SMC are demanding high molding molding equipment, and the price of a molded molding consumer line is about 10 million yuan. It is still difficult to advance on a large scale.
In recent years, the patch-type LED brackets have been generally selected from high-temperature modified engineering plastic materials, and PPA (polyphthalamide) resin is used as the material to enhance some physical and chemical properties of PPA materials by adding modified fillers. Therefore, the PPA material is more suitable for the application of injection molding and SMD LED brackets. PPA plastics have very low thermal conductivity, and their heat dissipation is mainly terminated by the metal lead frame, which has limited heat dissipation and is only suitable for low-power LED packages.
Following the industry's focus on LED heat dissipation, two new thermoset plastic materials, epoxy molding compound (EMC) and sheet molding compound (SMC), were introduced into the SMD LED holder. EMC is a powder molding compound in which a high-functional phenolic resin is used as a curing agent, a silicon micropowder having a high thermal conductivity is used as a filler, and a plurality of additives are mixed. SMC is mainly composed of about 30% unsaturated resin, about 40% glass fiber, inorganic filler and other additives. The heat curing temperature of these two thermosetting molding compounds is about 150 °C, and the thermal conductivity after modification can reach 4W/(m·K)~7W/(m·K), which is much better than PPA plastic, but the disadvantages It is difficult to cope with activity and thermal conductivity. When curing, the hardness is too high, and cracks and burrs are simple. EMC and SMC have long curing time and relatively low forming power. The demand for molding equipment, molds and other ancillary equipment is appropriately high. The price of a molded molding and supporting consumer line is about 10 million yuan. It is still difficult to advance on a large scale.
Metal core printed circuit board: production process messy practice use less
The processing and manufacturing process of aluminum substrates is disorderly and costly. The thermal shortening coefficient of aluminum differs greatly from that of chip materials, and is rarely used in practice.

With the LED package in the direction of thinning and low cost, the chip-on-board (COB) packaging skills are gradually emerging. At present, COB package substrates mostly use metal core printed circuit boards, and high-power LED packages mostly use such substrates, and the price is between medium and high price.


DPC <a href='/' style='color:blue;'>ceramic substrate</a>s


At that time, the high-power LED heat-dissipating substrate commonly used in consumption was extremely low in thermal conductivity of the insulating layer, and because of the existence of the insulating layer, it could not accept high-temperature soldering, which limited the optimization of the package structure and was not conducive to heat dissipation of the LED.
How to advance the thermal conductivity of the epoxy insulation layer has become a hot topic in the current stage of aluminum substrates. Now selected is a modified epoxy resin or epoxy glass cloth bonded with a highly thermally conductive inorganic filler (such as ceramic powder), and the copper foil, the insulator and the aluminum plate are bonded by hot pressing. Nowadays, a "all-glue aluminum substrate" has been announced in the world. The thermal resistance of the fully-coated aluminum substrate can be 0.05K/W. In addition, a company in Taiwan recently announced the release of a variety of carbon material DLC and its use in the insulation of high-brightness LED-packaged aluminum substrates. DLC has many superior material properties: high thermal conductivity, thermal uniformity and high material strength. Therefore, replacing the epoxy resin insulation layer of traditional metal-based printed circuit board (MCPCB) with DLC is expected to greatly advance the thermal conductivity of MCPCB, but its practical application has yet to be detected by the mall.
A more functional aluminum substrate is to create an insulating layer directly on the aluminum plate and then print the circuit. The biggest advantage of using this method is that it is strong and has a thermal conductivity of up to 2.1 W/(m·K). However, the processing and manufacturing process of the aluminum substrate is disorderly and costly, and the thermal shortening coefficient of the metal aluminum is greatly different from the chip material, and the thermal cycle often causes a large stress during the operation of the equipment, which may eventually cause failure, and thus is in practice. Less choice.
Silicon-based package substrate: face a good rate of less than 60%
The silicon substrate faces a battle in the preparation of the insulating layer, the metal layer, and the via hole, and the yield rate does not exceed 60%.
The use of silicon-based materials as an LED package substrate has gradually been introduced into the LED industry from the semiconductor industry in recent years. The thermal conductivity and thermal shortening of the silicon substrate indicate that silicon is a packaging material that matches the LED. The thermal conductivity of silicon is 140W/m·K. When used in LED packaging, the thermal resistance is only 0.66K/W; and silicon-based materials have been widely used in semiconductor manufacturing and related packaging, and related equipment and The materials are properly experienced. Therefore, if silicon is fabricated into an LED package substrate, it is easy to mass-produce.
However, there are still many skill issues with LED silicon substrate packages. For example, in terms of materials, silicon material is simply broken and the strength of the structure is also problematic. In terms of structure, although silicon is an excellent heat conductor, it has poor insulation and must be treated with oxidative insulation. In addition, the metal layer needs to be prepared by sputtering and electroplating, and the conductive holes should be stopped by etching. Generally speaking, the preparation of insulating layer, metal layer and via hole are faced with the challenge, and the yield rate is not high. Although some Taiwanese companies have announced the production of LED silicon substrates and mass production, the yield rate does not exceed 60%.
Ceramic package substrate: improve heat dissipation power to meet high power LED requirements
With the high thermal conductivity ceramic substrate, DPC significantly improves the heat dissipation power, and is the most suitable product for high power and small size LED deployment.
The ceramic heat sink substrate has a new heat conductive material and a new internal structure, which compensates for the shortcomings of the aluminum metal substrate, thereby improving the overall heat dissipation effect of the substrate. Among the ceramic materials that can be used as heat-dissipating substrates, BeO certainly has a high thermal conductivity, but its line shortening coefficient is very different from silicon (Si), and it is toxic during production, which limits its use; BN has a good comprehensive function. However, as a substrate material, it has no outstanding advantages and is expensive. It is only in the discussion and promotion. Silicon carbide (SiC) has high strength and high thermal conductivity, but its resistance and insulation withstand voltage are low. Unstable, it will cause changes in thermal conductivity and dielectric constant, and should not be used as an insulating package substrate material. Although Al2O3 ceramic substrate is the most widely used and widely used ceramic substrate, its thermal shortening coefficient is higher than that of Si single crystal, which makes the Al2O3 ceramic substrate not suitable for integration in high frequency, high power and large scale. Used in the circuit. The A1N crystal has high thermal conductivity and is considered to be an ideal material for a new generation of semiconductor substrates and packages.
AlN ceramic materials have been gradually developed since the early 1990s, and are now widely used in electronic ceramic packaging materials. The heat dissipation power of the AlN ceramic substrate is 7 times that of the Al2O3 substrate, and the heat dissipation effect of the AlN substrate for the high-power LED is obvious, thereby greatly increasing the service life of the LED. The disadvantage of the AlN substrate is that even if the surface has a very thin oxide layer, it will have a great influence on the thermal conductivity, and it is only necessary to stop the severe manipulation of the material and the process to produce a well-divided AlN substrate. Nowadays, the large-scale consumption of AlN is not sophisticated. Compared with the Al2O3 substrate currently used, the cost of the AlN substrate is about 3 to 5 times that of the Al2O3 substrate. However, if energy is produced in the future, the cost of the AlN substrate can be quickly dropped. At that time, the AlN substrate with strong heat dissipation will replace the Al2O3 substrate.
At present, ceramic substrates used in LED packaging can be classified into HTCC, LTCC, DBC, and DPC according to their preparation skills. HTCC is also known as high-temperature co-fired multi-layer ceramics. Its primary material is tungsten, molybdenum, manganese and other metals with higher melting point but poor conductivity. The cost of production is high, and it is less used now. LTCC is also known as low-temperature co-fired multilayer ceramic substrate, and its thermal conductivity is about 2W/(m·K) to 3W/(m·K), which is not much superior to existing aluminum substrates. In addition, LTCC uses thick film printing skills to complete the line production, the surface of the line is rough, and the alignment is not accurate. Moreover, the multi-layer ceramic lamination sintering process also has the problem of shortening the proportion, which limits the process resolution, and the promotion and use of the LTCC ceramic substrate is greatly challenged.
The direct copper-clad ceramic plate (DBC), which is developed according to the on-board packaging skills, is also a ceramic substrate with excellent thermal conductivity. The DBC substrate does not use a binder in the preparation process, so the heat conduction function is good, the strength is high, the insulation is strong, and the heat shortening coefficient is matched with a semiconductor material such as Si. However, the reaction between the ceramic substrate and the metal material is low, the moisture is poor, and it is difficult to carry out metallization, and it is difficult to deal with the problem of micro-pores between the Al2O3 and the copper plate, which makes the mass production and yield of the product suffer a large battle. It is still the focus of research by scientific research operators in the national watch.
DPC ceramic substrate is also called direct copper-plated ceramic plate. DPC products have the characteristics of high line precision and high surface flatness. They are very suitable for LED flip-chip/eutectic process. With high thermal conductivity ceramic matrix, the heat dissipation power is obviously improved. It is the most suitable ceramic heat sink substrate for high power and small size LEDs.
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