Future power LEDs will be packaged with DPC ceramic substrates

Future power LEDs will be packaged with DPC ceramic substrates

2021-11-10 17:21:41 9

As a carrier of heat and air convection, the thermal conductivity of DPC ceramic substrate plays a decisive role in the heat dissipation of LEDs. with its excellent performance and gradually decreasing price, DPC ceramic substrate shows strong competitiveness among many electronic packaging materials and is the future trend of power LED packaging development. With the development of science and technology, the emergence of new preparation processes, high thermal conductivity ceramic materials as a new electronic packaging substrate materials, application prospects are very broad.


As the input power of LED chips continues to increase, the large dissipation power brings large heat generation to LED packaging materials put forward newer and higher requirements. In the LED heat dissipation channel, the packaging substrate is the key link connecting the internal and external heat dissipation channels, and has the functions of heat dissipation channel, circuit connection and physical support for the chip. For high power LED products, the packaging substrate requires high electrical insulation, high thermal conductivity, and a coefficient of thermal expansion that matches the chip.


Resin-based packaging substrates: high cost of supporting the popularization is still difficult


EMC and SMC high requirements for molding equipment, a molding line price of about 10 million yuan, large-scale popularization is still difficult.


PPA plastic thermal conductivity is very low, its heat dissipation mainly through the metal lead frame for The heat dissipation capacity is limited and is only suitable for low power LED packages.


EMC is a high performance phenolic resin as a curing agent, high thermal conductivity of silica micropowder as filler, a variety of additives mixed into the powder molding plastic. SMC is mainly composed of about 30% unsaturated resin, 40% glass fiber, inorganic filler and other additives. These two thermosetting molding plastics heat curing temperature at about 150 ℃, after modification of thermal conductivity up to 4W / (m-K) ~ 7W / (m-K), compared with PPA plastic has been greatly improved, but the disadvantage is that fluidity and thermal conductivity is difficult to take into account, curing molding hardness is too high, easy to produce cracks and burrs. EMC and SMC curing time is long, molding efficiency is relatively low, the molding equipment The requirements for molding equipment, molds and other supporting equipment are quite high, and the price of a molding and supporting production line is about 10 million yuan, which is difficult to popularize on a large scale.


Metal core printed circuit board: the manufacturing process is complex and less practical applications

The processing and manufacturing process of aluminum substrate is complex and costly, and the coefficient of thermal expansion of aluminum differs greatly from that of the chip material, which is less used in practical applications.


With the development of LED packaging to thin and low-cost direction, chip-on-board (COB) packaging technology has gradually emerged. At present, most of the COB package substrate using metal-core printed circuit boards, high-power LED packages mostly use such substrates, the price between the middle and high price.


The current production of high-power LED thermal substrate, its insulation layer thermal conductivity is very low, and due to the existence of the insulation layer, making it unable to withstand high-temperature welding, limiting the optimization of the packaging structure, is not conducive to LED heat dissipation.


How to improve the thermal conductivity of the epoxy insulation layer has become a hot spot for research on aluminum substrates at this stage. At present, a modified epoxy resin or epoxy glass cloth adhesive sheet doped with high thermal conductivity inorganic filler (such as ceramic powder) is used to bond the copper foil, insulator and aluminum plate by hot pressing. In addition, a company in Taiwan has recently developed a kind of diamond carbon material DLC, and applied it to the insulation layer of aluminum substrate for high brightness LED package. 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 improve the thermal conductivity of MCPCB, but its actual use is yet to be tested in the market.


A better performance of the aluminum substrate is generated directly on the aluminum plate insulation layer, and then printed circuit. The biggest advantage of using this method is the strong bonding, and thermal conductivity up to 2.1W / (m - K). However, the processing and manufacturing process of this aluminum substrate is complicated and costly, moreover, the coefficient of thermal expansion of metallic aluminum differs greatly from that of the chip material, and the thermal cycling of the device often generates large stresses during operation, which may eventually lead to failure, so it is less used in practical applications.


Silicon-based packaging substrates: Challenging yields below 60%

Silicon substrates face challenges in the preparation of insulation layers, metal layers, and vias, with yields not exceeding 60%.


The use of silicon-based materials as LED packaging substrate technology has been gradually introduced from the semiconductor industry to the LED industry in recent years. The thermal conductivity and thermal expansion properties of silicon substrates have shown that silicon is a better match for LED packaging materials. The thermal conductivity of silicon is 140W/m-K, and when applied to LED packaging, the resulting thermal resistance is only 0.66K/W; moreover, silicon-based materials have been used in a large number of semiconductor processes and related packaging fields, and the related equipment and materials involved are quite mature. Therefore, if the silicon is made into LED packaging substrate, it is easy to form mass production.


However, LED silicon substrate packaging still has many technical problems. For example, the material, silicon is easy to break, and the institutional strength also has problems. Structure, although silicon is an excellent thermal conductor, but poor insulation, must be oxidation insulation treatment. In addition, its metal layer needs to be prepared by sputtering combined with electroplating, and the conductive holes need to be carried out by corrosion. Overall, it seems that the preparation of insulation layer, metal layer, and conductive hole all face challenges, and the yield rate is not high. Although some Taiwanese companies have developed LED silicon substrates and mass production, but the yield rate does not exceed 60%.


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