Kai Chang De Wu Zhaohui: from LED to VCSEL, the innovation of technology and application of DPC ceramic substrate

"Why can occupy a space for one person ceramic substrate in high power package? How to solve the LED industry pain points: thermoelectric separation? "In the market by 2018LED LEDinside, LED Chinese prospective analysis Network hosted the meeting, Kai Chang De technology ceramics department director Wu Zhaohui" from LED to VCSEL laser, innovative technology and application of DPC ceramic substrate as a detailed analysis of the solution of DPC ceramics the pain points of the present thermoelectric substrate technology separation.

Kai Chang De technology ceramics department director Wu Zhaohui

DPC ceramic substrates are used

Although in recent years, LED technology continues to upgrade, LED light effect is more and more high, the photoelectric conversion efficiency of high power LED chip can only reach 70% to 80%, which means that there are still 20% to 30% of electricity will be converted into heat. The heat generated by the LED, is sure to transfer out. At present, the main way is to transfer to the PCB board, but it will be found that the thermal conductivity of back channel chip and a conductive channel overlap, the choice of what kind of material for the heat conduction channel is the key.

The existing solution is the chip is directly fixed on the copper heat sink, but the copper heat sink is conductive channel, it is not the same light level, realize thermoelectric separation. The light finally encapsulated in the PCB plate, into an insulating layer to achieve thermoelectric separation still need to. At this time although not concentrated in the heat insulating layer near the chip, but concentrated in the light, once more power, the thermal problem is out. DPC ceramic substrate can solve this problem, the chip can be directly fixed on the ceramic substrate, make vertical interconnection hole in the ceramic, forming a conductive channel within itself is independent, ceramic insulator, and heat dissipation, so as to realize the power separation in the source level. The PCB board at this time, you do not need to consider the power separation structure, does not need the insulating layer above the PCB.

The definition and characteristics of DPC ceramic substrate

In order to solve the separation problem of thermoelectric ceramic substrate in the light level should have the following characteristics: first, it must have high thermal conductivity, thermal conductivity than the resin several orders of magnitude higher; the second is to have high dielectric strength; high resolution is third lines, so as to make the vertical connected with the chip or flip, not the problem is high; fourth of the surface roughness, the welding time will not empty; fifth is the ceramic and metal have high adhesion; sixth is the vertical interconnect vias, so as to achieve the circuit chip packaging, from the back to the front. A substrate to meet these conditions only DPC ceramic substrate. Now a lot of screen printing ceramic substrate is made, its process characteristics can not meet the requirements of DPC, so it can only be called not called circuit board, semiconductor package substrate.

DPC ceramic substrate

What is the name of the DPC ceramic plate? It is also called the direct copper plating ceramic substrate, the thin film metallization and electroplating process technology on ceramic substrate by way of image transfer made of metal wires with perforated electroplating technology for forming high density double-sided wiring and vertical interconnection. This is the product map, above is a solid crystal layer, below is the welding layer, the middle is arranged inside the ceramic vertical interconnection hole.

DPC ceramic material, the first is alumina ceramics, its thermal conductivity is relatively high, if you want to be a little higher, we can use the aluminum nitride, its thermal conductivity is very high, reaching 170, the coefficient of thermal conductivity of Aluminum Alloy was 220 to 230, which means it and metal thermal conductivity coefficient is almost but, its insulating strength is very high, this is a very good material. So when the power is high, aluminum nitride ceramic performance will be better.

DPC ceramic substrate in three areas application analysis

The traditional lighting: in high power LED lighting, stage lighting, street lighting, landscape lighting has been large-scale use; also widely used in flash, CSP, in addition, including the now hot car headlights, the LED light source are basically using DPC ceramic substrate.

Application of traditional lighting

UV LED: UV LED light source package because not containing organic compounds, in order to deal with this problem, the traditional silica gel filling mode can not meet the market needs a new packaging structure, namely the substrate into a 3D cavity structure, chip in three-dimensional structure in the lower chamber, vacuum or air environment, not filled with silica gel in. The solution is the launch of the Taiwan dam with a piece of aluminum metal in the ceramic base on DPC, using CNC technology to aluminum hollow, open a window, and then glue to stick it on DPC ceramic substrate, which can meet the requirements of packaging, but there are no glue solid, heat, waterproof and other issues. The solution of Japan and South Korea launched the HTCC ceramic substrate, namely high temperature cofired ceramic substrate is ceramic film and tungsten and ceramic slurry sintering chamber 3D under high temperature, the line of this scheme is rough, warping deformation, high cost.

While Kai Chang De launched DPC ceramic substrate 3D molding. First, the product line is still used in the underlying DPC process; second is the metal dam with the ceramic matrix without using adhesive, packaged air tightness is good; third is the process and now made of DPC is basically the same, in addition to a dam; fourth is the pattern design is very flexible. Dam modular manufacturing, new product development cycle is short.

Schematic structure of 3D forming DPC ceramic substrate

The full name of VCSEL:VCSEL is "vertical cavity surface emitting laser, its laser comes from perpendicular to the substrate, the LED is out of the perpendicular to the substrate, so VCSEL laser and LED chip structure, process and packaging technology is relatively close to. It has three structures, including the top of the reflector, emission cavity bottom reflector and the middle.

VCSEL structure

VCSEL can do hundreds of watts, but the chip conversion efficiency is very low, which means that heat is certainly a problem, and the chip is currently the main vertical structure, and the high power LED, facing the problem of thermoelectric separation, the ceramic substrate is to solve the birth of thermoelectric separation. Secondly, the power density of VCSEL is very high, can be done per square centimeter kilowatt, so only by vacuum package, namely substrate to do three-dimensional cavity, the lens erected above the chip. VCSEl has a high power density is so high, the chip and the substrate thermal stress caused by the mismatch problem is very serious, so the chip thermal expansion coefficient and the substrate must match these problems, DPC 3D ceramic substrate molding can be solved just. In short, the future of DPC ceramic substrate 3D molding in VCSEL laser will have a wide application prospect.

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