[Source: "High-tech led-technology and application" January issue / Ma Mingtuo] I. Introduction
The technical characteristics of LED products themselves determine the thermal conductivity characteristics of the chip's heat dissipation channel, which is the limiting factor for its technical conditions and service life. How to ensure the excellent characteristics of the chip, and the package solid crystal technology has a very high degree of process relevance. In this paper, the author only discusses the technical analysis and industrial extension effect of sapphire substrate chip and SMD stent eutectic bonding solid crystal production in combination with its own research and development work practice, in order to give readers useful enlightenment.
It is known in the industry that the heat accumulation caused by the chip silver paste solid crystal process is the main factor that causes the temperature rise, the light decay, and the reliability of the device to drop and eventually fail. There are three reasons for this:
One is due to the misunderstanding of technical judgment; the industry generally believes that the sapphire substrate of the chip has poor thermal conductivity, so the efficiency of the interface heat dissipation is neglected, and the inherent heat dissipation channel of the chip is not utilized to the maximum; in fact, the sapphire substrate of the chip The material has a high purity; the thermal conductivity is 46W/(mK), which is similar to medium carbon steel, and its thermal conductivity is only different between the specific heat capacity and the microscopic conduction mode and the medium carbon steel. Therefore, the current main heat dissipation channel of the chip is constructed with the electrode lead to derive heat. The heat dissipation design focuses on the external heat sink and ignores the original characteristics, which leads to the lack of comprehensive performance of the terminal product, which greatly inhibits the LED. The ability of downstream products to enter the huge application market.
The second is that the material properties of the silver paste itself can be defined as heat transfer materials as substances near the boundary between the heat insulating material and the heat conductive material. (The thermal conductivity is less than 0.8 w/mk for the thermal insulation material; the thermal conductivity of the silver adhesive is 1-3 w/mk); it is impossible to simultaneously take into account the dual requirements of chip fixation and heat dissipation.
The third reason is that due to the lack of industrialized eutectic soldering and solid crystal technology and process support, the use of the largest heat dissipation channel at the solid crystal interface has been abandoned.
Second, qualitative description and quantitative analysis
According to the basic law of Fourier heat conduction: the heat flux dΦ transmitted in a unit time by the micro-element area dA in the object is proportional to the temperature gradient at that point and the micro-element area dA perpendicular to the direction of the heat flow.
dΦ=-λdA gradt; (2-1)
Where: dΦ--heat of micro-element transmitted per unit time, W; λ-thermal conductivity, W/(mK); dA--area perpendicular to the direction of heat flow; gradt--temperature gradient, K/m2;
The negative sign indicates that the direction of the heat flow is opposite to the direction of the temperature gradient; the positive and negative poles are all the wire diameter d1=50um bond alloy wire as an example. The negative sign indicates that the heat flow direction is opposite to the temperature gradient direction; For example, the wire diameter d1=50um bond alloy wire,
Λ1=315W/(mK); the area perpendicular to the heat flow direction dA1=2d1x d1x3.14/4; the heat of the micro-element transmitted per unit time dΦ1=-λ1dA1 gradt; the chip of the sapphire substrate is 1m; the sapphire substrate λ2=46W /(mK); the area perpendicular to the direction of the heat flow dA2=1m2; the heat of the micro-element transmitted per unit time dΦ2=-λ2dA2 gradt; the gradt is assumed to be the same boundary condition; in fact, gradt2 is much larger than gradt1; that is, there is dΦ2/dΦ1=- λ2dA2gradt/-λ1dA1 gradt ;=5.08 ; (2-2)
It can be seen that the micro-component heat dΦ2 that can be transmitted in the solid crystal interface per unit time is much larger than the micro-element heat dΦ1 that can be transmitted per unit time of the electrode lead; and the thermal conductivity analysis of the silver-gel solid crystal and the eutectic solder solid crystal is followed by Fourier The basic law of heat conduction, obviously comparing the λ values ​​of both can be determined;
............
For more information, please refer to the "High-tech LED - Technology and Applications" January issue
The technical characteristics of LED products themselves determine the thermal conductivity characteristics of the chip's heat dissipation channel, which is the limiting factor for its technical conditions and service life. How to ensure the excellent characteristics of the chip, and the package solid crystal technology has a very high degree of process relevance. In this paper, the author only discusses the technical analysis and industrial extension effect of sapphire substrate chip and SMD stent eutectic bonding solid crystal production in combination with its own research and development work practice, in order to give readers useful enlightenment.
It is known in the industry that the heat accumulation caused by the chip silver paste solid crystal process is the main factor that causes the temperature rise, the light decay, and the reliability of the device to drop and eventually fail. There are three reasons for this:
One is due to the misunderstanding of technical judgment; the industry generally believes that the sapphire substrate of the chip has poor thermal conductivity, so the efficiency of the interface heat dissipation is neglected, and the inherent heat dissipation channel of the chip is not utilized to the maximum; in fact, the sapphire substrate of the chip The material has a high purity; the thermal conductivity is 46W/(mK), which is similar to medium carbon steel, and its thermal conductivity is only different between the specific heat capacity and the microscopic conduction mode and the medium carbon steel. Therefore, the current main heat dissipation channel of the chip is constructed with the electrode lead to derive heat. The heat dissipation design focuses on the external heat sink and ignores the original characteristics, which leads to the lack of comprehensive performance of the terminal product, which greatly inhibits the LED. The ability of downstream products to enter the huge application market.
The second is that the material properties of the silver paste itself can be defined as heat transfer materials as substances near the boundary between the heat insulating material and the heat conductive material. (The thermal conductivity is less than 0.8 w/mk for the thermal insulation material; the thermal conductivity of the silver adhesive is 1-3 w/mk); it is impossible to simultaneously take into account the dual requirements of chip fixation and heat dissipation.
The third reason is that due to the lack of industrialized eutectic soldering and solid crystal technology and process support, the use of the largest heat dissipation channel at the solid crystal interface has been abandoned.
Second, qualitative description and quantitative analysis
According to the basic law of Fourier heat conduction: the heat flux dΦ transmitted in a unit time by the micro-element area dA in the object is proportional to the temperature gradient at that point and the micro-element area dA perpendicular to the direction of the heat flow.
dΦ=-λdA gradt; (2-1)
Where: dΦ--heat of micro-element transmitted per unit time, W; λ-thermal conductivity, W/(mK); dA--area perpendicular to the direction of heat flow; gradt--temperature gradient, K/m2;
The negative sign indicates that the direction of the heat flow is opposite to the direction of the temperature gradient; the positive and negative poles are all the wire diameter d1=50um bond alloy wire as an example. The negative sign indicates that the heat flow direction is opposite to the temperature gradient direction; For example, the wire diameter d1=50um bond alloy wire,
Λ1=315W/(mK); the area perpendicular to the heat flow direction dA1=2d1x d1x3.14/4; the heat of the micro-element transmitted per unit time dΦ1=-λ1dA1 gradt; the chip of the sapphire substrate is 1m; the sapphire substrate λ2=46W /(mK); the area perpendicular to the direction of the heat flow dA2=1m2; the heat of the micro-element transmitted per unit time dΦ2=-λ2dA2 gradt; the gradt is assumed to be the same boundary condition; in fact, gradt2 is much larger than gradt1; that is, there is dΦ2/dΦ1=- λ2dA2gradt/-λ1dA1 gradt ;=5.08 ; (2-2)
It can be seen that the micro-component heat dΦ2 that can be transmitted in the solid crystal interface per unit time is much larger than the micro-element heat dΦ1 that can be transmitted per unit time of the electrode lead; and the thermal conductivity analysis of the silver-gel solid crystal and the eutectic solder solid crystal is followed by Fourier The basic law of heat conduction, obviously comparing the λ values ​​of both can be determined;
............
For more information, please refer to the "High-tech LED - Technology and Applications" January issue
Corn Sheller,Hand Corn Sheller,Corn Sheller Machine,Hand Crank Corn Sheller
Hunan Furui Mechanical and Electrical Equipment Manufacturing Co., Ltd. , https://www.thresher.nl