[Text / high-tech LED Xiong Yuheng] If you use the "no ignorance of the road, no one in the world does not know the king" to describe the CSP package, it is not too much. CSP is very hot. This is an indisputable fact. However, its stability is not good, and the heat dissipation problem is not well solved. It has long been criticized by people in the industry. The industry is also working on these defects, such as the emergence of NCSP and ceramic film substrate CSP.
From a structural point of view, NCSP and film substrate CSP are transitional products before the CSP technology is mature, largely to improve the reliability of CSP devices and improve their cost performance. In fact, as early as the beginning of 2015, Guoxing Guodian released the NS-CSP 1010 device, which uses an advanced ceramic film substrate (C-TFS) package structure.
Since the CSP package adopts a flip-chip structure, the GaN under the flip chip and the multilayer metal structure and the MCPCB have a large thermal expansion mismatch, and the direct solder structure after the solid crystal may leak or short circuit, and the leakage current is stopped after the power is turned off. The chip cooling time is significantly reduced as the chip lengthens. From this it can be inferred that the stress generated by the thermal expansion mismatch of the material is extremely liable to damage the GaN layer.
How to solve this problem? In the view of Li Cheng, deputy general manager of Guoxing Optoelectronics, adding a transitionable substrate to the flip chip CSP device is the most effective means to block the thermal mismatch stress of MCPCB to the chip. "Experiments show that after the introduction of the ceramic film substrate, the stress in the die bond region is reduced by 71.2%, and the GaN layer is decreased by 91.2%, which effectively ensures the high reliability of the CSP device."
“Guo Xing Optoelectronics will solidify the chip on the precision ceramic film with thickness of only 50~80μm, and use the high strength and low expansion coefficient of the ceramic material to buffer the epitaxial layer and external circuit of the chip to solve the problem of chip leakage or short circuit. To achieve high reliability of CSP devices." Li Cheng introduced.
At the same time, the thin film ceramic can effectively shorten the distance between the chip and the external heat flow channel, and offset the decrease in thermal diffusion performance caused by the reduction of the substrate size. Finally, the ceramic substrate effectively supports the phosphor layer on the side of the chip, which greatly reduces the possibility of the phosphor layer falling off and improves the airtightness of the device. Combined with an optimized secondary lens, system cost can be significantly reduced.
In terms of market applications, the thin film substrate CSP can be applied to backlights, high-density lighting, high-end displays, etc. due to its high compact package. It is worth mentioning that the technology has also obtained a number of patents (including new invention patents), which will undoubtedly serve as a good example for domestic companies that lack patent protection but are actively involved in CSP research and development. .
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