Due to the development and demand of the LED lighting market, LED lighting has gradually replaced traditional energy-saving lighting in performance and practical applications, and indoor lighting as an important component of the lighting market, in addition to high requirements for indoor LED lighting fixtures in addition to light efficiency The requirements for the light quality of lighting are also increasing. CSP package-free device is a new package device based on flip chip. It is a traditional LED device that is developed and improved to meet higher light quality, low material and low process cost. It is also the future development trend of device use in the indoor LED lighting market.
This paper takes the self-developed CSP package-free device as the research object, and focuses on the performance of CSP package-free device in terms of light quality and reliability. The light quality comparison between CSP package-free device and traditional 2835 white light illumination device is also explored. The performance of self-developed CSP package-free devices in terms of device dependence; research results show that CSP free-package devices are compatible with traditional 2835 white light illumination devices in terms of light quality, especially light consistency and light distribution curve performance. Compared with the advantages, at the same time, it tests and analyzes the performance of CSP package-free devices in terms of reliability, and finds out the main failure factors of CSP package-free devices. Through further improvement, it can have more traditional white light illumination devices. Applied dependence.
In recent years, with the LED industry's research progress and development in device materials, chip technology, packaging process, packaging technology, etc., especially the mature chip manufacturers in the flip chip and the phosphor coating technology gradually A new chip scale package CSP (Chip Scale Package) device came into being. The earliest definition of CSP package-free devices means that the package size and chip core size are basically the same. The concept is encapsulated by electronic IC, because of the maximum luminous flux of its cell area (high optical density) and the maximum cost of chip and package BOM (omitted gold The low package cost of the wire and bracket makes it possible to obtain excellent performance in the price/performance ratio of lm/$ [1]. The CSP package-free device has also attracted the attention of the industry. All powerful packaging manufacturers and package upstream manufacturers have invested in research and development. CSP package-free devices are not only expected by the industry, but also considered as a "ultimate" package. . In addition to the great advantages in cost reduction, in the luminaire application, due to the controllable size of the CSP package-free device, the luminaire design can be more flexible and compact; in performance, due to the small light-emitting surface of the CSP package-free device High optical density characteristics, optical directivity control can be realized, and wide-angle light distribution can be realized; flip-chip electrode design makes the current distribution balanced, suitable for larger current drive, reduces light absorption, and is favorable for CSP package-free Device reliability [2].
There are many ways to implement the white light process of the CSP package-free device. The most ideal implementation method is performed on the wafer Wafer. However, the device implemented by such a process can only cover the surface of the chip, and the blue light will leak from the periphery through the sapphire. , affecting the uniformity of the color space distribution. There are also sapphire removal methods, such as thin film chips, which can reduce the leakage of blue light, but the process cost is very high. Therefore, the mainstream technology route on the market is still to cut the chip, then carry out phosphor coating, and then test and tape, which is more similar to the traditional packaging process. The core of the process is still around the coating technology of phosphors, and the coating process includes various methods such as glue spraying, sealing, printing, and fluorescent film mounting. Each process has its advantages and challenges. At present, the CSP package-free devices on the market mainly have the following three mainstream structures (as shown in Figure 1): 1. It is made of silica gel phosphor, with five sides emitting light, high luminous efficiency, but the color temperature consistency between the top and the periphery. Poor control. 2 The surrounding titanium dioxide is used to protect the fluorescent film. Only the top one emitting surface has good light consistency and directivity, but the light output is lost for four weeks, and the light effect is low. 3 It is covered with fluorescent film and fixed with transparent silica gel. It is also a five-sided light, with high light efficiency and poor light quality. The CSP device used in this project is prepared by the preparation process of fluorescent glue pressing. It has the structure shown in Figure 1(1) (the device has no external sealing material), and the csp is regulated by the modification and configuration of the fluorescent glue. The thickness of the phosphor layer on the side and the top improves the spot problem caused by inconsistent color temperature [3].
Figure 1 Three implementations of CSP package-free devices
As a new technology, CSP package-free devices also face many limitations and challenges: First, over-reliance on the improvement of flip-chip technology, such as chip cost, light efficiency, reliability and chip ESD-resistant breakdown capability; The phosphor coating process and its uniformity require high precision, which directly affects the color temperature drop rate and color space distribution. Third, the CSP package-free device has higher precision for SMT patches due to its small size. Fourth, The reflow soldering process will affect the void ratio of the solder joints, thus affecting the heat dissipation and reliability of the product. Fifth, the difference in thermal expansion coefficient between the LED chip and the substrate is likely to cause stress, which will directly affect the reliability of the chip; therefore, the CSP is guaranteed. The package-free device achieves excellent light efficiency while ensuring device reliability is a key factor in its application development [4].
Based on the above, this paper intends to study the advantages of CSP devices in high-quality lighting applications by comparing the spectrum, light type and light distribution of CSP devices with commonly used patch white light illumination devices. The research on the reliability of CSP devices essentially solves the feasibility of CSP devices in replacing existing patch white light illumination devices.
FFC connector is a new type of data cable made of PET insulation material and extremely thin tin-plated flat copper wire, which is pressed by high-tech automation equipment production line. It is soft, bending and folding at will, thin in thickness, small in volume, easy to connect, easy to disassemble and easy to solve electromagnetic shielding (EMI).
FPC Flexible Printed Circuit is a form of Circuit produced on a Flexible surface, which may or may not have an overlay (usually used to protect FPC circuits). FPC is more and more widely used because it can bend, fold or repeat motion in a variety of ways and has the advantages of light, thin and flexible compared with ordinary hard board (PCB).
FPC composition materials
1. Insulating film
The insulating film forms the base layer of the circuit, and the adhesive attaches the copper foil to the insulating layer. In a multilayer design, it is then bonded to the inner layer.
They have also been used as a protective cover, in order to make circuit from dust and damp, and the ability to reduce stress during bending, copper foil to form the conductive layer. In some flexible circuits, adopted by the aluminum or stainless steel formed by the rigid member, they can provide the size stability, provides a physical support components and resettlement of the wire, as well as the release of stress.
2, the conductor
Copper foil is suitable for use in flexible circuits, it can use the electric deposition (Electrodeposited, ED.), or plating system.
3. Adhesive
In addition to being used for bonding insulating films to conductive materials, adhesives can also be used as cladding, protective coating, and cladding. The main difference between the two is in the application in which the covering layer is bonded to the covering insulating film in order to form a laminated structure of the circuit.
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