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4, CIS and CCD differences
As the saying goes, "Every ruler has his weaknesses and every inch has his strengths." CIS and CCD indeed have many outstanding characteristics, such as small size, low power consumption, low cost, but CIS still faces some unavoidable problems, such as heat dissipation, resolution, sensitivity, signal-to-noise ratio and so on.
CIS and CCD light signal acquisition method is different, CCD is passive, and CIS is active, the charge generated by the photodiode will be directly amplified by the transistor output. When CIS processes rapidly changing images, the current changes frequently and the flow rate increases, which causes it to overheat. This issue is also what CIS suppliers have always considered, so the choice of IC packaging materials is carefully screened. In a number of IC packaging materials, the ceramic circuit board has been a step ahead because of its own large carrying capacity in line with the CIS current requirements, and the ceramic itself has good heat dissipation, and the advantage of its matching thermal expansion coefficient is a good solution to the problem of overheating caused by frequent changes in the CIS circuit and can keep it at a constant temperature.
Because each CIS pixel contains an amplifier and A/D conversion circuit, too many additional devices compress the surface area of the sensitive region of a single pixel, so that the sensitivity of CIS is low, CIS suppliers have been working to reduce the pixel spacing. Only the image sensor has more pixels, the higher the resolution.
However, as the size of the pixel pitch gets closer and closer to the wavelength of light, pixel reduction becomes more and more difficult. Lindsay Grant, head of process engineering at OmniVision, said: "Now the R&D team must find new ways to avoid loss of sensitivity and increased crosstalk from the sensors." The other trend is that the pixel size of CMOS image sensors remains the same, and the improvement direction is shifting from reducing pixel size to improving image quality.
Whether it is reducing the pixel pitch or reducing the pixel size, it is undoubtedly indicating that the precision of the integrated circuit will be higher and higher, which means that the integration of the device should be high, the operation speed should be fast, the performance is better, and the sensor precision in the Internet of Things system also means that the system is more convenient and the performance is better. But at the same time, the requirements for hardware will also increase, the core of which is the sensor chip, the ordinary PCB on the market is far from meeting the requirements of CIS, and the ceramic circuit board has the advantage of high-density assembly, line/pitch (L/S) resolution can reach 20μm, so as to achieve the integration of equipment, miniaturization, to meet the requirements of CIS.
CIS signal noise has always been a big headache for its suppliers, compared with CIS,CCD chip substrate bias stability is better and less circuits on the chip, so it has a more significant low noise advantage, and even reach the level of no fixed mode noise. CIS imaging devices have high integration, the distance between photoelectric components and circuits is very close, and the optical, electrical and magnetic interference between each other is serious, and the noise has a great impact on the image quality.
The high degree of integration of CIS devices is also its advantage, so it is more appropriate to find a method from the stability of the chip. The ceramic circuit board adopts DPC film technology, the use of magnetron sputtering process to combine copper and ceramic substrate, so the ceramic circuit board metal crystallization performance is good, good flatness, the line is not easy to fall off and has reliability and stability, can well reduce CIS noise to reduce the impact on image quality.
Ceramic circuit board in addition to the above advantages, the conductive layer can be designed according to the needs of the circuit module arbitrary current, that is, the thicker the copper layer, the greater the current can be passed, our thickness can be customized within 1μm ~ 1mm, which can accurately match the conductive layer requirements of CIS.
The ceramic circuit board has the unique advantages of three wikis, three dimensional wiring, good corrosion resistance, long service life, etc., which is more conducive to the consolidation and strengthening of the performance and characteristics of CIS. According to market research and analysis, ceramic circuit boards have been widely used in developed countries, and ceramic circuit boards have become the apple of the eye of world-class sensor manufacturers with their absolute advantages.
5. CIS is in the future
At present, CIS is developing in the direction of high resolution, high dynamic range, high sensitivity, high frame rate, integration, digitalization and intelligence. There is no denying that CIS has an irresistible broad market and good prospects for development.
The future demand for CIS in emerging markets is also a new opportunity for the development of Chinese CIS manufacturers.
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