Since 2013 Apple iPhone 5s released for the first time since the fingerprint identification module, just four years of fingerprint recognition has become almost a standard smart phone. Fingerprint recognition module technology is mature, the module product yield improvement and the cost of production decline, making thousands of dollars below the intelligent machine also began to carry a large number of fingerprint identification module. At present, the fingerprint recognition mainly uses the pre-fingerprint identification and post-fingerprint identification and side fingerprint identification of three common programs, which, and before the home and rear program to identify the majority: such as Apple iPhone 7, millet 6, etc. is used in front fingerprint Identification program, Samsung Galaxy S8 and Huawei Nova is the fingerprint will be identified later.
In contrast, the fingerprint recognition front is better than the rear to enhance the user's user experience. With the 18: 9 full-screen spread, the mobile phone industry insiders can clearly feel the fingerprint recognition program and a comprehensive screen high-screen proportion of the design of the left, so under the screen, screen, optical, ultrasonic and other programs have been Proposed that we have reason to believe that fingerprint recognition will usher in a new round of gold development.
The development of fingerprint identification scheme
1、blind hole type Under Glass fingerprint identification program
Since the release of the news of the iPhone 8 has been broke since the news, Apple's fingerprint recognition program is also high-profile, there are news that it will use the screen Touch ID fingerprint identification solution, and this news came out, Andrews camp mobile phone manufacturers Sit still, have turned their attention to the positive fingerprint recognition. In the optical and ultrasonic fingerprint recognition technology program is not mature enough, it is necessary to achieve a positive hidden fingerprint recognition, but also had to use the case of capacitive solutions, blind hole capacitive fingerprint recognition has undoubtedly become the most promising under glass Program.
The three hidden schemes based on the capacitive principle are: the first (Under Cover Glass) is placed under the entire mobile phone glass panel; the second (In Glass) is the Sensor into the glass; Three (Glass) panels open the blind hole (both front and back) to 0.2-0.3mm deep, and then placed under the glass Sensor.
The first solution (Under Cover Glass) to identify the exact existence of a larger problem, beyond the limit of the principle of capacitance, the effect is not ideal. Although many manufacturers in the algorithm to optimize and improve the signal to noise ratio, but the program is still difficult to achieve the desired results. The second program (In Glass) has a very high technical difficulty, in the short term does not have the conditions of mass production. Need to integrate the fingerprint identification chip inside the cover glass, which requires chip manufacturers and glass factory and other aspects of the co-operation, in the short term mass production is unrealistic.
The third type of blind hole Under Glass is generally optimistic, with greater feasibility. Is the top of the technology, FPC and other manufacturers to push the identification program is in the cover glass above or below the trench, the thickness of the thin glass directly to 0.2-0.3mm, this time placed in the glass below the fingerprint chip, the signal can Penetrate the glass, in order to achieve a higher recognition accuracy. Compared with the first scheme, the accuracy of the technical scheme is far ahead, compared with the second scheme, the technical scheme is difficult to process.
2、the front cover "ultra-thin fingerprint identification program"
At present, the capacitive Under Glass scheme has very large difficulties in glass processing, even if commercial products have been introduced (such as Huawei P10), but the yield and cost of the product is still a big bottleneck.
At the same time, based on the mainstream of the current open-hole program upgrade products - can be embedded in the glass "ultra-thin" front glass / ceramic cover plate fingerprint identification, as can increase the screen ratio, this year may also be Some flagship models used, at present, the program has begun to test in a number of mobile phone manufacturers, is expected to become one of the trend this year.
The use of "ultra-thin" front glass / ceramic cover fingerprint identification module, can effectively reduce the size of the entire module, especially the thickness, so that the thickness of the entire module does not exceed the cover glass. In this case, the phone's display screen will be able to expand down, and fingerprint keys closer to the Home key (or even cover the Home button), which greatly enhance the screen share of the screen.
Analysis on the Industrial Chain of the Capacitive Underglass Scheme and the Front Cover "Ultra - thin" Scheme
At this stage, the opening of the fingerprint identification program is still the mainstream, according to the different front cover material, can be divided into Coating, sapphire cover, glass cover and ceramic cover four categories. From the industrial chain structure, the four programs are similar, the difference lies in the different materials cover.
Coating process is directly on the front of the chip coating, the signal is strong, low cost, the disadvantage is not wearable, easy to damage; sapphire program beautiful, wearable, but the processing is difficult, high cost, most for high-end models; Has been used in many low-end mobile phones, the cost is much lower than the sapphire; ceramic program recently popular, compared with sapphire its strength, low cost, productivity yield there are still some problems.
The Under Glass fingerprint recognition scheme has a very large change compared to the current fingerprint recognition. No need for special sapphire, glass, ceramic and other cover material, no metal ring, no touch switch, no need for chip front adhesive material; chip manufacturing will not change much, but the chip design and chip packaging , As well as the importance of glass processing more and more obvious.
1、chip packaging position to enhance, TSV package will become an inevitable choice
At present, most of the fingerprint identification program, the chip using wire bonding process for packaging, because of its mature technology, and low cost. As the surface needs to fit with the cover material, so the front of the chip will be plastic processing, the metal wire buried together to form a flat surface. The presence of plastic seals will affect the accuracy of the signal recognition, while increasing the thickness of the chip, but for today's mainstream open-ended fingerprints, the problem is not great, because the chip + cover material directly contact with the fingers, can still achieve better Fingerprint recognition experience.
Capacitive Underglass solution with front cover "ultra-thin" program is two important trends in fingerprint recognition. On the one hand, for the "ultra-thin" front glass / ceramic cover fingerprint identification program, because the glass is very thin, the traditional wire bonding package is difficult to effectively reduce the chip thickness, TSV package can solve the problem. On the other hand, for the capacitive Under Glass scheme, in order to improve the signal to noise ratio of the signal and reduce the loss of the signal in the plastic material, the chip package needs to adopt the advanced TSV technology; and the TSV fingerprint chip can realize the direct fit. Therefore, the "TSV + SiP" packaging process will be the key to the entire fingerprint chip, with advanced TSV and SiP packaging process manufacturers will benefit.
2、glass processing is essential, the process is difficult, yield problem is the bottleneck
At present, the difficulty of the Under Glass program is that the glass itself is very fragile. If the trench is torn, it will reduce the strength of the whole glass and increase the difficulty of glass processing. For Corning, AGC, Schott and other glass raw material suppliers and blue In order to improve the signal to noise ratio of the signal to reduce the loss of signal in the plastic material, the chip package requires the use of advanced TSV technology (which can effectively reduce the chip thickness), in order to improve the signal signal to noise ratio, ; Blind hole depth and flatness tolerance is difficult to control, and the use of TSV fingerprint chip needs to be directly bonded with the glass, so for glass processing has a higher technical requirements.
The flatness of the glass groove surface, the curvature of the right angle, the vertical degree of the edge of the fingerprint recognition of the final effect of a great impact, is the most critical of several factors, which is very high requirements for glass processing, much higher than the current glass Processing enterprises to ensure the level of yield. In summary, in the capacitive Under Glass program, Harvatek glass processing more and more obvious, the glass processing yield will directly affect the effect and cost of fingerprint chip, with high-quality, high-tech glass processing company will significantly benefit.
3、chip design and algorithm is the core factor to identify the effect
As the capacitive identification scheme in principle, the signal is difficult to penetrate the glass. Although the fingerprint recognition chip design company in all ways (including the success of adding RF function), making the fingerprint signal barely can break through the 0.1mm thickness of the sapphire / glass / ceramic, but the detection of the signal is very weak, the recognition algorithm is still off important. For the capacitive Under Glass scheme, the fingerprint signal needs to penetrate the glass thickness of 0.2-0.3mm, the traditional capacitive algorithm is unable to recover enough signal to noise ratio of the signal. In addition to enhance the signal-to-noise ratio of the driver IC, the software algorithm is more important. Another difficulty in the algorithm is because the image distance farther, the image is relatively virtual, how to make the image more clear? This involves the problem of image preprocessing; the other is the problem of image matching, because the image quality than the previous generation difference, image matching will become more difficult, where the algorithm is more complicated.
In summary, the fingerprint identification chip industry chain, including chip sensor circuit solutions and algorithm design, fingerprint identification chip sensor manufacturing, packaging and module manufacturing. And every time a new fingerprint identification program, will promote all aspects of the industrial chain of technology out of the new and upgrade, but also out of the relatively backward skills, whether the development of fingerprint identification program can make the industry chain what kind of Reaction, and let us wait and see!
