fingerprint sensor ic SW6888 protective coating user guide version 0.1 symwave, inc symwave technologies (shenzhen) co., ltd. 10180 telesis court, 3rd floor rm. 401, #8 building, software park, san diego, ca 92121 ke-ji-zhong rd. 2, hi-tech industrial park, nanshan district, shenzhen, p.r. china phone: (858) 450-2845 phone: 86-755-26984500 fax: (858) 453-1797 fax: 86-755-86168313 info@symwave.com info@symwave.com.cn
1.0 introduction symwave bioprint sensors are applied in a mechanically abrasive condition where finger print registration and matching are executed through physical swiping of a human finger on the bioprint sensor surface. a special swiping surface was developed to withstand the ware and tare nature of finger print swiping. this layer also serves as a protect covering for the exposed die area from scratches and miss-handling. 2.0 special protective coating for finger swiping. to ensure original die surface (s io2+ni) integrity is maintained and to extend the durability and reliability of bioprint sensors during its life, all se nsors are coated with a sy mwave special protective coating layer (yellowish in color). th is layer not only is used for serving as the application layer during finger swiping but also serves as a protective shielding against minor abrasive scratches to the die surface. the coating layer can withstand greater than 1m of repeated swipes of a human finger without any degradation of the finger capture image and sensor quality. experiment results also showed the protective coating layer remains on the sensor surface after greater than 1.2m physical swipes. original die surface coating of sio2 (passivation) remains undisturbed after greater than 1.2m physical swipes. 2.1 coating condition and quality due to the nature of bioprint sensor applications, the sensor area of the die is exposed for application used and thus, subject to potential physical abrasion on the coating surface. fine scratches from handling, testing, dry/ rough human skin, air bone particles and dirt are often observed on the coating surface. these scratches are normal causes of physical and mechanical abrasions to a surface. although the coating is transparent, and the sensor area is apparent under low magnification microscope, the sensor is actually protected by the coating layer just as if it is covered by mold compound found in standard ics. fig a shows a cross section of SW6888 with the protective coating covering over the original die passivation. refer to fig 1 and 2. (it is recommended that the sensor surface be covered during its transportation and when it is non-operating to avoid sharp hard objects of damaging the coating and the under laying passivation). fig a. SW6888 die cross section
the protective coating serves as an insulating buffer layer for the sensor area, as long as surface damage is on the coating layer (yellowish) and does not penetrate into the sio2 layer (white), the sensor quality and performance will be maintained. fig 3 shows an extreme case of a working/ functioning (non-degrading image) sensor with the protective coating severely damaged but without damage to the original sensor surface (passivation). note: fig 3 is a symwave visual reject and does not conform to symwave oqa visual standards, even though electrically, the part still functions (fig 4.). fig 1. scratches due to handling. or rough swiping. fig 2. scratches due to normal finger swiping during test or qa buyoff.
before scratch image after scratch image 3.0 protective coating durability test : greater than 1 million swipes can be achieved with out any damage to the original die surface (sio2 layer) and without any degradation to the capture image. number of swipes coating remain image quality 200k yes ?90% excellent 400k yes ? 80% excellent 800k yes ? 60% excellent 1000k yes ? 40% excellent 1200k yes -- 20% excellent table 1. coating and image results after swipe test. a 10 year average product life will allow the protective coating to be swiped 273 times a day to reach 1m swipes and still with 40% of the protective coating remaining on the sensor. 4.0 sensor reliability: bioprint have gone through jedec 47a standards for process technology, silicon design and assembly packaging reliability validation and passed. (refer to ta ble 2). all qualification vehicle units were subjected to symwave standard production flow with both ate and manual test insertions to ensure sensor functionality prior to reliability stress tests. mini mal ware and tare and fine scratches on the sensor surfaces are normal symptoms of a post production good unit. tests condition result htol 1000 hours @125c passed hast 196 hours 60rh/ 80c passed t/c 500 passed latchup jedec 78 passed esd 1000v cdm, 2000v hbm passed table 2. jedec 47a test reliability test results the bioprint sensor has met all jedec 47a requirement s for quality and reliability standards under normal physical and abrasive finger swiping on the sensor coating. fig 3. pencil lead point scratches over the protective coating but not damaging the fig 4. sensor captured images before and after pencil lead scratch on protective coating.
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