Ultra-High Light Extraction Efficiency and Ultra-Thin Mini-LED Solution

crystals

Article Ultra-High Light Extraction Eﬃciency and Ultra-Thin Mini-LED Solution by Freeform Surface Chip Scale Package Array

Che-Hsuan Huang 1,2, Chieh-Yu Kang 1, Shu-Hsiu Chang 2,3, Chih-Hao Lin 1 , Chun-Yu Lin 2, Tingzhu Wu 4,* , Chin-Wei Sher 1,5, Chien-Chung Lin 3, Po-Tsung Lee 1 and Hao-Chung Kuo 1,* 1 Department of Photonics and Institute of Electro-Optical Engineering, College of Electrical and Computer Engineering, National Chiao Tung University, Hsinchu 30010, Taiwan; [email protected] (C.-H.H.); [email protected] (C.-Y.K.); [email protected] (C.-H.L.); [email protected] (C.-W.S.); [email protected] (P.-T.L.) 2 LEDA-creative Co., Ltd., No.45, Zhengyi Rd., Pingzhen Dist., Taoyuan City 32457, Taiwan; [email protected] (S.-H.C.); [email protected] (C.-Y.L.) 3 Institute of Photonic System, National Chiao Tung University, Tainan 711, Taiwan; [email protected] 4 Department of Electronic Science, Fujian Engineering Research Center for Solid-State Lighting, Xiamen University, Xiamen 361005, China 5 HKUST Fok Ying Tung Research Institute, Nansha District, Guangzhou 511458, China * Correspondence: [email protected] (T.W.); [email protected] (H.-C.K.); Tel.: +886-35712121-31986 (H.-C.K.) Received: 5 March 2019; Accepted: 1 April 2019; Published: 11 April 2019

Abstract: In this study, we present a novel type of package, freeform-designed chip scale package (FDCSP), which has ultra-high light extraction efficiency and bat-wing light field. For the backlight application, mainstream solutions are chip-scale package (CSP) and surface-mount device package (SMD). Comparing with these two mainstream types of package, the light extraction efficiency of CSP, SMD, and FDCSP are 88%, 60%, and 96%, respectively. In addition to ultra-high light extraction efficiency, because of the 160-degree bat-wing light field, FDCSP could provide a thinner and low power consumption mini-LED solution with a smaller number of LEDs than CSP and SMD light source array.

Keywords: chip scale package; freeform design; mini LED; light emitting diode

1. Introduction For next generation liquid crystal display (LCD) displays, high dynamic range (HDR) is an important feature [1]. To achieve HDR, local dimming is a technique, which can effectively suppress the dark state and greatly enhance the contrast ratio [2–4]. For local dimming technique, segmented light emitting diodes (LEDs) are adopted in the LCD backlight unit, where the local zones can be independently dimmed to match the displayed image contents. For direct lit backlight system with local dimming function, two types of LED packages are widely used. One is traditional surface-mount device (SMD) LED [5,6], the other is chip-scale package (CSP) [7]. For SMD LED, it is the most popular design. Its process is to mount an LED chip in a cavity substrate, and then fill silicone mixed with phosphor into the cavity. This process is very simple and easy to mass production. However, its view angle is limited by the cavity substrate. When we apply SMD LED to a direct lit backlight system, it is necessary to add a secondary lens that can increase the view angle on the top of LED. Thus, the CSP solution, which is to deposit a phosphor layer on the top of Flip chip LED, was proposed to solve this issue these years since CSP has a larger view angle and better light extraction efficiency [8,9].

Crystals 2019, 9, 202; doi:10.3390/cryst9040202 www.mdpi.com/journal/crystals Crystals 2019, 9, x FOR PEER REVIEW 2 of 9 Crystals 2019, 9, 202 2 of 9 chip LED, was proposed to solve this issue these years since CSP has a larger view angle and better light extraction efficiency [8,9]. Recently,Recently, because because of of the the excellent excellent contrast contrast performance performance and and wide wide color color gamut gamut potential, potential, the micro-LEDthe micro-LED with witha chip a size chip smaller size smaller than 100 than μm 100 becomesµm becomes the mainstream the mainstream research research topic of topicdisplay of techniquedisplay technique [10–14]. [Though10–14]. Thoughthe micro-LED the micro-LED display display has huge has potential huge potential to be tothe be future the future display, display, the expensivethe expensive cost costand andlow low yield yield in inthe the mass mass transfer transfer process process obstruct obstruct the the popularize popularize progress progress of of micro-LEDmicro-LED [15,16]. [15,16]. On On the the other other hand, hand, mini-LED mini-LED has has a a larger larger chip chip size size (100–500 (100–500 μµm)m) than than micro-LED micro-LED andand its fabrication is much easier [17,18]. [17,18]. Thus, Thus, mini-LED mini-LED is is an an ideal backlight candidate to to enable locallocal dimming dimming for for LCDs. LCDs. Considering Considering the the cost cost and and performance, performance, the the mini-LED mini-LED solution, solution, which which has has a a lightlylightly largerlarger pitchpitch than than micro-LEDs micro-LEDs and and owns owns excellent excellent contract contract performance performance with the with local the dimming local dimmingtechnique technique is vigorously is vi developing.gorously developing. ToTo achieve the most suitablesuitable mini-LED solution, we we combine the concept of direct lit backlightbacklight solution,solution, which which has has a a secondary secondary lens lens like like SMD SMD LED LED to to reshape reshape the the light light field field to to the bat-wing type type and and hashas high light extraction efficiency efficiency like like CSP CSP LED. Then Then,, this kind of structure is called freeform-designed chipchip scale scale package package (FDCSP). (FDCSP). This This FDCSP FDCSP type LED arrays could provide both ultra-high light extraction efficiencyefficiency and and ultra-thin ultra-thin direct direct lit lit back backlightlight solution solution for for mini-LED mini-LED applications. applications. 2. Experiment 2. Experiment Figure1 shows the schematic diagram of three types of mini-LED, which are (a) CSP, (b) SMD, Figure 1 shows the schematic diagram of three types of mini-LED, which are (a) CSP, (b) SMD, and (c) FDCSP. 100 µm 100 µm flip chip is used in these three types of packages as their light sources. and (c) FDCSP. 100 μm× × 100 μm flip chip is used in these three types of packages as their light For CSP mini-LED, a 35 µm thickness and 90% concentration of phosphor layer is deposited on the sources. For CSP mini-LED, a 35 μm thickness and 90% concentration of phosphor layer is deposited chip, then a transparent silicone is molded on the top of the phosphor layer. The particle size called on the chip, then a transparent silicone is molded on the top of the phosphor layer. The particle size D50 and D90 of commercial phosphor is about 15 µm and 25 µm, respectively. D50 is the average of called D50 and D90 of commercial phosphor is about 15 μm and 25 μm, respectively. D50 is the particle size. D90 describes the diameter where 90 % of the distribution has a smaller particle size and average of particle size. D90 describes the diameter where 90 % of the distribution has a smaller 10% has a larger particle size. Based on these values, 35 µm for the phosphor layer is close to the design particle size and 10% has a larger particle size. Based on these values, 35 μm for the phosphor layer limitation. Using the phosphor concentration of 90% for both CSP and FDCSP can meet the backlight is close to the design limitation. Using the phosphor concentration of 90% for both CSP and FDCSP color temperature criteria, which is 10,000 K. The size of CSP mini-LED is 1.5 mm 1.5 mm 0.8 mm. can meet the backlight color temperature criteria, which is 10,000 K. The size of CSP× mini-LED× is 1.5 The optimization of thickness of CSP phosphor layer and CSP package referred to the previous work [6]. mm × 1.5 mm × 0.8 mm. The optimization of thickness of CSP phosphor layer and CSP package For SMD mini-LED, chip is mounted in a cavity substrate, and phosphor is evenly distributed in referred to the previous work [6]. For SMD mini-LED, chip is mounted in a cavity substrate, and the cavity with concentration 10% to meet the 10,000 K backlight color temperature. For FDCSP phosphor is evenly distributed in the cavity with concentration 10% to meet the 10,000 K backlight mini-LED, a 35 µm thickness and 90% concentration of phosphor layer is deposited on the chip, then a color temperature. For FDCSP mini-LED, a 35 μm thickness and 90% concentration of phosphor transparent lens with freeform surface design is molded. We analyzed the light source efficiency and layer is deposited on the chip, then a transparent lens with freeform surface design is molded. We illuminance angle by Light Tools™ (Synopsys Inc, Mountain View, CA, USA) for these three kinds of analyzed the light source efficiency and illuminance angle by Light Tools™ (Synopsys Inc, Mountain light sources, and then model the module as shown in Figure2. The size of module architecture is View, CA, USA) for these three kinds of light sources, and then model the module as shown in 30 mm 30 mm. For the light performance of module using CSP, SMD, and FDCSP, MATLAB is used Figure 2.× The size of module architecture is 30 mm × 30 mm. For the light performance of module to call the Lighttools API and numerical operations. There are two important parameters to analyze using CSP, SMD, and FDCSP, MATLAB is used to call the Lighttools API and numerical operations. the performance of the module. One is the distance between the light source and the receiving surface. There are two important parameters to analyze the performance of the module. One is the distance This parameter is called optical distance, “OD”. The other is the arrangement of the light source arrays, between the light source and the receiving surface. This parameter is called optical distance, “OD”. this parameter called “Pitch”. Spot uniformity and energy efficiency of module using three types of The other is the arrangement of the light source arrays, this parameter called “Pitch”. Spot packages will be evaluated based on these two parameters, OD and Pitch. These two parameters uniformity and energy efficiency of module using three types of packages will be evaluated based are very important to the evaluation of the direct-lit backlight system [19–21]. If the OD is smaller, on these two parameters, OD and Pitch. These two parameters are very important to the evaluation it means that this backlight module is thinner. If the Pitch is larger, it means that less LEDs are used in of the direct-lit backlight system [19–21]. If the OD is smaller, it means that this backlight module is this module. thinner. If the Pitch is larger, it means that less LEDs are used in this module.

Figure 1. Schematic diagram (a) CSP, (b) SMD, and (c) FDCSP. Figure 1. Schematic diagram (a) CSP, (b) SMD, and (c) FDCSP.

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Figure 2. Schematic diagram of (a) the Pitch and (b) the OD for a backlight module. Figure 2. a b Figure 2. SchematicSchematic diagramdiagram ofof ((a)) thethe PitchPitch andand ((b)) thethe ODOD forfor aa backlightbacklight module.module. 3. Result Result and and Discussion Discussion 3. Result and Discussion Firstly, we analyze the energy loss and spot ch characteristicsaracteristics of of the light source source components. components. ThroughFirstly, Lighttools we analyze simulation, the energy Figure loss 33 records recordsand spot thethe ch illuminationilluminationaracteristics anglesanglesof the ofoflight thethe source threethree light lightcomponents. sourcessources CSP,Through SMD, Lighttools and FDCSP, simulation, respectively respectively. Figure. The The 3 CSP CSPrecords source source the has hasillumination an an illumination illumination angles angle angleof the of of three130 130 degrees light degrees sources and and a GaussianaCSP, Gaussian SMD, distribution, distribution,and FDCSP, while respectively while the the SMD SMD. The hashas CSP an an sourceillumination illumination has an illuminationangle angle of of 120 120 angledegrees, degrees, of 130 which which degrees is is also and a a GaussianGaussian distribution. distribution, More while specifically, speciﬁcally, the SMD thehas FDCSPan illumination hashas aa 160160 degreesangledegrees of bat bat120 wingwing degrees, distributiondistribution which pattern.ispattern. also a Gaussian distribution. More specifically, the FDCSP has a 160 degrees bat wing distribution pattern.

FigureFigure 3. 3. ViewView angle angle of of CSP, CSP, SMD, and FDCSP. Figure 3. View angle of CSP, SMD, and FDCSP. Figure4 4 showsshows thethe rayray tracingtracing profileprofile simulatedsimulated byby Lighttools.Lighttools. TheThe systemsystem eefficiencyfficiency calculation resultsFigure ofof CSP,CSP, 4 shows SMD, SMD, andthe and ray FDCSP FDCSP tracing are areprofile 88%, 88%, 60%, simulated 60%, and and 96%, by 96%, Lighttools. respectively. respectively. The From system From Figure efficiency Figure4, it can 4, calculation beit clearlycan be clearlyobservedresults observedofthat CSP, the SMD,that system the and system effi FDCSPciency efficiency are is proportional 88%, is 60%,proportional and to the 96%, number to respectively.the nu ofmber rays outofFrom rays of the Figureout surface. of the4, itsurface. Duecan tobe Duetheclearly designto observedthe ofdesign the that free-form of thethe systemfree-form surface, efficiency thesurface, FDCSP is thproportionale hasFDCSP a low has to proportion thea low number proportion of theof rays total ofout beamthe of totalthe reflection, surface. beam reflection,resultingDue to the in resulting minimaldesign inof energy minimalthe free-form loss. energy As SMD surface, loss. is only As th eSMD a one-sidedFDCSP is only has illumination aa one-sided low proportion and illumination has noof curvedthe and total surfacehas beam no curvedcharacteristics,reflection, surface resulting thecharacteristics, number in minimal of rays the energy thatnumber the loss. beam of As rays isSMD reflected that is onlythe and beama totalone-sided is internal reflected illumination reflection and total (TIR)and internal has in the no packagereflectioncurved surface is (TIR) very in large,characteristics, the package thus causing is thevery a largenumber large, amount thus of rayscausing of energythat a largethe loss. beam amount is reflectedof energy and loss. total internal reflectionThen, (TIR) the CSP,SMD, in the package and FDCSP is very light large, sources thus are causing analyzed a large in the amount module, of respectively.energy loss. The module parameter “OD” is 4 mm to 10 mm, the step is 1 mm; and the module parameter “Pitch” is 30 mm, 15 mm, 10 mm, and 7.5 mm, respectively. Figures5–7 show the module operation results of CSP, SMD, and FDCSP, respectively. The file name format of each thumbnail in the picture is “Pitch-OD-Uniformity-Intensity”. For example, the name “7.5-4-87%-912259” of picture means that the pitch of LED array is 7.5 mm, OD is 4 mm, and backlight module uniformity is 87%, and the intensity is 912,259 nits. The uniformity is defined, as shown in Equation (1).

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FigureFigure 4. 4.Light Light tracing tracing profileprofile of ( a)) CSP, CSP, ( (bb) )SMD, SMD, and and (c) ( cFDCSP.) FDCSP. Then, the CSP, SMD, and FDCSP light sources are analyzed in the module, respectively. The In addition to uniformity, in order to properly express the ability of the program, this paper module parameter “OD” is 4 mm to 10 mm, the step is 1 mm; and the module parameter “Pitch” is defines the ratio of Pitch to OD as an evaluation index of the program ability, the “solution factor”, 30 mm, 15 mm, 10 mm, and 7.5 mm, respectively. Figure 5, Figure 6 and Figure 7 show the module S. A detailedoperation mathematical results of CSP, definitionSMD, and isFDCSP, defined respectively. as Equation The (2). file name format of each thumbnail in the picture is “Pitch-OD-Uniformity-Intensity”. For example, the name “7.5-4-87%-912259” of PITCH picture meansSolution that the f actor pitch S of(Minimum LED array uniformity,is 7.5 mm, OD minimum is 4 mm, and intensity backlight) = module uniformity (2) OD is 87%, and the intensity is 912,259 nits. The uniformity is defined, as shown in Equation (1). Taking S (85%, 100%) = 2 for example,minimum it means pixel value that theof image minimum uniformity and minimum Uniformity =×100% (1) intensity of backlight module are 85 %maximum and 100 pixel %, respectively, value of image and the Pitch is twice the value of OD. If theIn Pitch addition is large, to uniformity, it means thatin order a smaller to properly number express of LEDs the ability are used of the in program, the module, this leadingpaper to the lowdefines cost the and ratio power of Pitch consumption to OD as an evaluation for the backlight index of system.the program If the ability, OD isthe small, “solution it means factor”, that S. the backlightA detailed module mathematical is thin. Therefore, definition ais backlightdefined as moduleEquation with (2). the larger solution factor will be more cost-effective and thinner, and solution factor can be a quantitative indicatorPITCH for the performance of Solution factor S (Minimum uniformity, minimum intensity) = (2) direct lit backlight system using mini-LED. OD Taking S (85%, 100%) = 2 for example, it means that the minimum uniformity and minimum minimum pixel value of image intensity of backlightUni module f ormity are= 85 % and 100 %, respectively, and the Pitch100% is twice the value of (1) OD. If the Pitch is large, it means thatmaximum a smaller number pixel value of LEDs of image are used× in the module, leading to Crystalsthe low2019 ,cost 9, x FORand PEER power REVIEW consumption for the backlight system. If the OD is small, it means that the5 of 9 backlight module is thin. Therefore, a backlight module with the larger solution factor will be more cost-effective and thinner, and solution factor can be a quantitative indicator for the performance of direct lit backlight system using mini-LED.

FigureFigure 5.5. Array analysis of of CSP. CSP.

Figure 6. Array analysis of SMD.

Figure 5 is an image series of an array of CSPs. Qualitatively, when Pitch = 30 mm, since the illumination type of the light source is the Gaussian distribution, the light pattern cannot be effectively opened in the interval of OD = 4 mm to 10 mm. Therefore, the images all show obvious cross-dark characteristics (blue area). As shown in Figure 6, SMD also has the same characteristics, while FDCSP has no obvious cross-dark band when OD = 8 mm or more, such as Figure7. Based on the above results, the bat wing light type clearly has the ability to provide large Pitch solution on the display plane. On the other hand, as can be seen from Figure 5, Figure 6 and Figure 7, the image uniformity increases significantly as the Pitch shrinks and the OD increases until the OD is large enough or the Pitch is small enough to achieve saturation. As shown in Figure 5, Figure 6 and Figure 7, the uniformity of the image has not changed significantly when OD > 6 mm or Pitch < 7.5 mm. This parameter interval is the saturation interval. In addition, from the value of Intensity, it can be seen that Intensity basically decreases with OD increasing.

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Crystals 2019, 9, 202 5 of 9 Figure 5. Array analysis of CSP.

FigureFigure 6.6. ArrayArray analysisanalysis ofof SMD.SMD.

FigureFigure5 5 is is an an image image series series of of an an array array of of CSPs. CSPs. Qualitatively, Qualitatively, when when Pitch Pitch == 3030 mm,mm, sincesince thethe illuminationillumination type type of of the the light light source source is the is Gaussian the Gaussian distribution, distribution, the light the pattern light cannot pattern be ecannotffectively be openedeffectively in theopened interval in the of ODinterval= 4 mm of OD to 10= 4 mm. mm Therefore,to 10 mm. theTherefore, images the all showimages obvious all show cross-dark obvious characteristicscross-dark characteristics (blue area). As(blue shown area). in As Figure shown6, SMD in Figure also has 6, SMD the same also characteristics,has the same characteristics, while FDCSP haswhile no FDCSP obvious has cross-dark no obvious band cross-dark when OD band= 8 when mm orOD more, = 8 mm such or as more, Figure such7. Basedas Figure7. on the Based above on results,the above the results, bat wing the light bat wing type light clearly type has clearly the ability has the to ability provide to largeprovide Pitch large solution Pitch solution on the display on the plane.display On plane. the other On the hand, other as can hand, be seenas can from be Figuresseen from5–7, theFigure image 5, Figure uniformity 6 and increases Figure significantly7, the image asuniformity the Pitch shrinksincreases and significantly the OD increases as the untilPitch the shrinks OD is and large the enough OD increases or the Pitch until is smallthe OD enough is large to achieveenough saturation.or the Pitch As is shownsmall enough in Figures to achieve5–7, the uniformitysaturation. ofAs the shown image in hasFigure not 5, changed Figure significantly6 and Figure when7, the ODuniformity> 6 mm of or the Pitch image< 7.5 has mm. not Thischanged parameter significantly interval when is the OD saturation > 6 mm or interval. Pitch < 7.5 In mm. addition, This fromparameterCrystals the 2019 value, interval9, x FOR of Intensity, PEER is the REVIEW saturation it can be seeninterval. that IntensityIn addition, basically from the decreases value of with Intensity, OD increasing. it can be 6seen of 9 that Intensity basically decreases with OD increasing.

FigureFigure 7.7. ArrayArray analysisanalysis ofof FDCSP.FDCSP.

In order to further discuss the optical phenomenon in the unsaturated interval, we take the parameters of each image and normalize the simulation results of each condition based on the Intensity of CSP at OD = 4 mm and Pitch = 30 mm, as shown in Table 1. First of all, we can clearly observe that the module intensity of FDCSP scheme is much higher than that of CSP and SMD because the light extraction efficiency of FDCSP is better than CSP and SMD. Therefore, the overall efficiency of the intensity is more than 130%. In contrast, the SMD is not efficient due to the low package efficiency of initial light source. The normalized intensity value is only about 70%. Then, in order to further distinguish the capabilities of each light source scheme, this study is aimed at S (85%, 60%), S (85%, 70%), S (85%, 100%), and S (85%, 110%) to draw a strategy map with different conditions. Figure 8 demonstrates the strategy map of S (85%, 60%), S (85%, 70%), S (85%, 100%), and S (85%, 110%), respectively. Due to poor efficiency, the SMD series has no solution at S (85%, 100%) and S (85%, 110%). Additionally, the CSP only has smaller OD solutions at S (85%, 110%) as the threshold of intensity increases. It is worth mentioning that the FDCSP solution has not changed significantly under any conditions.

Table 1. Module modeling result. The numbers in the frame means that the uniformity of modulus is over 85%.

Uniformi Pitch OD Uniformity-S Uniformity-FDCSP Intensity-C Intensity-S Intensity-FDCS ty-CSP (mm) (mm) MD (%) (%) SP (a.u.) MD (a.u.) P (a.u.) (%) 30 4 5 3 1 100% 67% 117% 30 5 9 6 7 104% 71% 123% 30 6 13 11 20 106% 73% 127% 30 7 19 16 42 108% 74% 129% 30 8 26 22 68 108% 75% 131% 30 9 33 29 92 108% 75% 132% 30 10 41 37 87 107% 75% 132% 15 4 76 74 93 111% 76% 131% 15 5 83 82 96 111% 76% 133% 15 6 87 87 93 109% 76% 131% 15 7 89 89 86 107% 75% 126% 15 8 90 90 79 104% 73% 119% 15 9 89 89 75 100% 71% 112% 15 10 88 88 73 96% 69% 106% 10 4 88 89 96 114% 79% 131% 10 5 89 89 87 110% 77% 126%

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In order to further discuss the optical phenomenon in the unsaturated interval, we take the parameters of each image and normalize the simulation results of each condition based on the Intensity of CSP at OD = 4 mm and Pitch = 30 mm, as shown in Table1. First of all, we can clearly observe that the module intensity of FDCSP scheme is much higher than that of CSP and SMD because the light extraction efficiency of FDCSP is better than CSP and SMD. Therefore, the overall efficiency of the intensity is more than 130%. In contrast, the SMD is not efficient due to the low package efficiency of initial light source. The normalized intensity value is only about 70%. Then, in order to further distinguish the capabilities of each light source scheme, this study is aimed at S (85%, 60%), S (85%, 70%), S (85%, 100%), and S (85%, 110%) to draw a strategy map with different conditions. Figure8 demonstrates the strategy map of S (85%, 60%), S (85%, 70%), S (85%, 100%), and S (85%, 110%), respectively. Due to poor efficiency, the SMD series has no solution at S (85%, 100%) and S (85%, 110%). Additionally, the CSP only has smaller OD solutions at S (85%, 110%) as the threshold of intensity increases. It is worth mentioning that the FDCSP solution has not changed significantly under any conditions.

Table 1. Module modeling result. The numbers in the frame means that the uniformity of modulus is over 85%.

Pitch OD Uniformity-CSP Uniformity-SMD Uniformity-FDCSP Intensity-CSP Intensity-SMD Intensity-FDCSP (mm) (mm) (%) (%) (%) (a.u.) (a.u.) (a.u.) 30 4 5 3 1 100% 67% 117% 30 5 9 6 7 104% 71% 123% 30 6 13 11 20 106% 73% 127% 30 7 19 16 42 108% 74% 129% 30 8 26 22 68 108% 75% 131% 30 9 33 29 92 108% 75% 132% 30 10 41 37 87 107% 75% 132% 15 4 76 74 93 111% 76% 131% 15 5 83 82 96 111% 76% 133% 15 6 87 87 93 109% 76% 131% 15 7 89 89 86 107% 75% 126% 15 8 90 90 79 104% 73% 119% 15 9 89 89 75 100% 71% 112% 15 10 88 88 73 96% 69% 106% 10 4 88 89 96 114% 79% 131% 10 5 89 89 87 110% 77% 126% 10 6 87 88 78 106% 75% 120% 10 7 85 86 73 102% 72% 113% 10 8 84 84 70 97% 69% 106% 10 9 82 83 69 92% 66% 99% 10 10 80 81 70 87% 62% 91% 7.5 4 90 92 87 112% 78% 127% 7.5 5 87 88 78 107% 75% 120% 7.5 6 83 84 72 102% 72% 113% 7.5 7 80 82 68 97% 69% 106% 7.5 8 78 79 66 92% 65% 98% 7.5 9 76 77 67 86% 62% 91% 7.5 10 75 76 68 82% 59% 84%

In addition, from the strategy map, the ability of solution can be evaluated by the value of the “solution factor”. FDCSP’s solution factor S can reach up to 3.75, while CSP and SMD have a maximum solution factor S of 2.5. This means that FDCSP mini-LED can provide a larger pitch solution under the same OD conditions. Combining the above results, with a high solution factor value and high light extraction eﬃciency, FDCSP can be a highly eﬃcient light source for ultra-thin mini-LED display applications. Crystals 2019, 9, x FOR PEER REVIEW 7 of 9

10 6 87 88 78 106% 75% 120% 10 7 85 86 73 102% 72% 113% 10 8 84 84 70 97% 69% 106% 10 9 82 83 69 92% 66% 99% 10 10 80 81 70 87% 62% 91% 7.5 4 90 92 87 112% 78% 127% 7.5 5 87 88 78 107% 75% 120% 7.5 6 83 84 72 102% 72% 113% 7.5 7 80 82 68 97% 69% 106% 7.5 8 78 79 66 92% 65% 98% Crystals7.5 2019, 99 , 202 76 77 67 86% 62% 91%7 of 9 7.5 10 75 76 68 82% 59% 84%

FigureFigure 8. 8.The the strategystrategy map map for for (a ()a uniformity) uniformity> 85%, > 85%, Intensity Intensity> 60%, > 60%, (b) uniformity(b) uniformity> 85%, > 85%, Intensity Intensity> 70%, > (c70%,) uniformity (c) uniformity> 85%, >Intensity 85%, Intensity> 100%, > 100%, and (d and) uniformity (d) uniformity> 85%, > Intensity85%, Intensity> 110%. > 110%.

DueIn addition, to the direct from refracting the strategy light map, characteristics, the ability the of FDCSPsolution light can sourcebe evaluated has higher by the light value extraction of the e“solutionfficiency thanfactor”. the CSPFDCSP’s and SMDsolution light factor sources. S can According reach up to to Table 3.75,2, FDCSP,while CSP CSP, and and SMD SMD have light a sourcesmaximum have solution a light factor extraction S of e2.5.fficiency This means of 96%, that 88%, FDCSP and 60%, mini-LED respectively. can provide In addition, a larger due pitch to thesolution bat wing under light the type, same FDCSP OD conditions. has a higher Combining solution factor the above on the results, display with module, a high and solution can provide factor Svalue (85%, and 110%) high= 3.75, lightwith extraction a larger efficiency, Pitch and FDCSP high intensity can be schemea highly under efficient the light condition source of for OD ultra-thin= 4 mm. Onmini-LED the contrary, display since applications. both the light types of CSP and SMD are Gaussian-distributed, the solution factorDue is, at to most, the 2.5.direct Combining refracting the light above characterist characteristics,ics, the FDCSP FDCSP provides light ansource excellent has solutionhigher light for ultra-thinextraction mini-LED efficiency due than to the its highCSP eandfficiency SMD andlight high sources. solution According factor. to Table 2, FDCSP, CSP, and SMD light sources have a light extraction efficiency of 96%, 88%, and 60%, respectively. In addition, Table 2. Comparison of different light source. due to the bat wing light type, FDCSP has a higher solution factor on the display module, and can provide S (85%, 110%) = 3.75, with aCSP larger Pitch and high SMD intensity scheme under FDCSP the condition of OD = 4 mm.PKG On Effi ciencythe contrary, since both88% the light types of 60%CSP and SMD are Gaussian-distributed, 96% the solution factor is, at most, 2.5. Combining130 the above characteristics,120 FDCSP provides160 an excellent Angular ◦ ◦ ◦ solution for ultra-thin mini-LEDGaussian due distributionto its high efficiencyGaussian and distribution high solutionBat factor. wing distribution Array Efficiency 111% 76% 131% @OD4 Pitch10mm 1.5 < S (85%, 60%) < 2.5 1.4 < S (85%, 60%) < 2.5 2.1 < S (85%, 60%) <3.75 Solution Factor S Max intensity: 112% Max intensity: 78% Max intensity: 131% S (85%, 60%) Max OD = 10 Max OD = 10 Max OD = 10 1.5 < S (85%, 70%) < 2.5 1.4 < S (85%, 70%) <2.5 2.1 < S (85%, 70%) <3.75 Solution Factor S Max intensity: 112% Max intensity: 78% Intensity: 131% S (85%, 70%) Max OD = 10 Max OD = 9 Max OD = 10 1.5 < S (85%, 100%) < 2.5 2.1 < S (85%, 100%) <3.75 Solution Factor S Max intensity: 112% NA Intensity: 131% S (85%, 100%) Max OD = 9 Max OD = 10 1.5 < S (85%, 110%) < 2.5 2.1 < S (85%, 110%) <3.75 Solution Factor S Max intensity: 112% NA Intensity: 131% S (85%, 110%) Max OD = 5 Max OD = 10 Crystals 2019, 9, 202 8 of 9

4. Conclusions In this study, we develop a new package type FDCSP and simulate its performance by adjusting two parameters of the Pitch and the OD. Compared to the traditional CSP and SMD, FDCSP has a better light extraction eﬃciency (96%). In addition, the bat-wing light shape makes FDCSP more suitable for mini-LED display applications with a higher solution factor. For the realistic requirement in display applications, we expect the mini-LED backlight has local dimming function and slim thickness, with lower cost and low power consumption characteristics. Therefore, this FDCSP type of light source array could provide both ultra-high light extraction eﬃciency and ultra-thin direct type backlight solution for mini-LED application. FDCSP can be regarded as a model for practitioners who desire to improve the quality of mini-LED displays.

Author Contributions: Supervision, T.W. and H.-C.K.; writing-original draft preparation, C.-H.H., C.-Y.K. and C.-H.L.; project administration, C.-W.S. and P.-T.L.; Writing-Review & Editing, S.-H.C.; Resources, C.-Y.L. and C.-C.L. Funding: Ministry of Science and Technology, Taiwan (MOST) (MOST 105-2221-E-009-112-MY3, 107-2221-E-009-113-MY3, and 107-2221-E-009-114-MY3). Strait Postdoctoral Foundation of Fujian Province of China. Conﬂicts of Interest: The authors declare that there are no conﬂicts of interest related to this article.

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