R 10015 Chip-On-Glass (COG) - NXP Semiconductors
R 10015Chip-On-Glass (COG) - a cost-effective and reliabletechnology for LCD displaysRev. 2 — 18 June 2012White paper1. The Chip-On-Glass value propositionToday, many LCDs are implemented by connecting a cased1 LCD driver IC with thephysical display via a Printed-Circuit Board (PCB) (see Figure 1a). This concept - referredto in the following as the Surface Mount Device, or SMD concept - provides a robustmechanical solution but requires a more complex and more area intense PCB design.Chip-On-Glass (COG) technology is an alternative design methodology in which the LCDdriver is mounted directly on the display glass (see Figure 1b). This concept - in thefollowing referred to as COG concept - reduces the number of tracks and layers on thePCB, cutting the board size and complexity, and eliminates the IC package used in theSMD concept. The overall impact is a reduction in system cost.SMD displayLCDIC(5)chip(1)(2)COG moduleLCD(3)(4)PCB013aaa515In SMD displays, five connections are needed:(1) and (2) wire bond from chip to lead frame,only one connection013aaa516In COG modules, only one connection from driver todisplay is needed.(3) solder connection to PCB,(4) and (5) connection from the PCB to the LCD.a. SMD displayFig 1.b. COG LCD moduleSMD and COG LCDIn contrast to the SMD concept, COG requires tight production and design coordinationbetween the IC and the LCD module manufacturers. NXP is well-positioned to supportCOG applications based on its strong relationships with major LCD module manufacturersworldwide and has more than 10 years of experience in designing LCD drivers for COGapplications.1.An LCD driver IC in a package.
R 10015NXP SemiconductorsChip-On-Glass (COG) - a cost-effective and reliable technology2. The Surface Mount Device conceptFor an SMD LCD, the display and the display driver are directly mounted onto the PCB.The connection between the display and the PCB is made by using either fixed-pins orelastomeric connectors (ZEBRA). With an LCD segment driver featuring up to 240segments in multiplex 1:4 mode this results in up to 64 connections between the displaydriver and the PCB as well as between the PCB and the display. (see Figure 2 for anexample with a 128 segment display and 36 connections).Fig 2.SMD LCD display with fixed pinsIn Figure 3 the construction of an SMD LCD with elastomeric connectors (ZEBRA) isillustrated.Metal or plastic bezel,to clamp down the LCD cellZEBRA: elastomeric siliconeconnector making contactwith the tracks (usually goldplated) on the PCB.Printed Circuit Board (PCB)Fig 3.Illustration of an SMD LCD with elastomeric connectorR 10015White paper NXP B.V. 2012. All rights reserved.Rev. 2 — 18 June 20122 of 18
R 10015NXP SemiconductorsChip-On-Glass (COG) - a cost-effective and reliable technologyThe SMD display consists of the LCD cell, a metal or plastic bezel which clamps down theLCD cell onto the elastomeric connector (ZEBRA) which then makes the contact with thetracks on the PCB. The ZEBRA connector is composed of fine pitch conductive segmentsalternating with isolating segments, embedded between 2 isolating strips. The bezel,metal or plastic, applies as a force and squeezes the ZEBRA slightly to guarantee a firmcontact between the LCD and the PCB.R 10015White paper NXP B.V. 2012. All rights reserved.Rev. 2 — 18 June 20123 of 18
R 10015NXP SemiconductorsChip-On-Glass (COG) - a cost-effective and reliable technology3. Chip-On-Glass LCD conceptA COG module consists of: A display glass that represents the active display area. A seal ring around the display glass which protects and seals the display glass. A contact ledge which gives room for the LCD driver IC.The LCD driver IC itself generates the display control and the driving signals. A Flex PanelConnector (FPC) connects the display driver IC to the microcontroller (see Figure 4).Seal ring round the display glassActive display areaContact ledgeLCD driver/controllerFlex panel connector013aaa514Fig 4.COG LCD moduleIn a COG module, one of the two glass plates that make up the LCD is extended to giveroom for an LCD driver to be mounted and connected (see Figure 4 and Figure 5). Theconnections to the display are realized with Indium Tin Oxide (ITO) electrodes which areintegrated on the surface of the glass plates and connected via an Anisotropic ConductiveFilm (ACF) to the gold bumps mounted on the connecting pads of the driver IC.R 10015White paper NXP B.V. 2012. All rights reserved.Rev. 2 — 18 June 20124 of 18
R 10015NXP SemiconductorsChip-On-Glass (COG) - a cost-effective and reliable technologyLCD cellgold bumpsepoxy underfillchipITOsilver dotFig 5.glassanisotropicconductive filmIllustration of a COG LCD moduleCOG technology sets very few limitations on the LCD module design: For COG, an uncased display driver IC (display driver without a package) is sufficient;the only requirements are that the display driver IC has gold bumps to enable thecontact to the ITO tracks on the LCD glass. The placement of the LCD driver IC can be on any side of the active display area. Thisallows placing the LCD driver IC on the smaller side to minimize the required contactledge and with that save cost. The COG technology allows the cascading of several LCD driver ICs directly on thecontact ledge in order to allow for driving larger display resolutions. COG technology allows for connecting the display to the PCB wherever it is mostsuitable, even some distance away from the microcontroller.R 10015White paper NXP B.V. 2012. All rights reserved.Rev. 2 — 18 June 20125 of 18
R 10015NXP SemiconductorsChip-On-Glass (COG) - a cost-effective and reliable technology4. Surface-Mount Device compared to Chip-On-Glass4.1 Components and design effortIn the following an SMD and a COG display system will be compared (see Figure 6). Inthe SMD concept, the display as well as the display driver are directly mounted onto thePCB. In the COG concept, the display driver is mounted onto the display module and alsoconnected to the PCB via a Flex Panel Connector e-mount-device (SMD)chip-on-glass (COG)a. Surface-Mount DeviceFig 6.PCBb. Chip-On-GlassSurface-Mount Device compared to Chip-On-GlassThe two systems require the following components (see Table 1).Table 1.ComponentsSurface-Mount Device (SMD) Chip-On-Glass (COG) PCBMicrocontrollerCased LCD driver ICPCBMicrocontrollerSMD display, consisting of (see Figure 3):COG display module, consisting of (seeFigure 5):– Bezel– LCD cell– LCD cell– Uncased LCD driver IC (die with goldbumps)– Elastomeric connectors (ZEBRA)– Anisotropic Conductive Film (ACF)– FPCGiven these components, the following design and effort considerations must be takeninto account (see Table 2).R 10015White paper NXP B.V. 2012. All rights reserved.Rev. 2 — 18 June 20126 of 18
R 10015NXP SemiconductorsChip-On-Glass (COG) - a cost-effective and reliable technologyTable 2.Design and effort considerationsSurface-Mount Device (SMD) Chip-On-Glass (COG) PCB space:– Sufficient space on the PCB is requiredto accommodate the cased LCD driverIC as well as the SMD display Connectors and Connections:– No space on the PCB is required for theLCD driver IC or for the COG LCD– Space is only required for the Flex PanelConnector (FPC) – Only very few connections (supplies,bus) are required between themicrocontroller and the connector of theCOG LCD module– An elastomeric connector (ZEBRA) orfixed pins are required to mount theSMD LCD cell onto the PCB– Flex Panel Connector (FPC) Display location: Driver IC location:Flexibility/upgradability:Soldering, inspection and verification:– Soldering, inspection and verification ofcased LCD driver IC and SMD display isrequiredDriver IC location:– The uncased LCD driver must belocated on the COG LCD glass – No flexibility/upgradability toreplace/upgrade the cased LCD driverIC and/or SMD display easily Display location:– Location of the COG LCD module isunconstrained– The cased LCD driver should ideally beplaced as close to the SMD display aspossible to avoid disturbances on theLCD driving signals Connectors and Connections:– Many connections (supplies, segments,backplanes) are required on the PCBbetween the cased LCD driver IC andthe SMD display– The location of the display cell is boundto the PCB PCB space:Flexibility/upgradability:– High flexibility in changing/upgrading theCOG LCD module (simply exchange themodule and the driver software) Soldering, inspection and verification:– Soldering, inspection and verification ofthe LCD driver IC and the Flex PanelConnector (FPC) to the COG LCDmodule requiredRemark: In the Chip-On-Glass case specific design guidelines have to be followed toensure sufficient ESD and EMC immunity of the LCD module (see Ref. 1 “AN10170” andRef. 3 “AN10853”).R 10015White paper NXP B.V. 2012. All rights reserved.Rev. 2 — 18 June 20127 of 18
R 10015NXP SemiconductorsChip-On-Glass (COG) - a cost-effective and reliable technology4.2 Considerations with respect to costWith respect to cost, the following considerations can be made (see Table 3):Table 3.Cost considerationsSurface-Mount Device (SMD) Chip-On-Glass (COG)Less complex and likely smaller PCBCased LCD driver (with package) required Soldering, inspection and verification of theLCD driver and the SMD display required Only soldering, inspection and verificationof the connector to the COG LCD modulerequired Larger LCD glass required to accommodatethe uncased LCD driver Anisotropic conductive film required toconnect the uncased LCD driver to the ITOtracks on the display glassMore complex and likely larger PCB Smaller display glass (no extra space to theactive area needed) Bezel and elastomeric connector requiredto connect the SMD display to the tracks onthe PCBUncased LCD driver (die with gold bumps)is sufficientFrom Table 3, four key parameters2 can be identified which are determining the cost of anSMD or COG display system:1. the PCB,2. the LCD driver,3. the display glass,4. material and assembly.1. PCB: The PCB is a major cost factor; the larger and the more complex a PCB(number of layers, number of vias), the more costly. By moving from an SMD LCDmodule to a COG LCD module, the PCB can be off-loaded from the display moduleand the display driver, saving board space and reducing board complexity. This willhelp to reduce overall system cost.2. LCD driver: The LCD driver is also a major contributor to the cost. A large portion ofthe driver cost originates from the package. When moving from a cased LCD driver toan uncased LCD driver, considerable cost can be saved (see Figure 7). HoweverFigure 7 doesn’t reflect the additional cost for the gold bumps which are needed for aCOG LCD module:2.Note: For the following, the microcontroller is excluded.R 10015White paper NXP B.V. 2012. All rights reserved.Rev. 2 — 18 June 20128 of 18
R 10015NXP SemiconductorsChip-On-Glass (COG) - a cost-effective and reliable technology100%90%80%70%60%50%40%30%20%10%0%Package Cost128Fig 7.160240Share of package cost on total display driver cost as function of total number ofdisplay elementsMoreover, the higher the number of package pins, the higher the package cost,whereby the relationship is exponential (see Figure 8):48Fig 8.566480100Package cost as function of number of pinsAs a result, the package cost per display element increases when the number ofdisplay elements driven from a single package increases (see Figure 9):128Fig 9.160240Package cost per display element as function of total number of display elements3. Display glass: The display glass is the next major contributor to the cost of the LCDmodule and is directly proportional to the display area. In the COG case, additionalglass area is required to accommodate the LCD driver IC. The size of this additionalR 10015White paper NXP B.V. 2012. All rights reserved.Rev. 2 — 18 June 20129 of 18
R 10015NXP SemiconductorsChip-On-Glass (COG) - a cost-effective and reliable technologyarea heavily depends on (1) the physical dimensions of the driver IC and (2) theX-Y-dimensions of the LCD cell. Ideally the driver IC is designed as long as possibleto minimize its width. The less wide the driver IC, the less wide the additionallyrequired glass area. Most NXP COG LCD driver ICs are designed with this objectivein mind - long but less wide for lowest glass cost (see Figure 10).display-areadisplay-areasaved glass areaaaa-003205Fig 10. Required display area depending on the driver IC sizeTo reduce cost further, the display driver IC should ideally always be placed on thesmaller side of the active display area (see Figure 11): Suboptimal arrangement: display driver IC placed on the long side of the displaySegment TracksBackplane TracksSegment TracksBackplane Tracks Optimized arrangement: display driver IC placed on the short side of the displaySegment TracksBackplane TracksSegment TracksFig 11. Placing of display driver IC on the displayTo have full flexibility in doing so, the display driver IC should ideally have backplaneoutputs on both sides of the IC. All latest NXP COG display driver ICs are designedwith this objective in mind - two sets of backplane outputs, one on each long side ofthe IC (see Figure 12).R 10015White paper NXP B.V. 2012. All rights reserved.Rev. 2 — 18 June 201210 of 18
R P5BP4BP3BP2BP1BP0Chip-On-Glass (COG) - a cost-effective and reliable technologyS0S1NXP Semiconductors y 0SYNC0PCA8538UFig 12. Example of backplane location on an NXP COG display driver4. Material and assembly: In terms of material and assembly a COG LCD solution ismore cost-optimized compared to an SMD LCD solution. In the COG case, there is noneed for placing and soldering the LCD cell and the LCD driver onto the PCB,avoiding the cost of this processing step along with the cost for inspection andverification. Also in terms of material, depending on the number of connections to thedisplay, in the SMD case a considerable number of connectors (supplies, segments,backplanes) are required between the PCB and the LCD cell whereas in the COGcase only the supplies and interface pins must be connected.R 10015White paper NXP B.V. 2012. All rights reserved.Rev. 2 — 18 June 201211 of 18
R 10015NXP SemiconductorsChip-On-Glass (COG) - a cost-effective and reliable technology4.3 Case Study: Cost-structure of SMD compared to COGIn the following, the cost structure of SMD versus COG shall be further analyzed andcompared, based on a calculation model of a 160 segment TN LCD with a size of40 mm 24 mm. The display is assumed to be driven by a PCF8576DU in the COG case(40 4 LCD segment driver), and a PCF85176 in the SMD case (40 4 LCD segmentdriver for industrial applications, housed in a TSSOP56). In the SMD case, the display hasits original size (40 mm 24 mm). In the COG case, the display area is slightly bigger(40 mm 26 mm) as the driver has to be placed on the glass, which requires 2 mmadditional width. In this example, a PCB type FR4 is taken as a basis. The area in theSMD case is assumed to be 80 mm 40 mm; in the COG case the area is64 mm 40 mm.For an equivalent comparison both modules (SMD and COG) use Flex Panel Connectors(FPC) as shown in Figure ount-device (SMD)chip-on-glass (COG)aaa-002681Fig 13. LCD modules for cost comparisonA qualitative and quantitative analysis is done for the following cost parameters (1) LCDglass, (2) LCD driver IC, (3) PCB area, and (4) material, assembly, and testing (seeTable 4).Table 4.Cost parameters (see Figure 13)Surface-Mount Device (SMD) Chip-On-Glass (COG) LCD:– type TN – type TN LCD driver IC:– PCF85176 cased in TSSOP56 PCB area– PCB type FR4Material, assembly and testing: Material, assembly and testing:– Flex Panel Connector (FPC)– Flex Panel Connector (FPC)– Assembly FPC– Assembly FPC– Testing– IC bonding– Soldering– Testing– Misc.– Misc.R 10015White paperLCD driver IC:– PCF8576DU as bare die with bumps PCB area– PCB type FR4 LCD: NXP B.V. 2012. All rights reserved.Rev. 2 — 18 June 201212 of 18
R 10015NXP SemiconductorsChip-On-Glass (COG) - a cost-effective and reliable technologyIn Table 5, the cost and share structure of SMD versus COG will be compared. It showsthe cost structure and the percentage share of the different components as listed inTable 4.Table 5.Cost and share structureMatter of expenseTypeX (mm)Y (mm)A (cm2)QuantityCost share (%)Surface-Mount Device (SMD)LCDTN40249.6118Driver IC (TSSOP56)PCF85176---134PCBFR4804032125Flex Panel Connector (FPC)(number of tracks)----4412IC bonding (ACF)ACF---00Assembly LCDTN402610.4124Driver IC (bare die with bumps)PCF8576DU ---123PCBFR4644025.6125Flex Panel Connector (FPC)(number of tracks)----510Chip-On-Glass (COG)IC bonding (ACF)ACF---16Assembly [1]Source of the cost content of the driver and driver type is NXP; an established module manufacturer provided the cost and characteristicof the display, PCB, material, assembly, and testing.Figure 14 compares one on one the costs on each matter of expense. It shows that thelargest cost saving can be achieved with the display driver IC because in the COGconcept, it doesn’t have a package. On the other hand the COG concept requires anincreased display glass area. This reflects the increased cost on the COG side of thebalance. As shown in Figure 7, the package represents between 47 % and 62 % of thedriver cost, depending on the number of display elements.R 10015White paper NXP B.V. 2012. All rights reserved.Rev. 2 — 18 June 201213 of 18
R 10015NXP SemiconductorsChip-On-Glass (COG) - a cost-effective and reliable technology1.210.8SMD0.6COG0.40.20LCD cellDriver ICPCBFPCIC bondingAssemblyTes ngMiscFig 14. Normalized COG and SMD cost share structureIn this example, the overall cost saving amounts to 18 % in favor of COG (see Figure 15).However, the actual cost savings depend on many parameters including the profit marginsof the respective component suppliers which have not been taken into account in thismodel; altering these parameters will also alter the cost savings.18 %Cost savingMaterial Assembly TestingPCB areaDriver ICLCD displayCOG CostSMD CostCOG cost saving: 18 % in this example.Fig 15. Cost comparison COG vs. SMDR 10015White paper NXP B.V. 2012. All rights reserved.Rev. 2 — 18 June 201214 of 18
R 10015NXP SemiconductorsChip-On-Glass (COG) - a cost-effective and reliable technology5. Summary and ConclusionsThe Chip-On-Glass (COG) technology is an alternative design methodology where theLCD driver is directly mounted on the display glass. COG has significant advantagescompared to conventional methods like Surface-Mount Device (SMD). Removing the LCDdriver from the PCB relaxes the complexity of the PCB, ruggedizes the reliability,enhances the flexibility of the application design and redesign and therefore lowers thesystem costs. COG is a very reliable and well established technology, which is often usedin the automobile industry.Table 6.Summary of SMD compared to COGSurface-Mount Device (SMD)Chip-On-Glass (COG) Cased LCD driver IC: in a packagesoldered directly on the PCB Uncased LCD driver IC: bare die mounteddirectly on the display All connections have to be designed on thePCB The LCD module contains everything todrive the display Erratic arrangement of PCB and LCD The modularized constructionIncreased BOM– separates the functional parts of thePCB from the display connected via aFlex Panel Connector (FPC)More complex inventory handling– increases the flexibility in the design ofthe PCB and the application– allows the reuse of the LCD module inthe case of a redesign or in a newapplication design– simplifies the assembly process Lowered cos
NXP Semiconductors Chip-On-Glass (COG) - a cost-effective and reliable technology 4. Surface-Mount Device compared to Chip-On-Glass 4.1 Components and design effort In the following an SMD and a COG display system will be compared (see Figure 6). In the SMD concept, the display as well as the display driver are directly mounted onto the PCB.
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designers in these areas should strongly consider using Chip-on-Glass (COG) LCD modules. Chip-on-Glass (COG) LCD modules offer a very thin profile, enhanced reliability, and a reasonable price. Figure 1. COG Module flexible design, and are more Abstract: For industrial, automotive, and portable equipment designers, Chip-on-Glass (COG) liquid
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All Seal Smart glass packages are constructed using a full 1" overall Insulated Glass unit thickness. CH oo SING Y o UR GLASS Seal Smart SYSTEM The most basic type of insulated glass. This glass system is comprised of two pieces of clear glass with the space between the glass filled with air. Seal Smart includes Intercept Spacer as a standard .
Wired glass. Patterned glass. Etched, sandblasted, drilled, notched or grooved glass. Assumptions The procedures defined by ASTM E1300-02 include the following assumptions. Glass is properly glazed and free of edge damage. Glass has not been subjected to abuse. Surface condition of the glass is typical of in-service glass.
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10.3.5 Connecting ADC and DAC IPs into a Cortex-M system 242 10.4 243Bring an SoC to life – Beetle test chip case study 10.4.1 Beetle test chip overview 243 10.4.2 Beetle test chip challenges 245 10.4.3 Beetle test chip system design 246 10.4.4 Implementation of the Beetle test chip 24
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