COG vs COB LCD Modules: Construction Compared

HZY Engineering Notes · 2026-10-08

The choice between a COG and a COB LCD module is one of the first decisions a hardware engineer or buyer makes when specifying a monochrome display. Both constructions can run the same LCD glass and the same controller logic, yet they differ in thickness, mechanical robustness, repairability, and how cost scales with format and volume. This article compares chip-on-glass and chip-on-board construction, explains where the cost drivers sit in each, and gives practical selection guidance for instruments and meters.

What COG and COB Actually Mean

The acronyms describe where the display driver sits relative to the LCD glass.

Chip-on-Glass (COG)

In a COG module, the driver IC is mounted directly on the ITO traces of the LCD glass and connected by anisotropic conductive film (ACF) bonding. The chip is a bare die, so there is no package, no lead frame, and no separate PCB carrying the driver. The glass itself becomes the carrier for the electronics. External connection to the host board is typically made through an FPC or a small interface board, with the parallel 8080 bus, SPI, or another serial interface brought out to the connector.

Because the die footprint is bonded onto the glass edge, the module outline can be reduced to little more than the viewing area plus a narrow border. This is the construction behind compact COG LCD modules used in handheld instruments, portable meters, and small panel meters where depth and bezel space are tight.

Chip-on-Board (COB)

In a COB module, the driver IC is mounted on a PCB and wire-bonded, then encapsulated with an epoxy blob. The LCD glass is connected to that PCB by elastomeric zebra connectors or metal pins. The PCB carries the driver, the interface connector, and any passive components, so the electronics are physically separate from the glass.

COB is the traditional construction for character and graphic modules in through-hole and pin-header formats. It is mechanically taller than COG because the stack includes glass, connector, and PCB, but it is also easier to handle, socket, and replace on an older through-hole board. Character modules such as 1602 formats with HD44780-class controllers are commonly built this way; see the COB LCD module range for the standard formats available.

Thickness, Mechanical Stack, and Robustness

The most visible difference is the z-height. A COG module is essentially glass plus a thin FPC, often a few millimetres total. A COB module adds the zebra connector and PCB, so the stack is noticeably deeper and the module usually occupies a larger footprint because the PCB extends beyond the glass for mounting holes and connectors.

That difference cuts both ways in mechanical design:

• COG saves depth and bezel space, which matters in handheld enclosures, DIN-rail instruments with shallow cases, and products where the display sits close to a front membrane.
• COB offers a rigid PCB as the mounting datum. Screw bosses, connectors, and mounting holes are all on the board, so the module tolerates being handled, socketed, and reworked during assembly.
• COG glass is more exposed. The bonded die and the glass edge need care during handling; the module should be supported and the FPC strain-relieved in the enclosure design.
• COB is the more forgiving choice for products assembled by hand or serviced in the field, since a failed module can usually be unplugged and replaced without touching the glass.

For instruments with a sealed front lens and a fixed internal stack, COG is usually the cleaner mechanical fit. For bench meters, controller boards, and equipment with a pin-header display connector, COB remains the simpler integration.

Cost Drivers: Where the Money Goes

Cost in monochrome modules is driven by glass area, driver die, interface, tooling, and volume — not by the COG/COB label alone.

Glass and die area

The LCD glass area sets the bulk of the material cost, and a larger viewing area needs a larger driver with more output pins. A small COG module with a modest resolution can be very economical because the die is small and there is no PCB. As the resolution and glass size grow, the driver die grows with it, and the bonding cost per module rises. COB spreads the driver and passives over a PCB, which scales less aggressively for some formats but adds board area and assembly steps.

Interface and connector

A COG module using a serial interface such as SPI keeps the FPC small and the pin count low. A COB module with a parallel 8080 or MPU interface needs a wider connector and more PCB traces, which adds cost. Specifying the narrowest interface the application can tolerate is one of the most effective cost levers in either construction.

Tooling and minimum order

Custom glass and custom FPC tooling are one-time costs that amortise with volume. Standard listed formats avoid that tooling entirely, which is why catalogue COG and COB modules remain attractive for low and mid volumes. For custom segment displays, the tooling is quoted per design. Buyers comparing quotations should separate tooling from unit price and check what volume the unit price assumes.

Assembly and test

COG bonding is a specialised process — ACF attach and die bond — and its cost per unit is relatively fixed regardless of module size. COB assembly is a more conventional SMT and bonding flow on a PCB. In both cases, test coverage contributes to cost. A supplier that runs 100% functional inspection before shipment is building that step into the price, and it is usually worth paying for in instrument applications where a dead pixel line means a field return.

Repairability and Serviceability

Neither construction is designed for component-level repair in the field. The practical question is what happens when a module fails.

A COB module is generally replaceable as a unit: it plugs into a header or connects through a wire harness, and a service technician can swap it. The PCB also protects the driver and bond wires under epoxy, so handling damage is less likely during installation.

A COG module is bonded to its FPC and is replaced as a glass-plus-FPC assembly. Because there is no socket, the FPC connector on the host board becomes the service point. This is fine for sealed products that are replaced rather than repaired, and for designs where the display is not expected to be serviced separately. For repairable industrial equipment, designers should decide early whether the display is a field-replaceable unit and choose the construction accordingly.

Typical Formats in Each Construction

The two constructions have settled into different format niches.

COG formats

COG suits small to medium graphic displays with fine pitch and compact outlines. A representative example is a 128x64 COG module with an ST7567 controller and a 28.5 x 20.0 mm outline — a common fit for portable meters, thermometers, and small analysers. COG is also used for higher-resolution monochrome graphics where a fine-pitch die and a narrow border matter. Standard monochrome graphic sizes across COG and COB include 128x64, 192x64, 240x128, and 240x160; see the graphic LCD module range for the full list.

COB formats

COB dominates character modules and larger graphic modules where a pin-header or connector interface is expected. Character formats such as 8x2, 16x2, 20x2, 16x4, 20x4, and 40x2 are typically COB, with the 1602 family using HD44780-class controllers. These modules are widely used in bench instruments, power supplies, industrial controllers, and older designs where the display connects to a through-hole board.

Interface options track the construction. COG modules commonly use SPI, QSPI, or parallel 8080; COB modules typically use parallel MPU or 8080 interfaces, with serial variants available on some controllers. Driver selection follows the format — the ST7567 for many monochrome graphics in our range, HD44780-command-set controllers (ST7066U class) for character modules — and the interface should be matched to the host MCU early, because changing it later can affect both the FPC and the firmware.

Selection Guidance for Instruments and Meters

The following decision path covers most instrument and meter designs.

Choose COG when:

• Depth and bezel space are constrained, such as handheld or shallow-case instruments.
• The display is small to medium resolution and a serial interface keeps the FPC and pin count low.
• The product is sealed and the display is not intended to be serviced separately.
• You need a compact graphic format, for example a 128x64 COG with ST7567, in a narrow outline.
• Operating temperature is within the module's rating; monochrome modules in this class commonly cover -30 to +80 °C, but confirm the exact module.

Choose COB when:

• The host board uses a pin-header or socketed display connection.
• The product is assembled or serviced in the field and the display may be replaced as a unit.
• You need a standard character format such as 16x2 or 20x4 with a familiar controller and interface.
• Mechanical robustness during handling and assembly is a priority.
• The enclosure has enough depth to accept a PCB-backed module.

Questions to settle before requesting a quote

• Viewing area and resolution, plus the outline the enclosure allows.
• Interface: SPI, QSPI, parallel 8080, or MPU, and the host voltage.
• Viewing direction and polariser type — transmissive, transflective, or reflective — matched to the lighting environment. Transflective is often the right choice for outdoor meters.
• Operating temperature range and any backlight requirement; LED backlights are available in red, white, blue, green, yellow, and amber, including special shapes.
• Whether the display must be field-replaceable, which usually pushes the decision toward COB.
• Expected annual volume, so tooling and unit price are quoted on the same basis.

For designs that need colour rather than monochrome, the same supplier builds TFT modules from 0.71 inch to 10.1 inch, including transflective TFTs in 2.4, 2.8, 3.7, and 5.0 inch for sunlight-readable instruments. A common volume example is a 2.4 inch 240x320 SPI TFT; other options include a 1.3 inch 240x240 ST7789V2 SPI module and a 4.3 inch 800x480 RGB panel at 600 cd/m². These are separate from the COG/COB decision but often sit in the same product family.

Customisation and Lead Times

Both constructions support customisation of size, brightness, interface, FPC and backlight. A typical custom flow runs drawings in about three days, samples in about two weeks, and mass production in about five to six weeks. Standard listed models can start from very small quantities, while custom projects are quoted per design. Quality systems include ISO 9001, IATF 16949, and ISO 14001, with certificates available upon request.

If you are weighing COG against COB for an instrument or meter, send your panel requirements or target specification to our contact page — viewing area, resolution, interface, temperature range, and expected volume are enough for us to recommend a construction and a starting format.