SMD LED vs COB LED vs DOB LED – 3 Options for LED PCBs

RF & Microwave - 2 April 2024 - 3:50 am

What are SMD LEDs?

SMD (Surface Mounted Device) LEDs are the most widely used type of LED package. As the name implies, SMD LEDs are mounted directly onto the surface of a printed Circuit Board. Some key characteristics of SMD LEDs include:

Small package sizes down to 0201 (0.6mm x 0.3mm)
Wide range of available colors, brightnesses, and viewing angles
Machine placeable using standard SMT equipment and processes
Low cost and widely available from many suppliers

SMD LEDs come in various package sizes and formats. Some common ones are:

Package	Dimensions (mm)	Typical Power
0201	0.6 x 0.3	0.1W
0402	1.0 x 0.5	0.1W
0603	1.6 x 0.8	0.1W
0805	2.0 x 1.25	0.2W
1206	3.2 x 1.6	0.2W
3528	3.5 x 2.8	1W
5050	5.0 x 5.0	1W

SMD LEDs offer the most compact sizes and lowest costs. They are the best choice for most general indicator light and low-power illumination applications on PCBs.

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What are COB LEDs?

COB (Chip-on-Board) LEDs have the bare LED die bonded directly to a PCB Substrate or sub-mount, which is then encapsulated. Multiple dies can be packed closely together under a single encapsulation. Some distinguishing features of COB LEDs are:

High packing density enables very high luminous flux and intensity
Large light emitting surface produces “area lighting” effect
Simplified construction improves reliability and thermal management
Lower component count reduces assembly costs
Often custom-made for specific applications

COB LEDs are available in standard sizes like:

Size	Typical Chip Quantity	Light Emitting Surface (mm)	Typical Luminous Flux
3W	3-9	2.8 x 2.8	180-500 lm
5W	5-15	3.5 x 3.5	300-800 lm
7W	7-21	5.4 x 4.5	600-1200 lm
12W	12-36	6.5 x 7.0	1000-1800 lm

However, custom sizes and configurations are common to meet the needs of specific applications like spotlights, downlights, work lights, grow lights, etc.

The concentrated arrays of chips in COB LEDs make them suitable for applications requiring high lumen output in a small space. They are commonly used for indoor and outdoor area lighting, stage lighting, automotive headlamps, and more.

What are DOB LEDs?

DOB (Die-on-Board) LEDs have a similar structure to COB LEDs in that the bare die is mounted directly on a PCB. However, DOB LEDs have each die individually encapsulated rather than multiple dies under a single encapsulation. Some important attributes of DOB LEDs include:

Higher maximum drive current than SMD
Large area contacts improve thermal management
Undomed encapsulation enables flush mounting
Smaller footprint than COB for equivalent lumen output
Easier color mixing in RGB arrays

Like COBs, DOB LEDs are available in standard sizes but custom configurations are common. Some typical sizes are:

Size	Chip Quantity	Dimensions (mm)	Typical Luminous Flux
1W	1	3.5 x 3.5	100-130 lm
3W	1	6.8 x 6.8	200-260 lm
10W	1	12 x 8	800-1000 lm
10W RGB	3	12 x 8	300 lm

The ability to pack more power into a smaller space than SMD LEDs makes DOB LEDs a good choice for applications like LED bulb replacements, track lighting, light engines and more. Full color DOB arrays are popular for decorative lighting.

Comparison of SMD, COB and DOB LEDs

Here is a summary comparing the key characteristics of SMD, COB and DOB LEDs:

Feature	SMD	COB	DOB
Package Sizes	0201 to 5050	Custom & std sizes	Custom & std sizes
Packing Density	Low	Very high	High
Lumen Output	Low-Medium	High	High
Thermal Management	Poor	Very good	Good
Color Options	Many	White, limited colors	White & RGB common
Cost	Low	Medium-High	Medium
Best Uses	Indicators, backlights	Area lighting, spotlights	Bulbs, light engines

SMD LEDs offer the smallest sizes and lowest costs but are limited in power and light output. COB LEDs enable the highest luminous flux and intensity in a small footprint. DOB LEDs provide a balance of high power and small size.

FAQ

1. Can SMD LEDs be used for lighting applications?

Yes, SMD LEDs are commonly used for lighting applications that don’t require very high brightnesses, such as backlighting, linear lighting, accent lighting, and more. High-power SMD packages like 5050 are popular for these uses. However, COB and DOB LEDs are better suited for applications demanding higher lumen outputs.

2. Are COB LEDs more expensive than SMD and DOB?

In general, yes. The specialized packaging and assembly processes used for COB LEDs make them more costly than SMD LEDs. DOB LEDs sit in between, with costs higher than SMD but usually lower than COB. However, the total system cost may be lower with COB or DOB vs SMD in high power applications due to needing fewer LEDs to achieve the same light output.

3. Which is better for heat dissipation – COB or DOB?

Both COB and DOB LEDs have very good thermal characteristics compared to SMD. In a COB LED, the dies are mounted very close together which helps with heat spreading across the PCB. DOB LEDs have a larger footprint for the same lumen output as COB which increases the surface area for heat dissipation. Both types usually require additional heatsinking.

4. Are there standard PCB land patterns for COB and DOB LEDs?

For the most part, no. COB and DOB LEDs are usually custom designed for a specific application and don’t have standardized PCB land patterns like SMD LEDs do. The LED manufacturer will provide application notes with recommended PCB Designs and assembly information. Some standard sizes of COB and DOB are emerging but custom is still the norm.

5. What type of LED is best for color mixing?

DOB LEDs have an advantage for color mixing because each die is individually encapsulated. This allows for denser packing of different color dies than is possible with SMD LEDs. And precise placement of each color is easier than with the multi-die encapsulations used in COB LEDs. DOB is the most common type for RGB color mixing applications.

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