Chip Scale Packaged (Flip Chip) LEDs, a new LED technology

Usually, a light emitting diode (LED) has two key components, the LED chip that emits the light and the LED package which focuses it, enables assembly into lighting products and transfers the heat away to the heat sink.

Some common examples of packaged LED with power from 0.2 Watt or less (Mid-Power LED), to 10 Watt or less (High-Power LED) or 2 to 50 Watt for Chip on Board LEDs (COB).

Large LED manufactures design and build both LED chips and packaged LEDs. Small manufactures usually purchase LED chips and assemble them into packaged LEDs. This explains the enormous, sometimes confusing, variation in packed LEDs specification, performance and quality. Packaged LED attributes are defined by both chip and package design and production.

This picture has now got even more complicated with the increasing market penetration of Chip Scale Packaged LEDs, known as CSP or flip-chip LEDs.

If we consider a packaged LED to be the automobile with the LED chip its engine then a CSP LED is an engine on wheels, with minimum body work or other components.

A mid-power LED package (left) compared to CSP LED (right). Everything except the LED chip, yellow phosphor and connection pads have been removed. This process has results in a significant reduction in scale, leading to further miniaturization of LED based lighting.

Below, some examples of Samsung CSP LEDs, with different single variations and two array types (2x2 and 3x3).

 This bare-bones approach to LED structure has two goals: lower cost and more efficient heat transfer. In theory, this can result in a CSP LED fixture with lower price and a slimmer design compared with one that uses a packaged LED.

A CSP LED also has by default a wider viewing angle, of up to 180 degrees because the phosphor is applied on the sides too (see image below). This can be very important advantage for applications such as back light modules, replacement of traditional form factor lamps and tubes.

Even with these summed up advantages critics of CSP LED technology exist. They point out that CSP LED production will shift more tasks to LED chip manufacturers, as they will take the role of packaged LED manufacturers. Some might get overburdened or do a bad job.  

With CSP technology the package supplier disappears, together with many of production process (above, in red) while some move to the die supplier or integrator. Smaller packaged LED manufacturers that use third party chip will be kicked out of the market.

The ultra wide viewing angle of up 180 degrees is also mentioned as a disadvantage in the case of some applications. For CSP to be suitable it requires more optics with effect on product cost, or blocking of all the light emitting sides but the top with a hit at luminous efficacy.

Samsung CSPs for automotive applications.

While chip scale LEDs have been theorized for almost a decade, market ready CSP have only started to appear last year. Predictions for the near future range from the overly optimistic "CSP will replace both high power and middle power LEDs" to realistic/pessimistic "CSP will find find a niche in display, camera flash or street lighting".

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