As the name implies, Flip Chips are LEDs where the semiconductor has been flipped over. In other words, it has been turned face down.
The advantages over traditional LEDs are innumerable and some were mentioned in the previous post. The semiconductor is connected by multiple paths to the anode and cathode so that the mechanical robustness is reinforced, avoiding the fragility of the individual bounding.
In terms of thermal resistance, a direct contact with the anodes and cathodes allows the more efficient evacuation of heat. It is possible to reduce this resistance by almost a third, allowing higher currents for the same temperature.
The new lines of research are focusing their efforts on implementing a third dissipation pad so that the LED is directly connected to the IMS (Insulation Metal Substrate), reducing thermal barriers and improving the flow of heat to the exterior:
Wire-bond (a), conventional flip chip (b) and a 3-Pad LED flip chip (c)
This reduction of the thermal resistance also facilitates the construction of LED arrays with elements closer together, making it possible to improve the performance in terms of lm/mm2. This type of array is called COB (Chip On Board).
Finally, let’s not forget one of the initial objectives of this new technology, namely to reduce costs. Since most of the encapsulation is dispensed with, the economic improvement is direct.
So far it seems that these LEDs are the perfect solution, but unfortunately it’s not all advantages. Like any new technology, the return on investment in research and the lack of mass production capabilities make the final product considerably more expensive.
Similarly, from an EMS ( Electronic Manufacturing SErvices) point of view, the handling and manufacture of circuits with this type of LED requires more care and more precise tools, as well as an optimal design of the PCB ( Printed circuit board).
The silicone encapsulation presents a challenge for P&P machines since the pressure exerted on it directly affects the semiconductor.
Finally, from an optical point of view, the fact that they are covered by a silicone surface and not by a primary lens (especially in high power versions), raises well-justified doubts about the quality of light, due to the effect known as aberration.
That’s why this technology still has a long way to go. And it’s an area in which IKOR has already been working for a long time, both in the development of the technology and also investing in means of production. We are already in a position to offer our customers design and EMS services for CSP-based solutions.