Achieving miniaturisation success

26th September 2018

Alex Lynn

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As LEDs continue to shrink in size, there is a need for materials that dissipate heat quickly and solutions to ensure the effective electrical connection of micro LEDs. At the International LED professional Symposium 2018, Heraeus shows how this can be achieved.

It is a major trend. Light-emitting diodes (LEDs) are becoming ever smaller.

Stefan Mausner, Segment Marketing Manager at the 2018 International LED professional Symposium (LpS) in Bregenz, explained: “This opens up entirely new possibilities for fitting LEDs even more closely together, which is particularly advantageous for applications requiring high luminance.”

Examples include vehicle headlights and UV LED modules, which contain very tightly packed LEDs for exceptional brightness and high energy density.

Mausner added: “This progressive miniaturisation, however, also brings with it a number of technical challenges, which must not be underestimated.”

The specific question facing manufacturers is how to successfully connect micro LEDs, which can have an edge length of less than 150µm, successfully connected electrically when standard solder materials are no longer suitable?

Sinter paste for effective heat dissipation

Heat can be transported from the LED chip to the ceramic or metal substrate via the die-attach material, which connects the chip. Heraeus has specially developed a sinter paste for LED applications, which has a thermal conductivity value twice as high as gold-tin or tin-silver alloys. The heat loss can therefore be dissipated much faster, resulting in higher luminous efficacy and ultimately protecting the LED chip from damage.

Ultra-fine solder pastes for electrical connection

Extremely fine materials are required to electrically connect the micro LEDs on the backplane, as micro LEDs can have an edge length of less than 150µm. Conventional solder pastes, with particle sizes of between 20 and 45µm, cannot meet the bond line thickness and stencil opening requirements, meaning that solder alloys with a particle size of less than 11µm are called for. Heraeus WS5112 type seven solder paste, made with patented Welco solder powder, allows the printing of tiny solder bumps of up to 50µm.