Packages with promise

Will new LED packages bring brighter devices? Finland-based Inkron is poised to deliver this and more, reports Compound Semiconductor.

Siloxane-based encapsulants are set to boost LED light efficacy and take packaging processes into the future.

At a time when LED manufacturers are looking to squeeze every last ounce of performance out of their chips, many in the industry are turning to packaging to boost device efficiencies further. Today's high brightness LEDs typically come wrapped up in a robust, silicone encapsulant, but is this still enough?

On the plus side, the material provides optical clarity when exposed to heat and humidity, offering solid photo-thermal stability throughout an LED's lifetime. It also delivers high optical transmittance in the UV-visible wavelength regions, ensuring LED light is transmitted efficiently through the silicone material.

Crucially, the material can be synthesized as single-chain polymer with a range of different attached organic groups, to tailor its refractive index and boost light-extracting efficiency. But as LED technology matures and demands for ever-higher efficiencies continue to grow, industry wants more.

As Juha Rantala, chief executive of Inkron, a Finland-based developer of pastes, inks and dielectrics for electronics devices, puts it: "Our view is that the LED efficiency improvements so far have been coming from the chip, and this is now running out of steam."

"Chip efficiencies are getting closer and closer to physical limits so now we believe performance improvements must come from the packaging," he adds. "Thermal efficiency, heat dissipation, heat removal and light extraction all need to be addressed at the packaging level."

LED focus

Rantala's company has already developed a host of die attach pastes, dielectrics, encapsulants and more for power electronics, organic LEDs and and other devices, but now the company is intent on cracking the high brightness LED market.

"We've seen a lot interest coming from [manufacturers of LEDs for] general lighting and automotive applications," he says. "Right now the traditional silicone package market is dominated by Shin-Etsu and Dow Corning, but there is a need for innovation."

"[Customers] don't like the fact that there are only two suppliers, and are really looking for alternative solutions," he adds.

Which, of course, is where Inkron's latest product comes in. The company has developed a siloxane-based encapsulation resin designed for LED applications.

According to Rantala, the material offers excellent UV and thermal stability, providing a better barrier to air, water and sulphur, than conventional silicone packaging, and delivering some two and a half times more resistance to these environmental influences.

Importantly, while the refractive index of your typical silicone encapsulant comes in at around 1.4, Inkron's material will provide a higher refractive index of 1.6.

This figure is closer to the refractive index of the LED industry's favourite substrate, sapphire, enhancing light output from the substrate to the encapsulant, and according to Inkron, boosting light output efficacy by up to 10%.

Inkron's siloxane-based encapsulant enables wafer-level flip chip packaging

What's more, the company can disperse nanoparticles into the siloxane polymer to raise the refractive index to 1.8, which could boost efficacy by up to a further 15%, without any loss in light transmission.

"We have a product roadmap to reach a refractive index of 1.8 in the future, but first we want to go to market with our lower refractive index material, and then highlight to clients that if they want more light extraction in the future, out platform is compatible with this," he explains.

And, while siloxane-based material can be used to increase the performance of today's discrete LED packages, unlike current silicones, it has the mechanical strength to protect and support the die in vastly cheaper wafer-level and chip-scale packaging processes.

Traditional packaging currently represents up to 40% of the overall LED cost while figures from LumiLEDs suggest a move to chip-scale packaging would obliterate these costs, leaving LEDs at least 30% cheaper.

Rantala also reckons industry interest in alternative LED substrates could drive development towards chip-scale packaging.

"The industry has been dominated by chip volumes that are sapphire-based, and there's so much manufacturing capacity here," he says. "But we've been talking to, for example, Japan-based companies that are [considering] GaN-on-silicon LEDs, and they are looking at chip-scale packaging."

So where is Inkron right now? The company currently offers testing services, and now intends to scale up in-house production to meet current customer demands.

Throughout the last two months, the company has been sampling materials for LED applications and its focus will remain here for the foreseeable future.

As Rentala says: "We're also working on power electronics applications, but the qualification time for power devices can take two years. We can qualify LEDs in three to six months, which is important in terms of cash flow for a young company."

But as the chief executive asserts, he is open to either re-locating production from Finland to Asia, which is where the lion-share of LED packaging takes place, or partnering with a company in this region.

"We are seeing a demand for new materials in this industry, in the same way we saw this in the semiconductor industry ten years ago," he adds. "Siloxane materials with nanoparticles is the right approach, but we are realistic and know we, alone, can't handle the volumes that could come from this market."