Is silicon good for LED?

Silicones in LED lighting manufacturing

The design of each new LED lighting product means selecting components to fulfill important roles, from dissipating heat to protecting internal components from the elements. With multiple adhesive and sealant providers now producing formulations specifically with LED compatibility in mind, your options are more open than ever. 

You can find more information on our web, so please take a look.

By planning out each step of the manufacturing process early in design, you can find the ideal formulation for each requirement. You may be amazed by just how much silicones can accomplish for your LED lights.

Four areas of LED lighting need

The following are four different parts of any LED light design that have to be accounted for. The common thread between each of them is that silicones can play a role in improving both your manufacturing process and the finished product.

Thermal interface materials

Your LED lighting products need reliable thermal conductors to carry heat from the circuit board to the grid that will dissipate the heat. This system keeps your chip below its acceptable temperature range, typically 90 to 105 degrees celsius. Since air is an insulator, you can't leave empty space within the housing. Silicone formulations are often perfect for the job.

High-performance thermal conductive materials are especially important when you are developing lights that output more light in the same housing space as lower-output options. This emerging area of LED development is dependent on picking materials that can handle this increased thermal demand (heat). It is also important to note that the added cost of upgrading to high-performance chemicals is more affordable than redesigning the housing from the ground up to improve heat dissipation and heat sink area (radiators).

Circuit board coatings and pottants

The conformal coatings and potting materials are used to securely encapsulate LED circuit boards and keep moisture, dirt and other environmental factors from damaging the board mounted components and light engine. Your chosen formulation for this part of the manufacturing process will be determined by the intended use of the light. 

Light-duty LEDs meant for indoor use naturally require less protection for their components than ones used in settings such as garages or roadside light fixtures. By comparing price points and relative levels of protection from humidity, electrical integrity, shock and other potentially damaging factors, you can pick a conformal coating that matches your LED equipment's intended use.

Luminaire assembly adhesives and sealants

The adhesive and sealant that connect the internal components of the light will likely be different polymers than your chosen conformal coating, though it's normal for all three to be silicone based. 

Perhaps the most important variable to consider when picking your adhesives and sealants is usable life span: How long will a polymer hold up under real-world conditions? This effectively determines the reliability of your LED products.

Moldable optics

The design of the lens, which controls light distribution based on the intended use of an LED light, is another place where silicone formulations can play an important role. Versatile silicones that are easy to work with can enable designers to create lights that fit their needs without adding complexity or expense to the manufacturing process.

The quality of the substances used for optical elements helps determine the long-term viability of a piece of LED equipment. The ideal formulation for your purposes will hold up over both environmental stresses (essentially no lens discoloration versus polycarbonates and acrylics),  and the unavoidable heat that comes from LED elements.

Further uses for silicones in LED lighting

Beyond those major categories where silicones can help with LED equipment manufacturing, there are a few more use cases worth considering. For instance, you can select a silicone formulation for threadlocking purposes, holding your threaded components, such as screws, in place and helping the lights resist damage over time.

A silicone-based instant adhesive or hot-melt silicone adhesive could also be the ideal choice for assembly and wire tacking. When you finalize an LED light product design, you may have a list of five or more different silicone formulations, each fulfilling a different role in the manufacturing process and contributing to the performance of the finished equipment.

Alternatives to silicones in LED lighting

Even the most versatile polymer isn't right for every application, and in some LED light manufacturing scenarios, you may be better served by epoxies or urethanes. In lower-temperature scenarios (for example, LEDs used in boats, off-road vehicles and home office lights) it may not be necessary to go with high-performance silicones.

Furthermore, when there are concerns around having a volatile polymer in the manufacturing environment, silicones may not be the right choice. This goes back to the age-old issue of getting paint to adhere around silicones.

Is it time to design your next LED fixture? 

When it's time to start the design process for your company's next LED fixture, it can pay to take a closer look at silicones. There may be more use cases for these polymers than you've previously anticipated, as well as new and advanced formulations to deliver better performance.

For decades, researchers have tried to fashion an effective silicon LED, one that could be fabricated together with its chip. At the device level, this quest matters for all the applications we don&#;t have on our mobile devices that would rely on cheap and easily fabricated sources of infrared light. 

Silicon LEDs specialize in infrared light, making them useful for autofocusing cameras or measuring distances&#;abilities that most phones now have. But virtually no electronics use silicon LEDs, instead opting for more expensive materials that have to be manufactured separately.

However, prospects for the elusive, light-emitting, silicon-based diode may be looking up. MIT researchers, led by PhD student Jin Xue, have designed a functional CMOS chip with a silicon LED, manufactured by GlobalFoundries in Singapore. They presented their work at the recent IEEE International Electron Devices Meeting (IEDM).

Link to HumenChem

The chief problem to date has been, to be blunt, silicon isn&#;t a very good LED material.

An LED consists of an n-type region, rich in excited free electrons, junctioned with a p-type region, containing positively-charged &#;holes&#; for those electrons to fill. As electrons plop into those holes, they drop energy levels, releasing that difference in energy. Standard LED materials like gallium nitride or gallium arsenide are direct bandgap materials, whose electrons are powerful emitters of light.

Silicon, on the other hand, is an indirect bandgap material. Its electrons tend to turn that energy into heat, rather than light. That makes silicon LEDs slower and less efficient than their counterparts. Silicon LED makers must find a way around that indirect bandgap.

One way might be to alloy silicon with germanium. Earlier this year, in fact, a group at Eindhoven University of Technology in the Netherlands fashioned a silicon-based laser out of a nanowire-grown silicon-germanium alloy. Their tiny laser, they reported, might one day send data cheaply and efficiently from one chip to another.

That&#;s one perhaps elaborate approach to the problem. Another has been considered for more than 50 years&#;operating silicon LEDs in what&#;s called reverse-biased mode. Here, the voltage is applied backwards to the direction that would normally allow current to flow. This changeup prevents electrons from filling their holes until the electrical field reaches a critical intensity. Then, the electrons accelerate with enough zeal to knock other electrons loose, multiplying the current into an electrical avalanche. LEDs can harness that avalanche to create bright light, but they need voltages several times higher than the norm for microelectronics.

Since the turn of the millennium, other researchers have tinkered with forward-biased LEDs, in which electrons flow easily and uninterrupted. These LEDs can operate at 1 volt, much closer to a transistor in a typical CMOS chip, but they&#;ve never been bright enough for consumer use.

The MIT-GlobalFoundries team followed the forward-biased path. The key to their advance is a new type of junction between the n-type and p-type regions. Previous silicon LEDs placed the two side-by-side, but the MIT-GlobalFoundries design stacks the two vertically. That shoves both the electrons and their holes away from the surfaces and edges. Doing that discourages the electrons from releasing energy as heat, channelling more of it into emitting light.

&#;We&#;re basically suppressing all the competing processes to make it feasible,&#; says Rajeev Ram, one of the MIT researchers. Ram says their design is ten times brighter than previous forward-biased silicon LEDs. That&#;s still not bright enough to be rolled out into smartphones quite yet, but Ram believes there&#;s more advances to come.

Sonia Buckley, a researcher at the U.S. National Institute of Standards and Technology (NIST) who isn&#;t part of the MIT-GlobalFoundries research group, says these LEDs prioritize power over efficiency. &#;If you have some application that can tolerate low efficiencies and high power driving your light source,&#; she says, &#;then this is a lot easier and, likely, a lot cheaper to make&#; than present LEDs, which aren&#;t integrated with their chips.

That application, Ram thinks, is proximity sensing. Ram says the team is close to creating an all-silicon system that could tell a how far away its surroundings are. &#;I think that might be a relatively near-term application,&#; he says, &#;and it&#;s certainly driving the collaboration we have with GlobalFoundries.&#;

From Your Site Articles

Want more information on silicone materials for leds? Feel free to contact us.

• Light From Silicon - IEEE Spectrum &#;