LED and Display Conformal Coatings

As a result of new legislation, ongoing cost saving requirements and attempts to reduce energy consumption, the use of LEDs (Light Emitting Diodes) will continue to replace incandescent bulbs in public areas such as street lighting and traffic lights, where despite the initial high investment, authorities will derive large savings in power consumption and reduced service costs (LEDs have significantly longer life-times).

In fact, the use of LEDs in advertising signage, sports arena displays, passenger information panels, traffic signs, car headlights, warning systems, under-water lighting, and other applications continues to increase rapidly. One big difference with this new technology is that nearly all applications require drive/control circuitry, in the form of a printed circuit board, to control the functionality of these devices as the LED’s require low voltage Direct Current, as opposed to AC.

Most, if not all of these applications, will end up in exterior locations, where the units are likely to be exposed to a combination of temperature change, moisture (rain as well as humidity changes and condensation), corrosive gases, salt-spray etc.

For these exterior applications, the visual impression of the display is the key output, and importantly ensuring the output is consistent throughout the life of the product. A key requirement in ensuring consistent output throughout the lifetime, depends heavily on protecting the display and controls from the weather, without affecting the optical output. Further information on LEDs can be found here.

When the lights go out…

Most LEDs have a natural lifespan that ends in a wear out mechanism. Defects in construction in the active area can reduce the lifetime significantly and are particularly affected by current and temperature. Although these degradation failures are unavoidable, careful selection can ensure it will not be during the lifetime of your product.

Of more concern, are premature failures in-service, and for the purpose of this brief piece, we will not consider in-package failures only those at the assembly level.

LED Failure mechanisms: Opens and Shorts

There are basically two ways that corrosion can cause issues with the functionality of an LED device. At the LED package itself, or at a remote site that changes the current flow around the circuit.
At the package level, as shown in the following examples (both Through-hole and SMT design), the metallic anode and cathode leads are exposed metal to enable soldering to the drive assembly. It is these exposed metal leads that are most susceptible to corrosion from the aggressive end use operating environment.

Electro-chemical migration, or dendritic growth from the anode to the cathode would result in an electrical short, resulting in failure of the LED. Corrosion of either lead-frame would result in an open failure, and a failure in the LED.
Often, for reasons of solderability, the leadframe is of tin construction, and so tin whiskering, and potential shorting is as likely with an LED as any other component, although not strictly speaking a corrosion product.

Corrosion products in remote areas of the drive assembly can also cause issues with the functionality of the LED device. The presence of corrosion can alter the effective current or voltage flowing through the LED device, resulting in increased junction temperature. Prolonged temperature creep can lead to the emergence of thermal runaway.

Runaway occurs when the junction resistance continues to increase with temperature, added further heat to the package and thus raising the junction temperature in a self-propagating vicious circle.

Keeping the lights on…. The correct conformal coating can help

The use of the correct conformal coating on the drive circuitry and LED lead-frames can mitigate against the corrosive effects of the operating environment. This is achieved by the coating to behave as an effective barrier to extraneous contaminants, allowing for preservation of the circuit’s integrity, as well as mitigating against the potential effects of tin whiskers.

One of the unique challenges with coating SMT LED assemblies is the sensitivity of these devices to solvents and certain organic compounds present in certain coating materials. This incompatibility could result in discoloration and deterioration of the LEDs. More information on the effect, test & mitigation strategies and compatible materials can be found here.

Conformal Tech is a leading supplier of conformal coatings to the LED signage and display electronics, and has worked closely with most major LED manufacturers to ensure chemical compatibility.

With the widest range of high performance conformal coatings, from every major type of protective chemistry (including Acrylic, Urethane and Silicone), you can be certain of a high-performance solution for your specific application. We have a wide range of environmentally compliant, low-outgassing, solvent-free materials, in addition to a wide range of traditional solvent-borne chemistries. Whatever your requirements, Conformal Tech has the solution.

Detailed Information about LED & Display Electronics for

Selection

We offer the industry’s widest range of high performance coatings, drawn from the widest range of chemistries and able to be applied by any of the common application methodologies enabling you to select the product that best meets your project needs, production throughput , floor space and capital equipment requirements, whether you are upgrading an existing product, transferring a production process from another facility or are working on a new product introduction.

Total Process Solution

Our central philosophy is that a conformal coating is not simply a material, it is part of a process, and all of our materials are backed by an unparalleled level of process knowledge and applications experience, to ensure that whatever your process requirements, a perfectly tailored total process solution is available to ensure the results that you demand.

Total Process Consistency

The overall consistency of your process is largely governed by the consistency of the process inputs, of which your conformal coating material is one input. We go to very great lengths to ensure the consistency of batch-to-batch material characteristics. Take advantage of one of our pre-blended materials, to virtually eliminate any potential for on-site mixing or measuring mistakes and you can be assured of an industry beating level of consistent material inputs, to take you one step closer to your SPC or 6σ Key Performance Indicators (KPIs).

Total Process Support

With even the best process solution, occasionally things change, usually through no fault of the production-engineering department. Should this happen to your line, you can rest assured, wherever your factory is located, our team of Global Application Experts are on call to ensure that you resolve the situation to your complete satisfaction in the shortest time-frame possible and get your process running at optimum efficiency once again.

Designing quality into your product begins with understanding your products lifecycle and end use operating environment. Conformal Tech will work with you from project inception, to understand these key parameters and deliver a material solution that will enable you to exceed the level of quality and reliability that you require, and work closely with you during all stages of your project, from Design, Prototype, Pre-Production Process Approval (PPAP) and through to mass production, ensuring you are getting the quality levels you expect.

All the materials we offer to the automotive industry exceed the requirements of all relevant specifications and or standards to ensure they exceed the required levels of protective performance for your application.

Incoming Quality

Conformal Tech materials are manufactured in world-class, state of the art facilities, using computer-controlled, automated processes wherever possible to minimize the potential for human error. When automation is not possible or practical, Poke Yoke systems are used to further reduce the risk for errors. Conformal Tech uses a combination of FMEA, SPC and other 6σ tools to ensure the quality of its products from this manufacturing process, and batch characterization of key parameters as a final check. We use lean principles wherever possible and Kaizen Continuous Improvement methodologies to spot and reduce waste, as well as ensure the highest quality outputs are produced for our customers.

The coating products that we use are produced in facilities that are certified to ISO9000-2008. With the additional tools in place, and the emphasis on quality management, our vendors have been successfully audited to TS16649 automotive quality management standards by a variety of OEMs and Tier 1-3 subcontractors to ensure the highest quality levels of incoming shipments.

In Process Quality

By ensuring you have the highest standards of incoming material quality and consistency, Conformal Tech takes you one step closer to your In Process Key Performance Indicators and first-pass yields etc. However, the conformal coating material is but one-input into your overall coating process. Other factors will affect your in process quality, including the level of cleanliness of your assembly, presence of residues from soldering operations, and maintenance/set-up of your application equipment amongst others. Our process experts are always on hand to assist with all aspects of in process quality assurance to ensure your process meets your organizational goals.

In Service Quality

By ensuring you have the highest quality inputs (performance, & consistency) and ensuring your process is running under control and exceeding the required level of workmanship, you have taken great strides towards ensuring and protecting the reliability of your electronic assemblies. However, from time to time, field failures may still occur and should this happen, then you can rest assured that the Conformal Tech’s Process Experts are equipped to help you diagnose the failure’s root cause and associated corrective actions using an 8D problem solving methodology.

Design Engineering plays a crucial role in the overall reliability of a product produced, both in terms of the inherent robustness of circuit board layout and often times the qualification and selection of materials used for fabrication. Design engineers should be mindful of the expected operating environment of the assembly from the inception of the design, since if it is likely that conformal coating will or even maybe required, designing the product with this in mind can save many production headaches, especially with LED assemblies.

In general there are 3 types of areas to consider in designing for the conformal coating process; Definite areas and components that MUST be coated, definite areas that definitely MUST NOT be coated (e.g. connectors, thermal transfer or heatsinks), and areas that MAY or MAY not prove to need coating.

The designer should aim to keep the maximum spacing between an area that is known to require coating and one that is a definite coating free area. In a perfect world, all of the coating free areas and tall components would be kept to one edge of an assembly to aid the conformal coating process. However, there are of course other challenges relating not least to where the component will be situated and how it will interconnect with other components that may preclude this. In addition, if it is intended to coat the lens of the LED for ease of production, the refractive index and optical transmission properties of the coating need to be known or measured to ensure that there is no negative effect on the LED output.

Conformal Tech can help prospective designers at the outset of a project, by helping to decide the likely coating material choices and discussing application behavior and methodology in light of any constraints. Designing for conformal coating can ease production, raise overall quality levels and improve the long-term reliability of a design, as well as minimizing production costs.

Purchasing plays an important role in the end reliability and overall quality of a product. In the best examples, the purchasing department work closely as a team with the production, design and quality representatives. In the worst examples, the purchasing department works in a silo on delivering the cheapest individual components with the rationale that the cheapest Bill of Materials will result in the most economical design.

It is important to understand that product offerings are not necessarily equal and may result in efficiency or yield issues in production or inferior protective properties, which may result in reduced reliability. The costs associated with these issues may vastly exceed the savings on the material sets, although these costs often end up being born by other departments and thus remain hidden.

Conformal Tech can help explain the value that high-performance, high quality materials and thorough process understanding can bring to the overall cost of ownership model, so essential in the overall bottom-line of the business.