In addition to a brief fundamental consideration of the manual lead-free and lead-containing soldering process, this application note describes the essential influencing factors and their effect on the lead-free soldering process.

Furthermore, the basic rules and specific guidelines associated with the new manual lead-free soldering process are illustrated.

Also, possible risks are discussed and the general procedure of the lead-free soldering process is described.

In conclusion an overview of the solderability of the various LED types from OSRAM Opto Semiconductors are presented, along with their ability to be reworked and repaired.

Optical simulation software typically propagates light through an optical system by ray tracing. Light sources can be defined which emit rays from their surfaces or volumes. Many software packages accept rayfiles, which are virtual sources created from measured or calculated sources. Each ray in the file has a starting point, a direction, and associated power.

OSRAM Opto Semiconductors provides rayfiles in several software formats. The properties of those rayfiles are described in this application note.

Light Guides are used wherever the light of a lightsource should be distributed homogeneously over a particular area, when there is a spatial distance between light source and the area which is to be illuminated.

This application note offers an introduction to the definition and specification of the thermal resistance value for LEDs and IREDs (IR emitting diodes).

In addition, an overview is provided as to how OSRAM Opto Semiconductors specifies the thermal resistance for various types of LEDs, how the reference points are defined for the various product types and which values are used for the data sheets of the LEDs.

The interaction between RoHS-compliant SMD components and lead-free processing continues to lead to complications, as the previous know-how worked out with tin-lead processes is only partly applicable to the new material system. In addition to providing general notes on the lead-free reflow process, this document will show and explain in detail the crucial parameters for creating a soldering profile. To counteract uncertainties and the problems that result, it will also present a detailed recommendation for the processing of SMD light emitting diodes (LEDs).

Particular attention will be paid to the prevention of heat-induced damage to the SMD components and printed circuit board substrates that are used.

With reference to the application note „Further Details on lead free reflow soldering of LEDs” the present note provides details and recommendations for measuring of the temperature profile during the lead-free reflow solder process. Beside general information about thermocouples the critical selection of suitable measuring points is described, as well as different possibilities for the attachment introduced.

Mit Bezug auf die Applikationsschrift „Zusätzliche Hinweise zum Bleifrei Reflow-Löten von LEDs“ gibt die vorliegenden Schrift Hinweise und Empfehlungen für die Erfassung des Temperaturprofils während des Reflow-Lötprozesses. Neben allgemeinen Informationen über Thermoelemente wird die kritische Auswahl von geeigneten Messpunkten beschrieben, sowie verschiedene Möglichkeiten zur Befestigung von Thermoelementen vorge￯﾿ﾽstellt.

Im Zusammenspiel zwischen RoHS konformen SMD-Bauteilen und bleifreier Verarbeitung kommt es immer noch zu Komplikationen, da das bisher mit Zinn-Blei Prozessen erarbeitete Know-how nur bedingt auf das neue Materialsystem übertragbar ist. In der vorliegenden Schrift werden neben allgemeinen Hinweisen zum bleifreien Reflow-Prozess, die entscheidenden Parameter zur Erstellung eines Lötprofils aufgezeigt und detailliert erläutert. Um Unsicherheiten und daraus resultierenden Problemen entgegenzuwirken, wird außerdem eine detaillierte Empfehlung zur Verarbeitung von SMD Leuchtdioden (LEDs) dargestellt.

Besonderes Augenmerk liegt in der Vermeidung thermisch induzierter Schädigungen der verwendeten SMD Bauteile und Leiterplattensubstrate.

In order to guarantee constant brightness for LED illumination systems with long product cycle times, the availability of LEDs with constant brightness within the product cycle is often still required or expected. This application note is intended to show that in spite of the continuous further development of LED technology, the issue can be avoided or completely eliminated with a simple solution.

Nowadays LED components are used in a wide variety of application areas and are therefore exposed to a crossfire of influences and environmental conditions. In the automotive industry for example LEDs in lighting systems are exposed to extreme condition such as vibration, variations in temperature, humidity and others. In order to evaluate possible consequences, LEDs were examined regarding standard and user-specific criteria and operating conditions.

To achieve reliability and optimal performance of LED Light sources a proper thermal management design is necessary.

Like all electronic components, LEDs have thermal limitations. The allowed operation temperature for the specific lifetime is limited by the glass-point of the LED resin. Usually the maximum permissible junction temperature of common SMT LEDs is in the range of 95 - 125 °C. This means that the temperature of the die inside, doesnít have to exceed this value when exposed to the expected operation temperature. This brief will give the design engineer an introduction in the thermal basic of SMT LEDs.

Furthermore, some concepts are shown in order to improve the thermal design.

The Golden DRAGON LED consists of a leadframe with integrated heat spreader and a thermoplastic body. The chip is mounted in a reflector formed by the thermoplastic. In order to dissipate the heat the package has an additional thermal connection. This connection is soldered to a thermal enhanced PCB, on the backside of the housing. Therefore the Golden DRAGON package is suitable for high power dissipations in the range of 1 W. In order to achieve reliability and optimal performance a proper thermal management design is absolutely necessary.

Like all electronic components, the Golden DRAGON LEDs have thermal limitations. The allowed operation temperature for the specific lifetime is limited by the glass-point of the LED resin. This means that the temperature of the die inside, doesn't have to exceed this value when exposed to the expected operation temperature.

This brief will give the design engineer an introduction in the thermal basic of Golden DRAGON LEDs. Furthermore some concepts are shown in order to improve the thermal design.

In recent years, the brightness of LEDs has continually increased, allowing them to be used in completely new application areas. Due to the strong increase in brightness, the bonded system of chip and housing takes on increased significance. Generally, the lifetime of an LED is not due to the actual semiconductor chip itself, but primarily determined by the housing. The “lifetime“ refers to the period of time, whereby the brightness drops to half of its original value at a specific current. In order to achieve a lifetime in the range of 100,000 hours at room temperature for very bright LEDs, Osram has implemented a new sealing compound consisting of silicone.

The following application note represents a general guideline for mounting LEDs of the Golden DRAGON with Lens product family. A basic overview of the construction of LEDs and important design rules for the development of LED systems are provided.

In addition, the principal processing steps are illustrated for the Golden DRAGON ARGUS LED, and general information about mounting is summarized.

In the following, a recommended selective soldering method by means of laser diodes is also introduced, because it is not possible to process these LED type with a conventional standard soldering process. Thereby the important process parameters and steps for processing of the Golden DRAGON ARGUS LED are described.In a final manner alternative solder techniques are presented.

Various cleaning methods for LEDs are described in this Application Note: Dry cleaning. wet cleaning, ultrasonic cleaning.

As LEDs become more efficient and more compact their sensitivity to ESD events is also increasing in the majority of cases. Despite a great deal of effort in the semiconductor industry in the past decade, ESD still affects production yields, manufacturing costs, product quality, product reliability, and profitability of all semiconductor devices, including LEDs.

The Golden DRAGON LED is OSRAM Opto Semiconductors’ high performance LED requiring special considerations in thermal management and electrical implementation.

This application note is intended to help the design engineer with the special electrical considerations of the Golden DRAGON LED. With a higher current there is higher power, and therefore more heat to dissipate. The Golden DRAGON LED package is optimized for removing this heat efficiently. With an integrated heat slug (also known as a heat spreader) the thermal performance is far superior to standard LEDs.

The majority of LED manufacturers use units of luminous intensity (cd) for the measurement and classification of LED brightness. For numerous LED types, this procedure is reliable and reproducible. However, for LEDs with narrow emission angle characteristics, this method is insufficient. This application note describes the procedures for measuring luminous intensity, partial flux and luminous flux, along with the advantages and disadvantages relating to LED design.

This application note describes the procedure for adjusting the brightness of light emitting diodes (LEDs) in applications by means of resistors. For better repeatability, the calculation of the required resistance values is shown by means of an example.

This application note provides an introduction to the thermal fundamentals of the compact LED high power light source OSRAM OSTAR Projection. In addition, the general handling of the new light source will be briefly covered, and the requirements for the necessary heat dissipation and cooling will be described.

This application note describes two reference designs for LCD backlighting using the 6-lead MULTILED LRTB G6SG The feasibility of the designs is shown on two LCD sizes of 19“ and 24“ with a typical brightness of 250cd/m² required for office applications.

The uniform illumination of very large screens used in LCD televisions which require a typical brightness of 350-500cd/m² is described in a separate application note “LED Display Backlighting - Large Screen and TV Application“.

This document builds upon the fundamental concepts of LED backlighting described in the application note “LEDs, New Light Sources for Display Backlighting“.

This application note shows how radial and SMT LEDs can be processed, from the initial tape or reel to the soldering process.

Temperature measurement generally can be divided into two main categories - contact thermometry and radiation thermometry. Contact thermometry consists of a thermocouple which always remains in contact with the device under test, while radiation thermometry measures the radiation of the device under test without contact, by means of an infrared sensor. In order to guarantee a long lifetime for LEDs, the junction temperature must not be exceeded. The maximum junction temperature is specified in the data sheet for the LED.

This application note provides information about measurement procedures, the thermocouples used and their systematic errors as well as the ways in which thermocouples are mounted.

In recent years, Light Emitting Diodes (LEDs) have become a viable alternative to conventional light sources. The overriding advantages long life, high efficiency, small size and short reaction time have lead to the displacement, in ever increasing numbers, of incandescent bulbs. One of the markets where this change has become most evident is Automotive, where LEDs are used now not only for backlighting dashboards and switches, but also for exterior illumination in Center High Mounted Stop Lights (CHMSL), Rear Combination Lamps (RCL), turn signals and puddle lighting.

Despite the long life and low failure rates of LEDs, cars can be found, on occasion, with failed LEDs in their CHMSL. Most often this is due to a flawed circuit design wherein the LEDs were allowed to be overdriven. It is with that supposition in mind that this application note is written: to identify, characterize and comment on LED behavior and failure modes in serial and matrix circuits.

LEDs are currently used in many application areas. In the automobile sector, nearly all dashboards utilize LEDs for backlighting. For new application areas which require a higher light output, even more efficient and powerful LEDs are needed. Brake lights, turn signals and fog lights, for example, require powerful LEDs in order to fulfil statutory regulations.

Every application requires the selection of an appropriate LED. The Advanced Power TOPLED (APT) serves to complement the Power TOPLED and Golden DRAGON power components. With a maximum power consumption of approximately 0.5W and high optical efficiency, this package fills the light output gap between the Power TOPLED and the Golden DRAGON.

This application note describes the electrical characteristics of the Advanced Power TOPLED along with various electrical simulations.

Because of their low intensity, the use of light emitting diodes (LEDs) as a light source for backlighting was previously limited to usein small displays.The rapid advancement of semiconductor technology together with new concepts in packaging design has led to a significant increase in LED brightness, so that the use of light emitting diodes in backlighting applications has gained increasing importance. Due to their increased efficiency, LEDs are being used in many new application areas ranging from ever larger display panels to television screens. The following provides a general overview and comparison of light sources which are currently available for use in backlighting applications, with a focus on the differences between cold cathode fluorescent lamps (CCFL) and LEDs. Afterwards, the principle construction of backlighting is explained. In addition, various types of LEDs are shown, along with their possibilities for use and associated challenges relating to the development and implementation of backlighting technology.

The purpose of this application brief is to show a method to determine the maximum permissible power dissipation of the LEDs in a display application, and allow the junction temperature (T_J) to remain below its rated value. Junction refers to the p-n junction within the LED.

In recent years, advancements in the area of optoelectronics due to the deployment of new semiconductor materials in the manufacturing of LEDs have permitted a diversity of color and increased levels of brightness to be achieved. LEDs and LED modules have recently been produced which can be used as a replacement for conventional light devices such as light bulbs and fluorescent lights in many application areas. Backlighting of TFT monitors, for example, was previously accomplished by the use of cold cathode fluorescent lamps (CCFLs). Due to the disadvantages of CCFLs regarding their white balance, spectral distribution and low mechanical strength, new bright light diodes have been considered as a replacement to CCFLs.

For many years, surface mounted devices (SMDs) have been the standard component form used for construction of printed circuit assemblies. During the last decade, the new SMD packaging for light emitting diodes (LEDs) has replaced the classical radial LED in a majority of application areas.

This trend is based in part on the availability of numerous SMT packages from micro devices to high-power components, but is primarily due to the advantages that SMT offers for further processing in the assembly line. The most familiar and widely-used package type for LEDs is the P-LCC-2, followed by the newer P-LCC-4 packages (P-LCC - Plastic Leaded Chip Carrier).

Nowadays, applications increasingly make use of LEDs as a replacement for traditional light bulbs. For example, LEDs are frequently used in the design of automobile tail lights, signal lights, traffic signals, variable message signs, ...

LEDs provide several advantages over traditional light bulbs, such as smaller size and longer life. In many applications, the LEDs must be driven with intelligent control circuitry. According to the task at hand, this control circuitry must be able to fulfill various functions and tasks. In the following pages, solutions are provided for various application areas. These solutions are principal suggestions, not a concept ready for series production.

One possible task for control circuitry is regulation of intensity, in case the LED brightness must be set to various levels. A solution is described in the section “Dimming“. In addition, the specified brightness should be maintained at a constant level. Fluctuations in the supply voltage, for example, could lead to significant variations in current. In this case, one must insure that the current through theLEDs and thus the brightness is maintained at a constant level. This problem is covered in more detail in the section “CurrentRegulation“.

Another task for control circuitry is failure recognition. Modules consist of individual LEDs which can be tested for total failure. Additional information can be found in thesection “Failure Recognition“. A particular characteristic of LEDs is their strong temperature dependency. Since LED brightness is strongly dependent on temperature, the driver circuitry can carry out temperature compensation. Two possible approaches are described in thesection “Temperature Compensation“.

Furthermore, it may be necessary to adapt the driver for LEDs in different brightness groups by means of hardware selection. This is described in the section “Adjusting for Different Brightness Groups“. In the following applications, a PICmicrocontroller is used as a controlling unit.

In the automotive sector, the design and implementation of three-dimensional lamps presents a challenge. It is relatively easy to produce a flat, two-dimensional circuit board populated with LED components in which the optics (reflector and glass) match the appearance of the automobile. However, the increased use of free-formed, curved geometry in the design of car bodies necessitates new construction methods for such lamps.

This application note illustrates, how one can replace LEDs with old TSN chip technology (transparent substrate, n-doped) by state of the art AlInGaP (Aluminum Indium Gallium Phospide) low current (= LC) LEDs in existing designs.

The first true ancestors to the Indium Gallium Nitride (InGaN) LED evolved last decade. These took the form of blue LEDs utilizing Silicon Carbide (SiC) as the active, light-emitting material. These early LEDs were characterized by very low light output, less than 2cd/m². The next generation of blue LEDs relied upon SiC as a base layer only and employed Gallium Nitride (GaN), grown directly on the SiC substrate, as the active, light-emitting epitaxial layer. This process initially increased light output by a factor of eight. The final iteration saw the introduction of Indium (In) to the epitaxial layer to form InGaN. This development further boosted light output by a factor of five - a full 1300% increase in intensity over the first SiC LEDs. Today, through advances in process, packaging and thermal transfer technologies, light output continues to evolve.

Besides increasing the intensity of blue, and by extension, white LEDs (since all white LEDs use a blue chip in conjunction with a light converter, or phosphor), the InGaN process has replicated two new colors: verde and true green. These unique colors, alongside InGaN’s high intensity and inherent reliability, has greatly increased their proliferation into applications once reserved solely for incandescent lighting: traffic signals, realcolor displays, message boards, moving signs, dashboard backlighting, battery flashlights and toys.

While the InGaN process produces the brightest light output across blue, verde, true green and white, it is important to understand that the wavelength of the light emitted is strongly dependent upon the forward current driven through the device, and that in order to avoid shifts in color, careful consideration must be paid to dimming strategies. This application note, then, will examine methods for dimming InGaN LEDs with little or no effect on wavelength.

In the design of a driving circuit for LEDs, the dimming behaviour is an important topic to fulfil the end customer requirements. The intend of this application note is to describe the behaviour of LEDs in respect to brightness by varying the current and to suggest solutions for avoiding negative influence for the application.

Following items point out some topics where it is necessary to adjust the brightness of LEDs, if the customer specification is tight:

- LED brightness at the grouping current doesn’t fit to the specified brightness in the application, hence the LED grouping current doesn’t correlate to the application current,

- different brightness groups of the used LEDs,

- dimming of brightness in the application,

- different switches or displays to backlight.

SMT Replaces Through Hole Technology.

The use of SMT-TOPLED varies greatly from the use of traditional through hole LEDs. Historically through hole LEDs have been incorporated directly into front panels using the leads as a stand off. Due to the automated nature of SMT assembly, and the size constraints of SMT components and assemblies, SMT-TOPLED applications are different from through hole applications.

The OSRAM SmartLED is a compatible device to 0603 Chipled and can be used for the same application e.g. flat backlighting, cellular phones, switches, keypads and display illumination.

What is Surface Mounting? In conventional board assembly technology the component leads are inserted into holes through the PC board and connected to the solder pads by wave soldering on the reverse side (through-hole assembly). In hybrid circuits (thick and thin film circuits) ìchipsî, i.e. Ieadless components, are reflow soldered onto the ceramic or glass substrate in addition to the components already integrated on the substrate. Surface mounting evolved from these two techniques.

Some years ago, the color range of Light Emitting Diodes (LEDs) on the market was limited to the red to green spectrum. Then, blue LEDs were developed and introduced into the market. These blue devices made it possible to build so called “single-chip white“ LEDs, using a yellow converter material in combination with a blue die. Most of the blue and white LEDs use Indium Gallium Nitrite (InGaN) as an epitaxial layer. The wavelength (chromaticity coordinates) of the generated light of these InGaN-based LEDs shows a strong dependency on the driving current. This special property of InGaN based LEDs must be considered well in advance for new application solutions. This application Note is intended to enable the reader to avoid some common design mistakes when using InGaN-LEDs.