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.

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.

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

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.

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).

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.

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.