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DURIS S2 – Details on Properties, Handling and Processing Application Note

Abstract This application note provides information about the "DURIS S2" LED from OSRAM Opto Semiconductors. A basic overview of the construction and the optical characteristics of the LED is presented. In addition, details on handling and processing, as well an application example are provided.

Content

1. DURIS S2 2. Features & Construction 3. Handling 4. Storage 5. Cleaning 6. Processing 7. Example of Application 8. Summary

DURIS S2 The DURIS S2 (GW SBLMA1) combines high efficacy and a wide beam angle into a compact format (footprint 2.0 mm x 1.6 mm) and is currently the smallest package of the DURIS product family. The LED offers a wide range of driving current with high color quality and long life-time performance, which is an ideal choice for all indoor General Lighting Application.

Fig. 1: DURIS S2 With its optimized features – low power consumption (0.2W @ If = 65mA), wide radiation angle (150°) and high lumen efficacy (160lm/W @ 65mA), the LED is mainly targeted for homogeneous linear lighting or architectural and commercial illumination.

• Indoor General Lighting • Linear lighting / fluorescent replace-

ment tube • Troffer light • Retrofit and Fixture • Shop Lighting • Task Light

Used in tube lighting, for example, the DURIS S2 enables a reduction of the LED number without hot-spot effect at existing diffuser cover.

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Features and Construction The construction of the DURIS S2 follows the Quad Flat No Lead (QFN) package design and consists of an Ag-plated lead frame and a white epoxy mold compound. A highly efficient semiconductor chip is mounted and electrically connected on the lead frame, covered by a colored diffused silicone resin. In addition to mounting and electrical connection of the LED to the circuit board, the lead frame serves to dissipate the heat that arises during operation.

Fig. 2: Design of the DURIS S2 For DURIS S2, this construction results in a typical thermal resistance of 24 K/W. The design of the DURIS S2 possesses a driving capability up to 150mA, due to that the LED is also suitable for other indoor application with clustered arrangement and minimal number of LEDs like retrofits and down lights. As there is no ESD protection included the LED is assigned to the category “ESD sensitive device” according to ANSI/ESDA / JEDEC JS-001 - HBM, Class 0. Beyond that, the DURIS S2 fulfills the current RoHS guidelines (European Union & China), and therefore contains no lead or other hazardous substances. The DURIS S2 is available from 2700 K to 6500 K CCT for CRI 80 and from 2700 K to 4000 K for CRI 90.

Figure 3a-d show the radiation characteristics of the DURIS S2.

Fig. 3a: Radiation characteristics of the LED showing forward and backwards radiation

Fig. 3b: Power % over angular distribution

Fig. 3c: Radiation characteristics of the LED mounted on a highly reflective PCB

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Fig. 3d Illuminance tabulation on board Radiation Characteristics: ~25% of the light goes in backward direction (refer to Fig.3a & 3b). In combination with a highly reflective PCB, this leads to a very homogeneous light distribution in linear and area applications. The reflection of backward light on PCB/MCB is widening the radiation angle to ~150degree. This wide radiation angle allows to reduce the DURIS S2 LED count on system level while maintaining the same homogeneity as reached with a higher number of conventional LEDs. A high reflective (>90% reflectivity) and stable solder mask material is recommended for an efficient lighting system. The shape of solder mask is recommended to cover close to LED and no overlay texts are printed in the keep-out area to maximize backward light reflections (refer to Fig. 3d).

Handling Following general guidelines for the handling of LEDs, additional care should be taken to minimize mechanical stress on the silicone encapsulation (see also application note "Handling of Silicone Resin LEDs"). In general, all types of sharp objects (e.g. forceps, fingernails, etc.) should be avoided to prevent damages to the encapsulation,

which could lead to spontaneous failure of the LED. For manual handling of the component, the use of vacuum tweezer is recommended. By means of soft rubber suction tips, the effective mechanical stress on the LED is minimized (Figure 4).

Fig. 4: Examples of vacuum styluses Pick and Place The vacuum stylus functions such that by pressing on the button, a vacuum is created, similar to vacuum tweezers, with which the component (e.g. the LED) can be lifted. If there is no alternative to the exceptional use of a tweezers (anti-static), the LED must be picked and handled only at the epoxy mold compound (Figure 5).

Fig. 5: Manual Handling of the DURIS S2 Please keep in mind the DURIS S2 is an ESD sensitive device (Class 0, HBM), handling and processing must be ESD-conformed. When processing in automatic pick and place machines, care should be taken so that an appropriate pick and place tool is used and

PCB Keep-out area

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the process parameters conform to the package mechanical characteristics. As a starting point a placement force of 2,0N is recommended and should be minimized where possible. For camera teaching during the machine setup, ensure the camera teach the later package image (Figure 6) before continue the pick and place process.

Fig. 6: DURIS S2 package image DURIS S2 with the silicone surface may cause stickiness to the nozzle active area and below are the recommendation. Figure 7 shows the nozzle fit for ASM SIPLACE HF3 machine. Recommendation for JUKI pick and place machine as shown in Figure 8 with the model of number 503 type.

Fig. 7: Recommended pick & place tool for the HF3 m achine from ASM SIPLACE

Fig. 8: JUKI KE-2080RL – JUKI # 503 Nozzle Listed in Figure 9 is the custom nozzle from Ching Yi technology which fit for JUKI pick and place machine.

Fig. 9: Ching Yi Nozzle JUK-0049/15

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Another alternative pick and place machine evaluated will be Panasonic with standard nozzle from Ching Yi Technology is Nozzle 104590801403 [D] as shown in Figure 10.

Fig. 10: Panasonic NM-EJM7A – Ching Yi Nozzle 104590801403 [D] Storage Since the DURIS S2 is generally supplied in tape with dry pack, it should be factory-sealed when stored. The hermetic pack should only be opened for immediate mounting and processing, after which the remaining LEDs should be repacked according to the moisture level in the datasheet (q.v. JEDEC J-STD-033B.1 - Moisture Sensitivity Levels). Subcomponents of this LED are silver-plated. Silver will discolor when exposed to environments containing high concentrations of aggressive substances such as sulfur and halide. Corroded silver may lead to a worsening of the optical performance of the LED and can, in the worst case, lead to a failure of the LED. Do not expose this LED to aggressive atmospheres. Please note that corrosive gases may as well be emitted from materials close to the LED in the final product. PCBs or assemblies containing LEDs should not be stacked such that force is applied to the LED (Figure 14), or should not be handled directly at the LED.

Fig. 11: Incorrect storage of LEDs Generally, all LED assemblies should be allowed to return to room temperature after soldering, before subsequent handling, or the next process step.

Fig. 12: Correct storage of assemblies with LEDs Cleaning From today's perspective any direct mechanical or chemical cleaning of the DURIS S2 is forbidden. Isopropyl alcohol (IPA) can be used if cleaning is mandatory. Other substances or especially ultrasonic cleaning of DURIS S2 are generally not recommended. For dusty LEDs, a simple cleaning by means of purified compressed air (e.g. central supply or spray can) is recommended here. In any case, all materials and methods should be tested beforehand, particularly as to whether or not damage is associated with the component. Notes concerning cleaning can be also found in the corresponding data sheets.

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Processing The DURIS S2 is generally supplied in tape and reel format. Each reel contains only one single brightness group and one single wavelength or color group. The DURIS S2 is generally compatible with existing industrial SMT processing methods, so that current populating techniques can be used for assembly. For mounting the component, a standard reflow soldering process with forced convection under standard N2 atmosphere is recommended, in which a typical lead-free

SnAgCu metal alloy solder is used. Figure 15 shows the solder requirements and temperature curve for lead-free soldering of the DURIS S2. In this context, it is recommended to check the profile on all new PCB materials and designs. As a good starting point, the recommended temperature profile provided by the solder paste manufacturer can be used. The maximum temperature for the profile as specified in the data sheet should not be exceeded, however.

Fig. 13: Temperature profile for lead-free reflow s oldering according to JEDEC JSTD-020 In general, it is recommended that all twisting, warping, bending and other forms of stress to the circuit board should be avoided after soldering in order to prevent breakage of the LED housing or solder joints. Therefore, separation of the circuit boards should not be done by hand, but should exclusively be carried out with a specially designed tool.

PCB Type In addition to their primary function as a mechanical substrate and electrical contacting element for the components, modern circuit boards also have the task of ensuring stable characteristics within the

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circuitry to efficiently dissipate the heat which arises. The selection of appropriate materials for the circuit board is therefore of utmost importance, since the total thermal resistance of the system should be kept as low as possible. Materials or composites with insufficient thermal conductivity lead to an impairment of reliability or restrict operation at optimal performance, since the heat which arises cannot be dissipated in sufficient quantities. For further information about PCB type, solder pad, solder stencil, voids, post reflow inspection and verification of design, please see application note “Processing of SMD LEDs”. General information about PCB technologies can be found in the application note “PCB Technologies for LED Applications”. Solder Pad In the SMT process, the solder paste is normally applied by stencil printing. The amount to be applied as well as the quality of the paste deposits and the entire printing are primarily influenced and determined by the design of the printing stencil. In the end, this also has an influence on the solder quality, since effects such as solder bridges, solder spray and/or other soldering defects are largely determined by the design of the stencil apertures and the quality of the stencil printing (e.g. positioning, cleanliness of the stencil, etc.). The stencils and their apertures are thus specially laid out for the respective application. As an example, the recommended design and dimensions of the stencil apertures for the solder pad for the DURIS S2 are shown in Figure 10. Since the solder pad effectively creates the direct contact between the LED and the

circuit board, the design of the solder pad decisively contributes to the performance of the solder connection. The design has an influence on the solder joint reliability, the self-centering effect and heat dissipation. In most cases, it is therefore advantageous to use the recommended solder pad, since it is individually adapted to the properties and conditions of the LED. The corresponding solder pad can be found in the data sheet of each LED. Based on the given designs an optimized balance between good processability, the smallest possible positioning tolerance and a reliable solder connection can be achieved. However it should be noted that the self-centering effect is limited in its extent. Slightly misaligned components (less than 0.150 mm) will be automatically aligned during reflow due to the self-centering effect of the symmetrical pad design (Figure 11). If the placement position is greater than 150 µm from the center, the components should not be reflowed as electrical shorts resulting from solder bridges may be produced.

Fig. 14: Pick and place recommended placement position and self-alignment during reflow soldering If a narrow LED clustering is requested in the application, please note a direct side by side contact between the housings has to be avoided due to the risk of short circuits.

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Fig. 15: Recommended solder pad and solder stencil for DURIS S2 In general, the requirements for good thermal management should be taken into consideration in the application when designing the solder pads. In the end, this means that when designing the solder pads, the copper area should be kept as large as possible. This serves to dissipate and spread the generated heat over the PCB and is typically covered with a layer of solder resist. When printing with a stencil, the amount of solder paste is determined by the thickness of the stencil.

Fig. 16: 3D image for 120um solder paste For DURIS S2, a thickness of 120 µm is suitable and the Figure 12 shown the solder paste profile from the 3D Offline Solder Paste inspection system. However, the stencil thickness used may also depend on the other SMD components on the PCB. If needed, an appropriate solder stencil design can be found in the data sheet for the DURIS S2. Voids For a good thermal connection and a high board level reliability, it is recommended that

voids and bubbles should be eliminated in all solder joints. A total elimination of voids, particularly for the larger thermal pad, is difficult. Therefore, the design of the stencil aperture is crucial for minimization of voids. The recommended design openings in the stencil enables an out-gassing of the solder paste during the reflow soldering process and also serves to regulate the final solder thickness. Therefore, typical solder paste coverage of 50%-70% is recommended. In industry standards like IPC-A-610 D or J-STD-001D (which refer only to surface mount area array components like BGA, CSP, etc.) the amount of voids (verified by the x-ray pattern) should be less than 25%.

Fig. 17: X-ray image of a solder joint Internal studies and simulations at OSRAM Opto Semiconductors have determined, however, that for areas up to 50% of the thermal pad area, the voids only have a minor effect on the thermal resistance. The limit of the acceptable voiding can vary for each application and depends on the power dissipation and the total thermal performance

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of the system, affected by the PCB materials used. Solder Mask Due to the backward light of DURIS S2, the PCB surface needs to use high reflective white solder mask material to enhance the light extraction of DURIS S2. The white solder mask material should not discolour over time, which can affect the reflectance properties, when subjected to increase operating temperatures, pollution (deterioration of the finish material due to environment) or backward light of DURIS S2. It is recommended that customers work with their PCB suppliers to find out the most appropriate solder mask materials, which can fulfilled their application needs. Application example The main target application of DURIS S2 is for linear lighting such as T8 tube. This product has larger viewing angle in radiation pattern in term of FWHM. This key features enables the LED to be mounted with larger LED pitch compared to typical 0.2W E3/E5 devices. The mounting orientation of the DURIS S2 are recommended in Figure 18 to ensure good color homogeneity at system level viewed from all direction. High reflective coating materials are recommended at PCB to optimize the light output and minimize the hot spot detection at system level. The possible use of the DURIS S2 in different lighting environments will be demonstrated by means of the following example. Figure 19 shows a 2 feet (56mm in length) T8 linear tube in which 40 DURIS S2 LEDs with a brightness of 30 lm @65 mA) and a color temperature of 4000K are used as the light source.

With a total power of around 9 Watts including control circuitry, the LED module provides a luminous flux of 950 lm for the illumination.

Fig. 18: The mounting orientation of DURIS S2

Fig. 19: Shown the reference design for DURIS S2 inside T8 tube Summary Generally supplied in tape and reel, the DURIS S2 is compatible with existing industrial SMT processing methods, so that current populating techniques can be used for assembly. As the DURIS S2 is classified as an ESD sensitive device (Class 0, HBM), handling and processing must be ESD-conformed. It should also be kept in mind that the LED is not suitable for any direct mechanical or chemical cleaning. During handling and processing mechanical stress to the silicone encapsulation must be reduced or eliminated to the greatest extent possible. Penetration of the silicone should be avoided. Either can lead to impairment of the component. Specially designed and engineered to meet today’s linear lighting application needs, the DURIS S2 packs outstanding brightness into a low-power package making it the perfect light source for applications that require bright, homogeneous lighting. OSRAM Opto Semiconductors supports its customers during their development and design process in finding the best solution for a specific application.

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Appendix

Don't forget: LED Light for you is your place to be whenever you are looking for information or worldwide partners for your LED Lighting project.

www.ledlightforyou.com Revision History

Date Revision History Sept. 2015 Publishing of application note Aug. 2016 1. Add in the radiation characteristic of LED in forward and backwards

direction and guideline to optimize light output from the system. 2. Add in the general guideline for LED handling in aggressive

atmosphere. 3. Add in the recommendation for solder mask requirement.

Authors: Ng, Kok-Eng, Ch’ng Kar Siew, Lee Ee Lian, Tilman Eckert, Stich Andreas, Lang Kurt-Jürgen ABOUT OSRAM OPTO SEMICONDUCTORS OSRAM, Munich, Germany is one of the two leading li ght manufacturers in the world. Its subsidiary, OSRAM Opto Semiconductors GmbH in Regensburg (Germa ny), offers its customers solutions based on semiconductor technology for lighting, sen sor and visualization applications. Osram Opto Semiconductors has production sites in Regensburg ( Germany), Penang (Malaysia) and Wuxi (China). Its headquarters for North America is in S unnyvale (USA), and for Asia in Hong Kong. Osram Opto Semiconductors also has sales offices througho ut the world. For more information go to www.osram-os.com .

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