Application Note WICOP2 New Generation of WICOP Introduction This application note addresses the recommended assembly and handling guidelines for the WICOP2 series of LEDs. The WICOP2 series are Direct SMT LEDs, that due to their small size and construction, require special assembly and handling. This application note outlines the handling and assembly procedures that are, required to ensure reliable manufacturing, high lumen output and long lumen maintenance lifetime. Scope The assembly and handling guidelines in this application brief apply to the following products with the part number designations as described below. Z8 YXX-WA-CN XX Designates packaging size ( 19 for 1.81x1.81mm size, 15 for 1.41x1.41mm size) A White Color (0 for Cool, N for Neutral, W for Warm) N Designates CRI (7 for CRI min.70, 8 for CRI min. 80, 9 for CRI min. 90) WICOP Application Note © 2013 All Rights Reserved. Rev1.0, Sep 15, 2015 1 www.seoulsemicon.com Application Note WICOP2 - High-power LED Table of Contents Index • Introduction 1 • Scope 1 • Component 3 • Printed Circuit Board Design Guideline 6 • Thermal Measurement Guideline 8 • Assembly Process Guideline 10 • Array Design Guideline 13 • WICOP2 Characteristic Graph 15 • Company Information 19 WICOP Application Brief © 2013 All Rights Reserved. Rev1.0, Sep 15, 2015 2 www.seoulsemicon.com Application Note WICOP2 - High-power LED 1. Component 1.1 Description The WICOP2 Series of LEDs are based on Direct SMT LEDs. They are ultra-compact, high-power, surface mount white LEDs. Each WICOP2 LED consists of high brightness InGaN LED chip with a thin layer of silicone to protect the LED chip and phosphor from environment. An ESD diode is not included in the package. Anode 0,3 0,56 Cathode 0,56 The bottom of the WICOP2 LEDs have two different sized solder pads for the anode and cathode as shown in Figure 1. 1,41 BOTTOM VIEW Z8Y19 SIDE VIEW Cathode BOTTOM VIEW Z8Y15 SIDE VIEW Figure 1. WICOP2 Z8Y19, Z8Y15 Solder Pad Dimensions. WICOP Application Brief © 2013 All Rights Reserved. Rev1.0, Sep 15, 2015 3 www.seoulsemicon.com Application Note WICOP2 - High-power LED 1.2 Optical Center The theoretical optical center of the Z8Y19 is 0.905mm from the edges of the part. The optical center of the Z8Y15 is 0.705mm. (see Figure 2). 0.905mm 0.705mm Z8Y15 Z8Y19 Figure 2. Optical Centers of the WICOP2 Series 1.3 Handling Precaution Improper handling of WICOP2 may damage the LED and can impact the overall performance and reliability. In order to minimize the risk of damage to the LED during handling, WICOP2 should only be picked up by automated SMT machine or vacuum tweezers. At no times should metal tweezers be used to handle the LEDs as shown in Figure 3a. When handling finished boards containing WICOP2, do not touch the surface of the LED with fingers or any other material . Do not apply pressure on the top or sides of the LED. And avoid all contact to the LED. Do place the boards with the LED on the bottom side, on a table or stack multiple boards on top of each other as shown in Figure 3b. Since the silicone layer of the LEDs is soft, abrasion may cause catastrophic failure of the LED. WICOP Application Brief © 2013 All Rights Reserved. Rev1.0, Sep 15, 2015 4 www.seoulsemicon.com Application Note WICOP2 - High-power LED Figure 3 (a). Incorrect handling of WICOP2 LEDs Figure 3 (b). Incorrect handling of WICOP2 LEDs 1.4 Cleaning The WICOP2 should not be exposed to dust and debris. Excessive dust and debris may cause a decrease in LED performance. In the event that the surface of a the LED requires cleaning, a compressed gas duster at a distance of 6” away will be sufficient to remove the dust and debris or an air gun with 20 psi (at nozzle) from a distance of 6”. 1.5 Electrical Isolation The WICOP2 contains two electrical pads on the bottom of LED with a spacing of 0.3mm. In order to avoid any electrical shocks and/or damage to the WICOP2, board designs need to comply with the appropriate standards of creeping distance. 1.6 Mechanical Files Mechanical drawings for WICOP2 Series (2D and 3D) are available upon request. WICOP Application Brief © 2013 All Rights Reserved. Rev1.0, Sep 15, 2015 5 www.seoulsemicon.com Application Note WICOP2 - High-power LED 2. Printed Circuit Board Design Guideline WICOP2 is recommended to be soldered onto a Metal Core PCB (MCPCB) for optimal performance and to designed to minimize the overall thermal resistance between the LED and the heat sink. 2.1 WICOP2 Solder Footprint For proper operation, the WICOP2 anode and cathode need to be soldered onto corresponding pads on a PCB. The size of the pads and the corresponding size of the solder stencil are shown in Figure 4. 0,56 0,34 0,98 0,34 1,41 1,41 0,98 ST 0,3 0,56 Anode 0,3 0,56 Cathode 0,56 The electrical pads of the WICOP2 also serve as thermal pads between the LED and the PCB. To enhance heat dissipation from a WICOP2 into the PCB, we recommend extended the copper area around each electrode, where possible. 0,91 0,91 0,31 0,31 0,3 Cathode Figure 4. Recommended PCB Footprint for. WICOP2 All dimensions in mm. WICOP Application Brief © 2013 All Rights Reserved. Rev1.0, Sep 15, 2015 6 www.seoulsemicon.com Application Note WICOP2 - High-power LED 2.2 Silk Color The performance of an WICOP2 can be impacted by the color of the silk screen used on the PCB. There can be an efficacy loss due to optical absorption by a black color. It is recommended to either use yellow color for the silk screen or not to use any markings around a WICOP2 as shown in Figure 5. X O Figure 5. WICOP2 Silk color Recommendations 2.3 PCB Artwork The PCB design for the WICOP2 Series can impact the thermal performance of the end product. Figure 6 shows two different artwork designs for the same circuit. The red pattern indicate the copper traces. Wide copper traces should be used to allow a robust thermal path for the anode and cathode pads. X O Figure 6. PCB layout recommendations WICOP Application Brief © 2013 All Rights Reserved. Rev1.0, Sep 15, 2015 7 www.seoulsemicon.com Application Note WICOP2 - High-power LED 2.4 PSR (Photo Solder Resist) Seoul Semiconductor recommends a PCB with high optical reflectivity PSR for the WICOP2. Because of the radiation pattern of the LED, the reflectivity of the PCB (PSR) can impact the optical efficacy. It is recommended that the reflectivity of the PSR is greater than 80%. 2.5 Minimum Spacing Seoul Semiconductor recommends a minimum edge to edge spacing between adjacent WICOP2 of 0.2mm. The spacing of multiple WICOP2 can impact the performance of a LED system in two ways. 1) Heat dissipation: Close spacing of the LEDs may limit the PCB’s to ability to dissipate the heat from the LEDs. 2) Optical Absorption: Close spacing of the LEDs could impact the light output due to optical absorption or cross talk between adjacent LEDs. More information on this can be found in the array guidelines(Section 5). 3. Thermal Measurement Guidelines This section provides general guidelines on how to determine the junction temperature of a WICOP2 in order to verify that the junction temperature in the actual application does not exceed the maximum allowable temperature specified in the datasheet. The typical thermal resistance RƟjs between the junction and the thermal pad for WICOP2 is specified in their respective datasheet. For a WICOP2, both of the electrode pads serve as thermal pads. With this information, the junction temperature Tj can be determined according to the following equation: Tj = TS + RƟjs • Pelectrical In this equation Pelectrical is the electrical power going into the WICOP2 and TS pad is the temperature at the bottom of one of the WICOP2 electrodes or solder point temperature, assuming both WICOP2 electrodes are connected to copper pads on the PCB. Due to the size of the WICOP2, it may be difficult to measure the thermal pad temperature directly. Therefore, a practical way to determine the WICOP2 junction temperature is by measuring the temperature Ts of a predetermined sensor pad on the PCB close to the WICOP2 with a thermocouple as shown in Figure 7. WICOP Application Brief © 2013 All Rights Reserved. Rev1.0, Sep 15, 2015 8 www.seoulsemicon.com Application Note WICOP2 - High-power LED To ensure accurate readings, the thermocouple must make direct contact with the copper of the PCB onto which the WICOP2 electrode pads are soldered, i.e. any solder mask or other masking layer must be first removed before mounting the thermocouple onto the PCB. Figure 7. Recommended Ts configuration The following guidelines help determine appropriate Ts location in a densely packed array application in order to approximate the maximum junction temperature in the WICOP2 array: a. If there is no symmetry in the copper layout of the PCB, it is best to place the Ts point next to the electrical pad (anode or cathode) where heat spreading into the PCB is most impeded. This is typically the electrode with the least amount of copper. b. If different drive currents are used for each WICOP2, it is generally best to measure the temperature next to the LEDs which consumes the most amount of electrical power. The thermal resistance RƟjs between the WICOP2 junction and Ts point was experimentally determined to be typical 3K/W for a WICOP2 of the 1.5mm thick AlMCPCB board (2oz copper or 80~100µm thick 5W/m·K dielectric layer). LED board configurations with a larger number of closely packed WICOP2 may require additional thermal modeling to determine the pad temperature of the LEDs in the center of the array which are not easily accessible. WICOP Application Brief © 2013 All Rights Reserved. Rev1.0, Sep 15, 2015 9 www.seoulsemicon.com Application Note WICOP2 - High-power LED 4. Array Process Guideline 4.1 Stencil Design The appropriate stencil design for WICOP2 is included in the PCB footprint design (see Figure 4). The recommended stencil thickness is 100~120μm. The slightly smaller stencil pattern, compared to the solder resist opening, prevents the solder paste leakage from accidentally bridging between the electrodes, which are only spaced 300μm apart. (See 2.1 WICOP2 Solder Footprint) 4.2 Pick-and-Place Automated pick and place equipment provides the best handling and placement accuracy for WICOP2. Figure 8 shows pick and place nozzle designs. Based on these pick and place experiments, Seoul Semiconductor recommends to customers to take the following general pick and place guidelines : 1. The tip of the nozzle should be positioned on the flat surface above the LED chip area. 2. The nozzle tip should be clean and free from any particles. 3. During setup and any initial production runs, it is a good practice to inspect the top surface of the WICOP2 under a microscope to ensure the emitters are not accidentally damaged by the pick and place nozzle. Items Outer diameter X Remark 1.2~1.6 mm Inner diameter Y 0.5~0.65 mm Materials Rubber or Ceramic Figure 8. Pick and place nozzle design and dimensions WICOP Application Brief © 2013 All Rights Reserved. Rev1.0, Sep 15, 2015 10 www.seoulsemicon.com Application Note WICOP2 - High-power LED 4.3 Solder Paste Seoul Semiconductor recommends to use no-clean solder paste, SnAgCu (tin/silver/copper) of solder paste compositions. 4.4 Stencil Printing The recommended stencil thickness is 0.1~0.12mm. For good quality stencil printing, there are several important factors for consideration. 1. The stencil opening wall should be smooth, free from debris, dirt and burr. 2. The stencil surface should have uniform thickness throughout the stencil plate. 3. Positional tolerance between the stencil plate and the PCB should be small enough to ensure that the solder paste is not printed outside the footprint. Items Squeeze conditions Stencil mask Remark Pressure 2.5-5.0Kgf/㎠ Distance 2-4mm Velocity 20-100mm/sec Thickness 0.1~0.12mm Vacuum 0.5±0.05mpa Solder paste area X, Y Tolerance 90-100% ±150 um Table 1. Stencil mask and soldering information. WICOP Application Brief © 2013 All Rights Reserved. Rev1.0, Sep 15, 2015 11 www.seoulsemicon.com Application Note WICOP2 - High-power LED 4.5 Reflow Process A standard SMT reflow profile can be used to WICOP2. An example of the reflow conditions is shown in Figure 9 and Table 2. Figure 9. Solder reflow profile. Table 2. Recommended reflow conditions Profile Feature Pb-Free Assembly Average ramp-up rate (Tsmax to Tp) 3° C/second max. Preheat - Temperature Min (Tsmin) - Temperature Max (Tsmax) - Time (Tsmin to Tsmax) (ts) 150 °C 180 °C 80-120 seconds Time maintained above: - Temperature (TL) - Time (tL) 217~220°C 80-100 seconds Peak Temperature (Tp) 250~255℃ Time within 5°C of actual Peak Temperature (tp)2 20-40 seconds Ramp-down Rate 6 °C/second max. Time 25°C to Peak Temperature 8 minutes max. Atmosphere Nitrogen (O2<1000ppm) Table parameters established based on SMIC: M705-GRN360-K2-V (solder paste) Caution (1) Re-soldering should not be done after the LEDs have been soldered. If re-soldering is unavoidable, LED`s characteristics should be carefully checked before and after such repair. (2) Do not put stress on the LEDs during heating. (3) After reflow, do not warp the circuit board. (4) After reflow, do not clean PCB by water or solvent. WICOP Application Brief © 2013 All Rights Reserved. Rev1.0, Sep 15, 2015 12 www.seoulsemicon.com Application Note WICOP2 - High-power LED 5. WICOP2 Array Guide Seoul Semiconductor recommends a minimum edge to edge spacing between WICOP2 of 0.2mm. Placing multiple WICOP2 too close to each other may adversely impact the ability of the PCB to dissipate the heat from the LEDs. 5.1 Efficacy dependency on die spacing The efficacy of a WICOP2 array depends on die spacing. There is efficacy loss due to optical absorption by adjacent LEDs. The data indicates above 1mm between die spacing, the efficacy variation is saturated (Figure 11). For this test case, the WICOP2 array was operated at 2W/Pkg. The PCB used was a 1.5mm thick Al-MCPCB, 1.5mm X 1.5mm size board with 2oz copper. Figure 10. Simulation and device configurations Figure 11. Simulation and Device test results. WICOP Application Brief © 2013 All Rights Reserved. Rev1.0, Sep 15, 2015 13 www.seoulsemicon.com Application Note WICOP2 - High-power LED The results of a simulation based on optical absorption by adjacent WICOP2 and actual measurements are shown in Figure 11. The losses shown in the simulation do not take into account thermal effects only simulate the cross talk between the LEDs. The measurement were taken at 25°C with pulse condition with 2W operation. Simulation and device measurement results show some difference, but the efficacy variation trend is similar. This measured difference can be attributed to small differences in the LED flux or the assembly process. 5.2 Junction temperature dependency on die spacing Placing multiple WICOP2 too close to each other may also adversely impact the ability of the PCB to dissipate the heat from the LEDs. Board configurations with numbers of closely packed WICOP2 may require additional thermal modeling to determine the junction temperature. Figures 12 and 13 show the thermal simulation results of various LED spacing. Figure 12. Thermal simulation configurations. Figure 13. Thermal simulation results depend on WICOP2s’ distance. WICOP Application Brief © 2013 All Rights Reserved. Rev1.0, Sep 15, 2015 14 www.seoulsemicon.com Application Note WICOP2 - High-power LED 6. WICOP2 Characteristics Graph (Z8Y19) ◆ Junction Temperature vs. Relative Luminous Output , Current = 700mA 120 Response: Flux vs Temperature Temperature Relative Flux[%] 25 111.8 50 106.0 60 70 102.3 85 100 40 100 96.4 125 91.1 145 87.1 Relative luminous flux [%] 100 80 20 0 25 50 75 100 125 o Junction Temperature [ C] ◆ Junction Temperature vs. Relative Forward Voltage , Current = 700mA 0.25 Response: VF vs Temperature 0.20 0.15 0.10 VF 0.05 Temperature Relative Voltage 25 0.14 50 0.06 70 0.02 0.00 85 0 -0.05 100 -0.03 -0.10 125 -0.06 -0.15 145 -0.09 -0.20 25 50 75 100 125 o Junction Temperature [ C] WICOP Application Brief © 2013 All Rights Reserved. Rev1.0, Sep 15, 2015 15 www.seoulsemicon.com Application Note WICOP2 - High-power LED ◆ Forward Current vs. Forward Voltage , TJ = 85℃ 2.2 Response: Voltage vs Current 2.0 Voltage Current [mA] 2.71 100 2.88 300 3.01 500 1.0 3.12 700 0.8 3.26 1000 0.6 3.40 1400 0.4 3.44 1600 0.2 3.48 1800 0.0 3.51 2000 Forward Current [A] 1.8 1.6 1.4 1.2 2.6 2.8 3.0 3.2 3.4 3.6 Forward Voltage [V] ◆ Forward Current vs. Relative Luminous Flux , TJ = 85℃ 240 Response: Flux vs Current Relative Luminous Flux [%] 220 200 Current [mA] Relative Flux[%] 180 100 16.2 160 300 46.9 140 500 74.1 120 700 100 100 1000 136.1 80 1400 179.4 60 1600 198.9 40 1800 216.3 20 2000 233.7 0 0 200 400 600 800 1000 1200 1400 1600 1800 2000 Forward Current [mA] WICOP Application Brief © 2013 All Rights Reserved. Rev1.0, Sep 15, 2015 16 www.seoulsemicon.com Application Note WICOP2 - High-power LED 6. WICOP2 Characteristics Graph (Z8Y15) ◆ Junction Temperature vs. Relative Luminous Output , Current = 700mA 120 Response: Flux vs Temperature Relative luminous flux [%] 100 80 60 40 20 Temperature Relative Flux[%] 25 111.8 50 106.0 70 102.3 85 100 100 96.4 125 91.1 145 87.1 0 25 50 75 100 125 o Junction Temperature [ C] ◆ Junction Temperature vs. Relative Forward Voltage , Current = 700mA 0.30 Response: VF vs Temperature 0.25 VF 0.20 Temperature Relative Voltage 25 0.26 0.15 40 0.17 0.10 80 0.01 0.05 85 0 0.00 100 -0.04 -0.05 125 -0.08 -0.10 130 -0.09 145 -0.12 -0.15 25 50 75 100 125 o Junction Temperature [ C] WICOP Application Brief © 2013 All Rights Reserved. Rev1.0, Sep 15, 2015 17 www.seoulsemicon.com Application Note WICOP2 - High-power LED ◆ Forward Current vs. Forward Voltage , TJ = 85℃ 1.4 Response: Voltage vs Current Forward Current [A] 1.2 Voltage Current [mA] 2.52 100 2.74 300 2.93 500 3.09 700 3.16 800 3.23 900 3.30 1000 3.36 1100 3.42 1200 1.0 0.8 0.6 0.4 0.2 0.0 2.4 2.6 2.8 3.0 3.2 3.4 3.6 Forward Voltage [V] ◆ Forward Current vs. Relative Luminous Flux , TJ = 85℃ 160 Relative Luminous Flux [%] Response: Flux vs Current 140 Current [mA] Relative Flux[%] 120 100 18.2 300 49.1 500 76.0 700 100 800 111.2 900 121.8 1000 131.9 1100 141.6 1200 151.0 100 80 60 40 20 0 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 Forward Current [mA] WICOP Application Brief © 2013 All Rights Reserved. Rev1.0, Sep 15, 2015 18 www.seoulsemicon.com Application Note WICOP2 - High-power LED Company Information Published by Seoul Semiconductor © 2013 All Rights Reserved. Company Information Seoul Semiconductor (www.SeoulSemicon.com) manufacturers and packages a wide selection of light emitting diodes (LEDs) for the automotive, general illumination/lighting, Home appliance, signage and back lighting markets. The company is the world’s fifth largest LED supplier, holding more than 10,000 patents globally, while offering a wide range of LED technology and production capacity in areas such as “nPola”, "Acrich", the world’s first commercially produced AC LED, and "Acrich MJT Multi-Junction Technology" a proprietary family of high-voltage LEDs. The company’s broad product portfolio includes a wide array of package and device choices such as Acrich and Acirch2, high-brightness LEDs, mid-power LEDs, side-view LEDs, and through-hole type LEDs as well as custom modules, displays, and sensors. Legal Disclaimer Information in this document is provided in connection with Seoul Semiconductor products. With respect to any examples or hints given herein, any typical values stated herein and/or any information regarding the application of the device, Seoul Semiconductor hereby disclaims any and all warranties and liabilities of any kind, including without limitation, warranties of non-infringement of intellectual property rights of any third party. The appearance and specifications of the product can be changed to improve the quality and/or performance without notice. WICOP Application Brief © 2013 All Rights Reserved. Rev1.0, Sep 15, 2015 19 www.seoulsemicon.com