Metal Core Printed Circuit Board Research Articles

CVD processed ZnO thin film as solid thermal interface material in electronic devices: thermal and optical performance of LED

Purpose Polymer-based thermal interface materials (TIMs) are having pump out problem and could be resolved for reliable application. Solid-based interface materials have been suggested and reported. The purpose of this paper is suggesting thin film-based TIM to sustain the light-emiting diode (LED) performance and electronic device miniaturization. Design/methodology/approach Consequently, ZnO thin film at various thicknesses was prepared by chemical vapour deposition (CVD) method and tested their thermal behaviour using thermal transient analysis as solid TIM for high-power LED. Findings Low value in total thermal resistance (Rth-tot) was observed for ZnO thin film boundary condition than bare Al boundary condition. The measured interface (ZnO thin film) resistance {(Rth-bhs) thermal resistance of the interface layer (thin film) placed between metal core printed circuit board (MCPCB) board and Al substrates} was nearly equal to Ag paste boundary condition and showed low values for ZnO film prepared at 30 min process time measured at 700 mA. The TJ value of LED mounted on ZnO thin film (prepared at 30 min.) coated Al substrates was measured to be 74.8°C. High value in junction temperature difference (ΔTJ) of about 4.7°C was noticed with 30 min processed ZnO thin film when compared with Al boundary condition. Low correlated colour temperature and high luminous flux values of tested LED were also observed with ZnO thin film boundary condition (processed at 30 min) compared with both Al substrate and Ag paste boundary condition. Originality/value Overall, 30 min CVD processed ZnO thin film would be an alternative for commercial TIM to achieve efficient thermal management. This will increase the life span of the LED as the proposed material decreases the TJ values.

Influence of SiC reinforcement on microstructural and thermal properties of SAC0307 solder joints

The effect of SiC nano-phases (nano-particles and nano-fibers) addition into SAC0307 solder paste was investigated on the thermal and microstructural properties of the composite solder joints. The nano-phases were used between 0.125 and 1 wt%, and they were mixed into the solder paste by ball milling process. For the study power MOSFET (metal oxide semiconductor field effect transistor) components were soldered onto metal core printed circuit boards (MCPCBs). The thermal impedance Zth(t) and thermal resistance Rth of MOSFETs were measured by an indirect electrical method. Furthermore, the void formation and the microstructure of solder joints were also studied. The solderability and voiding properties of the composite solder alloys were acceptable. It was found that in 0.5 wt% amount, SiC nano-particles have positive effects on the thermal parameters of the solder joints, which could be explained by the IMC (intermetallic compound) layer growth suppression effect of the nano-phases. The microstructural analysis revealed that the microstructural refinement of the composite solder joints differs in the case of nano-particles and nano-fibers.

Arrangement of LEDs and Their Impact on Thermal Operating Conditions in High-Power Luminaires

Solid-state light sources are currently the fastest-growing group of light sources, replacing the previously used discharge and incandescent light sources. Thermal operating conditions of LEDs (Light Emitting Diode) play an important role in t maintaining long service life and constancy of luminous-electrical parameters. In the field of illumination, the service life parameter of light sources is important for the costs of maintenance of the illumination system, while the maintenance of the value of certain light parameters over time, such as luminous flux, color temperature and color rendering index, is related to the aesthetic effect of the illumination. In addition, limiting the junction temperature of solid-state light sources is particularly important in high-power luminaires dedicated to flood illumination. One of the elements shaping the thermal operating conditions of multi-source LED luminaires is the number of luminaires used, their arrangement, and the distance between LEDs installed on the MCPCB (Metal Core Printed Circuit Board) substrate. This article presents the results of simulation studies, realized using CFD (Computational Fluid Dynamics) software, where the temperature distribution and the junction temperature of the LED panel were determined for different configurations and distances between the LEDs. The results obtained were analyzed and conclusions were drawn based on them. Thermal tests performed and presented in the article cover scientific issues related to shaping the temperature distribution of the LED panel. They make it possible to determine the influence of thermal couplings between the sources, related to their number, distance and the value of the forward current, on the final temperature of the LED junction temperature. The presented research results may constitute auxiliary materials for designers of lighting luminaires, especially high-power luminaires, where a large number of high-power LED sources are installed in close proximity.

Improving the reliability of power LEDs with diamond boards

Despite being efficient devices, when compared to other light sources, high power light emitting diodes (LEDs) suffer from heating effects that have a negative impact on their reliability. Power LEDs are typically assembled on metal core printed circuit boards (MCPCBs) to facilitate the extraction of the heat. Diamond boards can also be used for the same purpose, since diamond is the best isotropic conductor of heat known to man and simultaneously an electrical insulator. In order to evaluate the impact of the boards on the device lifetime, high power Cree LEDs were mounted on FR4, MCPCB, and diamond boards. The case temperature was measured for different current ratings, and the aging acceleration factor of the devices mounted on FR4 and diamond boards was estimated relatively to the LEDs mounted on the MCPCB boards. Diamond boards were shown to have a tremendous impact on the lifetime; for the nominal current level, and depending on the activation energy of the aging processes, the LEDs mounted on diamond boards age 60–80 % slower than their counterparts mounted on the MCPCB boards.

Thermal Modelling an LED Bulb using IR Thermography and Bayesian Deconvolution

This study focuses on LED bulbs where LEDs are typically mounted on a metal core printed circuit board. A sample of LED bulbs having base E27 and a power range between 3.5-11.5 W have been measured. A thermal model will be found using thermal transient testing, infrared thermal measurements, and the Bayesian deconvolution. LED surface temperature will be measured without contact using a low-resolution IR imager. A test facility has been built which automatically switches power on and measures and records samples during the measurement cycle which typically lasts around one hour. This time duration was long enough for reaching the thermal steady-state condition. The procedure uses a measured thermal transient, first calculates the thermal impedance Zth, then the time constant spectrum Rζ(z) using the Bayesian deconvolution. An equivalent thermal network model will be found in Foster-presentation. This can be transformed to Cauer-presentation. The model is a driving point model for thermal impedance and includes thermal resistances and thermal capacitances. FEM simulation gives more detailed information about heat transfer paths and internal temperatures of an LED bulb.

The influence of SACX0307-ZnO nanocomposite solder alloys on the optical and thermal properties of power LEDs

PurposeThis paper aims to present the results of investigations that show the influence of ZnO composite soldering paste on the optical and thermal parameters of power light-emitting diodes (LEDs).Design/methodology/approachZnO nanocomposite solder alloys were produced via the ball milling process from the solder paste Sn99Ag0.3Cu0.7 (SACX0307) and 1.0 wt% of ZnO nanoparticle reinforcements with different primary particle sizes (200 nm, 100 nm and 50 nm). Power LEDs were soldered onto a metal core printed circuit board. A self-designed LED test system was used to measure the thermal and optical characteristics of the LEDs.FindingsThe influence of the soldering paste on the thermal and optical parameters of LEDs was observed. In all solder alloys, ZnO ceramic reinforcement, at a level of 1 wt%, increased the thermal parameters of LEDs and decreased their luminous efficiency. Thermal resistance values were10% higher, and junction temperature change over ambient temperature was 20% higher for the samples soldered with composite solder pastes than the reference sample. At the same time, luminous efficiency dropped by 32%.Originality/valueThe results prove that ZnO ceramic reinforcement of solder paste influences the thermal properties of solder joints. As was proven, the quality of the solder joints influences the whole assembly.

Influence of the soldering paste type on optical and thermal parameters of LED modules

PurposeThis paper presents the results of the investigations of LED modules soldered with the use of different soldering pastes.Design/methodology/approachThe tested power LED modules are soldered using different solder pastes and soldering processes. Thermal parameters of the performed modules are tested using indirect electrical methods. The results of measurements obtained for different modules are compared and discussed.FindingsIt was shown that the soldering process visibly influences the results of measurements of optical and thermal parameters of LED modules. For example, values of thermal resistance of these modules and the efficiency of conversion of electrical energy into light differ between each other even by 15%.Practical implicationsThe obtained results of investigations can be usable for designers of the assembly process of power LED modules.Originality/valueThis paper shows the investigations results in the area of effective assembly of power LEDs to the metal core printed circuit board (MCPCB) using different soldering pastes (REL22, REL61, LMPA-Q6, OM-5100, OM-338-PT, M8, OM-340, CVP-390). It was shown that the best thermal and optical properties of these modules are obtained for the OM5100 paste by Alpha Assembly.

Systematic Research on the Heat Dissipation Channel of High Power LED Street Lamps

This article mainly studies the thermal characteristics of light source of the street lamp, and systematically analyzes the effective ways of heat transfer and heat dissipation of street lamp. Based on experiments and finite element simulations, the heat dissipation channels of street lights were studied, and the weak links of heat transfer and heat dissipation were analyzed, and the heat dissipation structure of street lamp was optimized. The experimental results show that the junction temperature of the chip is lower than 90 °C in the steady state, and the luminous efficiency decreases by 5.93%. In order to ensure the efficiency and reliability of the street lamp, it is recommended that the junction temperature of the street lamp be controlled below 85 °C. After analyzing the arrangement of the chips, silicone grease with different thermal conductivity and aluminum substrate, it is found that the substrate is the bottleneck affecting effective heat transfer, and the use of diamond like carbon metal core printed circuit board (DLC-MCPCB) can reduce the junction temperature by 17.04 °C. Through the grid design of shell of the street lamp, the heat dissipation effect of the street lamp surface can be enhanced, and the junction temperature can be reduced by 7.04 °C. Based on these studies, the optimal design model of street lamp was obtained, which provides guidance for practical applications.

Impact of thermal interface material on luminous flux curve of InGaAlP low-power light-emitting diodes

Purpose One major problem in the lighting industry is the thermal management of the devices. Handling of thermal resistance from solder point to the ambiance of the light-emitting diode (LED) package is linked to the external thermal management that includes a selection of the cooling mode, design of heatsink/substrate and thermal interface material (TIM). Among the significant factors that increase the light output of the of the LED system are efficient substrate and TIM. In this work, the influence of TIM on the luminous flux performance of commercial indium gallium aluminium phosphide (InGaAlP) low-power (LP) LEDs was investigated. Design/methodology/approach One batch of LEDs was mounted directly onto substrates which were glass-reinforced epoxy (FR4) and aluminium-based metal-core printed circuit boards (MCPCBs) with a dielectric layer of different thermal conductivities. Another batch of LEDs was prepared in a similar way, but a layer of TIM was embedded between the LED package and substrate. The TIMs were thermally conductive epoxy (TCE) and thermally conductive adhesive (TCA). The LED parameters were measured by using the integrated system of thermal transient tester (T3Ster) and thermal-radiometric characterization of LEDs at various input currents. Findings With the employment of TIM, the authors found that the LED’s maximum luminous flux was significantly higher than the value mentioned in the LED datasheet, and that a significant reduction in thermal resistance and junction temperature was revealed. The results showed that for a system with low thermal resistance, the maximum luminous flux appeared to occur at a higher power level. It was found that the maximum luminous flux was 24.10, 28.40 and 36.00 lm for the LEDs mounted on the FR4 and two MCPCBs, respectively. After TCA application on the LEDs, the maximum luminous flux values were 32.70, 36.60 and 37.60 lm for the FR4 and MCPCBs, respectively. Moreover, the findings demonstrated that the performance of the LED mounted on the FR4 substrate was more affected by the employment of the TIM than that of MCPCBs. Research limitations/implications One of the major problems in the lighting industry is the thermal management of the device. In many low-power LED applications, the air gap between the two solder pads is not filled up. Heat flow is restricted by the air gap leading to thermal build-up and higher thermal resistance resulting in lower maximum luminous flux. Among the significant factors that increase the light output of the LED system are efficient substrate and TIM. Practical implications The findings in this work can be used as a method to improve thermal management of LP LEDs by applying thermal interface materials that can offer more efficient and brighter LP LEDs. Using aluminium-based substrates can also offer similar benefits. Social implications Users of LP LEDs can benefit from the findings in this work. Brighter automotive lighting (signalling and backlighting) can be achieved, and better automotive lighting can offer better safety for the people on the street, especially during raining and foggy weather. User can also use a lower LED power rating to achieve similar brightness level with LED with higher power rating. Originality/value Better thermal management of commercial LP LEDs was achieved with the employment of thermal interface materials resulting in lower thermal resistance, lower junction temperature and brighter LEDs.

Enhancement of luminous flux of InGaAlP-based low-power SMD LEDs using substrates with different thermal resistances

PurposeOptimization of light-emitting diodes’ (LEDs’) design together with long-term reliability is directly correlated with their photometric, electric and thermal characteristics. For a given thermal layout of the LED system, the maximum luminous flux occurs at an optimal electrical input power and can be determined using a photo-electro-thermal (PET) theory. The purpose of this study is to extend the application of the luminous flux equation in PET theory for low-power (LP) LEDs.Design/methodology/approachLP surface-mounted device LEDs were mounted on substrates of different thermal resistances. Three LEDs were attached to substrates which were flame-retardant fiberglass epoxy (FR4) and two aluminum-based metal core printed circuit boards (MCPCBs) with thermal conductivities of about 1.0 W/m.K, 2.0 W/m.K and 5.0 W/m.K, respectively. The conjunction of thermal transient tester and thermal and radiometric characterization of LEDs system was used to measure the thermal and optical parameters of the LEDs at a certain range of input current and temperature.FindingsThe validation of the extended application of the luminous flux equation was confirmed via a good agreement between the practical and theoretical results. The outcomes show that the optimum luminous flux is 25.51, 31.91 and 37.01 lm for the LEDs on the FR4 and the two MCPCBs, respectively. Accordingly, the stipulated maximum electrical input power in the LED datasheet (0.185 W) is shifted to 0.6284, 0.6963 and 0.8838 W between the three substrates.Originality/valueUsing a large number of LP LEDs is preferred than high-power (HP) LEDs for the same system power to augment the heat transfer and provide a higher luminous flux. The PET theory equations have been applied to HP LEDs using heatsinks with various thermal resistances. In this work, the PET theory luminous flux equation was extended to be used for Indium Gallium Aluminum Phosphide LP LEDs attached to the substrates with dissimilar thermal resistances.

120 W급 LED 가로등 개발을 위한 열전반도체 이용 강제방열

This study was carried out to develop 120 W class light-emitting diode (LED) security lights with smaller heat dissipation devices by improving the heat dissipation efficiency compared to existing security lights. Four 30 W class chip-on-board (COB) LED modules were placed in a luminaire, with three modules subjected to forced heat dissipation using thermoelectric elements. The thermoelectric element and LED module were packaged as a unit to improve the performance of the thermoelectric element, and the unit satisfied the optimal conditions for low power energy consumption of the thermoelectric element. When the electric power was 6.4 W, a 24.9% temperature decrease was achieved at the lowest temperature of the metal-core printed circuit board (76.2℃) through forced heat dissipation. Based on the results, the arithmetic lifespan of the LED light could be extended by 100.5%.

The Improvement of Bonding Metal Layers in a GaAs Vertical Structure Light-Emitting Diode Package

This paper presents an investigation into the reliability of substrate bonding between metal layers and gallium arsenide vertical-injection light-emitting diodes (GaAs VLEDs). In this study, molybdenum (Mo) acts as a buffer layer between the GaAs VLED and the aluminum-based metal core printed circuit board (MCPCB). The thermal expansion coefficient (CTE) value of GaAs is approximately equal to that of the Mo layer under the substrate. This is beneficial for slowing the decay of the adhesive bond due to temperature cycling from − 40°C to 125°C for 50 cycles. The experimental results show that the use of the Mo buffer layer greatly improved the electrical and optical performance of the LED packages. The average leakage current was reduced from 33.63 mA to 2.37 mA at the reversed voltage of − 3 V and the increase in light output power was 130% at an injection current of 0.7 A. The results also show that a Mo buffer layer can reduce the risk of cracking on bonding wires after the thermal shock test (TST). These results are useful for improving the aging of GaAs VLEDs.

The influence of soldering process parameters on the optical and thermal properties of power LEDs

PurposeThis paper aims to present the results of investigations that show the influence of soldering process parameters on the optical and thermal parameters of power LEDs.Design/methodology/approachThe power LEDs were soldered onto metal core printed circuit board (MCPCB) substrates in different soldering ovens: batch and tunnel types, characterized by different thermal profiles. Three types of solder pastes based on Sn99Ag0.3Cu0.7 with the addition of TiO2 were used. The thermal and optical parameters of the diodes were measured using classical indirect electrical methods. The results of measurements obtained were compared and discussed.FindingsIt was shown that the type of oven and soldering thermal profile considerably influence the effectiveness of the removal of heat generated in the LEDs tested. This influence is characterized by thermal resistance changes. The differences between the values of this parameter can exceed 20%. This value also depends on the composition of the soldering paste. The differences between the diodes tested can exceed 15%. It was also shown that the luminous flux emitted by the diode depends on the soldering process used.Practical implicationsThe results obtained could be useful for process design engineers for assembling power LEDs for MCPCBs and for designers of solid-state light sources.Originality/valueThis paper presents the results of investigations into the influence of the soldering profiles and soldering pastes used on the effectiveness of the removal of heat generated in power LEDs. It shows and discusses how the factors mentioned above influence the thermal resistance of the LEDs and optical parameters that characterize the light emitted.

Influence of the area of a thermal pad on optical and thermal parameters of LED modules

Purpose The purpose of this paper is to present and discuss the results of measurements illustrating influence of the area of a thermal pad and the kind of the used base on thermal and optical parameters of LED modules. Design/methodology/approach LED modules including six power LEDs are designed. In the layout of these modules, different areas of a thermal pad of each LED are used. These modules are made using the classical FR-4 base and metal core printed circuit board (MCPCB). Thermal and optical parameters of all the tested modules are measured using the method elaborated by the authors. Findings The obtained results of measurements prove that increasing the area of a thermal pad causes a decrease in thermal resistance of the tested LED modules and an increase in power density of the emitted light. The role of the area of a thermal pad is more important for the classical FR-4 base than for MCPCB. Research limitations/implications Investigations were performed for only two values of the area of thermal pads and selected values of LEDs forward current. Originality/value The presented results of investigations show how the used layout and type of the used base of these modules influence optical and thermal parameters of LED modules. Changing the base of a module can cause even a double decrease in thermal resistance and a double increase in power density of the emitted light.

Efficiency improvement of power LED modules using a hybrid aluminum nitride substrate

This study combined experimental and theoretical analysis to investigate the hybrid aluminum nitride (AlN) substrate that can effectively improve efficiency and heat dissipation of multi-chip LED modules. The experimental results showed that hybrid AlN substrate can effectively reduce the thermal resistance from junction to substrate ∆Rjs by 46% compared with metal core printed circuit board (MCPCB) as driving current increased from 0.6 A to 1.6 A. Under the rated current of 1.2 A, the Rjs and chip temperature of the AlN module was approximately 0.73 K/W and 10 °C lower than that in the MCPCB module. Compared to MCPCB, the hybrid AlN substrate also had 25% higher luminous flux at 1.2 A. Simulating results provided insight understanding of temperature distribution inside the LED modules and showed good consistency with experiments. Additionally, the decreasing rate of substrate temperature (Ts) outside the chips in AlN LED module is higher than in MCPCB LED module. This study demonstrated that the hybrid AlN substrate is a reliable and a cost effective design that can effectively improve both efficiency and heat dissipation of high power LED modules.

Thermal Performance of Double-Sided Metal Core PCBs

Thermal management in printed circuit boards is becoming increasingly more important as the use of LEDs is now widespread across all industries. Due to availability of the preferred electronic LED current drivers and system constraints for a machine-vision application, the design dictated the need for a double-sided metal core printed circuit board (MCPCB). However, design information for this relatively new MCPCB offering is sparse to non-existent. To fill-in this missing information in the literature, experiments were conducted where LEDs were arranged on a double-sided metal core printed circuit board (MCPCB), and their impact on the board temperature distribution was tested in a static fan-less configuration where the first condition was at room temperature, 23 °C, and the second configuration was for a heated environment, 40 °C. Two MCPCB orientations were tested (vertical and horizontal). Additionally, several LED arrangements on the MCPCB were configured, and temperatures were measured using a thermocouple as well as with a deep-infrared thermal imaging camera. Maximum temperatures were found to be 65.3 °C for the room temperature tests and 96.4 °C for the heated tests with high temperatures found in near proximity to the heat sources (LEDs), indicating less than ideal heat-conduction/dissipation by the MCPCB. The results indicate that the double-sided MCPCB topology is not efficient for high thermally loaded systems, especially when the target is a fan-less system. The results of testing indicate that for fan-less systems requiring high-performance heat-transfer, these new MCPCB are not a suitable design alternative, and instead, designers should stick with the more traditional single-sided metal-back PCB.

30 W급 COB LED의 열전소자 이용 강제방열

This study focuses on the development and production of 120 W LED street-lamps using four 30 W chip on board (COB) LED modules. The lamps’ heat dissipation efficiency was improved by packaging 30 W COB LEDs and thermoelectric modules. This study was also conducted to reduce the thermoelectric element driving power consumption and minimize the thermoelectric element driving power, resulting from forced heat dissipation.BRResults indicated that the minimum metal temperature of the metal core printed circuit board (MCPCB) reached 68.1℃ when the thermoelectric power consumption was 0.7 W; a temperature drop effect of approximately 16.1% occurred. The life extension effect is expected to be approximately 48.5% according to the lifespan arithmetic.BRThus, this technology can be applied to reduce the temperature and extend the life of COB LED modules; small-sized and lightweight luminaries can be realized by addressing the thermal problem of LED modules.

Parametric Compact Thermal Models of Power LEDs

Light-emitting diodes are nowadays the most dynamically developing type of light sources. Considering that temperature is the main factor affecting the electrical and lighting parameters of these devices, thermal models are essential subcomponents of the multidomain models commonly used for simulation of their operation. The authors investigated white power light-emitting diodes soldered to Metal Core Printed Circuit Boards (MCPCBs). The tested devices were placed in a light-tight box on a cold plate and their cooling curves were registered for different diode heating current values and various preset cold plate temperatures. These data allowed the computation of optical and real heating power values and consequently the generation of compact thermal models in the form of Foster and Cauer RC ladders. This also rendered possible the analysis of the influence of the considered factors on the compact model element values and their parametrization. The resulting models yield accurate values of diode junction temperature in most realistic operating conditions and they can be easily included in multidomain compact models of power light emitting diodes.

Effects of Substrate on Thermal and Optical Characteristics of High-Power ThinGaN White LED

Thin Gallium Nitride (ThinGaN)-based light-emitting diodes (LEDs) demonstrate high extraction efficiency and brightness. Their slim designs make them appropriate for lighting applications that demand high luminous flux, small space, and stability. Thermal resistance and junction temperature values under different boundary conditions can help in understanding thermal management of ThinGaN-based LEDs. In this paper, thermal and optical characteristics of ThinGaN (UX:3) white LED mounted on Metal-Core Printed Circuit Board (MCPCB) and a SinkPad MCPCB are investigated. Thermal and optical parameters of the LED are measured by thermal transient tester (T3Ster) and spectrometer devices. Results show that the LED attached to the SinkPad MCPCB obtained lower thermal resistance and junction temperature than MCPCB.

The influence of a soldering manner on thermal properties of LED modules

Purpose This paper aims to present the results of the influence of a manner of soldering light emitting diodes (LEDs) to the metal core printed circuit board on thermal parameters of the module LED containing these diodes. Design/methodology/approach Using the authors’ elaborated measuring method and the dedicated measurement set-up, transient thermal impedances of LED modules, mounted using different soldering processes and mounted to the heat-sink with different values of the moment of force, are measured. The obtained results of measurements are discussed. Findings It was shown experimentally that the manner of soldering could strongly influence efficiency of dissipation of heat generated in the module. The best thermal properties were obtained for soldering using vapour phase technology with vacuum and paste LFS-216LT. It was also proved that the moment of force used while mounting the considered modules on the heat-sink can result in a change of the value of thermal resistance of this module exceeding even 12 per cent. Research limitations/implications The investigations were performed for five LED modules operating at one, arbitrarily selected value of power dissipated in these modules mounted on the heat-sink of arbitrarily selected dimensions. Practical implications The obtained results of measurements could be usable for designers of mounting processes of power LED modules. Originality/value This paper presents the results of investigations of thermal properties of LED modules, in which different techniques of soldering are used. It was shown experimentally that the manner of soldering could strongly influence efficiency of dissipation of heat generated in the module. It was also proved that the moment of force used while mounting the considered modules on the heat-sink is important.