Bogdan Mihailescu

PCBs with different core materials assembling in vapor phase soldering technology

The increasing demand for high integration with continuous decreasing dimensions, maintaining quality and low cost for electronic modules brought on the market new types of printed circuits boards (PCBs), having different material core as substrate. Taking into account only rigid PCBs, glass for applications requiring high levels of cleanliness (medical apparatus) or dedicated to work in high humidity environmental conditions. In the practice, the EMS companies become to have difficulties for assembling the PCBs with glass core determined by high differences of the thermophisical properties compare to classical FR4, being hardly to adjust the SMT lines parameters. In this paper it is analyzed the influence of the PCB substrate thermophysical properties over lead-free solder joints quality and reliability as results of two soldering technologies, classical infrared-convection (IRC) and vapor phase (VPS). The experiments emphasize the differences regarding soldering thermal profile determined by the glass core of the PCB substrate. The optimum soldering solution for this PCB type will be provided. The results are undeniably that PCB support material is very important for the statement of the thermal profile of the process.

Lead/lead free solder joints comparative electrical tests as function of microstructure and soldering thermal profile

The solder joints properties are determined by the specific morphology of their microstructure. In the paper are presented the comparative resistance measurements of the solder joints resulted by usage of lead/lead-free solder pastes from Vapor Phase Soldering Processes (VPS) having thermal profile with two different cooling rate, slow one (0.5 K/s) and rapid one (4 K/s). The results will be promote to develop the practical applications of this soldering technology and to contribute at realization of a data base useful for better selection of lead-free solder paste in the design and manufacturing area.

Power LEDs operating temperature measurement using the protection reverse diode

Determination of the junction temperature of power LEDs is a great challenge. Indirect calculation of the junction temperature can be done by calculations, starting from the temperatures that could be measured with thermocouples in the accessible points and taking into consideration the thermal resistances of the materials included in the LED structure and in the mounting PCB used as heatsink. In this paper the authors proposed to use as temperature sensor the protection diode embedded in most of the power LED structures.

VPS control module EMC modeling and evaluation

The present paper is the result of studies, experiments, modeling and simulation regarding electromagnetic compatibility (EMC) of an electronic module able to control and vary the power requirements of a Vapor Phase Soldering (VPS) machine in order to obtain the desired thermal profile. The original electronic solution has been designed to obtain very low radiated electromagnetic emission during operation by switching the power device when the AC main is zero-crossing. Electromagnetic compatibility (EMC) performance and field effects have been analyzed using 3D EM simulation software, REMCOM XFdtd by considering the VPS process control module the source of radiations. EMC evaluations of the electronic module regarding conducted and radiated emissions have been done in laboratory in order to validate the modeling and simulations results. In order to complete the design for excellence (DFX) activities in case of new products development processes the authors intend to develop a design methodology which will include modeling and EM simulation for optimum electromagnetic compatibility within the Vapor Phase Soldering system.

Electrical characterization of ink-jet printed organic capacitors on flexible substrate

The present paper describes the fabrication and electrical characterization of printed capacitors using polyvinylphenol (PVP) as dielectric. The recently developed drop-on-demand inkjet printing technology was used to fabricate the components. The printing ink SunTronic EMD 5603 with silver nanoparticles was used to deposit the capacitors’ plates. Two different types of structures have been produced. One structure has a single layer of PVP dielectric material, while the second capacitor has two layers of insulating material. The aim of the work was to determine the influence of the dielectric thickness on the overall capacity of the device. The structures were submitted to thermal curing treatment prior to measurements. The measured capacity of the devices ranges from 40pF to 400pF depending on the thickness of the dielectric layer.

Start Soft Stop for controlling a reversible electric motor used in automotive

Accumulators used in electric vehicles being in production to date have the disadvantage of a limited number of charge-discharge cycles (lead-acid accumulators) or high acquisition price (NiMH, Li-Ion) and long full recharge duration. This paper presents a study on a solution to increase the life cycle of a typical battery pack used in automotive applications by recovering the deceleration energy (power generation control) and its storage in a battery of Electrochemical Double-Layer Capacitor (EDLC). Electronic module named Start Soft Stop (SSS) allows the control of energy transmitted to the electric motor, including the start and stop phases. The method used has minimal electromagnetic interference due to switching of the power semiconductor device as it passes through zero voltage. EDLC allows rapid storage and release of energy of 300–400A if needed without using the energy stored in the battery system.

The modeling & EM simulation assessment as part of DFX methodology

The paper is the result of studies, experiments and simulations regarding electromagnetic compatibility (EMC) performance of an intelligent electronic module used to obtain variable and controllable power injection during the Vapor Phase Soldering process (VPS) including the power-on and power-off phases. The module represents an original solution for low conducted and especially low radiated emissions by switching the power semiconductor devices close to the zero crossing of the mains voltage. The necessity to be optimized from EMC points of view is resolved by modeling and simulating using 3D EM simulation software, REMCOM XFdtd, for evaluating the performance and electromagnetic field effects of the VPS process power control module considered as a radiating device. The modeling process is based on preliminary measurements already taken and validated by other complex measurements which imply the need for the new experiments design. The authors intend to develop a design methodology based on the works presented in the paper which will include modeling and EM simulation, in order to complete the design for excellence (DFX) activities in case of the new products development processes.

Comparative assessment of maxwell and Helmholtz coils magnetic field for biotechnological applications

The studies regarding magnetic field (MF) biotechnological applications in the range of Extremely Low Frequency (ELF: 3Hz to 300Hz, ITU Recommendation V.431-7) were generally based on Helmholtz coils (HC) systems in order to obtain a constant intensity for a determined volume. The paper presents the comparative studies of HC and Maxwell coils (MC) consisting in modelling, simulations and measurements of MF intensity. For this the geometry of the external coils of the MC system was designed identically with HC type. Based on the obtained results, there are defined the internal field intensity distribution for both coils systems used to design biotechnological applications.

Investigation on current capabilities of Ni-based conductive pastes for PCB repair

The paper presents some electrical and thermal tests and experiments related to the current capabilities of PCB traces repaired with Nickel-based conductive paste. The lack of available scientific information in this topic motivated us to perform this investigation regarding the heating of a PCB trace segment made from conductive paste during current flowing through it. Based on the experimental results, the authors want to offer a reliable technical resource in the case of traces repaired with Ni-based conductive paste or other applications where traces made of conductive paste are used.

Device for multiple environment parameters measurements for agriculture use

The paper presents improvements made for the experimental model of a Device for Multiple Environment Parameters Measurements for Agriculture use. The aim was to obtain a better water management by providing complete information for soil characterization in terms of moisture, as well as rain water presence. One novelty of the work is the possibility of determination of the water absorption by the soil by using three electrodes instead of two. The electrodes are placed from the very bottom of the Multi-sensor device rod towards the top at 100 mm pitch one another. There will be two measurements that will characterize the soil moisture at different depths. Another novelty is the reduction of the polarization of the electrodes. Since the soil moisture determination is not done using AC voltage, but pulsed DC voltage signal with respect to the ground, a method was designed in order to change the voltage reference each measurement.