Bálint Sinkovics

Thermal Simulation of UV Laser Ablation of Polyimide

Our aim is to provide a simulation tool for manufacturing processes that takes the influence of temperature distribution thus the underlying copper pattern and pulse repetition frequency into account. To establish such simulation software a finite element model was set up which is able to describe the thermal processes and ablation induced by laser irradiation of polymers. The etch rate description usually applied for excimer lasers was slightly altered to be adequate for Gaussian lasers by writing pulse energy instead of fluence. This theoretical consideration was proved by experiments. The experiments also revealed the temperature dependence of etch rate and the influence of pulse repetition frequency on the amount of ablated material. The experimental and simulation results are in good agreement.

Board level investigation of BGA solder joint deformation strength

Abstract In this paper we present a method to determine the stress in BGA solder joints on complex, real assembled circuit boards. To be able to investigate the mechanical effects of post-reflow assembly within the solder joints of BGA components, it is necessary to undertake a mechanical investigation at board level by taking into consideration the effect of the adjacent components and the interconnection layer layouts. In our project, we have developed a method of how to investigate the board level deformation strength of BGA joints. The elastic properties of a real assembled circuit board and of a circuit bare board are measured; an FEM model is then created, both of the bare board and of the assembled printed circuit board taking into account the layout of the interconnection layers. The advantage of this PCB FEM model is that the deformation of a PCB of any size and for any load can be calculated quickly using any ordinary computer. In our project, we also have created another detailed FEM model for the BGA solder joints. Using the constructed FEM models, we are able to determine the stress in BGA solder joints on a real electronic product for a typical type of load (i.e. bending of PCB) thereby verifying our method. Since the simulated results correspond well to previous literature written on this topic, we consider that our method is appropriate for calculating stress in the solder joints of multi-lead components on complex, fully assembled circuit boards.

Improved method for determining the shear strength of chip component solder joints

Abstract In this paper an improved method has been presented to determine the solder joint shear strength of passive discrete surface mounted (SMD) chip components (like resistors and capacitors). To calculate the stress in a solder joint in the case of shear loading, the force applied should be measured and the amount of joined surface (wetted area of the component metallization) calculated. Using the method we suggest, we first measured the exact position of the chip component after soldering according to the guidelines set out in standard IPC 9850 (Institute for Interconnecting and Packaging Electronic Circuits). To determine the accurate value of the joined surface, a 3D profile calculation was carried out taking into account the exact position of chip components after soldering. The calculation of the profile was based on the principle of minimum energy. Then, the next stage was to determine the maximum force experimentally that the solder joint was able to withstand before failure in shear. The evaluation of the shear load results verified that the standard deviation coefficient of the results was lower when the shear strength of the solder is characterized by the maximum stress instead of maximum force. It was proved by our experiments and by simulations that the shear strength of misaligned components solder joints depends on the degree of component misalignment after reflow soldering.

Simulation and indirect measurement of temperature change in polyimide induced by laser ablation at 355 nm

Thermal effect plays an important role during frequency tripled nanosecond Nd:YAG laser ablation of polyimide. This paper describes simulation results and experimental investigations of laser induced temperature change in polyimide. The experimental results show that the ablation rate is temperature dependent, which means the underlying copper layer and the pulse repetition frequency (PRF) influence the etch depth. Based on our model it is possible to control the processing parameters according to the pattern geometry for a better exploitation of laser micromachining

Predicting Component Self-Alignment in Lead-Free Reflow Soldering Technology by Virtue of Force Model

Since lead-free soldering is initiated in the electronic industry in 1st of July 2006, studying the behaviour of lead-free solders in depth is more important than ever. Several studies and articles have claimed that lead-free solders do not promote the self-alignment of components, what is in contradiction with the observation of our previous experiments. Dynamic behaviour of SMT (surface mount technology) chip components during lead-free reflow soldering will be demonstrated, especially focusing on movement. A force model will be given whereby component self-alignment can be predicted in the case of using lead-free solder pastes. Experiments have been made by misplacing chip components with different sizes and the results are presented in the paper

Feasibility-based investigation of wind turbines power prediction

In the last century people started to prefer using long-term sustainable alternative energy sources because of environmental impact of the vast primer energy consumption increase. This papers investigations based on a Hungarian wind parks predicted and measured power datasets from February to September. Firstly, it is needed to turn out the applied measured and predicted wind values from available datasets using power curve. Knowing the statistical properties of the wind speed is very helpful with regard to the prediction of power output as the wind speed is the main input variable fed into the power prediction system. For this reason it is important to investigate the role of the power curve was used in transforming the distributions of the wind speed and its error into those of the power output. It is examined on different predicted wind ranges to draw conclusions about the specialty of the relation of wind and speed parameters. This investigation gives a theoretical base for a further wind prediction system.

Characterization of microstructure of lead free solder by different image processing algorithms

The microstructure of lead free solder joints was investigated by three different image processing techniques. Tin (Sn) was extracted from the cross sectioned samples by selective etching technique. Samples were generated by laser soldering. The cellular network of the Sn-Ag intermetallic compound remained intact. The images were taken by SEM and the compounds were identified by EDX measurements. A special Elastic String Image Processing (ESIP) algorithm was developed in order to measure the average gap size of this network. The results of the algorithm were compared to results prepared by basic thresholding and watershed techniques. The experiments show us that due to the fibrillose structure the thresholding methods does not fulfil the requirements, while using either the watershed, or our new algorithm, the average grain size of the microstructure was determined. ESIP algorithm results carry some further information about the surface energy of the crystallite grains, so technological parameters could be concluded only by the observation of the microstructure of the solder

Studying the Dynamic Behaviour of Chip Components during Reflow Soldering

Since lead-free soldering is initiated in the electronic industry in 1st of July 2006, studying the behaviour of lead-free solders in depth is more important than ever. The small chip components of present day demand for very accurate component placement machines, in order to prevent common reflow failures such as skewing or tombstoning. The ability of components to be self-aligned during soldering works against these failures, therefore it matters to what extent the solder promote this effect. Dynamic behaviour of SMT (surface mount technology) chip components during lead-free reflow soldering is demonstrated in the paper, especially focusing on movement. A force model is given by the virtue of the four forces, which have effect on the chip during reflow soldering, namely: the force originating from hydrostatic and capillary pressure, the force of gravity, the force of dynamic friction and the force originating from the surface tension. The self-alignment of 0603 size chip components has been investigated in our experiment. The experiments were carried out using lasercut stainless steel stencil and SAC305 type lead-free solder paste. The results have shown that the self-alignment of components does occur even in the case of 400-500 mum misplacements.

Description of 355 nm Laser Ablation of Polyimide as a Thermal Process

UV Nd:YAG lasers are widely used in the electronics industry for microvia drilling, cutting, window opening and other selective material removal processes. The models of the laser-material interaction describing these manufacturing processes are mainly based on the experiences of excimer lasers. The different wavelength and energy distribution of frequency tripled Nd:YAG lasers, however require some new approaches. It is still contradictory in the literature how important role the thermal and photochemical processes play in the ablation process. The experimental results presented in this paper show that the models used for excimer lasers are not adaptable to the Gaussian Nd:YAG laser beam. Our model describes the ablation process as a simple thermal process. The simulation and experimental results presented in this paper are in qualitative agreement

A microfluidic electrochemical cell based on microsystem packaging technologies applicable for biosensor development

A new miniaturized electrochemical cell has been designed and constructed by utilization of different electronics technologies. The 25-50 /spl mu/l capacity of the cylindrical shaped electrochemical cell has been built up by cutting circles in 5-10 overlapping layers of 400 /spl mu/m thick Teflon foil. This multilayer structure enables very flexible solutions for in- and outlet of different materials into the electrochemical cell. The number of the working electrodes of the biosensor substrates can vary between 1-80. The reference electrode has been made of a silver wire. The circular symmetry of the counter and reference electrodes and the pattern of the working electrode array allows bipotentiostatic measurements, thus, this flexible platform is suitable for wide range of experiments of both bipotentiostatic biocatalytic sensors and DNA sensors with electronically addressed immobilization.