Alexandr Otáhal

Impact of solder paste drying on the solderability

This paper deals with the influence of the dried no-clean SAC305 solder paste on the spreading factor. Drying was defined by time between stencil printing and reflow soldering. Main investigated parameter was spreading, which is percentage difference between diameter of circle of solder paste after printing and diameter of circle after soldering.

Study of atmosphere influence on BGA solder balls process

This article deals with the influence of different atmosphere (normal, vapor, nitrogen) on some mechanical parameters, as shear strength, for BGA solder balls (Sn63Pb37, SAC305). There are also micro-sections of solder balls studied. Main objective of this work is to establish the optimal and necessary concentration of nitrogen for each application.

Influence of heat flow direction on solder ball interfacial layer

Abstract This paper deals with the research of an intermetallic layer of SAC305 solder balls soldered from three directions of the heat flow in the ball-attach process for BGA package. From the point of view of the heat flow direction, the samples were soldered by infrared heating. The heat sources were placed on the top, bottom and both lateral sides of the BGA package. After the solder balls-attach process, a metallographic cross-section was performed, followed by selective etching to visualize the relief of the intermetallic layer. Images of the interfacial between the solder and solder pad were taken from the created samples, followed by measurement of the average thickness and root mean square roughness of the intermetallic layer. The results showed changes in the intermetallic layer. The largest thickness of the intermetallic layer was observed on samples soldered from the top and both sides. Soldering with the bottom infrared heater resulted to the smallest thickness of the intermetallic layer. The same trend was in the roughness of the IMC layer. The greatest roughness was found for samples soldered by the top and both side heaters. The top soldered samples exhibit the smallest roughness.

Designing of infrared heater with homogenous heat transfer

This paper deal with the description of possibilities in designing of infrared heaters for reflow soldering. Main work was divided into two parts, simulation and realization. Simulation helps find the best solution of IR heater arrangement. The research was focused on the homogeneity of transferred heat to soldered component. In realization part, there was manufactured a prototype of IR heater in the best solution.

System for maintaining the dispensing capillary at a constant height above the surface

This article describes a system for maintaining the dispensing capillary at a constant height above the surface of the substrate. Used substrates are not sufficiently planar and it is therefore necessary to correct the height of the capillary during dispensing process (constant height with +/- 5 μm tolerance above substrate is necessary). Non-planarity of substrates is typically 150 microns over the entire surface.

Innovative methods for through holes plating

The main aim of this work was to investigate the influence of additional parameters in plating process of through-holes technology. Vacuum, ultrasound and the combination of both was used during the activation process of holes surface. Therefore, research was focused on the activation process, which was revealed as the cause of plating problems. The samples used in this work were prepared with reverse pulse plating.

The vibration testing as tool for optimizing of two PCB connection

This article deals with the use of mechanical testing to optimize the configuration of PCB. Specifically, the system of two connected boards is being investigated under the vibration load. Vibration measurement of such system is compared with the computer simulation and results from both methods are then evaluated including defining the main parameters. This research is related to the European project Board on Board (BOB), which focuses on new technology of two board interconnection, which is dedicated for high density assembly and interconnection.

Influence of the cavities on the PCB mechanical properties

Purpose – The main aim of this paper is to investigate the influence of the cavity coverage on the printed circuit boards (PCB) to the resonant frequency, acceleration and displacement. Design/methodology/approach – Tests were realized on four PCBs with different cavity areas. Frequency range of tests was between 10 and 2,000 Hz with 0.3 g acceleration amplitude. In addition, more simulations were performed to check different setups of the boards. Findings – From the calculated and measured data, it is clear that with the larger cavity area the resonance frequency drops. In case a greater number of components placed in cavities are needed on board, it is appropriate to use multiple smaller cavities than the bigger ones. Originality/value – Results in this paper could be very useful for PCB manufacturers and designers during designing of the new PCBs with cavities for dipped components.

Mechanical testing of PCB using computer simulations

This paper deals with the usage of the computer simulation for the mechanical testing of the PCBs to obtain optimal configuration for mechanical reliability. The main target is to determine factors that are the most important role for this kind of analysis. For this purpose sensitive analysis were made and following critical data were defined. The critical step is to determinate correct material data as well as properties of the board including its attachment.

Investigation of the Mechanical Properties of Lead-Free Solder Materials

Reliability and life-time of electric/electronic products is still a highly actual and discussed topic. Every electric/electronic product is heterogeneous system which consists not only from components and constructional parts, but also from many interconnections. Basic segments of interconnection are solder joints, recently created by lead-free materials. The passing from well-proven lead solders to lead free compositions brought many new aspects in reliability and life-time of electronic systems. Some of the negative factors are their poor electro-mechanical properties, which are based on complicated microstructure of interlayer interface. This fact causes defects in solder joints and consequential failure of the function. This article is focused on an investigation of mechanical properties of lead-free solder joints. There are investigated various properties of common lead-free solder paste depending on various concentrations of O2 by reflow process and on various components size. Next, there are shown microstructures by micro sections for various concentrations of O2. Mechanical properties (mechanical strength) are tested by shear test equipment DAGE 2400.