Influence of PCBs coatings wettability on lead-free SMT solder joints reliability
The paper presents results of wettability study of PCBs with immersion Sn, Ni/Au and SnCu coatings before reflow soldering process. Furthermore the solder joints were made in the optimal lead-free reflow soldering conditions using chosen materials with different wettability value of PCBs coatings and their reliability assessment was executed. The results of investigations have shown that exist direct influence PCBs coatings wettability on reliability of solder joints. It was find also that by using special procedure of PCBs coatings wettability assessment it is possible to predict future solder joints reliability.
Assembly Problems in Lead-free and Mix Production
Some electronic assemblers are faced to face with the necessity to use heterogeneous assembly of both very large and very small components on the same board and mix tin-lead and lead free soldering technology. Authors try to solve the problems with pick and place very small components by special design of stencil and adjust printing and assembly parameters. The solution of the soldering problems they try to solve by optimization the soldering profiles for mix technology.
Quantitative and qualitative relationship between swirl burner operatingconditions and pulverized coal flame length
Abstract Currently, there are used in power plants two types of burners to combustion the pulverized coal: jet burners and swirl burners. Most of the published works in the field of analysis of burners operating conditions are related to jet burners and are limited to initial region of the flame at the outlet of the burner. For jet burners an offset between the burner outlet and the flame beginning point could be analyzed. In the case of swirl burners with the pre-mixing diffuser chamber an offset between flame ignition point and burner outlet is usually not visible. Because already in the pre-mixing diffuser chamber of swirl burner occurs the ignition of coal-dust together with oxidant-gas cloud and thereby the formation of the flame. Therefore, the analysis of operating conditions for this types of burners requires a different approach. There is a lack of researches, in which will be analyzed changes of the flame length, that are caused by changes of design and operating parameters of swirl burner with the pre-mixing diffuser chamber. Therefore the aim of this study was to implement and verify the methodology for estimating the flame length, which will allow monitoring changes of operating conditions, that are caused by changes of design and operating parameters of swirl burner with the pre-mixing diffuser chamber. To carry out the analysis of the image of the coal flame, the two algorithms have been presented. This two algorithms, being based on the video images of the coal flame allows to specify and detect the end point of the flame and on that basis the length of the flame, as well as the fluctuation changes of flame length can be later determined. Both, the change thermal loads of coal burner, streams of secondary air, as well as the constructional change of the angle of swirler assemblies, resulted in distinct changes in the length of the pulverized coal flame.