Improved soldering of components with different thermal masses by hybrid printing of solder pastes
In this work are shown the results of an improved Pin in Paste (PiP) technique. With the purpose of soldering of SMD and PTH (Pinthrough Hole) components, the PiP technique is making use of solder paste printing. The problematic PtP soldering due to thermal shading of areas under large size connectors, which results from their big thermal masses, has been considered. The actual temperatures under such connectors differ from the optimum thermal profile needed for the particular solder paste which profile can be monitored by a KIC instrument. A solution of this problem is suggested by making use of a solder paste, whose optimum thermal profile corresponds to the actual thermal profile under the connector components. For that purpose are used two different kinds of solder pastes. The proposed method, named Hybrid Printing, of two kinds of SMD pastes is based on the special design of a rakel which allows depositing of more than one kind of solder paste within one processing step. The effect of the use of Bi containing, Pb containing and Pb-free solder pastes has been investigated. The application of hybrid printing in a real production line has been demonstrated. The results of the X-ray and metallographic assessment of the fabricated solder joints are presented.
Influence of geometry on the applied solder paste in technology Pin in Paste(PiP)
PiP (Pin in Paste) is a technology for soldering with the least expenses and high quality because it is carried out fast (in one step for all components) and without human intervention. In the report it is shown the influence of geometry of the laid paste on the quality of soldering. It is examined in what geometry and in what ways of laying a reliable and repeated soldering can be achieved. There are some rules for successful laying of solder paste which are fixed by the experiments. The most important conclusions are: after a precise estimation of the quantity of paste for every point of soldering it is necessary to define the type, the dimensions and the place of the figure of the laid paste on PCB, which is connected to the design of the stencil's aperture, the place of laying of PCB, the way of laying and the qualities of the solder paste. Some producers of pastes for soldering created and offer special designed pastes for PiP. This process is used by EMS (electronic manufacturing services) producers more and more, especially by decreasing the dimensions of the components and increasing the degree of integration. More and more producers of electronic components offer such ones for PiP technology.
Mechanical behaviour and durability of high volume fly ash cementitious composites
The purpose of this research is to separate different morphological particles of ASTM class F fly ash, and study their effect on mechanical behaviour and durability of high volume cementitious mixtures. In this research wet separation of raw fly ash is carried out, which resulted in three layers of different morphological particles. The first layer of particles float, comprise of about 1-5% of fly ash, is identified as cenospheres or hollow spheres. The second layer of particles is measured to be 55-60% of raw fly ash and consisting of porous spherical and rounded particles rich in Si and Al. The third layer particles is measured to be about 35-40% of raw fly ash. High volume fly ash cementitious composites containing second or third layer particles are tested under compression and bending, highlighting a higher strength and ductility in comparison to cementitious ones containing raw fly ash particles. KEYWORDS. Cementitious matrix; Raw fly ash; Second layer particles; Third layer particles.