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.
Examining the Times for Melting of Different Solder Pastes at the Same Temperature Profile
The report provides results from the study of the melting times of various solder pastes. Typical of this study is that different couples of pastes are tested at the same temperature profile. Securing such a profile is effected by simultaneous effects on different pastes. For this purpose, a developed hybrid printing method is used. The application of this printing is in Pin in Paste technology (PiP) and components with different thermal mass. Times are given for melting the different pastes using footprints with varying amounts of paste, different topology and different pads. Lead, typical lead-free pastes and lead-free bismuth-based pastes were studied. The experiments were conducted using convective and convectional soldering in air. To determine the melting times, a digital microscope video capture and subsequent scanning treatment was used. The temperature of the process is controlled by a thermocouple.
Evaluation of Lapping Grains based on Shape Characteristics.
The shape and size of abrasive grains during lapping varies complicately and irregularly. In this study, the aspect ratio of grain size and the fractal dimension of the grain external form were used as shape characteristics of grain in order to evaluate grains with lapping time. The results obtained are summarized as follows : (1)The fractal dimension increases due to microscopic fracture and decreases due to macroscopic fracture or attritious wear. (2)The aspect ratio and the fractal dimension, which are grain shape characteristicsis of the macroscopic shape and the microscopic surface complication of grain respectively, can be used for evaluating grain shape variation during lapping.