In our research, we performed comparative analyses concerning various lead-free SAC (Sn96.5Ag3Cu0.5, Sn95.5Ag4Cu0.5) and two types of micro-alloyed SAC (SnAgCu + Bi + Sb) solder alloys. It was proven that our new variable described the different Ag3Sn IMC morphologies obtained at different cooling rates better it was more sensitive at both aforementioned solder alloys (4 and 0.3 % Ag content) than the widely applied parameters, like the mean-intercept length or the average area of particles. It was found that the area of Ag3Sn intermetallic compounds followed exponential distribution, so a new state variable could be introduced, such as the amplitude of a certain exponential curve fitted to the area histogram of the Ag3Sn IMCs. The captured images were processed then with an in-house developed automatic image processing algorithm. Images were taken about the cross-section of solder joints by brightfield light-microscope to calculate the explicit state variables, which describe the morphology of precipitating Ag3Sn intermetallic compounds. In the experiment, samples were prepared by melting standard Ag-content (4 % in wt%) and low Ag-content (0.3 % in wt%) solder alloys, and solidifying them at five different cooling rates between 0.8 and 3 K/s. In this paper, a new explicit state variable was introduced which describes the Ag3Sn intermetallic morphology inside of lead-free solder joints at different cooling rates. Also a new approach on profiling data evaluation based on the heating factor is presented and suggested for wider use. – The paper presents the reliability of the presented methods for VPS and present suggestions for the use of different TC ends and attaching materials during condensation heating of the PCBs. It was presented that the heating factor (Q?) gives more reliable comparison overview the time period-based comparisons may be affected by the thermal inertia, while heating factor also includes temperature conditions at the given time points. Alu-tape is the preferred all-around method, for fast, exchangeable, cheap, reliable and repeatable profiling in a VPS oven. – According to the specific attachment requirements, HTS and Alu-tape are the suggested methods for better profiling reliability and repeatability. Heating experiments were performed in a batch-type VPS oven with Galden LS240 fluid and fixed oven parameters.

– Bare printed circuit boards (PCBs) were prepared for standard K-Type TCs attachment with industry standard materials: kapton polyimide tape, aluminium tape, SMD adhesive and high-temperature solder (HTS). Temperature measurements based on TCs are also affected this way it is important to investigate the process for deeper understanding. The condensate is a flowing layer on the board, where the dynamic behaviour also affects the local conditions on the surfaces. The heat transfer process during VPS is different from common methods, while the required heat for reflow is provided by the condensation. – The paper aims to present a comparative study of various thermocouple (TC) attaching methods for the proper measurement of soldering temperature profiling during vapour phase soldering (VPS).

Bga reflow temperature