Journal of SMT Article

The Effects of Reflow Profile Parameters on Sn-Ag-Cu Solder Bumps and Cu Substrate Using Full Factorial Design

Authors: Gabriel Takyi, Ph.D. and Peter K. Bernasko, Ph.D.
Company: Kwame Nkrumah University of Science and Technology and University of Greenwich
Date Published: 10/1/2014   Volume: 27-4

Abstract: The objective of this paper is to establish an optimal reflow profile for tin-silver-copper (Sn-Ag-Cu) solder volumes and factors influencing solder joint reliability. The optimum reflow soldering process parameters for different volumes of solder bumps were considered. A full factorial design technique was used to study the effects of the reflow soldering process parameters. Sixteen experimental runs were carried out with two levels for each factor on three different solder volumes (diameter): 0.944mm3 (Ø3.1mm), 1.344mm3 (Ø3.7mm) and 1.81mm3 (Ø4.3mm). A relationship between all four factors was established through the use of normal probability plot of factor effect, Pareto plot, optimal plot and Analysis of Variance (ANOVA). This was used to recommend optimal reflow profile for the three solder volumes.

The results indicate that time to peak temperature is the most significant factor in the reflow soldering process and the optimum reflow profile settings depend on the solder volume. By means of Minitab software, it was found that high time to peak temperature leads to an increase in intermetallic compound (IMC). Furthermore, the findings indicate that the ramp-up rate is a function of preheat temperature and time. While establishing an optimum reflow profile for (Sn-Ag-Cu) alloy using full factorial design technique, time to peak temperature emerged as the significant factor and that the solder volume affects the IMC growth.

In practical terms, a single reflow profile must be obtained by further optimization of the process window obtained in this work. This is due to the fact that a single circuit board will have different volumes of solder.

Keywords: 

Soldering, Pb-free solder, reflow optimal setting, solder bumps, Intermetallic compound layer thickness



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