SMTA International Conference Proceedings


Authors: Brian Roggeman, Ursula Marquez de Tino and Denis Barbini
Company: Universal Instruments Corporation and Vitronics Soltec
Date Published: 10/4/2009   Conference: SMTA International

Abstract: The electronics manufacturing industry has continued its search for a single alloy that can be utilized throughout the manufacturing line. To date, there is minimum success in the implementation of an alloy across the manufacturing process as compared to the tin lead based processes. The ability to employ one alloy will allow manufacturers to reduce complexity and cost while increasing yield.

The Sn/Cu/Ni alloy (SCN) has been widely used in wave soldering applications due to its applicability in achieving acceptable soldering results for many printed circuit board types. In addition, the SCN alloy is characterized by lower rates of reaction with base materials such as copper and iron [1]; the lack of precious metals makes the SCN alloy less expensive; and, the cosmetics of the final solder joint is similar to that of tin lead. However, the SCN alloy’s focus and integration into reflow soldering applications has been hampered by its higher melting point temperature of 227°C. At temperatures required for complete and homogeneous mixing of the paste deposit with the component lead/bump, there are concerns such as possible damage of heat-sensitive components and joint reliability. Before widespread use of the alloy is adopted for surface mount applications, extensive qualification is required [2].

Through a previous study [3], it was shown that typical SAC assembly profiles achieved satisfactory SCN solder joints, and the vibration reliability results indicated similar performance of SCN solder joints to SAC305. In this study, the reliability is further quantified through both thermal cycling and further mechanical test. Drop testing was chosen as the mechanical test and a comparison in the solder’s performance is made to SAC305 and SAC105.

The results show that, while SCN better matches SAC105 in solder ball strength testing, the performance in board level drop is very similar to SAC305. Thermal cycling results also appear very similar to SAC305.

Key words: Sn/Cu/Ni, Sn/Cu, SCN, Lead Free Solder Paste, Thermal Cycling, Drop Testing

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