SMTA International Conference Proceedings

The Effects of Surface Finish on Solder Paste Performance - The Sequel

Author: Tony Lentz
Company: FCT Assembly
Date Published: 9/22/2019   Conference: SMTA International

Abstract: This is a second study on how solderable surface finish affects solder paste performance in the surface mount process (SMT). The first study was presented at SMTA International 2018 [1] and included print, reflow and voiding data on 6 different surface finishes run with 4 different solder pastes. The performance of the surface finish - solder paste combinations were scored and ranked and recommendations given for optimal pairings.

This work explores some of the surface finish - solder paste combinations in more detail with an expanded set of SMT parameters. Three surface finishes were studied including electroless nickel immersion gold (ENIG), organic solderability preservative (OSP), and immersion silver (ISilver). Two lead-free solder pastes were used including a no clean SAC305 solder paste and a water soluble SAC305 solder paste. Three different reflow conditions were tested including a ramp-to-spike (RTS) profile, a ramp-soak-spike (RSS) profile, and reflowing two times through a RTS profile to simulate double-sided surface mount work. Print speeds were varied at 25, 50, and 100 mm/second and printed solder paste volumes measured. Reflow performance was measured including wetting, solder balling, and graping. Quad flat no lead (QFN) components were placed and voiding was measured.

All of the test results were summarized. Discussion of the strengths and weaknesses of each combination of surface finish and solder paste were given with respect to the various SMT parameters. Recommendations were made for optimal combinations of surface finish and solder paste.

Key Words: 

surface finish, solder paste, print speed, reflow profile, wetting, solder balling, graping, voiding

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