SMTA International Conference Proceedings


SOLDERABILITY AND PROCESS INTEGRATION STUDIES OF IMMERSION SILVER AND TIN SURFACE FINISHES

Authors: Dongji Xie, Ph.D., et al.
Company: Flextronics International
Date Published: 9/22/2002   Conference: SMTA International


Abstract: This paper presents intensive experimental results from wetting balance and solderability tests of immersion silver (I_Ag) and tin (I_Sn) finishes in comparison to those of hot air solder leveling (HASL) and electroless nickel immersion gold (ENIG).

To test the wettability and spreadability quantitatively of solder paste, a novel wetting scale bar was designed, which proved to be more convenient and presentable compared to the standard solder paste-wetting test (IPC-TM-650). The results from both wettability test and wetting balance tests show that fresh immersion silver and tin coupons have superior wetting performance. Process integration in printing and reflow using immersion silver and tin finished boards was also investigated.

The results show both I_Ag and I_Sn boards have sustained 3 mis-printings and washes without degradation of the solderability. Both surfaces also passed the multiple reflow tests up to 3 reflows at 230°C. In summary, both I_Ag and I_Sn surface finishes can also be dropped in to replace HASL and ENIG from the study of the manufacturability.

However, the aging test results at 155°C and 85°C85%RH suggest both surface finishes have relatively short shelf life as compared to ENIG and HASL.



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