SMTA International Conference Proceedings

A Study Of Lead-Free Low Silver Solder Alloys With Nickel Additions

Authors: Munehiko Nakatsuma, Takehiro Wada, Kimiaki Mori, Koichi Shimokawa, Takeshi Shirai, Atsushi Irisawa, Roberto Garcia, Jasbir Bath
Company: Koki Company Limited and Bath & Associates Consultancy LLC
Date Published: 10/13/2013   Conference: SMTA International

Abstract: The electronics industry, particularly for consumer electronics, has started adopting low silver solder paste alloys for lead-free reflow soldering applications. One of the alloys being used as a cost-saving low silver solder paste alloy in the global market is Sn0.1Ag0.7Cu0.03Co. This alloy has been widely adopted for consumer electronic devices with its improved reliability due to the cobalt addition. The demands for low silver solder alloys are gradually increasing for applications requiring equivalent to or even better reliability than Sn3Ag0.5Cu (SAC305), such as in automotive and industrial sectors. To explore new more reliable low silver solder compositions with additional elements, the company continued the study on the effects of additive elements.

Specifically, this focused on the improved effect on thermal cycling reliability by adding nickel to the SnAgCu type lead-free solder alloys. The study indicated that adding a small amount of nickel to the SnAgCu lead-free solder alloy with around 1% silver content produced equivalent solder joint reliability to conventional Sn3Ag0.5Cu (SAC305). However, reduction of silver content from 3% to 1% increased the melting temperature of solder and may result in a reduced process window during assembly operations. Therefore, additional work was conducted to understand the affect of increasing the process window with the low silver nickel containing lead-free alloy using the addition of bismuth and its subsequent affect on reliability.

The results of the work are reported which include solder paste printing analysis together with mechanical property, melting temperature, wetting, reflow profile window (minimum solder joint peak/ time above melting temperature), voiding, thermal cycling, solder joint strength, visual and cross-sectional analysis of the low silver leadfree soldered joints compared with Sn3Ag0.5Cu.

Key Words: 

Lead-free, Low Silver, Reflow, Reflow Profile, Thermal Cycling.

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