SMTA International Conference Proceedings


LEAD-FREE SOLDER JOINTS AND FAILURE MECHANISM ON DIFFERENT FINISHES

Author: H.-J. Albrecht
Company: Siemens AG
Date Published: 9/25/2005   Conference: SMTA International


Abstract: Based on experimental analysis of different ball materials for BGA / LFBGA components the quality of Pb-free interconnections, specially the formation of intermetallics will be discussed followed by any reliability results. The damage mechanism for LFBGA components on different board finishes at elevated operating conditions is not sufficient understood. The reason is the extended growth of intermetallics and the related brittle properties.

Further demands from portable electronics are the drop test, characterizing interface performance of different package constructions in relation to decreased pad constructions / solder volumes and therefore interfaces. The ratio of the pad diameter to the solder volume is one of the key parameter influencing the concentration gradients and therefore the metallurgical interaction. The paper discusses the characterization of interfaces based on SnAgCu and SnAgCuXYZ ball materials, the stability after accelerated tests and the description of modified interfaces strictly related to the assembly conditions, dissolution behavior of finishes on component and board side and the influence of intermetallic formation.

The type of intermetallic as well as the quantity of intermetallics are observed, primaliry the constitution, hardness, E modules describing the ability of strain/stress compensation. Results of board level reliability are presented after TCT, HTS and drop tests. Ball materials, finishes at interposer and pcb influencing damage mechanisms at interfaces, the progress using new ball materials is demonstrated.

Recently, the lead-free activities has taken center stage in the electronics package and assembly industry wordwide. Environmentally friendly products have been very well accepted into the market place indicating the favorable marketing impact Pb-free products have worldwide.

In this paper, environmentally benign ball materials in combination with lead free solders were discussed related to the ability of interaction to different surface finishes on package and board side, investigated for compatibility with existing or modified process parameters and to discribe the board level reliability compared to conventional solder materials. The material selection is done based on demands to implement lead-free solders successful (Leadfree, low melting, high fatigue resistant for extended applications under the operating point of view).



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