SMTA International Conference Proceedings


BOARD LEVEL RELIABILITY OF LEAD-FREE SOLDERED INTERCONNECTIONS

Authors: H.-J. Albrecht, K. Wilke, D.S. Brodie
Company: Siemens AG
Date Published: 9/22/2002   Conference: SMTA International


Abstract: The lead-free activities has taken center stage in the electronics package and assembly industry wordwide. Lead is widely reported to be related to certain health risks. That is one of the reasons that Japan, USA and Europe have taken initiatives to reduce and eliminate lead as interconnection materials. Three drivers currently exist for eliminating lead in electronic assemblies.

The Japanese Ministry MITI proposed a take-back legislation in Japan. Several major Japanese electronic manufacturers have initiated road maps and announced plans to eleminate lead solder by the end of 2003.

In Europe exists the 6th draft of European Community Directive on WEEE (Waste from Electrical and Electronic Equipment), which proposes a phasing out of lead by January 1, 2006.

In North America the IPC is collecting most promising lead-free candidate alloys and summarizes all the preconditions for a succesful implementation. The IPC J-STD-006 test method will be used to quantify the lead impurity level /1/. It is recommended that lead-free would imply that elemental lead is < 0,1 wt.-% in solder alloys.

As would be expected these three driving forces have influenced widely cooperations and corporations to create application related solutions.

In this paper, environmentally benign solders were discussed related to the ability of interaction to different surface finishes on package and board side, investigated for compatibility with existing process parameters and to discribe the board level reliability compared to conventional solder materials. The material selection is done based on the results of the European Ideals Project /2/ and the further demands to implement lead-free solders successful (Lead-free, low melting, high fatigue resistant for extended applications under the operating point of view).

Including the Ideals activities SnAgCu alloys (pastes) were tested related to wetting, spreading, dissolution, reflow profile optimization, 3-dimensional defects in comparison with organic vehicles used in the solder paste, interaction to conventional and lead-free finishes on package and board side, intermetallic formation and fatigue properties.

With the pressure of green assemblies, one of the challenges is to select and analyse an alternative solder alloy that is manufacturable (as powder as well as bath solder), cost effective, available, reliable compared to conventional solder alloys.



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