Surface Mount International Conference Proceedings


Author: H.-J. Albrecht
Company: Siemens AG
Date Published: 8/23/1998   Conference: Surface Mount International

Abstract: The packaging revolution of the ‘90s, powered by the development of new package types with smaller dimensions, increasing the interconnection density on the assembly level, is placing increasing demands on the electronic materials sector. The paper outlines preconditions and integration factors of successful implementation of new finish layers on package and laminate level to ensure an assembly process with the highest level of planarity for peripheral and area array type components. For elevated temperature application of assemblies fundamental material-related limits must be taken into account. The selection of finish layers on the board side is combined with new tasks for interconnection technologies. The board finish layers in the project are: Hot air leveling for comparison, bare copper, copper with organic coating, Ni-Au, immersion Pd, immersion Sn and immersion Ag. The first observations on the finish layers were: A study of the contamination level and of the decreasing mechanisms of surface tension, requirements of layer thicknesses and topology. For the conventional assembly process it is necessary to analyze the interaction quantity of solids with liquid solders. For this reason we study the surface tension of solids as a function of the process flow dependent parameters and calculate the polar part of the surface tension as a selection criterion for joining materials. This paper focuses primarily on the influence of finish layers and interfaces on the reliability of the interconnections (BGA and CSP solder joints). One of the important influences for the later reliability, is the wetting behavior, the interaction of the finish layer with the stressable solder volume (dissolution rate and speed on the component and on the pcb side). For the solution analyses it is important to measure the thermal conditions of joining procedures. The basic data for the later fatigue properties of the interconnections are the interface property and the quantity of intermetallics. By using destructive and nondestructive evaluation methods we look for a complete description of the degradation process. For example thermal cycle tests, power cycle tests, high temperature or climatic storage were used. Decision aid for fictional materials in interconnection technologies means to create selection rules of functional materials, alternative finish layers in combination with interconnect ion materials and future demands on interconnection quality and reliability, corresponding to the miniaturization and integration quantity on the package and assembly level.

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