SMTA International Conference Proceedings


Water-Soluble Lead-Free Process Chemistry For High Voltage And High Reliability Hardware Requirements

Authors: Matt Kelly, Mitchell Ferrill, Wai Ma, Nandu Ranadive, and Cheikhou Ndiaye, Simin Bagheri and Prakash Kapadia
Company: IBM Corporation and Celestica Inc.
Date Published: 10/14/2012   Conference: SMTA International


Abstract: Over the past decade, no-clean flux chemistry usage has continued to rise and is correlated with the transition to lead-free printed circuit board assembly adoption by consumer electronics market segments. It is estimated that well over 90% of lead-free hardware built today uses no-clean flux chemistry. Even before EU RoHS directive promulgation in July 2006, firms building consumer products were largely using no-clean based flux chemistries. With the required migration to lead-free assembly material usage, early adopter demand for no-clean lead-free chemistry solutions rose even further.

During this same time, numerous RoHS exemptions have been in place; most notably exemption 7b “Lead in solder for server applications”. Firms manufacturing electronics using this exemption continued building product with SnPb solder. Despite an overall industry trend toward no-clean fluxes, many exempt SnPb built products employed water-soluble based assembly materials. Exercising allowable exemptions, firms building high complexity, high reliability products continued using SnPb water-soluble assembly materials and processes.

Six years have now passed since original RoHS directive enforcement; products in several market sectors continue to exercise exemption 7b. As these product roadmaps now begin conversion activity, there is a growing need for lead-free water-soluble chemistry solutions. However, the major R&D investment by material suppliers has been made to offer no-clean lead-free chemistry supporting consumer segments. As a result, there are limited published data or options available to support lead-free water-soluble solutions for high complexity, high reliability hardware assembly.

With this as background, IBM set out to examine the industry’s latest lead-free water-soluble chemistry options with the intent of selecting two top performing material sets for use with server and storage class hardware. This paper discusses details relating to the various tests conducted including manufacturability screening experiments, surface insulation resistance testing of IPC B-52 test coupons per IPC standards, and high voltage 550V / 2,150V hipot testing protocols. The result of this work yielded an end-to-end lead-free water-soluble chemistry solution, suitable for IBM’s highest complexity, highest reliability server class hardware systems.

Key Words: 

lead-free, water-soluble chemistry, flux interactions, high voltage applications, ultra high cleanliness requirements, hipot testing, surface insulation resistance



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