SMTA International Conference Proceedings

Critical Process and Chemical Parameters Affecting the Assembly Performance of Organic Solderability Preservatives (OSP)

Author: Michael Carano
Company: OM Group Electronic Chemicals, LLC
Date Published: 9/28/2014   Conference: SMTA International

Abstract: Complex PCB assembly presents significant challenges with respect to the solderable finish selected. And while there are many choices available to the assembly engineers and OEMs, some finishes such as OSP and ENIG occupy a significant market share. There are many questions related to OSP including the performance of the coating under multiple lead-free reflows, solder flow up and creep corrosion among others. In addition, as with all finishes, there are limitations. In this paper those limitations will be presented along with a thorough discussion key equipment and chemical process parameters that influence the performance of the OSP.

While many questions remain about the efficacy of OSP for lead-free complex assembly, the author will present comparative data with OSP and other finishes. Additional information will relate how the pre-OSP coating steps such as micro-etching affect the performance of OSP.

The author will present an overview of the chemistry involved in OSP technology with particular emphasis on the progression of performance improvements with complex azole type molecules in the last 24 months. Key metrics for evaluation include solder joint strength, solder paste spread, solder flow-up, OSP coating’s resistance to oxidation and corrosion resistance and the coatings ability to function as a selective finish with mixed metals.

Key Words: 

OSP, solderability, tarnish resistance, corrosion, galvanic, solder joint

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