SMTA International Conference Proceedings

No-Clean Flux: A Potential Ionic Contaminant

Authors: Phil Isaacs, Terry Munson
Company: IBM Corporation, Foresite, Inc.
Date Published: 9/17/2017   Conference: SMTA International

Abstract: The manufacture of printed board circuit assemblies (PCBAs) is a challenging business. There are many conditions which can lead to defects or latent flaws. One such condition is ionic contamination. There are many sources of ionic contamination. The worst sources of ionic contamination are usually process induced. For example, during raw card processing one of the chemical operations after solder mask apply is an acid micro-etchant used to clean the exposed copper surface in preparation for the application of Organic Solderability Preservative (OSP) coating. OSP is used to prevent copper oxidation of the solderable surfaces. If this is not rinsed off well, or if it becomes entrapped in plated-thru-holes (PTH’s) it can lead to corrosion and an electrical failure of the board.

The ionic species that this paper will address are no-clean fluxes. Most PCBA’s today are soldered utilizing no-clean flux. Depending on how the flux is applied and what process conditions the flux sees, it may be totally reliable, or, it may provide a medium for electrochemical migration (ECM).

This paper will explore what process conditions and which components have a higher probability of leading to ECM. With this in mind, which tests are best suited to detect conditions which may lead a board to electrical failure.

Key Words: 

No-clean, Flux, Process, Fails, SIR, C3 and IC

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