Pan Pacific Symposium Conference Proceedings


CONTROLLING LOCALIZED CONTAMINATION ON MICROELECTRONIC ASSEMBLIES WITH THE CHANGE TO LEAD FREE ASSEMBLY

Author: Terry Munson
Company: Foresite Inc.
Date Published: 1/17/2006   Conference: Pan Pacific Symposium


Abstract: The sensitivity and complexity of microelectronics creates an imperative need to control ionic cleanliness, specifically in localized areas where contaminants can become trapped and cause failures. This paper outlines the methods currently available to assess the cleanliness and reliability of microelectronic assemblies including ROSE testing, modified ROSE testing, Ion Chromatography, Ion Chromatography with localized extraction and SIR testing. Comparing and contrasting the information garnered from each of these methods, this discussion will specify the purposes of each test and how the results correlate with reliable field performance. It will also take an in-depth look into how ionic cleanliness results translate for use with lead free performance parameters, and examines the new cleanliness issues brought forth through lead free production. One of the main topics discussed in this paper is localized extraction techniques for use with ion chromatography, and how these techniques are specifically pertinent in the cleanliness control of microelectronic assemblies. Due to the compact packaging of microelectronics, there is a great risk of residue entrapment that can be highly detrimental to product performance, and can be overlooked by cleanliness testing methods commonly used by the industry. By taking a localized extraction from sensitive areas of circuitry, concentrations of ionic residues overlooked by current net extraction techniques can now be quantified and specified. This paper discusses a localized steam extraction technology that collects a sample from a 0.1 in2 area of an assembly, and how this sample can be used in ion chromatography testing to determine an indication of field performance. Taking several cases encountered by Foresite Inc. into account, we will see how the phenomenon of localized residues is causing large-scale performance problems for today’s assemblers, and how this occurrence can be prevented. The studies will look into how commonly found ionic residues such as chloride, bromide, sulfate, phosphate, nitrate, nitrite and weak organic acids affect product performance, and what the common sources are that introduce these harmful contaminants. In addition to outlining the methods of determining and interpreting ionic cleanliness, this paper will also discuss the new contamination concerns brought forth with the introduction of lead free manufacturing. Using several studies performed by Foresite Inc, we will see how ionic contamination contributes to the propensity for tin and zinc whisker growth, as well as the propagation of copper sulfate crystals. It will also approach the cleaning challenges brought forth through heightened oxidation of processing residues through the higher temperatures required of lead free assembly processes. Looking at the cleaning methods and chemistries available in today’s marketplace, it will discuss how to optimize cleaning processes for compatibility and effectiveness in cleaning lead free assemblies, and what levels of cleanliness lend to reliable field performance.



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