How Clean is Clean Enough?

In the world of manufacturing, cleanliness is a term often talked about but rarely clearly defined. It encompasses more than adherence to specified limits; true cleanliness reflects a comprehensive understanding of the entire production process. Because different stages of the production process introduce circumstances and create variables impacting a desired level of ‘clean.’

This includes the critical aspects of residue management at key locations on the line. Residues can amass in pad to pad and hole to hole locations. The net effect of a process can be positive or negative depending on how cleanliness is both monitored and controlled.

A crucial determinant of cleanliness lies in the quantity of residues that are present on the surface. Conductive residues potentially create disruptive parasitic leakage pathways. These problematic parasitic pathways due to electrochemical migration or dendrite shorting can cause malfunction or damage to sensitive components.

To address these complexities, there is a push to establish a clear definition of cleanliness that is both practical and relevant.

This involves setting standards that answer the question: How clean is clean enough?

Key documents, such as those detailing chloride levels (e.g., five micrograms per square inch versus less than three) or No clean flux weak organic acid (e.g., WOAs at 25 µg/in2 or 150 µg/in2), provide valuable benchmarks for assessing cleanliness and its impact on performance metrics like SIR (Surface Insulation Resistance) and C3 performance.

Still, though, the exact standard for cleanliness can vary depending on the methodology applied to cleanliness testing. As an example, many of the standards today focus on particulate cleanliness and do not address ionic or organic cleanliness, despite the fact that these other sources of residues are commonly implicated when product failures are analyzed.

Evolving Standards

The debate over cleanliness testing highlights significant challenges with evolving methodologies. Traditional methods like ROSE (Resistivity of Solvent Extract) are criticized for their broad applicability and outdated relevance, particularly as new flux technologies emerge. The industry has questioned why standards like J-STD-001 don’t uniformly define limits across all flux types, underscoring concerns about the adequacy of current testing practices in ensuring field performance.

Historical analysis using Ion Chromatography (IC) reveals discrepancies between residue levels permitted by different tests, suggesting a disconnect in standards. This underscores the need for more precise, localized testing approaches that can better predict and control contamination effects, especially with modern no-clean fluxes and smaller, more complex circuit assemblies.

Emerging tools promise enhanced process control by focusing on localized extraction methods, potentially replacing conventional IC for routine monitoring. This will allow for the collection of more targeted data.

Defining and Maintaining Cleanliness

In conclusion, achieving and maintaining cleanliness in the manufacturing process is not a static endeavor. Cleaning procedures themselves can introduce and subtract residues. These residues can originate from cleaning solutions, partially solubilized flux residues, and water entrapment, each contributing to the overall cleanliness profile. Thus, when you move to fabrication, assembly and component manufacturing, what was once thought to be clean is no longer.

That’s why defining cleanliness requires a holistic approach. Despite the complexities introduced by various cleaning processes, establishing clear criteria and benchmarks is essential for ensuring consistent product quality and reliability.

Foresite allows the manufacturers to navigate the nuances of cleanliness with clarity and precision. Going beyond the surface to understand root causes of unclean parts ultimately leads to both improved product performance and customer satisfaction.