Minimizing Printed Circuit Board Warpage in Assembly Process
The purpose of this paper is to present a cleaning process for difficult no-clean, lead-free and high temperature flux residues on reflowed PCBs.
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Authored By:
Srinivasa Aravamudhan, Christopher Combs, Abhishek Prasad, and Amit Abraham
Intel Corporation
Hillsboro, OR, USA
Summary
Advancements in the electronics industry are continuously leading to more sophisticated, more intricate and more miniaturized circuitry. In conjunction with increasing regulations on electronics manufacturing, many changes have been made to the electronics world, and thus the circuit board manufacturing process. Lead-free, no-clean and halide-free flux formulations have introduced new cleaning obstacles, especially on ever-shrinking component sizes. In order to maintain high cleanliness standards for modern circuitry, new sophisticated cleaning chemistries are required.
The purpose of this paper is to present a cleaning process for difficult no-clean, lead-free and high temperature flux residues on reflowed PCBs. The proposed cleaning solvents are drop-in replacements for outdated solvent technology, or alternatives for elaborate aqueous systems. These cleaning technologies are used in traditional vapor degreaser systems, which allow for fast cleaning times and spot-free results without the need for additional rinsing or drying equipment. The improved formulas have low surface tensions (less than 20 dynes/cm), which allow access to low stand-off components and high solvency to combat the most difficult flux formulations and white residues. Visual and quantitative data are presented to assess the overall cleaning efficiency of the solvent system. Cost analysis is investigated to assess the efficacy of solvent vapor cleaning for PCB industry.
Conclusions
New flux and solder formulations with better safety profiles and processing efficiency hold an importance in modern electronics assembly; however, these benefits come with hurdles of their own, including potentially detrimental residues. Processes that require high-reliability electronics require high-reliability cleaning. Modern vapor degreasing techniques and solvent formulations are environmentally conscientious, time efficient, safe and effective on some of today's most difficult soils. Although ionic residues may be an issue for current vapor degreasing solvents, there are new technologies available to combat even the toughest flux residues. Solvents A and B showed major visual improvements over the Classic Solvent when cleaning noclean and lead-free flux residues. The advanced solvents were able to remove at least 50% of the flux residue from all of the different flux formulations during the cleaning cycle. Increasing cleaning cycle times or utilizing ultrasonic agitation may be able to further improve the visual results. The SIR evaluation confirmed that the cleaning formulations did not impact the circuit operation and that any remaining residue was not detrimental to the circuit performance.
Initially Published in the SMTA Proceedings
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