Authored By:
Ed Kanegsberg, Ph.D.
BFK Solutions LLC
Pacific Palisades, CA, USA
Barbara Kanegsberg
BFK Solutions LLC
Pacific Palisades, CA, USA
Summary
We report results from on-going studies with ultrasonic cleaning systems that support using ultrasonic technology for cleaning electronic assemblies. Ultrasonics is an important option especially when assemblies contain hard to reach regions between or under components. Electronic assembly performance criteria have become more demanding and assembly parameters have become more challenging. Residues can limit product performance and lifetime. Cleaning to acceptable levels is difficult. Currently accepted cleaning techniques, whether in-line or batch processing, may not adequately clean flux and other residues from between or under components. Cleaning is frequently the limiting time and cost bottleneck.
Traditionally there has been a reluctance to use ultrasonics, in part because of a concern with the potential for substrate and component damage. However, as assemblies have become more densely-populated, current techniques must also be evaluated in terms of efficacy of cleaning and the potential for product damage. Many predominant cleaning methods are limited because they require line-of-sight technology. This means that assemblies must be optimally oriented to avoid shadowing of the cleaning force. In contrast, ultrasonics is, in general, not a line-of-sight technique. It therefore can overcome limitations of spray cleaning, including meticulous maintenance and orientation of spray nozzles, slow throughput, or the potential damaging high pressures needed to get cleaning and rinsing fluids to their destination.
We are studying ultrasonic cleaning parameters including frequency, power, time, temperature and chemistries. Results demonstrate that developments in technology require rethinking of our older assumptions. With appropriate process controls, ultrasonics can significantly reduce both the potential for damage and also allow the appropriate cleaning energy and chemistry to reach the area to be cleaned. Our findings indicate that cleaning times might be reduced from large fractions of an hour for conventional techniques to a few seconds. Cleaning resources including capital investment, floorspace, water and energy use may also be favorably reduced.
Conclusions
Ultrasonics should be considered as an option for cleaning of electronic assemblies, especially when there are hard to reach regions such as under low stand-off components. The availability of high frequency ultrasonics, as well as optimization of other parameters such as temperature and cleaning chemistry, minimizes the potential for erosive damage to leads, boards and components. Our tests also show that ultrasonic cleaning can be both quick and effective when the flux residue or other soils are in regions with small gaps.
Ultrasonic cleaning shows the potential for increased throughput through significantly shorter clean times, reduced equipment footprint, and lower energy and water resource consumption. Our tests are continuing and will continue to study the effects of different cleaning agents, temperature, and other parameters to achieve a balance that optimizes cleaning while minimizing potential damage.
Initially Published in the SMTA Proceedings
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