September, 2018
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PCB Cleaning: It’s Not All Black and White Continued from previous page
ing the reliability of an electrical component based on the strength and quality of the signal that comes through the component after cleaning. A full SIR test takes 28 days and is usually
performed offsite in a lab. It consists of measuring the difference in an electrical current over time and in differing temperatures and humidity levels after cleaning. SIR also measures the corrosive- ness of a residue by looking at the formation of dendrites. Any contamination will lower the resist- ance of electrical flow across the traces on a PCB caused by conductive contamination, such as the ionics from fluxes. High resistance is good and means the board is clean. A less precise, but faster and far more user-
friendly, measurement of cleanliness is the indus- try accepted practice of ionograph or resistivity of solvent extract (ROSE) testing. This measures the degree of ionic contam- ination. During the process, the PCB is immersed in a bath of deionized water for 15 minutes or so. After the water has had a few
moments to circulate around the com- ponents, the water is tested automat- ically for ionic contamination. Since the deionized water will dissolve ion- ics from the boards, any change in resistivity of the water would indicate the relative dirtiness or cleanliness of the board. Although an industry staple,
ROSE testing cannot ensure contami- nation is not present under dense, low-standoff areas of the PCB, or if the entire flux residue was removed and examined. The best practice available to
the industry is to assess and control contamination through ion chro- matography (IC) testing, currently the gold-standard for judging cleanli- ness. IC is the only test that detects and quantifies “weak organic acids” and individual ions. It is an excellent process to quickly troubleshoot the source of contamination and predict
Finding a cleaning fluid that can ensure the clean- liness of the newest PCB designs is critical. There are companies devel oping modern cleaning solvents that make a substantial enhancement to the performance, reliability
and longevity of electronic devices.
the effect of each ionic type. Because of the expense, very few PCB manu- facturers define quality standards based on IC results. The only way to offer peace of
mind when it comes to cleanliness is to run the time-consuming and more expensive methods of SIR or IC test- ing. These will certify that the prod- ucts being used to clean are doing the job right the first time. If this is not a possibility, then the choice of cleaning solvent will make a huge difference.
Choosing Cleaning Fluid Finding a cleaning fluid that can
ensure the cleanliness of the newest PCB designs is critical. There are com- panies developing modern cleaning sol- vents that make a substantial enhance- ment to the performance, reliability and longevity of electronic devices. These new cleaning solvents
have all the desired chemical traits, for example, they are non- flammable, have low viscosity, low surface ten- sion and high Kauri-butanol (Kb) val-
Together in Process Perfection
ITW EAE brings together the world-leading brands of electronics assembly equipment. Brands with reputations for advancing process perfection. The combined knowledge and experience of the ITW EAE group is driving further innovation and speeding the development of next generation technology. New technology like those being added to the MPM Momentum Printer line can dramatically improve productivity and yield while reducing maintenance and cost of ownership.
Come see all our latest developments at SMTAi Booth 615
Page 71
ues, which allow them to de-flux PCBs very effec- tively, even under tight-stand-off components. They can guarantee that all the surfaces of the PCB are successfully cleaned, with no white residues. This assurance can eliminate vigorous testing.
Innovative advances in cleaning fluids and
technology mean not only impressive cleaning results, but better economics as well. Modern crit- ical cleaning processes offer new solutions for design engineers in the electronics industry. Progressive cleaning fluids allow for better PCBs to be built and deployed, therefore creating new capabilities for the future of electronics. Contact: MicroCare Corp., 595 John Downy
Ionic contamination on a PCB in the form of white residue.
Drive, New Britain, CT 06051 % 860-827-0626 E-mail:
info@microcare.com Web:
www.microcare.com r
Momentum II Printers NEW
A proven, highly-productive printer platform now with a new set of enhanced technologies.
Learn more at
www.itweae.com See at SMTAI, Booth 615
A division of Illinois Tools Works
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