Special feature: Cleaning chemistry vs. mechanical impingement
Special feature:
Cleaning chemistry vs.
mechanical impingement
This cleaning panel took place during the Virtual PCB trade show (www.virtualpcb) on February 25, 2009. The
panel was moderated by Trevor Galbraith, Global SMT & Packaging’s editor-in-chief. Panelists included Michael
Konrad, president of Aqueous Technologies, Steve Stach, president of Austin American Technologies and Dr.
Harald Wack, president of ZESTRON Worldwide. Viewers logged into the chat were invited to ask questions.
Trevor Galbraith, Global SMT & Our company has researched the topic rinses for inner layers, water quality rinses
Packaging: Welcome to the cleaning of climatic reliability for almost 20 years for outer layers, HASL fluids (HO) and fi-
debate “Cleaning chemistries vs. mechani- now in close cooperation with Fraunhofer nal rinses (all from board fab as well as flux
cal impingement.” As the title suggests, Institute. Dr. Helmut Schweigart, material and operator residues from assembly).
we’re looking forward to a robust debate science background, has allowed him to
on the virtues of chemistry versus mechani- draw direct links between remaining flux
Galbraith: How big a problem are board
cal impingement, as well as some other hot residues on the surface and induced failure
finishes?
topics associated with cleaning electronic mechanisms such as electrochemical migra-
assemblies. To set the scene, cleaning tion, corrosion and leakage currents. Silver
Wack: Typically not the main concern we
equipment and chemistries are typically hydroxide dissociates though an electrical
encounter. However, some silver-containing
used to remove flux residues. Specifically current on electronic assemblies, which
ones can be introduced to the process and
what flux residues are the most harmful forms silver hydroxide a very water-soluble
might remain on the substrates.
and what other contaminants are you look- salt. It then helps to grow dendrites which,
Konrad: Board finishes are a contributing
ing to clean? depending on their strength, burn off,
factor. Combined with no-clean flux resi-
and start to grow elsewhere. Numerous
Dr. Harald Wack, ZESTRON: The re-
dues, moisture and electrical, they combine
technical articles on this phenomenon are
moval of flux residues has been the major
to form dendrites.
available and we would be glad to provide
concern of most customers. Especially
them to you.
Galbraith: How clean do the boards need
due to the higher level of acidic activators
to be, and what are the most effective
in lead free products recently. No-clean, Michael Konrad, Aqueous Technologies:
methods for validating this?
synthetic fluxes are the most harmful. While flux is the obvious target to be
This is mainly due to the fact that if they removed, it is important to note that there
Konrad: Actual board cleanliness require-
remain uncleaned, it provides an oppor- any many harmful substances that may be
ment is based on use, location, reliabil-
tunity to failure down the road, when the harmful to an assembly. These include etch
ity expectations, etc. The best test is ion
assembly is exposed to climatic stressors. residues, developer chemicals, water quality
26 – Global SMT & Packaging – May 2009 www.globalsmt.net
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