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July, 2012


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Debunking Urban Legends about PCB Cleaning


By Mike Konrad, President and CEO, Aqueous Technologies Corporation, Rancho Cucamonga, CA


ture of science, tribal knowledge, contradictions and urban legends. As the electronics assembly industry again embraces cleaning as a main- stream process, it may be prudent to


W


ithin the cleaning sectors of the electronics assembly industry lays a strange mix-


In many cases, their knowledge of cleaning machines and processes is obsolete. The second group is com- prised of “younger” people who have had no direct experience with cleaning and who frequently lack any reference point. Those in either group may find this information helpful. So many things have changed


since cleaning was considered to be a mainstream process. Today’s assem- blies, due in part to miniaturization, have a much lower “contamination


tolerance” threshold. While some assemblies function reliably with a specific volume of contamination, others rapidly fail. Clock speeds, component densities, assembly geog- raphies, solder alloys, environmental influences and other factors deter- mine how much contamination an assembly can handle without failure.


Urban Legends Debunked


Water may be used to remove water-soluble (OA) flux but not


rosin. False. Water, mixed with a low concentration of a water-based defluxing chemical, removes all flux types (water soluble, rosin, no-clean).


Solvents work better than water. False. While solvent technology works well, a water-based process works better — in most cases. Some in this industry may remember the pre-1989 days when an assembly that had to be “extra” clean — i.e. for conformal coating purposes — was


Continued on next page


Page 61


Trident batch cleaning system.


review the “conventional wisdom” as it relates to contamination removal from circuit assemblies. First, let us begin with some


basic historical facts. Cleaning is not a new process. In fact, cleaning has been a staple of the electronics assembly process from the invention of the elec- tronic circuit board. In the cleaning industry, we divide our world into two sections; pre-1989 and post-1989. Before 1989, virtually all circuit


assemblies were cleaned after reflow. Flux and other contamination were removed from the assembly prior to


CFCs were determined to be harmful to the Earth’s ozone layer and, thus, were restricted or eliminated from production.


use. We stuffed the board full of com- ponents, cut and clinched the leads, soldered the components to the board, then removed the flux. Much of that changed in 1989.


CFCs Banned from Cleaning Chemicals containing CFCs


were determined to be harmful to the Earth’s ozone layer and, thus, were restricted or eliminated from produc- tion. The most common cleaning sol- vents used to clean assemblies con- tained CFCs that presented a prob- lem for the electronics industry. While some manufacturers con-


verted to environmentally responsi- ble water-based cleaning technology, another option soon presented itself. So-called “no-clean” flux was intro- duced. No-clean flux was designed to not be cleaned. The majority of the electronics industry embraced no- clean technology except for military, medical and a handful of other high- reliability manufacturers. Virtually overnight, the cleaning industry shrank to a fraction of its pre-1989 size. Cleaning for the majority of manufacturers was dead. Today, buyers of cleaning/ -


defluxing systems fall into two groups. The first group is comprised of people who were in the industry before 1989.


See us at Semicon West / Intersolar, Booth 6287


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