A dishwasher for circuits

You have always been told that electronic devices fear water. However, at the Surface Mount Devices (SMD) Workshop here at CERN all the electronic assemblies are cleaned with a machine that looks like a… dishwasher.



The circuit dishwasher. Credit: Clara Nellist.

If you think the image above shows a dishwasher, you wouldn’t be completely wrong. Apart from the fact that the whole pumping system and the case itself are made entirely from stainless steel and chemical resistant materials, and the fact that it washes electrical boards instead of dishes… it works exactly like a dishwasher.

It’s a professional machine (mainly used in the pharmaceutical industry) designed to clean everything that can be washed with a water-based chemical soap. This type of treatment increases the lifetime of the electronic boards and therefore the LHC's reliability by preventing corrosion problems in the severe radiation and ozone environment of the LHC tunnel in the presence of beams. “We use an alkaline cleaning agent specifically designed for electronics,” explains Sylvain Kaufmann, of the Machine Protection and Electrical Integrity group (TE-MPE-EM). “The cleaning agent removes soldering residuals, contamination particles and manipulation traces like fingerprints.”

Tap water can be used to wash the circuits but not to rinse them. “Indeed, ionised water can generate major problems for the electronics decreasing the reliability of the integrated circuits. It leaves residue on the surface of the boards, which may be detrimental to the reliability of the assembly. The main associated risk is electromigration – the transport of material caused by the gradual movement of the ions in a conductor,” explains Kaufmann. “Therefore, we use de-ionised water in the rinsing process.”

by Rosaria Marraffino