You received an inquiry regarding solvent cleaning of disc drive parts using "exotic" solvent and alcohol in a vacuum style vapor degreaser. Our company manufactures these units and we have one that cleans disc drive platters. This unit is used for final clean. So far in our testing, yield is increased. The current unit uses megasonics. In future testing we want to use ultrasonics for comparison and also a combination of both. Density of the solvent does seem to have a positive affect on particulates. We have several disc drive companies interested worldwide because of problems with water cleaning and the need to increase yield. A.G.
The information above is a follow-up to my February column regarding disc drive parts cleaning. In that column, A.G. commented that they had seen improved cleaning results when going to a mix of "exotic" solvent and alcohol. In my commentary, I suggested that the improved particulate removal was probably due more to reduced surface tension than the increased solvent density.
More information surfaces this month regarding specifics of the cleaning equipment. It is noted that the current equipment uses megasonics. This is valuable information since the sonics are a more effective means of cleaning than a static solvent bath. This would better explain why they have seen an improvement in particulate removal more than any other reason.
The megasonic region they are working in is a very high frequency (approaching 1 MHz). This high frequency is generally reserved for more delicate materials that can be damaged at lower frequencies. As they lower the frequency, the physical action of cleaning will tend to be more aggressive, therefore particulate removal may be more efficient. However, this needs to be balanced against the risk of part damage. As the ultrasonic frequency becomes lower, there is a greater chance of part damage, particularly for something like a disc drive.
The exchange from these couple of columns shows how important it is to get the entire story before drawing conclusions. The equipment plays just as important a role as the solvent does in getting parts sufficiently clean.