Simco - Particle Contamination on Medical Devices Caused by Static Attraction

Roger Peirce – Simco an ITW Company


In the semiconductor manufacturing industry, yield losses resulting from increased particle contamination on wafers due to the effects of static charging are well documented1-8. If ionization techniques are not implemented properly, yield losses are quite common. Similarly, medical devices (such as catheters, stints, optical lenses, etc., etc. – essentially all plastic or insulative devices in medical applications) have been identified as having very similar yield loss mechanisms during manufacturing operations. This white paper summarizes our recent studies across a number of companies manufacturing these types of medical devices – that have led to substantial yield improvements when the electrostatic attraction (ESA) problems were eliminated.

Charging of Plastic Devices During Manufacturing:

The basic issue we are observing frequently in the medical device manufacturing industry is simple in nature. When the plastic devices are contacted, rubbed, handled, etc., they generate tremendous static charges. It is common to have plastic materials charge into the tens of thousands of volts during such “triboelectric” charging (i.e., charging resulting from friction). In the case of stints and catheters, for example, charge generating operations include simple handling, heating of the tubes, stretching or ballooning, laser welding, etc., etc.

When these products are charged to those levels, they attract more particles to their surface than their noncharged counterparts. All that is common knowledge. However, the studies we have concluded recently clearly point to the fact that static attraction is usually the overwhelming major contributor in contamination yield losses during manufacturing of these devices – in many cases, the contamination yield losses were determined to be almost 100% caused by static attraction. When charges were removed from the plastic devices (via ionization) - in all manufacturing areas in these facilities - the vast majority of their contamination yield losses were removed with them – and the resulting positive financial impact was invariably substantial...

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