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Case Study

Jewellery and Watch

With the rising popularity of depositing ceramics and precious metal coatings on watches and jewellery, ASMAC receive requests from overseas buyers to develop an affordable testing solution for regular checking of the composition and thickness of these two components.

Jewellery and Watch

Unlike traditional electroplating layer which has a typical thickness of several microns, a ceramics layer such as titanium nitride or carbide type coating employed for decorative purpose has a thickness of about 1 micron. PVD gold layer in Ion Plating Gold/Ion Plating Rose Gold (IPG/IPRG) structure has an even lower thickness of about 0.1-0.2 micron. For this reason, routine X-ray Fluorescence (XRF) technique and optical microscopy are no longer appropriate for obtaining the coatings composition and thickness information.

To cater for these two coating specifications, we need a surface sensitive analysis technique that can capture the composition information from layer this thin. We eliminate the possibility of using Energy Dispersive X-ray (EDX) as it has an analytical volume of a few microns depth. We come up with the suggestion of using X-ray Photoelectron Spectroscopy (XPS) out of the various surface sensitive techniques because its surface sensitivity is as thin as 10 nanometers. We can therefore obtain information on the composition of the PVD gold layer after removing the outermost 10 to 20 nanometers of coating materials which usually come with adventitious carbon. After gaining the PVD gold layer composition, the underneath ceramics coating, which is usually titanium based nitride or carbo-nitride, can be determined by “stripping” off the top PVD gold layer by the ion sputter gun.

Measurement of the multi-layers thickness conventionally involves cross-section sample preparation procedure. However, the typical use of optical microscopy is again not appropriate in this case. We therefore advise the use of an electron microscope, which can magnify the cross-section to tens of thousands magnification so as to allow us to discriminate the very thin PVD gold and the underneath ceramics coating layers, and measure the respective layer thickness accordingly.

Reliable and efficient coating quality checking is very important to buyers because having those un-qualified coatings reaching the end-users may end up with very costly recall and rework procedures; and above all, it could severely damage the image of a brand. With our long-built reputation for integrity and professionalism, ASMAC has worked hand in hand with buyers as well as suppliers to develop functional testing procedures that meet their specific needs to safeguard the quality of their products.