Low-cost automatic visual inspection system for media in hard disk drive mass production

In the modern high-volume hard disk drive production process, if an assembled product fails the final test it is normally not just discarded, but is sent for Teardown, whereby it is disassembled to the constituent components. These components are thoroughly examined, and if pass the test, they are then used again in new products. Traditionally Laser Doppler Vibrometry (LDV) has been employed for media surface inspection. At the same time, LDV test is lengthy, thus reducing overall efficiency of the teardown process. In order to increase the teardown process efficiency, manual visual inspection is often performed as a preliminary filtering step. Such an arrangement is not optimal as it is open to human error factor and has throughput limitations. The aim of this research is to increase efficiency of the media surface inspection process during the teardown stage by replacing the manual media visual inspection with a low-cost automatic visual inspection system. The paper explores the factors influencing successful and rapid image acquisition of micrometer level defects on a media surface, namely camera spatial resolution, spectral properties, image system Signal to Noise Ratio (SNR), and lighting methods. A detection as well as classification scheme is proposed to classify four major types of commonly occurring HDD media defects.