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Title: The characterization and reliability analysis of green electronics manufacturing processes for hard disk drive head assembly
Other Titles: Ying die ji ci tou zu zhuang yu l{uml}u se huan bao dian zi sheng chan guo cheng zhong de te xing ji qi ke kao xing fen xi
Authors: Luk, Chi Fai (陸志輝)
Department: Dept. of Electronic Engineering
Degree: Doctor of Philosophy
Issue Date: 2006
Publisher: City University of Hong Kong
Subjects: Electronic apparatus and appliances -- Environmental aspects
Electronic industries -- Environmental aspects
Lead-free electronics manufacturing processes
Notes: CityU Call Number: TK7870.L78 2006
Includes bibliographical references (leaves 152-157)
Thesis (Ph.D.)--City University of Hong Kong, 2006
xx, 161 leaves : ill. (some col.) ; 30 cm.
Type: Thesis
Abstract: In order to protect our health and the environment, a new European Union (EU) directive 2002/95/EC came into effect on 1st July 2006. All manufacturers of electronic and electrical equipment sold in Europe should comply with the EU’s restrictions on hazardous substances as laid down in the (RoHS) Directive. This directive lays down the maximum concentration level for six hazardous substances which are lead, mercury, cadmium, chromium (VI) and flame retardants (PBB and PBDE). The immediate repercussions of non-compliance may include serious fines, damaged brand reputations and potentially, even jail time. Among these six banned substances, there is no doubt that the replacement of lead is the biggest challenge to industry. Lead has been widely used in solder paste and solder bars for electrical connections and electronic component plating on electrical terminals for over half of a century., It is hard to find a perfect, lead-free replacement with a comparably reliable performance. In this project, difficulties and concerns during the phase-in of lead-free soldering process in hard disk drive products have been discussed. Different process parameters such as reflow profile settings (pre-heat time, peak temperature and dwell time); the condition of the inert atmosphere (concentration of oxygen level) and a new stencil design have been studied. Since the lead exemptions permitted by the EU for certain high-reliability products such as military applications, control circuits, servers and telecommunication, some tin-lead manufacturing will coexist with lead-free manufacturing at the same time. Serious defects due to mixing up the usage of lead-free solder and the traditional lead-tin ball grid array (BGA) solder bumps were evaluated. Lead impurity is a contamination which is the major cause of the failure of solder joints. Since the melting point of lead-free alloys is much higher than the eutectic lead-tin alloy, the re-melting problem of the lead-tin solder bumps causes immediate failure because of “open-circuits” or “open-joints”. As per the market demands, the size of products such as MP3s, mobile phones, digital cameras and even personal computers is getting smaller and smaller. However, the storage memory needs to be increased rapidly for high-quality photo processing and large amounts of data processing. Head stack suppliers in the hard disk drive industry are constantly working on high density interconnection technologies to provide faster, higher capacity and cheaper head stack components for disk drives. As per the prediction, the I/O pitch for devices will decrease from 60µm in 2004 to 20µm after 2012. The traditional solder joint electrical connection will have to follow this trend. There is an urgent need to develop other lead-free interconnection techniques such as gold-to-gold interconnection flip chip bonding and the adhesive bonding technique using anisotropic conductive film which have been used in hard disk drive head assembly. The new method of gold-to-gold bonding for a chip-on-suspension application has been described in this project. The option of this design will bring exciting new products to the market and help to keep the hard disk drive industry in business. The reliability performance of this new technology has also been studied by means of the values of bias current through the high temperature storage, and by thermal shock testing up to 1000 hours. Apart from the gold-to-gold bonding, a low cost method to manufacture hard disk drive heads using anisotropic conductive film (ACF) bonding for flex-to-flex interconnection has been developed. Through the finite element analysis (FEA) method, a new bond pad was designed for the ACF process. The electrical and mechanical properties of the interconnection were reported, after the pad had passed through several reliability tests. The FEA software tool ANSYS was used to predict the internal stress of the ACF bonded joints and samples were built to verify the computation results.
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