Glazing and Polishing

A major ingredient in glazes is shellac. This material is an insect exudate and is completely natural and biodegradable. Kosher grades are available if required. 

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Stannic oxide (SnO ) is a whitish powder used as a ceramic glaze and polishing agent. 

Function Candy glaze and polish raw material for flavoring agent. 

Any and all of these particles can become attached to the pad. As the surface of the pad accumulates more and more particles, the surface glazes and becomes smoother and less abrasive. Consequently, the removal rate declines. Also, as the pad becomes glazed it becomes smoother, which causes a decline in the ability of the polish pad to distribute slurry under the wafer. At present there is considerable debate as to whether CMP takes place in a contact regime or in a lubrication regime. It is likely that resolution of this issue will be necessary to establish what fundamental limits there are on slurry flow, as well as how these limits affect pad conditioning. 

An end effector, also called a pad dressor or a pad conditioner, is used to condition the polish pad to retrieve polish rate. If this is not done, the surface of a pad can become glazed and the pad austerity lost (see Fig. 9). The austerity of a pad is required in CMP otherwise, hydroplaning will occur, which means that contact between a pad and a wafer surface no longer exists. 

Fig. 9. Schematics of a microscopic view of a polish pad before and after conditioning. Before conditioning, the pad is glazed and filled with dried slurry after conditioning, the top layer of the pad is removed and the austerity is restored.

The effect of pad glazing and conditioning on polish rate. An extended conditioning sequence was performed between the 25th and 26th wafer. After which, the standard conditioning sequence maintained a stable polish rate. (From Ref. (16), reprinted by permission of the publisher.)... 

Zirconia powder serves as a polishing agent, as an opacifier in glazes and enamels and as a component of chemically resistant glasses and enamels stabilized Zr02 is used in the manufacture of highly refractory ceramics. 

Figure 7.12 (a) Effect of pad glazing and conditioning on polish rate.9 (b) (After Ali and Roy.10) (c) Rate degradation without conditioning.11... 

In addition to the extensive use of tin metal itself and its alloys, various compounds of tin are used in industry and commerce. Tin(IV) oxide is used as an opacifier for vitreous enamels, in ceramic glazes and as a polishing powder. Tin chlorides are used to weigl t natural silk, stabilize soap perfumes, silver glass mirrors and as chemical reducing agents. Tin(II) fluoride finds extensive use as an additive to dentifrices. ... 

Sheet can be produced by melt extmsion, but in this case a three-roll stack of quenching roUs is generally used (Fig. 2). More than three roUs may be used where necessary. The roUs may be mounted vertically or horizontally. The web is extmded through a slot die in a thickness close to the desired final thickness. The die is in very close proximity to the first chill roU or chill-roll nip. The web may be cast horizontally directly onto the upper chill roU of the stack as shown (Fig. 2), or it may be extmded into the first nip directly. The roUs quench the sheet and provide the surface polish desired. In some applications, matte or embossed roUs maybe used to impart special surface characteristics for certain functions. Where the utmost in optical (glazing) quality is desired the trend has been to mount the roU stack horizontally. The hot melt is then extmded vertically down into the first nip. This avoids problems associated with sag of a horizontal hot melt no matter how short the distance between die and quench. 

The sliced sheet will still contain large quantities of alcohol and it is necessary to season the sheet at elevated temperatures. This may only take three days at 49°C for 0.010 in (0.025 cm) thick sheet but will take about 56 days for 1 in (2.5 cm) thick blocks. The removal of alcohol, as might be expected, is accompanied by considerable shrinkage. Fully seasoned sheet has a volatile content of 2%, the bulk of which is water but there is some residual alcohol. The sheet may be fully polished by heating in a press between glazed plates under pressure for a few minutes. Because the material is thermoplastic it is necessary to cool it before removal from the press. 

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