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66 The PCB Magazine • June 2014 by Karl Dietz Karl dietz consulting llc Supporting Thin Structures c o l u m n karl's tech talk In the world of PCB fabrication, there are few examples of special support features for thin substrates. But they do exist in the form of assist features in conveyorized spray modules designed to prevent mishaps during the transfer of very thin innerlayers, or in the transport of flex circuit boards, em - ploying the use of leaders or frames. On the other hand, tape supports have been used in wafer-level pro- cessing for quite some time, such as dicing tapes to support and hold in place the wafer and the diced chips during singulation, and more re- cently, support systems that en- able backgrinding of wafers, and post-backgrinding processing steps such as sputtering and plating. This application pres- ents challenging material and process control require- ments that are worth becoming familiar with. Background Information Wafer backgrinding is the process of grind- ing the backside of the wafer to the correct wa- fer thickness prior to assembly. It is also referred to as "wafer thinning." Wafers are ground back from about 300 mi- cron thickness down to 50 micron, for example. Wafer backgrinding has not always been necessary, but the drive to make packages thin- ner has made it indispensable. Most package types in the semi- conductor industry today would require a wafer thickness rang- ing from 8–20 mils. Wafers normally undergo a cleaning and surface lamina- tion process prior to the actual backgrinding process. Sur- face lamination involves the application of a protective tape over the surface of the wafer to protect it from mechanical 66 The PCB Magazine • June 2014

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