Cmos standard pad layouts can be used to facilitate

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Unformatted text preview: tended package outline should be overlaid on the die layout – Verify package selection – Check for packagability prior to MEMS fabrication – Avoid redesign of custom packages – Plan for a larger than normal die edge to bond tier spacing to accommodate placement and attach processes using tweezers (if necessary) Cross section of a typical package (CQFJ) >0.050 die edge to cavity edge spacing Suggestions apply to other package types Microsystems Packaging: An Introduction Page 77 © 2003 Sandia National Laboratories Design Features and Packaging • Many assembly issues involve bond pad layout and their position relative to the wire bond tier in a package – Typical MEMS devices are relatively low I/O, large die area – Space bond pads uniformly around the perimeter – Simple fast assembly – Increased wire spacing vs. CMOS – Standard pad layouts can be used to facilitate multiple use probe cards View down onto top of die and package wire bond tier Avoid ‘bunching’ of pads Microsystems Packaging: An Introduction Page 78 © 2003 Sandia National Laboratories Design Features and Packaging (2) • Die bond pads arranged in a singular row around the perimeter – prevents crossing over structures – minimizes the chance of damage – avoids wire to wire shorting – simplifies re-work when needed – Avoid routing conductors outside of bond pad perimeter – Keep probe pads away from mechanical structures • Disallow bad practices up-front to avoid unlearning bad habits later Microsystems Packaging: An Introduction Page 79 © 2003 Sandia National Laboratories Design for Packaging Example: Original • Bad Features: – Poor fit of die to package – Bond wires cross over comb drives – Multiple angle bonds increases chance for wire to wire shorting – Long bond wire lengths prone to sagging, potential for shorting to die – Bond pad locations increase difficulty in probing at wafer level Microsystems Packaging: An Introduction Page 80 © 2003 Sandia National Laboratories Interior view of package, wire bonding tier and die Design for Packaging Example: Revised • Revisions: – Customized package – Reroute leads so bond wires no longer cross over mechanical structures – Spread pads so potential for wire to wire shorting eliminated – Shortened bond wire lengths well below 100 mils – A standardized bond pad layout was defined to simplify test probing Microsystems Packaging: An Introduction Page 81 © 2003 Sandia National Labora...
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