Interdiffusion microsystems packaging an introduction

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Unformatted text preview: ackaging: An Introduction Page 58 © 2003 Sandia National Laboratories Epoxy Wire Bonding — Electrical Connections • Al wedge to Al pad, Au wedge to Au pad Typical Al wedge bond to Al pad • Au ball to Al or Au pad Typical Au ball bond to Al pad Microsystems Packaging: An Introduction Page 59 © 2003 Sandia National Laboratories Al or Au Wedge Wire Bonding • Al wedge to Al pad, Au wedge to Au pad – Room temperature, pressure, and ultrasound – Metal intermixing results in solid joint – Ultrasound helps disrupts oxide films, enhances interdiffusion Microsystems Packaging: An Introduction Page 60 © 2003 Sandia National Laboratories Au Ball Bonding • Au ball to Al or Au pad – 150°C w/US, ~300°C w/o US – Au and pad metal deform and interdiffuse – Au-Al intermetallics grow as f(t, T) – Bond strength depends on surface cleanliness – Used extensively for commercial plastic packaging – Bond loop higher than wedge Microsystems Packaging: An Introduction Page 61 © 2003 Sandia National Laboratories Wire Bonding: Design Rules • Square bondpads, 4 - 8 mils (100 - 200 µm) in size (this is the dimension that can be bonded not the outside dimension) • At least 8 mil pitch (200 µm) • Length of wirebond less than 100 mil (vibration) • Enough headroom for package lid and die attach (15 mil + 2 mil) • Placement of bondpads on periphery of chip with uniform spacing required for automatic wire bonding Microsystems Packaging: An Introduction Page 62 © 2003 Sandia National Laboratories 100 µm 80 µm Chipped bondpad due to small size 80 x 80 and cantilevered construction Microsystems Packaging: An Introduction Page 63 © 2003 Sandia National Laboratories Wire Bonder Wire • Be aware of maximum current capacity • Larger wires available for high current applications Microsystems Packaging: An Introduction Page 64 © 2003 Sandia National Laboratories Wire Bonding This is a standard wedge bonder and a bondpad 1. bondpads should be at least 100 µm x 100 µm (look at end of tip) 2. Bondpads should have at least a 200 µm p...
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