A. Gerlach et al., Influence of gold thin-film interlayers on anodic bonding of copper microstructures produced by LIGA, MICROSYST T, 5(2), 1998, pp. 100-104
Neither pure copper nor solid gold can be anodically bonded to glass. It is
only the gold coating on the copper which allows a joint to be built up as
a result of the copper ions diffusing into the gold layer, but not many of
them being able to migrate into the glass. To encapsulate microstructures
produced by the LIGA technique, anodic bonding of gold-coated copper to Com
ing 0211-type glass was studied. For demonstration purposes, a glass platel
et made of Coming 0211 was anodically bonded to a LIGA linear actuator cons
isting of electroplated copper coated with 1 mu m of gold. A better underst
anding about the decisive parameters in anodic bonding was obtained by vary
ing the bonding temperature and the thickness of the gold layer. Glass can
be bonded on to the entire surface of gold layers 0.5-1 mu m thick at tempe
ratures as low as 300 degrees C; however, when the systems cool to room tem
perature, stress-induced cracks arise in the glass. On the other hand, thic
ker gold layers of 2.5 to 10 mu m thickness require higher bonding temperat
ures for the same period of heating, but prevent the occurrence of such cra
cks because of their higher ductility.