Characterization of a photosensitive dry adhesive film for wafer level MEMS packaging

In this paper we present the results of initial studies of a new dry film polymer, PerMX developed by Du Pont for wafer level packaging applications. PerMX is a high resolution permanent photosensitive dry film material with low temperature processing capability. Dry film is easy to deposit on large wafers compared to the liquid form materials. We have carried out initial chip scale characterization of the material for MEMS packaging applications. A PerMX film of thickness of 20 mum was used to create sealing rings on glass wafers. The outer dimensions of the polymer rings are 5 mmtimes5 mm with a track width of 100 mum or 400 mum. Glass substrates with a polymer ring were bonded to polished silicon chips for investigation of the polymer as a bonding material for MEMS packaging. A range of bonding parameters was studied in order to obtain high bond quality. Shear test and gross leak test were conducted to evaluate the bond strengthen and hermeticity. The results show that the PerMX polymer can produce a strong bond between the glass and silicon substrates. Bond strengths of ~7 kgf have been obtained for the samples with a bonding track width of 100 mum. The samples produced under the optimal bonding conditions passed the gross leak test. In addition the surface roughness was also measured and it is less than 60 nm. These results show that the PerMX is a potentially suitable material for MEMS packaging applications.