Adhesion improvement of electroless copper (Cu) thin films deposited on Low Temperature Co-fired Ceramics (LTCC)

Low Temperature Co-fired Ceramic (LTCC) is widely used for micro and millimeter wave devices. Typically it is metallized by printing high cost silver or gold pastes prior to firing. However, direct metallization of the post fired material is an alternative, for which low cost electroless plating methods can be used. Activation of the ceramic is usually achieved with a Pd/Sn based catalyst, but the adhesion of the electroless coatings can be limited without additional pre-treatments. In this study, the effect of sodium hydroxide (NaOH) solution treatment on the surface morphology of LTCC as a function of concentration and immersion time was investigated, together with its effect on the adhesion of electroless copper deposits. SEM and white light interferometry measurements were used to characterize the morphology changes. NaOH concentrations in the range of 3M to 7M were found to alter the surface morphology and roughness of the LTCC with immersion periods of 7.5 hrs to 24 hrs. After the NaOH treatment, samples were activated with Pd/Sn catalyst and electroless copper was successfully plated. However, qualitative adhesion measurements using a tape test revealed significant variations between the effects of the NaOH treatments.