Wettability Of Glass Surface And The Joining Between Glass And Copper At Low Temperature

Glasses is an ideal optical material because of its excellent optical properties,oxidation/ablation and low density. For its intrinsic brittleness, poor resistance ofthermal shock and be sensitive of stress and strain, its optical properties may be affectedmore or less. In order to reduce the stress and strain，joining of metal and glass cantaking advantage of metal’s good thermal conductivity to slove this problem. In thispaper, the metallization process on glass surface and the wetting of In-Sn solder oncoating was investigated. The wetting and non-wetting mechanism was also analyzed.The joining of glass and copper was successfully realized by using In-Sn solder at lowtemperature. The joining of glass and copper with auxiliary electric field was preliminarystudied, bonding mechanism was also analyzed by calculating and testing. The influenceof soldering parameters on microstructure and mechanical properties of joints wasstudied. The optimal soldering parameters were identified.The composition of glass surface was SiO₂, Na₂O and CaO，which was amorphousstructure. To protect the solder from oxidizing, the flux was fabricated and its functionalmechanism was analyzed. The In-Sn solder can not wet glass at each temperature, and itssurface tension is larger than glass’ critical surface tension. The groove structure whichwas fabricated by sandblasting on glass surface can enhance the―mechanical interlock‖effect. The adhesion strength would decrease when the electroless nickel plating timeextends, the adhesion strength can reach maximum（40N）when plating time was50min.In-Sn solder can wet the Ni-P plating and the wetting angle would decrease atelevated temperature. When the temperature was210℃, the wetting angle can reach to42.9°. At low temperature, the dissolution of Ni-P coating contributed the wetting. Atelevated temperature, solder diffusing, Ni-P coating dissolving and the change ofgeometrical morphology contributed the wetting together. The addition of Bi can refinethe microstructure and make the solder’ melting point decrease, but its addition can alsoincrease solder’s melting range. When the wetting temperature was210℃and holdingtime1min， the addition of Bi can increase the wetting angle, when its addition was1.5wt%, the wetting angle can reach65.2°.The interfacial structure are Glass/Ni-Pcoating/P-rich layer/（Ni,Sn）₂₈In₇₂/β-Sn（s,s）/β-Sn（s,s）+Cu₃（In,Sn）/Cu₃（In,Sn）/Cu insequence when soldering temperature was190℃and holding time was5min respectively.With the increasing of temperature, the P-rich layer and intermetallic compound（Ni,Sn）₂₈In₇₂formed along with the glass interface. The higher temperature can cause theforming of through-wall cracking. The joining of glass and copper with auxiliary electric field was realized. Thetypical interfacial structure are: Glass/β-Sn+（Sn-Al）eutectic/Cu₆Sn₅+Cu₃Sn/Cu insequence when soldering temperature was420℃,holding time was10min and electricvoltage was1200V respectively. The bonding quality lies in the electrostatic interfaceattraction, the forming of≡Si-O-Sn and≡Si-O-Al chemical bonds. The formation ofAl₂O+3and SnO as well as the diffusion of Al⁺³into the network structure of glass alsocontributed to the bonding quality. With the increasing of temperature and voltage, theinterface adjacent to glass had no change, but the shear strength increased. When thejoining temperature was400℃, holding time was10min and the voltage was1400V, thejoints achieved the maximum shear strength about11.5Mpa. All the crack initiated fromthe seam adjacent to glass and then propagated inside the seam,finally the cracks endedin the intermetallic layer.