Formation of fine pitch solder bumps on polytetrafluoroethylene printed circuit board using dry film photoresist

We demonstrated the applicability of dry film photoresists (DFR) in photolithography process for fine pitch bumping on the polytetrafluoroethylene (PTFE/Teflon/spl reg/) printed circuit board (PCB). The copper lines were formed with 100/spl mu/m width and 18/spl mu/m thickness on the PTFE test board, and varying the gaps between two copper lines in a range of 100-200/spl mu/m. The DFRs of 15/spl mu/m thickness were laminated by hot roll laminator, by varying laminating temperature from 100/spl deg/C to 150/spl deg/C and laminating speed. We found the optimum process of DFR lamination on PTFE PCB and accomplished the formation of indium solder bumps. The optimum lamination condition was temperature of 150/spl deg/C and speed of about 0.63cm/s. And the smallest size of indium solder bump was diameter of 50/spl mu/m with pitch of 100/spl mu/m.