| Popis: |
Solders of various compositions are used in the electronics industry to interconnect components. To obtain proper reflow of the solder pads to be joined, surface oxides must be removed using an appropriate chemical flux. In this paper, we describe an alternative fluxless joining technique in which an ion beam is used to simultaneously sputter clean and melt solder pads prior to joining, and can also provide the heat needed to perform the joining step itself. Using a Si circuit chip with solder pads of 95% Pb, 5% Sn, the melting temperature of the solder (312 °C) is reached within 25 s in an argon ion beam of 1000 eV, 1.0 mA/cm2. The solder pads are etched about 500 A during this time, and reflow into clean spherical shapes suitable for joining. Electron microprobe analysis shows that the Pb and Sn are uniformly distributed through the solder pad after reflow. Chips have been sucessfully joined to metalized ceramic substrates using either auxiliary heating or using the heat from a focused ion beam. Pull tests show that ion beam reflowed joints are as strong as those obtained by the standard flux joining process. |
