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The deposition of copper into the through holes and vias of printed wiring boards (PWB’s) has been done using vacuum processing techniques such as evaporation and sputtering. One of the most important limiting factors for any deposition process is the substrate heating. The temperature of epoxy-glass PWB’s should not exceed 180 °C (350 °F). For evaporation, there are two major contributions, the heat of condensation and radiant heating, with the heat of condensation dominating at deposition rates 2 μm/min. The radiant heating is very dependent on α ε, the product of the substrate absorptivity and the source emissivity. Sputter deposition has two main sources of substrate heating: the heat of condensation and the kinetic energy of the incident atoms and ions. The experimental apparatus used to measure the power absorbed by a PWB substrate is described. Data are presented for the power absorbed by the substrate as a function of deposition rate for sputtered copper. These data are compared with the results obtained by other investigators for evaporated aluminum and sputtered aluminum and copper. The various contributions to substrate heating are theoretically determined for both evaporation and sputtering systems. The absorbed power per unit area is calculated as a function of deposition rate and agrees very well with experimental results. It is discovered that the heating rate of a substrate is very similar for evaporation or sputtering of copper for deposition rates ≲3 μm/min. Sputtering heats the substrate more than evaporation at higher deposition rates, primarily because of heating by energetic atoms and ions.
A. N. Pargellis (Sun,) studied this question.