| 摘要 |
Drilled holes in circuit boards with high ratio of hole dia. to circuit board thickness are cleaned by plasma etching with a CF4/O2 mixt., using the following steps: (a) charging a plasma reactor with the circuit boards and evacuating to a first predetermined pressure; (b) introducing gas mixt. of ca. 50-80 (vol.)% CF4 and 50-20 (vol.)% O2 to a second predetermined pressure; (c) switching on a H.F. generator connected to the plasma (d) maintaining the plasma over a period long enough to clean the drilled holes; and (e) switching off the H.F. generator, introducing air and discharging the plasma reactor. The circuit boards pref. have dimensions of 600 x 700 mm and holes with a ratio of hole dia. to board thickness of ca. 1:11-13. The first pressure is pref. 0.066 mbar. Gas mixt. pref. consists of 55-70, esp. 60% CF4 and 45-30, esp. 40% O2 and is introduced at a rate of 1.2 l/min. to a pressure of 0.1-1, esp. 0.333 mbar. H.F. generator pref. has an output of ca. 3-6, pref. 3.5 kW. Plasma treatment is carried out for 60 min., pref. for 2 periods of 25 min., with an intervening 10 min. break, at a temp. of 80-150, pref. 74-121 deg.C. Desired etching front is obtd. by regulating the CF4 concn. in O2.
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