Page 1 of 2
0 M
MOTOROLA INC. Technical Developments Volume 14 December 1991
BATCH FABRICATED FINISH PLATE MASKS FOR QUARTZ FILTERS
by Thomas Knecht
The following configuration describes finish plate masks for monolithic crystal filters, leaded or surface mount. Batch fabrication of finish plate masks using anise- tropic etching of wafers is shown.
For leaded devices, the prior art is a 2 pc. plastic "hang on" mask. This is fabricated by precision milling two halves separately, and aligning and fastening them together with tiny screws.
These masks cost - $lOO.OO/unit to make. Fish plating is accomplished by plating (depositing) metal from both sides. Misalignment has a range of +/- .007!' At least 113 of this can be attributed to the mask construc- tion itself. They are, of course, made one at a time in machine shop fashion.
The invention is now descrii It is shown in Figure 1.
with. One silicon wafer has two etched apertures per cell, and the other silicon wafer has one apetire for bandwidth adjust. The Pyrex wafer in the middle is isotropically etched, where the opening is slightly larger than the diameter of the quartz blank that the mask slips over. The silicon wafers (- 15 mils thick) can be anodically bonded to both sides of the Pyrex wafer (after being aligned by one of several methods). This bonding method does not add thickness uncertainty to the thickness of the glass, and hence the spacing between the two sets of Si apetires. The wafer sandwich is then diced up to produce a multitude of ftish plate masks. Typic...
