The Mounting and Fabrication of Plated Quartz Crystal Units

HIS paper is one of a series on piezoelectric quartz plates and deals primarily with the methods employed in mounting crystal plates operating up to approximately one megacycle for practical utilization in communication equipment. The theoretical aspects of mounting crystals have been covered in Chapter VII. The discussion is confined to plates 1 having definite nodal lines or points, such as + 5 ° and --18° 25' X cuts, GT, CT, DT, MT and NT cuts. The mounting of high-frequency crystal plates such as AT and BT cuts, which vibrate in thickness shear modes, is not included. It should also be noted that the subject matter is treated descriptively and that no attempt is made to go into the more intricate details of design or to give performance characteristics. These matters will be dealt with fully in a later paper. The designs and methods outlined are up to date for each type of unit, the results of many years of development on the part of Bell System engineers to evolve practical designs for commercial manufacture and use. Expanding on the contributions of the early investigators mentioned by W. P. Mason in Chapter I, 1 these engineers had, in the ten years prior to 1939, worked out practical designs and developed suitable tools and processes for wide commercialization in telephone applications. In the last five years, under the impetus of war, further improvements have been made in the design and manufacture of crystal units, particularly those for use by the Armed Forces. The term "Crystal Unit", originally adopted by the Bell System to designate the complete assembly of a crystal plate in its mounting and case, has new been standardized quite generally in the art, replacing a variety of names by which these devices were formerly called.