CHAPTER XIII* 



The Mounting and Fabrication of Plated Quartz Crystal Units 



By R. M. C. GREENIDGE 

 13.1 Introduction 



THIS 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^ 

 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 commer- 

 cial manufacture and use. Expanding on the contributions of the early 

 investigators mentioned by W. P. Mason in Chapter I,^ these engineers 

 had, in the ten years prior to 1939, worked out practical designs and devel- 

 oped suitable tools and processes for wide commercialization in telephone 

 appUcations. 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 desig- 

 nate the complete assembly of a crystal plate in its mounting and case, has 

 now been standardized quite generally in the art, replacing a variety of 

 names by which these devices were formerly called. The basic design fea- 

 tures of a crystal unit involve the use of: 



1. Electrodes, on or near to the crystal surfaces for impressing voltage 

 across the plate, 



* Chapters IX, X, XI and XII, which will be included in a forthcoming volume are 

 omitted from the Technical Journal because they deal largely with details of manufacturing 

 operations. 



1 "Quartz Crystal Applications", W. P. Mason, B.S.T.J., Vol. XXII, Page 191, July 

 1943. 



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