Abstract There is disclosed a specialized composite contact for use with piezoelectric crystal frequency standards in which the contact area is minimized at the nodal points of the crystal so as to decrease damping of the crystal by the contacts and therefore increase its Q. The contacts are compatible with reflow soldering techniques thereby eliminating the compressive stress placed upon crystals by thermal compression bonding. Reflow solder is confined to the area of the contact by use of a patterned aluminum electrodes contacting the crystal. On the top of the aluminum electrodes are the composite contacts which are layered, with chromium being the layer next adjacent the aluminum electrode followed by copper and then gold. These contact layers are deposited through a mask whose openings are positioned over the nodal points of the crystal and whose aperture sizes are limited such that contacts formed through this mask approach ''''point contact'''' characteristics. The reflow solder adheres only to the gold-copper outer portion of the contact and not to the aluminum metallization.
The apparatus as recited in claim 1 wherein said crystal vibrates in a flexure mode by flexing about two nodal axes within the body of said crystal.
Claim 2
Dependent Claim
15 words
The apparatus as recited in claim 2 wherein said crystal is a NT cut crystal.
Claim 3
Dependent Claim
35 words
The apparatus as recited in claim 1 wherein said chromium layer is 1000 angstroms in thickness, wherein said copper layer is 10,000 angstroms in thickness and wherein said gold layer is 2000 angstroms in thickness.
Claim 4
Dependent Claim
58 words
The apparatus as recited in claim 1 wherein said crystal is in the form of a bar having a flexure mode of vibration, said crystal being contacted at a multiplicity of contact points, said contact points being located at the intersection of one of the nodal axes of said crystal and the exposed surface of said aluminum layer.
Claim 5
Dependent Claim
37 words
The apparatus as recited in claim 5 wherein said crystal is contacted at two of said contact points, said two points being on one side of said crystal and said crystal being supported from said two points.
Claim 6
Dependent Claim
64 words
The apparatus as recited in claim 5 wherein said crystal is contacted at two pairs of said points, the pairs being on opposite sides of said crystal such that points on opposite sides of said crystal lie on a line perpendicular to the flat sides of said bar, said line being a nodal axis of said crystal, whereby a four-point suspension system is formed.