Frequency shifts minimization experiments for miniature surface-mount RF crystals

Piezoelectric quartz blanks are typically supplied in either leaded or surface mount packages. The blanks in a surface mount package are mounted either in a “cantilever” mount or a “double-ended” mount. The “cantilever” mount attaches one blank end to the carrier (with the other end floating), while the “double-ended” mount attaches the blank to the carrier at both ends of the blank. The mount system must provide mechanical shock isolation and thermal compliance to insure that mechanical and thermal conditionings do not result in unacceptable shifts in the device parameters. An additional requirement is that the adhesive and the sealing methods do not expose the quartz element to excessive contaminants and gases, because this would lead to similar unacceptable shifts. Once the basic mount system was developed, further experiments were used to minimize the frequency shifts through reflow, accelerated aging, thermal shock, vibration and mechanical shock. These experiments dealt with oven types and the time and temperature of the cure and post cure conditioning. The ideal method of performing experiments is to combine all of the variables at the same time in a large replicated factorial experiment. During the process development stage, portions of the fixtures and equipment were not available. Thus, by necessity, the development consisted of a series of small factorial experiments rather than one large experiment