Development of SMD 32.768 kHz tuning fork type crystals

Abstract

Abstract Taguchi's design of experiment method and statistical F-test were used to further optimize design parameters for as-fabricated resonance frequency of tuning forks for use in Qualcomm® mobile station modem (MSM)-3000TM series central processing unit chips of code division multiple access, personal communication system, and global system for mobile communication systems. After much trial and error, finite element method modeling and Taguchi's design of experiment method enabled selection of essential design parameters to effectively manufacture tuning fork test samples using photolithography with subsequent photoresist spray coating. As-fabricated resonance frequency values of a tuning fork blank thus manufactured remain almost the same prior to final frequency adjustment of the mounted crystals, regardless of pressure change from ambient to the designated packaging pressure of 6 × 10−5 Torr. The tuning fork test samples thus fabricated were characterized and analyzed using Taguchi's design of experiment method and statistical F-test to evaluate the sensitivity of as-fabricated resonance frequency for various design parameters fror ambient to the designated packaging pressure of 6 × 10−5 Torr. As-fabricated resonance frequency is most sensitive to tine width (x) and variance analysis results showed that only x and y (tine length) are significant design parameters and no design parameter significantly affects the as-fabricated resonance frequency change with the vacuum level of the package: the as-fabricated resonance frequency change with vacuum level turned out to be independent of design parameter contributions.