Patent Application
20080169730
Automatic test equipment (herein “ATE”) typically uses one or more clocks to generate accurate timing for testing and for the purpose of time measurements. Historically, a clock that introduced little or no jitter with very good overall timing accuracy is desirable. Traditionally, quartz crystals have been limited to approximately 20 MHz, beyond which frequency the crystal blank became too thin for known processing techniques.
In traditional processing of crystal substrates, the substrate is mechanically lapped to create the appropriate thickness to obtain the desired frequency. This creates a uniform thickness across the entire substrate. In the areas where the wire bond must be attached to the crystal substrate to provide the feedback path for the electrical circuit, the crystal must be mechanically robust and strong enough to withstand the wire bonding process. Hence, the crystal could not be thinned too much during the lapping process. However, a thinner crystal creates a higher frequency. Thus, the crystal would usually crack into several pieces, when an attempt was made to engineer it beyond 20 MHz.
Therefore, in order to obtain a time base reference beyond 20 MHZ, a phase lock loop has been used to increase frequency from 20 MHZ up to the desired frequency. Phase lock loops (herein “PPL”) multiply the frequency well into the hundreds of megahertz frequency range. Unfortunately, in doing so, the phase lock loops also tend to introduce short cycle and long cycle random jitter or noise into the ATE system.
Therefore, there is a need for an ATE clock that improves overall timing accuracy (herein “OTA”) of the ATE system, is capable of higher frequencies, and introduces less random jitter than traditional PPLs, in order to enable the ATE systems to test new device types and at higher date rates.
An understanding of the present teachings can be gained from the following detailed description, taken in conjunction with the accompanying drawings of which like reference numerals in different drawings refer to the same or similar elements:
In the following detailed description, for purposes of explanation and not limitation, example embodiments disclosing specific details are set forth in order to provide a thorough understanding of the present teachings. It is apparent to one having ordinary skill in the art with benefit of the present disclosure that other embodiments according to the present teachings that depart from the specific details disclosed herein remain within the scope of the appended claims. Moreover, descriptions of well-known apparatus and methods may be omitted so as to not obscure the description of the example embodiments. Such methods and apparatus are considered within the scope of the present teachings.
With specific reference to
With specific reference to
A quartz crystal may be made of crystalline quartz or other piezoelectric material. A quartz crystal blank or substrate may be approximately 5 mm square to 10 mm square dimensions. The thickness of the outer regions 110 may be approximately 10 mil thick. The width of the outer regions 110 may be approximately 2 mm. The inverted mesa 120 may be approximately 3 mm×3 mm and approximately 1 mil thick. It will be appreciated that the frequency of the quartz crystal may be controlled by modifying the size of the mesa or the material used. The leads 130 may be made of Gold wire bond or other similar material and attached by ball bond or wedge bond or other known means.
Empirical evidence shows that the overall timing accuracy of the ATE system was improved from +/−1000 ps to +/−650 ps by use of this inverted mesa quartz crystal oscillator as the time base reference over prior clock references. By using ion beam etching to create the inverted mesa 120, the outer perimeter 110 of the crystal blank to remain thick enough to withstand the wire bonding process without cracking or otherwise sustaining damage.
Embodiments of the teachings are described herein by way of example with reference to the accompanying drawings describing various embodiments of an apparatus and method to improve an ATE system clock. Other variations, adaptations, and embodiments of the present teachings not specifically disclosed will occur to those of ordinary skill in the art given benefit of the present teachings. For example, other embodiments with variants and combinations of components not specifically disclosed are also contemplated. For example, the inverted mesa may be etched in other than the center of the quartz crystal substrate or blank.
