Modern electronic design and machine placement of components has led to the development of a variety of surface mount quartz crystal units.
The earliest configuration utilized an leaded metal holder placed on its side with formed gull-wing leads and a formed top wire. The advantage of this device is the high level of precision that can be achieved in the metal holder. The disadvantages include increased cost, non co-planarity of the leads and destruction of the hermetic when leads are formed too close to the base.
Today there are a number of surface mount options available, some derived from metal HC-types and others in metal/plastic and ceramic packages.
HC-49 type crystals have been configured into SMT devices by placing a insulating pad on the base with castellations for soldering. A short version, theHC-49/S is also available in either 3.3 mm or 4.4 mm heights. The hybrid HC-49/KSM is similar to the HC-49"/, however, the footprint is that of the EPSON SG-615 4 pad plastic device. Applications for these holders are typically micro-processor drivers, MPX.
For precision applications, a ceramic 0.320 X 0.320 X0.100 inch package, AE100 is recommended. Due to the versatility of the package, a customer has the ability to custom specify a crystal anywhere in the range from 4.000 MHz. and 200 MHz.
Other ceramic SMT packages include 5 mm X 7 mm and 3.2 mm X 5 mm packages. These, too, are typically non-precision devices used for MPX applications but lend them selves to machine insertion and soldering in large volumes.
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