These windows are fabricated without adhesive, are fully compatible with LTCC processing, and remain optically clear. Integral windows in LTCC have been fabricated for use in both lids more » and circuits where either a short term need for observation or a long-term need for functionality exists. In this case, a rolled tube has been employed to provide hermetic external contacts to electrodes and structures internal to the tube. Unique shapes in LTCC permit the simplification of complete systems, as in the case of a miniature ion mobility spectrometer (IMS). In particular, the ability to customize processing order and material choices in Low Temperature Cofired Ceramic (LTCC) has enabled new features to be constructed, which address needs in MEMS packaging as well as other novel structures. « lessĬeramic interconnect technology has been adapted to new structures. Configurations using both surface-printed and suspended thermistors have been evaluated. The thermistors and heating element are used together as a thermal anemometer to measure the flow rate through the tube. Thick-film thermistor lines are printed to monitor the temperature near the chemical sensor and at upstream locations to monitor the incoming ambient flow. A heating element is embedded in the rolled tube to maintain a constant temperature in the vicinity of the chemical sensors. Multiple chemiresistors have been integrated into a single smart channel to provide chemical discrimination through the use of different polymers. The change in resistance is calibrated to the chemical concentration. Volatile organic compounds passing through the tube are absorbed into the polymers, causing the polymers to reversibly swell and change in electrical resistance. The chemical transducer is fabricated by depositing a conductive polymer 'ink' across a pair of electrodes that acts as more » a chemical resistor (chemiresistor) within the rolled LTCC tube. Devices developed in this study have employed rolled LTCC tubes, but grooves or other channel shapes can be fabricated depending on the application requirements. The uniqueness of this device lies in the fabrication and processing of low-temperature co-fired ceramic (LTCC) materials that act as the common substrate for both the sensors and the channel itself. This paper describes the development of 'smart' channels that can be used simultaneously as a fluid channel and as an integrated chemical, temperature, and flow sensor.
Solderability was poorer when the firing temperature was higher. However, the primary factor in solderability was the firing temperature. Solderability appeared to degrade by the added processing steps needed for the triple print and dielectric window depositions. The solderability of the thick film pads was also observed to be sensitive to the firing conditions.