115 CHAPTER 5 PACKAGING STRATEGIES FOR RF MEMS SWITCHES 5.1 Introduction The packaging technique for RF MEMS switches is the complex and expensive step, which will ultimately decide the cost of the switch. MEMS switches are very sensitive to humidity and contaminants. Packaging contributes to almost 80% of the total cost of the device and its functioning and reliability strongly depend on the packaging. Therefore, MEMS packaging tends to be customized to the specific application, with emphasis on the cost, performance and reliability. Without packaging, the operation of RF MEMS switches can be severely affected by the presence of water vapor, contaminants, hydrocarbons and other gases in the atmosphere. As the pull-up forces are very small (50-500 μN) and are not enough to overcome the adhesive forces of water molecules or puncture through any contaminants in between the capacitive contact, the performance gets highly affected due to the presence of above. To avoid the failure of RF MEMS switches, proper RF and hermetic packaging is required. A lot of general packaging issues make the packaging of RF devices a quite complex process, such as; package sealing material, sealing curing temperature, alignment of package with device, package material & external connections etc. The package can be composed of LTCC, ceramic material, beryllium oxide & aluminum etc. The hermetic seal can be achieved using seam sealing, roller sealing or laser sealing techniques, and these methods have been proven to satisfy long-term satellite and defense applications [1]. The high temperature packaging processes are generally avoided to improve the mechanical reliability of MEMS switches. Several different technologies can be used for the RF MEMS switch packaging; such as [2] • Epoxy Seals • Metal - to - metal solder bonding • Glass - to - glass anodic bonding • Glass frit bonding
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115
CHAPTER 5
PACKAGING STRATEGIES FOR RF MEMS SWITCHES
5.1 Introduction
The packaging technique for RF MEMS switches is the complex and expensive step,
which will ultimately decide the cost of the switch. MEMS switches are very sensitive to
humidity and contaminants. Packaging contributes to almost 80% of the total cost of the
device and its functioning and reliability strongly depend on the packaging. Therefore,
MEMS packaging tends to be customized to the specific application, with emphasis on the
cost, performance and reliability. Without packaging, the operation of RF MEMS switches
can be severely affected by the presence of water vapor, contaminants, hydrocarbons and
other gases in the atmosphere. As the pull-up forces are very small (50-500 µN) and are not
enough to overcome the adhesive forces of water molecules or puncture through any
contaminants in between the capacitive contact, the performance gets highly affected due to
the presence of above. To avoid the failure of RF MEMS switches, proper RF and hermetic
packaging is required. A lot of general packaging issues make the packaging of RF devices a