**6. Wire bonding**

Wire bonding is a process by which interconnections are made between the die to the suitable location on the substrate or package. Wire bonding has the advantage of being low cost and flexible method of interconnection and is widely used to assemble majority of semiconductor packages. They also have the advantage that they can be used upto a frequency of 100 GHz if properly designed. Thus it is most suitable for RF MEMS switches.

this adhesive was done at room temperature of 25°C for 72 hours. **Figure 23(b)**

Hermetic seals are airtight seals that prevent the invasion of oxygen, moisture, humidity, and any outside contaminant to enter a sealed environment. This kind of a sealing is of utmost importance in semiconductor devices and MEMS devices. In the case of MEMS devices this is a top priority since the performance of a MEMS sensor or actuator directly depends on the ambient conditions under which they operate. This work proposes the use of epoxy resins to seal the package lid to the base package. The top can/case is attached to the base package using a non-conductive epoxy H74 and cured at a room temperature of 25°C for 48 hours. The package with the top case attached is as shown in **Figure 24**. This method of curing was tested on samples in order to ascertain the complete curing. The specification sheets states that this epoxy requires a temperature of 150°C for 5 minutes and a temperature of 100°C for 20 minutes, for curing. However, curing at room temperature of 48 hours has led to the complete sealing. This was ascertained by performing a leak test on the packed RF MEMS switch. There are several types of leak tests to confirm the hermiticity of sealed packages. The Helium leak test was performed following a procedure as explained below. The vacuum method is the most sensitive leak detection technique. It requires that part of the package be placed under hard vacuum and the other part to be pressurized with helium. The side which is placed under vacuum is connected to the leak detector. If there is a leak, the helium that penetrates this side will be detected by the leak detector. The package under test passed the standard leak test with a test value of 5.0 x 10<sup>8</sup> std. atm.cc/sec.

In order to characterize the packaged MEMS switches Sub Miniature version A

(SMA) connectors have been used. These connectors are designed to be used between DC and 18 GHz. The SMA's chosen for this work with part number 1367– 000-G91P-35 were procured from Delta Electronics Manufacturing Corporation.

shows the adhesive covered wire bonds.

*RF MEMS Switch Fabrication and Packaging DOI: http://dx.doi.org/10.5772/intechopen.95003*

**Figure 24.** *Lid sealed package.*

**Figure 25.**

**273**

*Package with SMA connectors.*

Thermosonic bond is formed by the combination of three parameters, ultrasonic, thermal and mechanical force. A thermosonic bonding machine uses a piezoelectric transducer which converts the electrical energy to a vibratory/ultrasonic motion. This is in turn converted to an amplified oscillatory motion using a velocity transformer. This oscillatory motion is delivered to a heated bonding tip. The thermal energy and the ultrasonic motion together create a softening of the lead wire and hence its deformation leading to a required contact area using low temperature and low force.

Hence, in the proposed work thermosonic bonding has been chosen as the wire bonding technique due to its desirable properties of operation at low temperature and low force. A Kuilelle and Soffa thermosonic bonder is as shown in **Figure 22** which is used for the wire bonding process. Ball and wedge bonds of Gold wire of 2 mil are used for wire bonding between bare die to the package base pads as shown in **Figure 23(a)**. The NDPT test was also performed to ensure the strength of the wire bonds. The wire bonds were then covered with Epotek-301-2FL, a low stress adhesive especially used for glob top encapsulation over wire bonds. The curing for

**Figure 22.** *Kulicke and Soffa thermosonic ball bonder.*

**Figure 23.**

*Wire bonding. Hermetic sealing and soldering of SMA. (a) Gold wire bonding. (b) Gel dispensed on bonding Wedge.*

#### *RF MEMS Switch Fabrication and Packaging DOI: http://dx.doi.org/10.5772/intechopen.95003*

**6. Wire bonding**

suitable for RF MEMS switches.

*Nanofibers - Synthesis, Properties and Applications*

perature and low force.

**Figure 22.**

**Figure 23.**

*Wedge.*

**272**

*Kulicke and Soffa thermosonic ball bonder.*

Wire bonding is a process by which interconnections are made between the die to the suitable location on the substrate or package. Wire bonding has the advantage of being low cost and flexible method of interconnection and is widely used to assemble majority of semiconductor packages. They also have the advantage that they can be used upto a frequency of 100 GHz if properly designed. Thus it is most

Thermosonic bond is formed by the combination of three parameters, ultrasonic, thermal and mechanical force. A thermosonic bonding machine uses a piezoelectric transducer which converts the electrical energy to a vibratory/ultrasonic motion. This is in turn converted to an amplified oscillatory motion using a velocity transformer. This oscillatory motion is delivered to a heated bonding tip. The thermal energy and the ultrasonic motion together create a softening of the lead wire and hence its deformation leading to a required contact area using low tem-

Hence, in the proposed work thermosonic bonding has been chosen as the wire bonding technique due to its desirable properties of operation at low temperature and low force. A Kuilelle and Soffa thermosonic bonder is as shown in **Figure 22** which is used for the wire bonding process. Ball and wedge bonds of Gold wire of 2 mil are used for wire bonding between bare die to the package base pads as shown in **Figure 23(a)**. The NDPT test was also performed to ensure the strength of the wire bonds. The wire bonds were then covered with Epotek-301-2FL, a low stress adhesive especially used for glob top encapsulation over wire bonds. The curing for

*Wire bonding. Hermetic sealing and soldering of SMA. (a) Gold wire bonding. (b) Gel dispensed on bonding*

this adhesive was done at room temperature of 25°C for 72 hours. **Figure 23(b)** shows the adhesive covered wire bonds.

Hermetic seals are airtight seals that prevent the invasion of oxygen, moisture, humidity, and any outside contaminant to enter a sealed environment. This kind of a sealing is of utmost importance in semiconductor devices and MEMS devices. In the case of MEMS devices this is a top priority since the performance of a MEMS sensor or actuator directly depends on the ambient conditions under which they operate.

This work proposes the use of epoxy resins to seal the package lid to the base package. The top can/case is attached to the base package using a non-conductive epoxy H74 and cured at a room temperature of 25°C for 48 hours. The package with the top case attached is as shown in **Figure 24**. This method of curing was tested on samples in order to ascertain the complete curing. The specification sheets states that this epoxy requires a temperature of 150°C for 5 minutes and a temperature of 100°C for 20 minutes, for curing. However, curing at room temperature of 48 hours has led to the complete sealing. This was ascertained by performing a leak test on the packed RF MEMS switch. There are several types of leak tests to confirm the hermiticity of sealed packages. The Helium leak test was performed following a procedure as explained below. The vacuum method is the most sensitive leak detection technique. It requires that part of the package be placed under hard vacuum and the other part to be pressurized with helium. The side which is placed under vacuum is connected to the leak detector. If there is a leak, the helium that penetrates this side will be detected by the leak detector. The package under test passed the standard leak test with a test value of 5.0 x 10<sup>8</sup> std. atm.cc/sec.

In order to characterize the packaged MEMS switches Sub Miniature version A (SMA) connectors have been used. These connectors are designed to be used between DC and 18 GHz. The SMA's chosen for this work with part number 1367– 000-G91P-35 were procured from Delta Electronics Manufacturing Corporation.

**Figure 24.** *Lid sealed package.*

**Figure 25.** *Package with SMA connectors.*

These connectors were soldered to the Alumina substrate using solder wire (Sn 63: Pb37) as shown in **Figure 25**.
