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Building RF/microwave assemblies requires a variety of equipment to complete the entire process. A microwave multichip module (MCM), for example, contains an assortment of monolithic microwave integrated circuits (MMICs) to enable the desired functionality of the complete assembly. Depending on its complexity, a microwave MCM can have numerous MMICs incorporated into its design. Between this potentially large number of MMICs and all of the requisite interconnections, it’s essential to have the proper equipment in place to succeed in creating a microwave assembly.
Several steps are required to build a complete microwave assembly. Die bonding, or die attachment, is the process of attaching a semiconductor die either to its package or to a substrate. Epoxy and eutectic bonding are two commonly used techniques for die attachment of MMIC devices.
When using epoxy to attach a MMIC die, a small amount of epoxy is typically applied to the mounting surface. The MMIC is then placed in the proper position to make the bond. Once in place, the epoxy is cured in accordance with the manufacturer’s requirements.
A eutectic system involves a mixture of chemical compounds or elements that has a lower melting point than any composition made from the same ingredients. A commonly used eutectic material for die bonding of MMIC devices consists of 80% gold (Au) and 20% tin (Sn). This composition, which has a melting point of 280°C, is available as a preform. Once the preform and die are properly placed, the die-bonding machine performs the task of bonding the die onto the surface. Due to its good thermal-conductivity characteristics, the AuSn eutectic mixture is well-suited for higher-power applications.
A number of manufacturers offer die-bonding equipment. Palomar Technologies, for example, offers a selection of die bonders. In fact, the company recently unveiled its 3880 model, which offers customers multiple options in a single machine.
One benefit of the 3880 die bonder is its z-theta, bidirectional bond-head with voice-call technology. This allows for improved force-range and reliability, tool index speed, tool-to-tool index precision and planarity, and easy setups. The 3880 will find homes in a wide range of applications, from microwave modules to RF packages and RF power amplifiers (PAs).
West Bond, another manufacturer of die-bonding machines, offers a selection of manual die bonders. Its 7372E model can actually perform both epoxy and eutectic bonding thanks to interchangeable tool-head assemblies (Fig. 1). It utilizes the company’s patented 8/1-ratio micro-manipulator to reduce the strain on the operator when making small, repeated movements.
Once all devices have been bonded to an assembly, wire bonds must be installed to provide electrical interconnectivity. Ball bonding and wedge bonding are two techniques used to apply wire bonds to microwave assemblies. Palomar Technologies, as well as other resources, offer a more detailed description of both types of wire bonding.
Wire bonding obviously requires wire-bonding equipment, which is available from a number of manufacturers. Hybond maintains a selection of both ball and wedge bonders. It also offers the 626 model, which is a multi-purpose-bonder (Fig. 2). This bonder can operate as a ball, wedge, bump, or peg bonder. When used for ball-bonding applications, the 626 can bond gold wires with diameters ranging from 0.7 to 2.0 mils.
Additional wire-bonding machines from Hybond include the 676 digital thermosonic wedge bonder. It can bond wires with diameters from 0.5 to 3.0 mils, and is able to bond ribbons with dimensions extending to 1.0 × 12.0 mils. Both the 626 and 676 models are used throughout the RF/microwave industry by companies like Northrop Grumman, Raytheon, BAE Systems, K&L Microwave, and others.
In addition, the company’s ball-bonding machines include the 522A model. This thermosonic ball-bonder machine is capable of bonding gold wires with diameters ranging from 0.7 to 2.0 mils.
West Bond offers a variety of manual, semi-automatic, and automatic wire bonders. Among the company’s products is the 353637F series of automatic wire bonders. These machines can automatically bond arrays of wire connections by means of a software program. A range of bonding functions is available as well, such as the conventional 45° wire-feed, deep-access 90° wire- or ribbon-feed, ball-wedge, ball-stud, and single-point tab/lead bonding.
Palomar Technologies also enters the fray in this space with the 8000i—a fully automatic, thermosonic, high-speed wire bonder. In addition to conventional wire bonding, its capabilities include ball, stud, wafer, and chip bumping. The 8000i also offers customized looping profiles.
Various companies provide complete manufacturing services for RF/microwave assemblies. For example, SemiGen, a contract manufacturer, offers standard services such as die attachment, wire bonding, ribbon bonding, and much more. SemiGen also has the ability to perform testing at frequencies as high as 40 GHz.
Another player in this field is Teledyne Microelectronics, which provides electronic manufacturing services. The company’s process technology enables it to manufacture RF/microwave assemblies via die attachment, wire bonding, and hermetic packaging. They also can test assemblies to 65 GHz. Customers include the U.S. government as well as prime contractors.
To summarize, the assembly process of a microwave module is just as important as the design and testing stages. With that being case, suppliers of these products have many options to meet a customer’s assembly needs, and a vast array of equipment on tap. On top of that, contract manufacturers can provide solutions to those companies that prefer to have an outside source handle the entire assembly process.