Electronics

One of the more interesting future scenarios is where a large number of these additive technologies survive and are used in combined and complementary ways to solve complex problems. This may even be the most likely scenario because each technology seems to have particular and somewhat mutually-exclusive advantages, and none are especially capital intensive. The more specialized technologies being developed for electronics will almost certainly be used in conjunction with those that will be applied to the mechanical aspects of engineering problems. In some cases, the very same technology using different materials and/or machine parameters, may be used for both the electronic and mechanical aspects of a design.

Electronics lends itself strongly to additive fabrication. For the most part, it's small in size, and while often made in huge quantities, batch fabrication of smaller quantities is also frequently important. The ability to avoid tooling is a strong driving force for low volume production. Many electronic materials lend themselves to deposition techniques, and polymers with electronic properties have become available in the last decade or so, and are undergoing strong development.

Interestingly, the shape of most present electronic devices is usually quite simple. Even the most complex semiconductor chip is mostly constructed of simple shapes repeated many times. Most discrete electronic components and transducers are also elementary geometric repeating structures. This means that rapid manufacturing's ability to create complex geometries and graded materials offers the field some extremely powerful and previously unavailable options to explore.

MICE and Direct Writing
This DARPA program was aimed at simplifying manufacture and providing greater flexibility than is possible using existing technologies. In size, mesoscale devices fall between integrated circuits and surface-mount components, and have important applications in military, RF communications and medical areas. Direct fabrication methods would make it possible to use almost any material as a substrate while eliminating conventional PCB's, high-temperature processing and chemicals. In addition, it would be possible to generate a new circuit in a matter of hours, eliminate tooling, and greatly reduce the need to inventory components. A number of commercial companies and university and government labs participated in the program, including Optomec, Sciperio and SRI International which have resulted in several ongoing commercialization efforts.

The Direct Write Association (DWA) is a UK umbrella organization similar in scope to the MICE initiative. With members from both academia and industry, it aims to facilitate communication in developing additive technology to fabricate a wide range of electronic, biomedical and other devices.

Many variations of direct-write circuitry fabrication are being investigated. Some are related to direct deposition techniques like inkjets and extrusion methods similar to FDM, and others are based on indirect laser transfer of materials to a substrate. Some methods can be used to write on non-planar, low-temperature surfaces making it possible to directly combine electronics with mechanical components. These processes are capable of making passive components such as resistors, capacitors, conductive elements and the like, and some work is also being done to make active semiconductor devices. Antennas and waveguides are among the less-typical components that can also be fabricated.

Additive fabrication technologies and their applications in electronics.
Stereolithography is being considered for the fabrication of semiconductor packaging, test components and other items such as ceramic devices. One company, Micron Technology, Inc., is building a wall of patents in the application of stereolithography to semiconductor packaging. The company has pursued more than 500 patents covering every aspect of the area. Some of the topics are shown in the table.

Table 2. Selected Topics Covered in Micron Technology's Intellectual Property.
Bond wire protective structures Conductive bumps and elements Contact pad rings and protective layers Dams Die to die connections Flip-chip component encapsulation	Heat sinks Hermetic packages Imaging device packaging Interposers Lead encapsulation Micromachine housings Optically interactive device packages Semiconductor markings	Solder masks Solder masks for confining encapsulant material Spacers Stabilizers for flip-chip devices Stacked semiconductor device packages Tape stiffeners

Other technologies are being applied where they offer specific advantages. For example, selective laser sintering is being considered for use in making components that benefit from porosity, such as capacitors. Laser powder forming technologies are being applied to making graded material conductors for power transmission applications. Such conductors offer the potential for being better able to handle overloads. Solidica's Ultrasonic Consolidation is being applied to a wide array of electronics applications such as embedded sensors and antennas. One unobvious benefit of the method is that it provides low temperature bonding and packaging for thermally-sensitive components.

Another technology of particular interest in electronics is Electrochemical Fabrication (EFAB) from Microfabrica Inc., a batch layered-fabrication method that allows producing parts and assemblies from the micron scale up to the mesoscale of a few millimeters. The method has particular use in fabricating miniature RF and microwave components.