Materials

Although sapphire and alumina have the same elemental composition, Al₂O₃, they have very different applications. Since sapphire is a single crystal it is used extensively in optics. It is found where durability, resistance to corrosion, and heat, and ultraviolet transmission are critical. All of these require very careful handling and machining techniques to prevent chipping and to maintain polished surfaces. Kadco Ceramics has over 30 years of experience controlling these defects to deliver finished components meeting tight tolerances with on-time delivery.

Alumina is the multi-crystalline form of Al₂O₃. It is much less expensive and commonly available in many sizes and shapes. This allows it to be used wherever tensile and compressive strength is important, particularly in association with electrical resistance. Alumina also exhibits moderate heat conductivity in spite of its high electrical resistance. Kadco Ceramics has an extensive inventory of formed alumina parts to meet your needs for fast delivery of custom machined components.

The most common forms of alumina Kadco Ceramics machines are:

* 99.6% alumina

This is normally used for thin-film microwave circuits operating at high frequencies because it can be polished to a 1 microinch or better surface finish. This lets the circuit designer obtain precise values for thin-film resistors such as tantalum nitride (TaN) or nichrome (NiCr). 99.6% alumina is also useful for capacitor fabrication because of its relatively high thermal conductivity, low dielectric loss, and low dielectric constant of 9.9.

* 96% alumina

This has a higher filler content and consequently is somewhat easier to cut with a diamond saw. It is normally used for thick film fired circuits because the thick film pastes do not adhere as well to purer alumina. The surface is frequently lapped for circuit applications, but can be polished if required.

* 92% alumina

This has even more filler and is useful for packaging applications where multiple layers of ceramic and conductive layers are built up. While softer than the previous types of alumina, it can present challenges for accurate dicing because of the thicker layers and pattern distortion during firing. It is also used as a refractory material.

Composites are produced from two or more diffent materials to take advantage of desirable properties of both. Ceramic composites maybe formed as a matrix or as sandwiched layers involving glass, carbon or other hard materials. These fillers can present challenges to conventional tooling that diamond machining can solve. Kadco Ceramics has successfully machined composites such as reinforced plastics (Torlon, G-10, Vespel),ceramic composites (Macor, Mycalex) and layered structures (quartz on silicon, nickel/gold plated on ceramic and copper substrates, direct bond copper on aluminum nitride).

Ferrites are ceramic materials composed of iron oxide with various combinations of nickel, zinc, strontium, cobalt, barium and manganese. They are used as magnetic cores in transformers for motors, speakers, microwave transmitters and other magnetic applications. Ferrite in standard shapes can be molded in high volumes very inexpensively. When unusual shapes with tight tolerances at low volumes are required, Kadco Ceramics has the experience and machining capabilities to meet stringent demands

Quartz (SiO₂ or silica) is useful in electronics for its piezoelectric and dielectric properties and has many and varied photonic applications. With various additives and processing conditions, silica can be made into many types of glass (e.g. soda-lime, borosilicate, lead glass, aluminosilicate) and into composites such as Macor. All of these are very brittle and are subject to fracturing and chipping. This can present problems for diamond dicing and machining if the cutting parameters aren’t carefully selected initially and monitored during the course of cutting. Kadco Ceramics has expertise in processing both natural and fused silica for applications as varied as crystal oscillators for clocks and lenses for spectrometers. Contact us to discuss your requirements.

Silicon is most noted for its semiconductor applications. Kadco Ceramics specializes in dicing silicon wafers as well as wafers of many different materials. Silicon also has extensive optical applications in infrared transmission and reflection. Kadco Ceramics has experience machining bulk silicon into lenses, prisms and windows for military and research requirements.

Piezoelectricity was first discovered by Pierre and Jacques Curie in 1880. They realized that certain crystals were able to produce a voltage proportional to the mechanical pressure applied to them. Basically them change electrical energy to mechanical energy and vice-versa. For electronic applications lead zirconate titanates (PZT) or barium titanates (BaTiO₃) are frequently used in substrate form. These materials tend to be very fragile and friable compared to other electronic substrates. Kadco has experience metalizing, dicing and machining these materials to minimize chipping and maintain proper adhesion of metal on the surfaces.

Hard and Soft Piezoelectric Materials

Piezoelectric materials are usually classified as hard or soft formulations. This depends on the mobility of the magnetized dipoles in the material. Piezo materials that are ferroelectrically hard can endure high electrical and mechanical stresses and have substantial advantages including:

• good stability
• operating field strength
• high mechanical qualities

Soft piezo materials are easily polarized. Some advantages are:

• large piezoelectric charge coefficients
• moderate permittivity that will enable electrical energy storage
• high coupling factors

Common Piezoelectric Materials

Most piezoelectric systems today are manufactured from PZT. This is a mixture of lead, zirconate and titanate crystals. Substrates are poled after metalization by a combination of heat and high voltage. Once that process is complete, diamond machining is the most common and efficient way to form the desired shape.

Along with PZT and barium titanate, some of the most common materials used are:

• PMN-PT (lead magnesium niobate-lead titanate)
• Quartz
• Lithium niobate
• Potassium niobate
• Sodium tungstate

Applications for Piezoelectric Materials

Piezoelectric materials have a long list of useful applications:

• Piezoelectric speakers
• Sound detectors
• Cigarette Lighters
• Quartz Watches
• Sonar devices
• Inkjet Printers
• Lithotripters, and many more

Kadco Ceramics has developed expertise in machining many of these materials into precise shapes for critical applications.

Zirconia is best known as a gemstone. However it has important industrial applications because of its three crystal phases: monoclinic (<1170° C), tetragonal (1170° - 2370° C), and cubic (>2370° C). The unusual characteristic of these three phases is that the lower temperature monoclinic phase has a larger crystal size than the higher temperature tetragonal crystal. This feature causes bulk articles to have a high resistance to crack propagation. When blended with dopant oxides of magnesia, yttria, calcia, or ceria, the tetragonal phase becomes metastable at room temperature. If a crack starts forming the stress concentration causes the tetragonal phase to convert to the larger monoclinic phase, thereby stopping the growth of the crack. This transformation toughening makes these zirconia materials useful for applications such as tooth replacements, ceramics knives, wear-resistant gears, and medical implants.

Kadco Ceramics can help you select the most cost-effective materials for your design.

Aluminum Nitride (AlN)

• Useful for high power circuits which require a lot of heat dissipation because it has high thermal conductivity and a low thermal expansion coefficient.
• Thermal conductivity: 80-100 W/m-K
• Can be polished with a finish similar to alumina
• Alkaline solutions such as many detergents can form a surface oxide which may be detrimental to the performance or appearance of the circuit. Our engineers will discuss the proper processing techniques to assure that your circuits have the optimum performance.

Beryllium Oxide (BeO)

• Useful for circuits which must dissipation large amounts of heat.
• Thermal Conductivity: 248 W/m-K (higher than many ceramics including alumina and aluminum nitride)
• Dielectric Constant: 6.5 (low for a ceramic circuit substrate)The primary limitation is the potentially hazardous dust. Our engineers are prepared to discuss tradeoffs in the properties of various ceramics in the design of circuits requiring heat dissipation.

Copper (Cu)

• Ductile metal that has very high electrical and thermal conductivity.
• Typically machined with metal cutting tools instead of diamond saws. However, many electronic applications require precise cuts or unique coatings on copper plates or wires.
• We can plate copper with nickel/gold (Ni/Au) for example and then diamond machine it to burr free shapes for submounts and other applications.
• Copper submounts have a burr after dicing due to smearing of the soft copper and gold. Our exclusive process will remove the burrs, resulting in a submount that will lie flat in the package.

Gallium Arsenide (GaAs)

• Useful to the electronics industry for its semiconductor properties.
• Considered a rival to silicon in this industry because it requires less electric power and may process data faster.
• Gallium arsenide wafers are typically diced on tape or wax mounted on glass depending on the final requirements for chipping and cleaning. Tape cutting simplifies handling but can cause more edge chipping than wax mounting on glass. Wax mounting on glass will allow more precise thru cuts and grooves, but requires more handling during demounting and cleaning.

Garnet

• Garnets are metal silicates such as calcium aluminum silicate (Ca₃Al₂(SiO₄)₃). There are a variety of types with different compositions that exist in various colors.
• Better known as gemstones than substrates, but they do have applications in electronics and optics.

Lithium Niobate (LiNbO₃)

• Useful in photonics for its nonlinear optical properties.
• A synthetic crystal that is hard, transparent, and dense.
• Switches, multiplexers and waveguides made on lithium niobate substrates may require the intricate machining and singulation where Kadco has experienced capabilities.

Molybdenum (Mo)

• Hard metal that has electronic applications as a submount for soldering chips into packages.
• Kadco can plate metals such as nickel and gold (Ni/Au) on molybdenum shapes and then diamond machine submounts which are burr free and ready for soldering.
• We have many different sizes in stock

Plastic

• Plastics are not normally thought of as substrates for dicing because of their softness. However, laminates of ceramics or metals and Kapton for example may require diamond machining.
• Two critical issues that require expertise in processing are mounting the substrate and avoidance of stringers. Since many plastics don’t adhere well to dicing tape or wax, the engineer must plan for appropriate fixturing. Plastic stringers can form if the dicing parameters are not carefully investigated.

Pyrex

• Also known as borosilicate glass
• Occasionally used as a substrate because of its low coefficient of thermal expansion.
• Not likely to shatter and will not break easily.
• Dicing parameters must be carefully determined to minimize chipping and fracturing.

Yttrium Aluminum Garnet (YAG)

• Well known for its optical applications.
• Diamond machining may be required for isolation cuts on the surface or other patterning.
• Kadco’s engineers have experience with controlled depth grooves to give you high yields on your product.

Silicon Carbide (SiC)

• Silicon carbide is most commonly experienced as Carborundum and used for abrasive machining. However, its properties of wear resistance, high heat conductivity, and chemical resistance have found varied applications throughout the industry. It also has many electronic applications due to its semiconductor properties. Not surprisingly innovative researchers have developed many formulations which vary in hardness and machinability. Contact Kadco Ceramics for recommendations on the best material composition and design considerations for your application.