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Direct Bonding and Thick Films

    By Terry J. Barber, Dynamic Hybrids, Inc., Syracuse, NY

    Direct Bond Copper (DBC) has traditionally been the province of a
    few large companies. This process involves bonding highly conductive
    copper foils directly to substrates, and is especially useful for
    manufacturing packages with high power-handling capability.
    Substrates used are most commonly ceramic, alumina, and beryllia,
    which all have excellent high-temperature characteristics.

    Suppliers who have a limited scope, catering to a specific service
    or single venture, cannot be competitive in today's market. Buyers
    are cautious, and companies in general are seeking to keep their
    manufacturing costs as low as possible. Many of them are looking to
    outsourcing as a viable option. Whether outsourcing or procuring
    product, it is important to partner with a subcontractor that can
    supply a wide range of products and capabilities as well as being
    responsive to the buyer's requirements, coupled with the experience
    and technology that is needed.

   Controlling the manufacturing environment from start to finish
    becomes possible with this marriage of direct bond copper and thick
    film all under one roof.

    While the DBC market has so long been handled by larger firms, thick
    film printing has been produced by smaller independent companies.
    One company, Dynamic Hybrids, Inc. (DHI), has broken this /status
    quo/ by combining the benefits of DBC for a conductor base or heat
    sink, and the ability to screen print thick film pastes to form
    passive, conductive, resistive, or insulating circuit elements. With
    the ability to control environment, thick film copper can be
    incorporated along with these elements. This only heightens surface
    mount possibilities.

    Thick film, including copper, engineering capabilities, and now DBC,
    top off this well rounded company that has the idea in mind that,
    "dynamite comes in small packages." One benefit of circuit boards
    made from the rigid substrates of ceramic and alumina is that they
    can operate under more power and withstand a much higher
    temperature. Power dissipation of any device is limited by the
    medium to which it is mounted. This is critical for surface mount
    and chip devices. When the mounting medium is fiberglass (FR4), the
    boards have poor thermal conductivity. This causes higher component
    temperatures, and therefore increased reliability issues. DBC can
    take the power load with the ceramic/alumina as the insulating
    element. By utilizing thick film and/or DBC technology on ceramic it
    becomes possible to increase the circuit's ability to dissipate
    power dramatically. This type of substrate and circuit creation
    becomes especially attractive if a circuit design has suffered from
    heat-related component failure. It also provides a ready solution in
    situations where SMT board designs have been limited because of
    thermal considerations.

   Multilayers on Ceramic

    Multilayer copper traces thicker than 3 oz. are also difficult to
    achieve with a fiberglass board. DHI utilizes a minimum of three or
    more layers of dielectric between conductive layers, depending on
    application requirements. With today's substrates, DBC circuits can
    be printed that have as many as 10 conductor layers. Screen-printed
    resistors can be multilayered and laser trimmed from 10 ohms to 10
    Megohms with less than 0.1 percent tolerances, and higher values can
    be achieved using special processes. Capacitors can also be
    multilayered and laser trimmed.

    DBC can be double-sided and use feedthroughs for interconnection.
    Holes in the ceramic can either be utilized to attach
    power-generating components for the current-carrying ability or
    ground connections directly to the DBC. The holes can also be used
    for attaching to a heat sink. Wraparounds to meet the board
    designer's requirements are also available. This is especially
    helpful when there are real estate issues or shielding problems due
    to adjacent high-frequency interference.

    In another area, meeting the special needs of operating in harsh
    environments can also be handled by DBC. In fact direct bonding is
    an especially appropriate technology to use in the manufacture of a
    hermetic package designed to operate in harsh environments.
    Off-hanging leads for input/output and pin connectors to the next
    higher assembly can be integrated in the design with no additional
    lead frames needed.

    Combining these technologies is not only convenient for the
    customer, it also cuts costs and minimizes the conflicts of
    different processes used between companies.

    There are three classes of DBC available, which can be etched in a
    heat-spreading pattern. Electroless plating atop the DBC is always
    an option that provides a solution to potential problems with
    oxidization when wire bonding and soldering. The sizes are as
    diversified as the applications, with the largest thick film
    printing size being 6 x 6-in., and the largest DBC size 3 x 5-in.,
    and up to 12 mils thick. Combining these technologies is not only
    convenient for the customer, it also cuts costs and minimizes the
    conflicts of different processes used between companies. Shipping no
    longer involves a complex process of fragile pieces shuttling
    between companies ? a procedure that can be both time-consuming and
    expensive. The process also can fit readily into each company's
    schedule, meeting difficult-to-impossible deadlines.

    Dynamic Hybrids, Inc., founded in 1992, provides engineering and
    management people with many years of experience in the hybrid
    circuit industry. The company is well known as a high-quality,
    low-cost source for hybrids. While it has primarily been a
    thick-film gold, silver, and copper manufacturer, DHI now offers
    direct bond copper technology, wirebonding, seam/seal welding, and
    solder assembly reflow ? and this can all be in combination for a
    truly problem-solving hybrid product. Approximately 60 percent of
    the company's output is directed to the military sector, a fact that
    attests to the products' inherent reliability. Products range from
    high reliability microwave/radar applications to high volume
    commercial products. In addition, DHI offers design support options
    utilizing internal CAD design techniques, and the company is
    MIL-I-45208 compliant.

    Using the available design and engineering expertise, upgrades can
    be implemented more easily when the design and production
    development issues are already to the engineers. This experience
    comes through for modifications of preexisting designs.

    Facilities include state-of-the-art test equipment such as x-ray
    inspection to assure QC for Medical, Fiberoptic, Microwave, Military
    and Surface Mount Device assemblies. The company can create
    specialty designs and meet military applications, all including
    assembly as well as providing a variety of wirebonding and packaging
    capabilities to meet virtually any problem-solving hybrid need.

    For more information, contact:
    Dynamic Hybrids, Inc.,
    1201 E. Fayette St,
    Syracuse, NY 13210.
    Tel: 315-426-8110; Fax: 315-475-8460.
    Web: http://www.hybridcircuit.com