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1990 Edition, October 1990

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Guidelines for Molded Interconnection Devices

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Description / Abstract:

This document was created to increase general understanding of molded interconnect technology. Information on candidate materials, molding processes, fabrication processes and test methods is included for suppliers, designers, and end-users. This document is not intended to be a complete Designer's Guide to Molded Interconnects. If you are considering using molded interconnects you should discuss your needs with the appropriate suppliers and designers.

Purpose Molded interconnects can be divided into three major subgroups:

Subgroup 1-Interconnects having two dimensional features with conductive patterns in two dimensions.

Subgroup 2-Interconnects having three dimensional features with conductive patterns in two dimensions.

Subgroup 3-Interconnects having three dimensional features with conductive patterns in three dimensions.

Each subgroup requires different levels of design and fabrication expertise.

Subgroup 1 can be compared with existing planar circuit board applications, although the design and fabrication techniques may be completely different, some properties may improve, and the cost may be lower.

Subgroup 2 begins to incorporate the real benefits of molding through 3-dimensional features as the interconnection part encompasses both mechanical and electrical functions.

Subgroup 3 takes full advantage of the benefits available through molding and includes applications not possible with conventional planar printed circuit boards. Molded interconnects evolved to meet new demands in the electronics industry. The following are some of the potential advantages of this new technology:
  • Lower system cost through part integration and elimination of manufacturing steps.
  • Low dielectric constants and low dielectric loss properties of thermoplastic materials compared to conventional base materials.
  • High resistivity to electrical leakage and good electrical properties.
  • Low coefficients of thermal expansion (CTE) in the Z-axis and improved thermal performance.
  • Some base materials are inherently flame resistant and meet UL-94V0 requirements.
  • Suitable for hostile environments.
  • Suitable for elevated temperature use.
  • Improved mechanical tolerances.
  • Improved consistencylreliability through molding.
  • Reduced Fiberglass exposure reduces assembly problems and related health concerns
  • Ability to mold-in functional 3-dimensional features.
  • Ability to mold-in recessed pads for reliable placement of surand related health concerns. face mounted components.

Of course, there can be potential disadvantages to molded interconnects, such as the following:
  • Up-front tooling costs and long lead times for molds.
  • Costs to change electrical andlor mechanical design.
  • Limited source of supply of fabricated parts due to newness and diversity of technology.
  • Significant volumes may be required to make it cost competitive.
  • Fine line widths and spacings may not be possible or economically feasible for some fabrication processes.
  • Modified process controls may be required during the soldering operation due to thermal limitations of some base materials.
  • Limited multilayer capability
  • Adhesion values andlor test methods on molded interconnects may not be comparable to conventional printed circuit boards.
  • Limitations of conductive pattern andlor component placement on or near 3-dimensional features may exist.
  • Overall product size is limited.

Close working relationships between customers and suppliers are necessary to take full advantage of the benefits offered by this new technology and to'appreciate its limitations. In addition, early involvement of both electrical and mechanical designers is advantageous in order to realize the full potential of this technology.

Various methods of molded interconnect design and fabrication currently available are outlined in this document. Since each method varies in its capabilities and limitations, a close review of each will help you determine if the technology of molded interconnects is a viable and valuable alternative for your needs. Whichever method you choose for your electronic packaging needs, molded interconnect technology may allow a product design never feasible before.