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DuPont Microcircuit Materials

Diffusion Patterning™ Reduces Size and Layer Count of In-Ear Hearing Aid Circuit

HEI Inc., Victoria, Mn., is a world leader in the design and manufacture of miniaturized thick film amplifiers for hearing aids and other applications, such as pre-amplifiers for disk drives, where circuit size is critical

Challenge: Reduce size and layer count of in-ear hearing aid circuit

The size of the complete package is 0.198x0.115x0.110 inches (5 x 2.9x2.8 mm) and the circuit contains three metal layers, two layers on one side and one layer on the other side. Diffusion Patterning™ is used to define 0.005 inch (125-µm) vias. Standard screen-printable thick film dielectrics would require 6 metal layers to interconnect the same circuitry.

Solution: DuPont's Diffusion Patterning™

Use of Q42DP Diffusion Patterning™ dielectric allows increased routing efficiency, robust processing and high reliability in designs in which silver-bearing conductors need to be located under Au wire bond pads. The small size circuit is made in multiples of 144 circuits per substrate, with over three thousand 0.005 inch (125-µm) vias per substrate.

The complete package contains two ICs, a standard hearing aid amplifier chip, which is flip chip-mounted, and an active high pass filter chip which is wirebonded using Au bond pads. In a unique packaging design, the active filter is epoxied to the top side of the flip chip to achieve increased circuit density. QM80 Series resistors, which were designed for high yields and reliability when processed on top of Q42DP dielectric, also contribute to reducing circuit size.

In addition to Q42DP Diffusion Patterning™ dielectric and QM80 Series resistors, the hearing aid circuit uses 6:1 Ag-Pd conductor for through-hole, interconnect and via fill, a Ag-Pd-Pt conductor for solder pads, and 5715 Au conductor for wire bond pads.

Diffusion Patterning™ provides a low investment, low risk path to extending Hei's capability to circuit designs requiring higher density.

For help in selecting the right material for your application, send us an e-mail, or call us at 1-800-557-4505.