Low Temperature Co-fired Ceramic (LTCC) Technology

Plextek can undertake the design of LTCC components and highly integrated multifunction LTCC modules. Our LTCC design experience includes RF front-end module design and the development of custom microwave components such as the differential DRO module shown to the right. Our proven RF and microwave design experience, coupled with a detailed understanding of the LTCC fabrication process and capabilities makes us ideally suited to undertaking the design of custom LTCC components. Other examples of Plextek's previous LTCC component designs are described below.

LTCC technology is a low cost process for fabricating multi-layer ceramic structures. Its a versatile technology that is well suited to realising innovative RF and microwave components and sub-systems. These can range from simple passive filter structures to complex assemblies containing bare die, discrete SMD's and printed passives. A wide range of ceramic materials are available and a number of companies offer an LTCC fabrication service for custom designed parts. Plextek is a design partner for C-MAC MicroTechnology and is able to offer custom design services using their UK based LTCC manufacturing process. We also have experience of designing on the LTCC process of Scrantom in the USA and are familiar with the capabilities of a number of other LTCC vendors around the world.

Compared to a conventional multi-layer laminate structure, such as FR4, LTCC offers a number of advantages:

Although these features are also available from some conventional thick film ceramic processes, a multi-layer format is not so readily available. The multiple layer structure of LTCC allows the realisation of innovative printed structures, such as baluns and filters, and facilitates miniaturisation. In addition to this, the fact that the layers are produced in parallel results in shorter fabrication times, reduced costs and increased yields.

A 3-dimensional image of an LTCC assembly incorporating a bare die, SMT components and integrated passives is shown to the right.

Plextek has worked with a number of clients on the development of LTCC based RF and microwave components. A photograph of the top side of a tri-band (900MHz, 1800MHz and 1900MHz) GSM transmit/receive switch is shown below left. All of the discrete components are solder attached SMD's. Contact to the switch is made using a Land Grid Array (LGA) on the underside of the tile. The design includes a number of quarter wavelength transmission lines that are realised as buried stripline structures on the inner layers. This demonstrates the advantages that LTCC integration can offer in reducing component size. If the component size can be kept down this helps keep down the cost and allows the realisation of low-cost, and high volume components.

The photograph above right shows the top side of a PA module for GSM 900MHz handsets. It includes a bare GaAs die PA, SMD de-coupling and matching components and a drain switch. As with the transmit/receive switch, contact with the component is made using an LGA on the underside of the tile. More highly integrated front-end LTCC modules could also be developed giving further added value to the resulting multifunction component.

In addition to designing components on LTCC processes, Plextek has worked with C-MAC on the characterisation of a range of their LTCC materials at RF frequencies. Details of this work have been published and copies are available from the technical papers page of Plextek's web site. The graph left shows the relative permittivity versus frequency for Dupont 943 material measured on a range of resonators. Results of a similar uniformity were obtained for the other materials measured during the characterisation programme. Characterisation of loss tangent versus frequency was also carried out.

The results of the material characterisation programme are summarised in the table on the right, some conventional RF and microwave substrate materials are also included for comparison.

Although the LTCC materials don't exhibit the very low loss tangents of high purity ceramics they are undoubtedly low loss materials. This fact combined with the advantages of the multi-layer structure, printed passives and low cost processing mean that LTCC has much to offer for the realisation of RF and microwave components.

In summary, LTCC is well suited to realising high volume, high performance, low-cost RF components at frequencies up to mm-wave. For more information about how Plextek could help you realise LTCC components please contact us.