High density interconnection technology

CMST/IMEC has a history of research in various substrate technologies, such as thin film, thick film and laminate technology.

Recently we have focused on laminate and thick film technology while the thin film activity was shifted towards back-end processing of CMOS wafers for microdisplays.

Both in laminate technology and thick film technology the objectives are to realise advanced high-density substrates to be used in RF applications.

Laminate technology

Figure 1 Metallized 50 µm microvia's

The build-up technology was chosen as the way to solve the interconnection bottleneck in laminate technology. Using either a photo-via technique or a laser-drilling procedure, microvia’s of 50 µm are defined. An advanced electroless Cu, galvanic Cu and electroless Ni/Au metallisation scheme yields Cu tracks and spacings of 50 µm. This technology was applied in the Esprit project Hiperprint.

In co-operation with Thomas Walter and Solectron sub-module ADSL demonstrator boards were made for Alcatel Telecom. This technology will be further refined in the IST project Lidcat using direct laser-writing and a novel graded build-up approach. The objective is to develop the future generation of gsm boards for Alcatel Business Systems applying a direct die attach.

Figure 2 Test board for reliability tests

In a joint Pidea effort with Barco, CS2, Alcatel and Bull our photo-via technology will be applied in automotive, telecom and aeronautic products. Figure 1 shows a cross section of a metallised microvia, while Figure 2 shows a test board for reliability tests.

In collaboration with Alcatel Telecom the build-up technology will be extended towards the integration of optical wave-guides using photo-imageable polymer waveguides.

Thick-film technology

In order to refine standard thick film technology a photo-imageable approach has been adopted[6]. First a Au base multi-layer system has been developed, which has been evaluated in several functional demonstrators and could be used up to several GHz [7].

Figure 3 A fine line thick film substrate

Later a more cost-effective Pd based multi-layer technology was developed yielding tracks and spacing of 50 µm [8,9,10,11]. This technology was successfully transferred to C-MAC-Electromag. Within the Pidea project VCO passive components will be integrated in an RF circuit on ceramic, using this advanced thick film technology. In Figure 3 a fine line thick film substrate is shown.