Continuing our look at the 2013 GaTech Interposer Conference.
CORRECTION to IFTLE 178:
A reader has written in to indicating that the FPGA chip described in the Xilinx/SPIL paper was fabricated by TSMC not UMC .
Corning and Schott Glass
As discussed in IFTLE 170, Windsor Thomas of Corning gave a presentation entitled “The manufacturing readiness of Glass interposers” and Schott glass followed with a presentation entitled “New Ultra-thin Glass for Microelectronics.”
Since the whole LCD infrastructure is based on thin glass we certainly did not need any convincing that large panel, uniform, thin glass is available in roll and/or large panel format. Corning like Asahi Glass and Schott glass has been researching the formation of TSV (or TGV) for several years now and all appear somewhat able to form through vias down to maybe 25um. The real question is how do we than use this feedstock to get low cost glass interposers.
Though we were shown some Cu fill experiments, neither Corning nor Schott indicated that they would enter the interposer market, did not indicate who such a partner would be and in fact stated that their discussions with the FPD industry( which they most certainly now supply) indicate that there is absolutely no interest in FPD suppliers entering the interposer supply market.
IFTLE concludes that if any of the current glass suppliers want to see glass become a interposer substrate material and more broadly a preferred packaging substrate material, they must resolve who will actually be supplying the final packaging products.
Asahi glass has attempted to fill this void with Triton, their JV with nMode [see IFTLE 141, “100GB Wide IO memory; AGC Glass Interposers; Nvidia talks stacked memory” ] Corning and Schott have not yet indicated what their proposed solutions are.
Koizumi-san of Shinko discussed glass substrate prototyping status. Shinko points out that glass cores can be used to mimic Si like interposers or build-up PCB substrates.
He showed data on a 200um glass core PCB with a 5/0/5 build up process ( 30um polymer/18um thick Cu per layer) . When diced such structures resulted in what they called “Se-wa-re” (loosely translated back split) which was fracture through the glass core layer due to the stresses built up on both sides of the core. Modeling calculations show that the glass internal stress is mainly caused by the total copper layer thickness.
John Xie of Altera examined the use of organic interconnect for stacked die integration. Altera’s take on Interconnect resolution trends are compared below. The proposal is that organic build up (BU) substrate (dry processed) is rapidly approaching the capabilities of this film BE of line packaging on silicon.
Xie contends that high end substrate suppliers are quickly approaching 2/2 L/S and will allow direct attach to substrate and elimination of the interposer as shown below. This in turn will be a cost reduction driver. He calls this 2.1D or Ultra high density organic interconnect. They can currently get 92um bump pitch, 8um lines and 80um vias. Their 2 year goal is to obtain 55um bump pitch, 2um lines and 20um vias.
Zeon introduced their ultra tine dry films for Interposer RDL applications. Properties of the Zeon “cyclo olefin” polymer film are shown below.
Ushio addressed large area litho tools for 1 – 5µm L/S. They claim their tool is capable of 2µm L/S in a 70 x 70 sq mm area.
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