By Dr. Phil Garrou, Contributing Editor
The GaTech group ad many of their members have been studying the applicability of glass as 2.5D interposers for several years now. Some of the papers presented at this year’s meeting updated the industries status in this area.
LPKF Vitrion updated the attendees with their latest Through Glass Vias (TGV) technology status which is shown below.
Shinko updated their 2014 presentation on the status of Glass interposer R&D and manufacturing. Shinko is looking at glass as an alternative to silicon interposers. Their proposed process flow is shown below.
An example of a fully assembled glass interposer is shown below.
Shinko points out that there are voids inside the TGVs and they are very difficult to avoid. These voids increase the via resistance ~ 8.5%. They are in the process of determining what the acceptable void content is.
They are capable of 2um L/S RDL on the glass. They are in the process of reliability studies and failure analyses.
They are currently examining 250mm sq panels which increase unit production 2.7X vs 200mm wafers.
DC Hu from Unimicron shared their perspective on glass technology readiness. Hu lists the following requirements for glass mass production readiness:
Based on 510 x 510mm panels and 2/2 L/S fine line capability
– glass process readiness
- Thin glass handling
- Via forming technology
- Via filling technology
– production equipment readiness
He compared TGV formation from Via Mechanics, LPKF, Corning, Schott and Asahi Glass and via filling by seed and plate vs screen printed paste technologies. The paste technologies appear capable of 20um vis on 50um pitch.
While plating can be done on a 500mm sq panel, fine line patterning (2um L/S) requires a large panel stepper.
Technology status vs silicon is shown below.
TDK discussed what they claim is the first glass based Rf modules. Rf integration is clearly the key enabler for next gen smartphones. Key technologies for Rf modules are shown below.
The glass Rf module concept, which is being developed with GaTech, is shown below.
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