Product Code: ICAL08_M305

Hermetic Joining of Micro-Devices using a Glass Frit Intermediate Layer and a Scanning Laser Beam
Authors:
Qiang Wu, Heriot Watt University; Edinburgh Great Britain
Norbert Lorenz, Heriot Watt University; Edinburgh Great Britain
Changhai Wang, Heriot Watt University; Edinburgh Great Britain
Kevin Cannon, Ge Aviation Systems; Suffolk Great Britain
Andrew J. Moore, Heriot Watt University; Edinburgh Great Britain
Duncan P. Hand, Heriot Watt University; Edinburgh Great Britain
Presented at ICALEO 2008

Many micro-electro-mechanical-systems (MEMS) devices require hermetic sealing to prevent moisture and dust ingress. A number of different joining techniques have been developed for the packaging of MEMS devices. Techniques currently used for localised joining include resistive heating , microwave heating and induction heating. An alternative solution is to use a laser as a highly localized and remotely directed heat source, thus avoiding heating the whole package, important if there are temperature-sensitive materials in the MEMS device. There are a number of reports about applications of laser based joining such as joining of cemented carbides to steel, magnesium and aluminium, and borosilicate glass to fused silica. These applications are laser based direct bonding without any intermediate layer, which normally require both high temperature and highly cleaned polished contact surfaces. Joining with an intermediate layer has advantages such as low joining temperature, low requirement for contact surface smoothness etc. The intermediate layer could be Au/Sn solder, Zinc, Al or Au, indium, Ti, thermosetting polymer benzocyclobutene (BCB), or glass frit, etc. Glass frit bonding is an ideal bonding technology for encapsulation of MEMS devices such as bulk micromachined sensors, pressure sensors, accelerations sensors or gyroscopes. Glass frit requires a relatively low bonding temperature (less than 450°C ), and can deliver a hermetic seal with non-smooth bonding surfaces; it is also possible to include metallic feed-throughs. However current glass frit-based technologies are based on furnace heating which will heat the whole device. Laser based joining should allow the advantages of glass frits to be applied to temperature-sensitive devices. To our knowledge there has however to date been no report on laser-based joining with a glass frit intermediate layer. In this paper we present localised laser bonding of LCC (Leadless chip carrier) packages, top-hat packages and TO5 Kovar cap packages by using a fibre-delivered high power laser diode array to cure an intermediate layer of glass frit. Standard leak testing demonstrates that all those samples have excellent hermetic sealing with leak rates at the level of 10-9 atmcc/s.