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Method of simultaneously forming electrical and/or thermal conductive interconnections on opposite chip surfaces of vertical transistors in direct chip attach (DCA) technology, using no-flow/ fluxing underfill material.

IP.com Disclosure Number: IPCOM000031166D
Original Publication Date: 2004-Sep-15
Included in the Prior Art Database: 2004-Sep-15
Document File: 5 page(s) / 48K

Publishing Venue

Motorola

Related People

Robert Bauer: AUTHOR [+3]

Abstract

Vertical transistors in direct chip attach (DCA) technology provide electrical contacts on opposite chip sides. The front side of the transistor device is connected to a carrier or substrate via solder bumps, while the back side contact is established by soldering or gluing a conductive member to the transistor backside and the carrier or substrate. In the traditional process flow as known today, the two connections are build in at least two different, consecutive process steps. This document introduces a new process solution that allows the simultaneous formation of front side & backside connections on semiconductor devices in DCA technology together with all other required electrical and/or thermal connections on a carrier or substrate in a single process step, utilizing the presence of no-flow fluxing underfill, thereby saving one complete assembly cycle.

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Page 1 of 5

Method of simultaneously forming electrical and/or thermal conductive interconnections on opposite chip surfaces of vertical transistors in direct chip attach (DCA) technology, using no-flow/ fluxing underfill material.

Robert Bauer, Joerg Feige, Anton Kolbeck

© 2004 Freescale Semiconductor, Inc.

Page 2 of 5

Abstract

Vertical transistors in direct chip attach (DCA) technology provide electrical contacts on opposite chip sides. The front side of the transistor device is connected to a carrier or substrate via solder bumps, while the back side contact is established by soldering or gluing a conductive member to the transistor backside and the carrier or substrate. In the traditional process flow as known today, the two connections are build in at least two different, consecutive process steps.

This document introduces a new process solution that allows the simultaneous formation of front side & backside connections on semiconductor devices in DCA technology together with all other required electrical and/or thermal connections on a carrier or substrate in a single process step, utilizing the presence of no-flow fluxing underfill, thereby saving one complete assembly cycle.

Background on no-flow, fluxing underfill material

No-flow, fluxing underfill materials are dedicated epoxy compounds for FlipChip assembly.

Different from the traditional capillary flow underfill materials, which are applied after the DCA interconnect has been formed, no-flow fluxing underfill (alias reflowable underfill, alias self fluxing underfill) is pre-deposited ahead DCA device placement. The typically epoxy resin based underfill material contains flux, which fully reacts with heat during reflow/cure and converts into epoxy resin. The epoxy content of the underfill fully cures during reflow. Some material types do require additional post- reflow curing.

© 2004 Freescale Semiconductor, Inc.

Page 3 of 5

                       Body Semiconductors in DCA technology have been successfully introduced into many applications. Vertical transistors in DCA technology (which means typically FlipChip) represent a variation within this technology group.

Differing from standard devices, which utilize only the active device side for interconnections, they provide electrical contacts such as source, gate, drain and sense on opposite chip sides. Therefore, they require appropriate methods in order to establish electrical connection to chip front side and chip backside. This is usually accomplished by first forming the contacts on the active device side by reflowing pre- applied solder bumps, followed by the application of capillary flow underfill in order to enhance the mechanical strength of the completed assembly. Application of the newly introduced no-flow (fluxing) underfill materials enables the user to establish this interconnection in one process step (see figure 1). In a second, additional process step the connection to the device backside is established by soldering or gluing a contact me...