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BGA ASIC on Screened PET Sensor

IP.com Disclosure Number: IPCOM000031375D
Publication Date: 2004-Sep-22
Document File: 2 page(s) / 224K

Publishing Venue

The IP.com Prior Art Database

Related People

Joseph (Kurth) Reynolds: INVENTOR

Abstract

Plastic, such as PET (polyethylene terephthalate), sensors, with screened conductors offer an opportunity to lower the cost of manufacture for touch sensitive devices. Connecting multiple analog signals to an external PCB (printed circuit board) is both more costly and less reliable than connecting fewer digital signals. Interpretation and conversion of multiple analog signals into a serial digital format by an IC (integrated circuit)directly connected to a screened PET sensor can achieve the result of a more simple, reliable, and lower cost connection.

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BGA ASIC on Screened PET Sensor

1.    Inventor(s): Joseph (Kurth) Reynolds

2.    Synaptics Incorporated, San Jose, CA, USA

3.    Short Summary

Plastic, such as PET (polyethylene terephthalate), sensors, with screened conductors offer an opportunity to lower the cost of manufacture for touch sensitive devices. Connecting multiple analog signals to an external PCB (printed circuit board) is both more costly and less reliable than connecting fewer digital signals. Interpretation and conversion of multiple analog signals into a serial digital format by an IC (integrated circuit)directly connected to a screened PET sensor can achieve the result of a more simple, reliable, and lower cost connection.

Figure 1.  An IC integrated onto a PET sensor allows many-wire analog to few-wire digital conversion.

4.    Some Problems Solved

Typical bonding techniques between ICs and PET are not possible due to the differences in pad pitch and bonding temperature between the two. In particular Tape Automated Bonding and Chip on Flex require expensive high temperature flex like Kapton® (DuPont’s polyimide film). For conductive adhesive formulations, they also require a very fine pitch on the flex to connect directly to the pads on a silicon IC. When packaged ASICs are surface mounted, the ASICs require a solderable (wetting) surface and temperatures not available on screened PET processes.

5.    General Description

The solution to this is to use a PET compatible Anisotropic Conductive Film or Z-Axis Conductive Adhesive (ACF) with a packaged IC. The bonding temperature (<150 oC) of the ACF is compatible with both package and PET, and the pitch (>0.5 mm) of the package and PET is compatible.

In particular, commonly used BGA (ball grid array) packages of 0.6 to 1.0 mm pitch could be used with standard screened PET processes that allow 0.3 to 0.6 mm pitch. The ACF would be required to allow minimum contact areas of less than 0.4 mm, and accommodate ball heights of 0.150 mm. It might be necessary to use low profile balls/bumps (< 0.05 mm) or flat no-ball contacts without solder mask to for...