0
RESEARCH PAPERS

Fabrication and Characterization of Flexible Substrates for Use in the Development of Miniaturized Wireless Sensor Network Modules

[+] Author and Article Information
Bivragh Majeed

 Tyndall National Institute, Lee Maltings, Prospect Row, Cork, Irelandbmajeed@tyndall.ie

Kieran Delaney, John Barton, Niall McCarthy, Sean C. O’Mathuna, John Alderman

 Tyndall National Institute, Lee Maltings, Prospect Row, Cork, Ireland

J. Electron. Packag 128(3), 236-245 (Nov 24, 2005) (10 pages) doi:10.1115/1.2229221 History: Received February 13, 2005; Revised November 24, 2005

In this paper we describe the materials-related challenges in applying folded flex packaging technology to wireless sensor networks and propose solutions for implementing miniaturized 5mm cube platforms. The focus is to apply thin silicon stacking methods using thin flexible substrate interconnect and in particular to investigate the behavior of the selected materials. Both commercial and in-house polyimide substrates, in the thickness range 25μm down to 3μm (each with 4μm of sputtered copper) were analyzed for appropriate electrical, chemical, and mechanical properties. The characterization highlighted that in flex of thickness below 10μm, a dramatic decrease in stiffness occurs and the polyimide wrinkles due to stresses generated by the copper sputtering process. An evaluation determined that specific steps, such as polymer support ring formation, could be employed to eliminate impact of wrinkling on the process of developing the 5mm cube prototypes.

Copyright © 2006 by American Society of Mechanical Engineers
Your Session has timed out. Please sign back in to continue.

References

Figures

Grahic Jump Location
Figure 1

Cross section of a two-die folded stack implemented by Tessera (see Ref. 9)

Grahic Jump Location
Figure 2

Schematics showing varying bonding techniques for folded chip assembly by Tessera (see Ref. 9)

Grahic Jump Location
Figure 3

Graph showing the impact of flex thickness on the overall effective volume of thin packages

Grahic Jump Location
Figure 4

A schematic showing the overall experimental and characterization work for this program

Grahic Jump Location
Figure 5

Spin curve for PI5875

Grahic Jump Location
Figure 6

This shows polyimide samples being released using a mechanical technique

Grahic Jump Location
Figure 7

Two checkerboard patterns used to chemically etch the backside of the silicon carrier wafer

Grahic Jump Location
Figure 8

A schematic of flex release mechanism that applies when using UV laser ablation

Grahic Jump Location
Figure 9

A 16-μm thick flexible polyimide circuit successfully delaminated using laser ablation

Grahic Jump Location
Figure 10

A 3.9-μm thick flexible substrate after release showing a significant level of wrinkling

Grahic Jump Location
Figure 11

A wrinkle-free 3.9-μm polyimide flexible test circuit constrained using a polymer ring

Grahic Jump Location
Figure 12

FTIR transmittance spectrum of polyimide samples (labeled SAM1-4) where SAM1 is a commercial 25μm sample, SAM2 is 3μm in-house sample, SAM3 is a post-HF buffer solution release sample, and SAM4 is a post-KOH treated 3μm sample

Grahic Jump Location
Figure 13

A graph of stress in cured polyimide samples as the thickness is varied

Grahic Jump Location
Figure 14

Tensile strength and Young’s modulus for increasing thickness of polyimide substrate

Grahic Jump Location
Figure 15

This graph shows the “percentage elongation at break” as the polyimide thickness decreases

Grahic Jump Location
Figure 16

This graph shows measured polyimide material stiffness as substrate thickness decreases

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In