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.

1.
Delaney
,
K.
,
Barton
,
J.
,
Bellis
,
S.
,
Majeed
,
B.
,
Healy
,
T.
,
O'Mathuna
,
S. C.
, and
Crean
,
G.
, 2004, “
Creating Systems for Ambient Intelligence
,”
Silicon: Evolution and Future of a Technology
,
P.
Siffert
and
E.
Krimmel
eds.,
Springer-Verlag
,
Berlin
, Chap. 24, pp.
489
514
.
2.
Bellis
,
S.
,
Delaney
,
K.
,
Barton
,
J.
,
Razeeb
,
K.
,
O'Flynn
,
B.
, and
Majeed
,
B.
, 2004, “
Development of Wireless Sensor Networks for Ambient Systems
,”
Wireless Sensor Networks and Applications
, 14–19 March, Dagstuhl, Germany, http://www.dagstuhl.de/04122/Materials/http://www.dagstuhl.de/04122/Materials/
3.
Barton
,
J.
,
Majeed
,
B.
,
Dwane
,
K.
,
Delaney
,
K.
,
Bellis
,
S.
,
Rodgers
,
K.
, and
O'Mathuna
,
S.
, 2004, “
Development and Characterization of Ultra Thin Autonomous Modules for Ambient System Applications Using 3D Packaging Techniques
,”
Proc. 54th Electronic Components and Technology Conference ECTC 2004
, June 1–4,
Las Vegas, NV
, pp.
635
641
.
4.
Kada
,
M.
, 2003, “
The Dawn of 3-D Packaging as System-in-Package (SIP)
,”
IEICE Trans. Electron.
0916-8524 Special Issue on Integrated Systems with New Concepts,
E84
-C, pp.
1763
1770
.
5.
Wu
,
L.
,
Wang
,
Y. P.
, and
Hsiao
,
C. S.
, 2002, “
Innovative Stacked Die Package—S2BGA
,”
Proc. 52nd Electronic Components and Technology Conference
, May 28–31, San Diego, CA, pp.
250
253
.
6.
Chen
,
K. Y.
,
Zenner
,
R.
, and
Arneson
,
M.
, 2000, “
Ultra Thin Electronic Package
,”
IEEE Trans. Adv. Packag.
1521-3323,
23
(
1
), pp.
22
26
.
8.
Sunohara
,
M.
,
et al.
, 2002, “
Development of Wafer Thinning and Double Sided Bumping Technologies for Three Dimensional Stacked LSI
,”
Proc. 52nd Electronic Components and Technology Conf
, May 28–31, San Diego, CA, s06p2.
10.
Kim
,
Y. J.
, 2002, “
Folded Stack Package Development
,”
Proc. 52nd Electronic Components and Technology Conf
, May 28–31, San Diego, CA, s32p3.
11.
Flip Chip Packaging Technology Solutions: Enabling Technologies; Amkor Technologies Inc, http://www.amkor.com/enablingtechnologies/3D/index.cfmhttp://www.amkor.com/enablingtechnologies/3D/index.cfm
12.
Savastiouk
,
S.
,
Siniaguine
,
O.
, and
Korczynski
,
E.
, 2000, “
3D Stacked Wafer-Level Packaging
,”
Advanced Packaging
, pp.
28
34
.
13.
McKenny
,
D. J.
, 2000, “
Material Roadmap for High Density Flex Circuits
,”
6th Annual National Conference on Flexible Circuits
, June, Dallas, TX, pp.
30
41
.
14.
Meyer
,
J. U.
, 2001, “
High Density Interconnects for Flexible Hybrid Assemblies for Active Biomedical Implants
IEEE Trans. Adv. Packag.
1521-3323,
24
(
3
), pp.
366
374
.
15.
Mayer
,
J.-U.
, 2000, “
Biomedical Micro-Devices for Neural Interfaces
,”
1st Annual Int IEEE-EMBS Spec Topic Conf on Microtechnolgies in Medicine and Biology
, Oct 12–14, Lyon, France, pp.
447
453
.
16.
IPC TM-650 Test Method Manual, 2.5.6.3, Dielectric Breakdown Voltage and Dielectric Strength.
17.
Jason
,
J. G.
, 1998, “
Surface Studies of Polyimide Thin Films Via Surface-Enhanced Raman Scattering and Second Harmonic Generation
,”
Macromol. Rapid Commun.
1022-1336,
19
, pp.
619
623
.
18.
Karamancheva
,
I.
, 1999, “
FTIR Spectroscopy and FTIR Microscopy of Vacuum-Evaporated Polyimide Thin Films
,”
Vib. Spectrosc.
0924-2031,
19
, pp.
369
37
.
19.
ASTM Standard D 570-98, Standard Test Method for water absorption of plastics.
21.
Technical datasheet of the polyimide used in the experiments, Product Bulletin, HD Microsystems™, http://www.hdmicrosystems.com/tech/techinfo.htmlhttp://www.hdmicrosystems.com/tech/techinfo.html
22.
Martyak
,
N. M.
, 1997, “
Microcracks in Chromium Electrodeposits
,”
J. Mater. Sci.
0022-2461,
32
, pp.
6069
6073
.
23.
Billmeyer
,
F. W.
, 1994,
Textbook of Polymer Science
,
3rd ed.
,
Wiley-Interscience
,
New York
, pp.
427
428
.
24.
Haghiri-Gosnet
,
A. M.
,
et al.
, 1989, “
Stresses in Sputtered Tungsten Thin Films
,”
Appl. Surf. Sci.
0169-4332,
38
, pp.
295
303
.
25.
ASTM Standard D882-88, Standard Test Method for Tensile Properties of Thin Plastic Sheeting.
You do not currently have access to this content.