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Research Papers

In Situ Chip Stress Extractions for LFBGA Packages Through Piezoresistive Sensors

[+] Author and Article Information
Ben-Je Lwo

Department of Mechatronic, Energy, and Aerospace Engineering, Chung-Cheng Institute of Technology, National Defense University, Ta-Shi, Tao-Yuan, 33509, Taiwan, R.O.C.lwob@ccit.edu.tw

Jeng-Shian Su1

Department of Weapon System Engineering, Chung-Cheng Institute of Technology, National Defense University, Ta-Shi, Tao-Yuan, 33509, Taiwan, R.O.C.samsuccit@gmail.com

Hsien Chung

School of Defense Science, Chung-Cheng Institute of Technology, National Defense University, Ta-Shi, Tao-Yuan, 33509, Taiwan, R.O.C.g990408@ccit.edu.tw

1

Current address: Chi-Mei Optoelectronics, Sinshih, Tainan 74147, Taiwan.

J. Electron. Packag 131(3), 031003 (Jun 23, 2009) (9 pages) doi:10.1115/1.3144149 History: Received March 24, 2008; Revised April 16, 2009; Published June 23, 2009

Piezoresistive sensors have been demonstrated to be an accurate and efficient tool for stress measurements on chip surfaces inside microelectronic packaging. In this work, test chips with piezoresistive stress sensors, diode temperature sensors as well as heaters were first designed, fabricated, and calibrated. We next packaged the test chips into low profile, fine pitch ball grid array (LFBGA) packaging with 196 balls and measured the stresses on chip surfaces inside the packaging. After measuring the packaging induced stress as well as the stress under stable environmental temperature rises, it was found that compressive stresses were obtained at room temperature, and the stresses were relaxed as temperature went up at a rate between 0.45MPa/°C and 0.60MPa/°C. For thermo-stress experiments, the temperatures on chip surfaces at different power levels were measured, and compressive chip stresses were first extracted. As the chip power increased, the compressive stresses became tensions. Since the LFBGA structure is thinner with higher packaging efficiency, different results from our earlier plastic quad flat package stress measurements were observed and discussed. In addition, the final comparisons between the experimental data and the finite element simulations show good consistency.

Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

The test chip layout with sensor and heater locations

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Figure 2

The five-element rosette cell

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Figure 3

The simple assembled structure for calibration

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Figure 4

LFBGA configurations: (a) top view with chip and ball locations and (b) cross section view on half of the structure (unit: mm)

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Figure 5

The finite element model for the simulations

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Figure 6

The experimental setup for oil-bath measurements

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Figure 7

Temperature-voltage plots for four typical diodes. Only diode A is fitted for simplicity.

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Figure 8

σx at different temperatures for a typical sample: (a) sensors A∼D and (b) sensors α∼δ

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Figure 9

σy at different temperatures for a typical sample: (a) sensors A∼D and (b) sensors α∼δ

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Figure 10

σx—temperature relationship for the average of the samples: (a) sensors A∼D and (b) sensors α∼δ

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Figure 11

σy—temperature relationship for the average of the samples: (a) sensors A∼D and (b) sensors α∼δ

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Figure 12

The standard deviation distribution for the data points in Figs.  1011.

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Figure 13

The thermal and thermo-stress experimental setup

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Figure 14

Thermal results and comparisons along chip surface: (a) diagonally and (b) horizontally (m: measurements; s: simulations; L: half chip length)

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Figure 15

σx—power relationship for a typical sample: (a) sensors A∼D and (b) sensors α∼δ

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Figure 16

σy—power relationship for a typical sample: (a) sensors A∼D and (b) sensors α∼δ

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Figure 17

σx—power relationship for the average of testing samples: (a) sensors A∼D and (b) sensors α∼δ

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Figure 18

σy—power relationship for the average of testing samples: (a) sensors A∼D and (b) sensors α∼δ

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Figure 19

The standard deviation distribution for the data points in Figs.  1718

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Figure 20

Comparisons on thermo-stress increments: (a) σx and (b) σy (s: simulation; m: measurement average; d: diagonally; h: horizontally)

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