Research Papers

Development of Accelerated Method for Thermal Cycling in Electronic Packaging Application

[+] Author and Article Information
Michael Mayer

e-mail: mmayer@uwaterloo.ca

Michael McCracken

Microjoining Laboratory,
University of Waterloo,
Waterloo, ON, N2L 3G1, Canada

John Persic

Microbonds Inc.,
Markham, ON, L3R 3B3, Canada

1Corresponding author.

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received October 9, 2012; final manuscript received December 7, 2012; published online March 28, 2013. Assoc. Editor: Yi-Shao Lai.

J. Electron. Packag 135(2), 021007 (Mar 28, 2013) (6 pages) Paper No: EP-12-1096; doi: 10.1115/1.4023911 History: Received October 09, 2012; Revised December 07, 2012

The method is based on a microheater integrated next to a wire bonding pad (test pad) on a test chip. It is fabricated in CMOS technology without additional micromachining. The microheater consists of two polysilicon resistor elements, placed at opposite sides of the pad, operated in parallel using a constant voltage, each element extending over 30 × 70 μm with a resistance of ≈140 Ω at room temperature, and is operated based on Joule heating. The polysilicon is located at least 20 μm but not more than 50 μm from the pad aluminum. To characterize the microheater, Al serpentine resistors are placed on and between the heaters next to the pad, serving as resistive temperature detectors, having resistances of about 9.4 Ω at room temperature. With a constant operation voltage of 15 V, ≈140 mA of current and ≈2.1 W of heating power are generated, resulting in a heat flux of ≈500 MW/m2. The thermal resistance of the heater is 200 K/W (i.e., loss coefficient of 5 mW/K). The maximum temperature measured on one of the microheater resistors was above 396 °C and was reached using 18 V within less than 5 s of voltage application starting at room temperature. When heating from 101 °C to 138 °C, even faster heating is possible, allowing the performance of highly accelerated thermocycles. These cycles are applied to a ball bond on the test pad. Compared to the 20 min cycles used by a standard test, the new microheater device performed cycles lasting 10 ms (5 ms on, 5 ms off) which is 5 orders of magnitude faster. The released energy is typically 10 mJ per cycle. A 50 μm diameter ball was made using 25 μm diameter Au wire and bonded to the test pad. The effect of the microheater-cycling on the contact resistance values of ball bonds is described. Starting with typical contact resistance values around 2.5 mΩ, the increase observed is between 4% and 7% after 5 × 106 10 ms cycles (≈14 h).

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Fig. 1

Micrograph of test pad, integrated microheater, and RTDs.

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Fig. 2

Electrical diagram of microheater. Connection lines vary in real structure.

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Fig. 3

(a) Layout illustration of pad contacts for four-wire measurement of ball bond contact resistance. (b) SEM micrograph of two bonds on top of each other on test pad with surrounding structures. Three Al RTDs shown bright, electrically floating, "illuminated" by electrical charges in the SEM. One Al RTD (behind bonds) electrically connected to package and, therefore, not illuminated.

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Fig. 4

Temperature characterization of microheater and west RTD resistances. Quadratic fit for microheater, linear fit for RTD.

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Fig. 5

Resistances measured during microheater operation under various constant voltage levels.

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Fig. 6

Temperatures measured while microheater under various constant voltage levels.

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Fig. 7

Characterization of drift behavior of (a) RW, (b) RH, and (c) TN. Temperature fluctuations are likely caused by changes in room temperature.

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Fig. 8

Measured resistances and consumed power when RN is maintained at 14 Ω (ΤΝ = 161 °C) until heater failure.

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Fig. 9

Setup used for measuring the heater resistance during fast thermal cycling.

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Fig. 10

Setup used for measuring RN using (a) oscilloscope and (b) multimeter.

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Fig. 11

Unfiltered microheater resistance data. Applied voltage = 12 V at 50 Hz.

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Fig. 12

Profiles of individual heating cycles at 1 min, 5 min, and 10 min into heating, with unfiltered cyclic heating data. Cycling parameters = 16 V, 100 Hz.

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Fig. 13

Ball bond contact resistances measured during experiment of microheater cycling with 18 V. RC measured using four-wire method and ball-on-ball configuration.




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