# Presentation: 880776

## Reliability of Embedded Active Assemblies 

- Linda Del Castillo,1 Alina Moussessian,1 Toshiro Hatake,1 R. Wayne Johnson,2 Michael Lou,1
- Benjamin J. Blalock,3 and William B. Kuhn4
*1**Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109*
*2**Auburn University, Auburn, AL 36849*
*3**The University of Tennessee, Knoxville, TN 37996*
*4**Kansas State University, Manhattan, KS  66506*
- New Electronic Technologies Insertion into Flight Programs Workshop
- NASA/Goddard Space Flight Center, Greenbelt, MD
- January 30- February 1, 2007

## Applications

- Integrating microelectronics into membrane materials to provide multifunctional and adaptive capabilities will enable new mission concepts for NASA and DoD.
- Such highly integrated, multifunctional, large area, flexible membrane structures would allow low cost, low launch volume and high performance future missions.

- Specific applications are membrane antennas for space-based radar, membrane solar arrays for space power systems, integral health monitoring sensors for membrane radar and solar sails.
- One example of a NASA application is a Synthetic Aperture Radar (SAR) for determining surface deformation, topography, soil moisture and land cover change.

## Materials Selection

- LCP was selected for this project based on the following:
- capability of laminating die within this thermoplastic material
- excellent electrical properties even up to millimeter wave frequencies (eg. loss tangent is 0.002 at 20 GHz);
- Virtual impermeability to moisture, oxygen and other gases;
- Low coefficient of thermal expansion (CTE) 8 ppm/°C;
- Excellent dimensional stability (< 0.1%);

- “Microfabrication Techniques for Liquid Crystal Polymer Substrates," Brian Farrell, Paul Jaynes, Damian Kubiak, Robert Dean, IMAPS Annual Meeting 2002, Denver, Colorado.

## Materials Selection - Temperature

- The mechanical behavior of LCP was evaluated as a function of temperature and compared with that of Kapton H.

## Materials Selection – Wrinkling

- Structure wrinkling, folding crease, and random handling testing were conducted on the .002 inch thick LCP and Kapton H sheets, to determine their comparable capability to withstand deformation and wrinkling.
- When held in the configuration shown in Figure A, LCP exhibited a low-level wavelike deformation at low loads and some rippling at the attachment points at higher loads.
- During the random handling and crease tests shown in Figures B and C, LCP was observed to retain deformation longer than Kapton H.

- B

- C

- A

## Assembly Description

- For the embedded assemblies, electrical connections are made through holes in the LCP dielectric (Figure A) to the sides of the traces that were initially in direct contact with the LCP.
- Therefore, the active circuitry on the thinned silicon chip and the traces on the flexible substrate are facing the same direction (Figure B).
- A second layer of dielectric is then laminated onto the backside of the assembly, thereby embedding the silicon chip within two layers of flexible LCP material (Figure C).

**Au Stud**
**Bump**

**LCP**

**A**

**B**

**C**

## Passive Assemblies

- A set of daisy chain die were thinned to 50 **m and bonded onto the LCP daisy chain circuit shown to the right.
- After attachment, a second layer of LCP was bonded onto the backside of the assembly.

**Backside and frontside photographs of an embedded daisy chain assembly**

**Cross-section of a series of stud bump interconnects**

**Daisy chain**
**die.**

## Thermal Cycling

- Daisy chain assemblies have been cycled according to the Mil Std temperature range (-55 to 125°C) and an Extreme Low temperature range (-135 to 85°C).
- Thermal cycling evaluation results are as follows:
***1446*** Mil Std thermal cycles (no failures).
***618*** Extreme low temperature cycles (1 of 6 failed at 348 cycles).
- Problem with liquid nitrogen valve resulted in two exposures to -196°C.
- Failure occurred prior to exposure.

## Operational Amplifier Assemblies

- A Honeywell MOI5, custom-designed quad op-amp chip targeted for low-temperature and wide-temperature range applications was used for this task.
- Just as with the previously described daisy chain die, the quad op-amp was thinned to 50 **m, and embedded between two layers of LCP.
- No changes in performance were observed between the as-received and the thinned/embedded devices.

**Low and high magnification photographs of embedded OpAmp assemblies**

**Photograph of Quad OpAmp**

## Flex Testing – Preliminary Results

- Embedded operational amplifier circuits were evaluated under the test conditions described below and at room temperature.
- Results indicate a minimal influence of flexure on the behavior of the device for all parameters other than offset voltage.
- Further evaluation is currently being conducted to confirm this finding.

**FLAT**

**6 inch diameter**

**3 inch diameter**

**Active circuitry on the die is in tension**

**Silicon die substrate is in compression**

## Low Noise Amplifier Assemblies

- A Honeywell MOI5 L-Band (1.2 GHz) Low Noise Amplifier (LNA) was used for the present task.
- Challenges associated with the embedding of RF devices include the following:
- Ground plane must be included on the same side of the dielectric as the die (microstrip).
- Previously, this location provided a continuous LCP to LCP bonding area.
- A tradeoff between electrical performance and mechanical adhesion must be performed to determine the optimum grid density for this layer.
- Due to the delicate nature of RF devices, it is critical to test following each stage of the process (i.e. unthinned, thinned and singulated, embedded).
- Processing continues for these assemblies.

**Photograph of L-Band Low Noise Amplifier**

## Summary

- A series of mechanical tests performed to evaluate the feasibility of using LCP materials for future multifunctional radar applications, yielded favorable results.
- A process of embedding thinned Si die within flexible circuitry has been developed, and the procedure has been extended to include the embedding of active devices.
- Thinned daisy chain assemblies have been thermal cycled under both the Mil Std temperature range and an extreme low temperature range, with only one failure in the extreme low range (618 cycles) and no failures in the Mil Std range (1446 cycles).