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Wong, C. P.

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Author: Wong, C. P. × Author: Wu, Jiali × End date: 1999 × Start date: 1998 ×

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Now showing 1 - 3 of 3
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    Novel Bi-Layer Conformal Coating for Reliability Without Hermeticity MEMS Encapsulation
    (Georgia Institute of Technology, 1999-07) Wong, C. P. ; Wu, Jiali ; Pike, Randy T.
    A flexible, smooth, and low profile conformal coating was developed to accomplish the encapsulation of a microelectromechanical system (MEMS) device that will be applied to sense the static pressure on aircraft during real flight testing. The encapsulant should be able to protect the MEMS device and the multichip module (MCM) from adverse environmental conditions, i.e., mechanical shock, temperature fluctuation, engine fuel and oil contamination, and moisture/mobile ion permeation. Presently, conventional packaging schemes for electronics cannot satisfy this specific outdoor application, and a new encapsulation combination has been designed in accord with the requirement of reliability without hermeticity (RWOH). A bi-layer structure was selected because of property limitations of a single material. Pliable elastomeric silicones, are typically flexible, water repellant, and abrasion resistant. The silicone encapsulant will be first applied to planarize the MEMS surface and function as durable dielectric insulation, stress-relief, and shock/vibration absorbers over a wide humidity/temperature range. To compensate for the deficiency of silicone on engine fuel/oil contamination, Parylene C is to be deposited afterward. This bi-layer coating can achieve excellent bulk properties, such as moisture and mobile ion barrier resistance, chemical compatibility, and electrical insulation characteristics. However, the poor adhesion of Parylene C to silicone greatly restricts its application. To address this problem, silane coupling agents were used as an adhesion promoter. Significant adhesion im provement was achieved by placing an interlayer silane coupling agent to provide interfacial bonding to the silicone elastomeric surface and the Parylene C film. Furthermore, a possible mechanism of adhesion enhancement will also be presented in this study. Index Terms— Bi-layer conformal coating, micro-electromechanical system (MEMS), multichip module, Parylene C, reliability without hermeticity (RWOH), silane coupling agent, silicone elastomer.
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    Correlation of Flip Chip Underfill Process Parameters and Material Properties with In-Process Stress Generation
    (Georgia Institute of Technology, 1999-01) Wong, C. P. ; Palaniappan, Prema ; Baldwin, Daniel F. ; Selman, Paul J. ; Wu, Jiali
    Electronic packaging designs are moving toward fewer levels of packaging to enable miniaturization and to increase performance of electronic products. One such package design is flip chip on board (FCOB). In this method, the chip is attached face down directly to a printed wiring board (PWB). Since the package is comprised of dissimilar materials, the mechanical integrity of the flip chip during assembly and operation becomes an issue due to the coefficient of thermal expansion (CTE) mismatch between the chip, PWB, and interconnect materials. To overcome this problem, a rigid encapsulant (underfill) is introduced between the chip and the substrate. This reduces the effective CTE mismatch and reduces the effective stresses experienced by the solder interconnects. The presence of the underfill significantly improves long term reliability. The underfill material, however, does introduce a high level of mechanical stress in the silicon die. The stress in the assembly is a function of the assembly process, the underfill material, and the underfill cure process. Therefore, selection and processing of underfill material is critical to achieving the desired performance and reliability. The effect of underfill material on the mechanical stress induced in a flip chip assembly during cure was presented in previous publications. This paper studies the effect of the cure parameters on a selected commercial underfill and correlates these properties with the stress induced in flip chip assemblies during processing.
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    Use of Compliant Adhesives in the Large Area Processing of MCM-D Substrates
    (Georgia Institute of Technology, 1998-10) Wong, C. P. ; Wu, Jiali ; Pike, Randy T.
    Large area substrate processing is a key solution for improving the productivity of multichip module deposition (MCM-D) technology. This project is focused on high temperature polymeric adhesives for attachment of silicon tiles to suitable pallets to facilitate large area film processing of MCM structures. Current polymeric high temperature adhesives are predominately polyimide-based that are not reworkable, which places an obstacle to remove the coated substrates and to reuse the high cost pallets. However, an approach will be presented in this paper to address this demand by introducing thermally cleavable links in the thermoset polyimide-amide resin. A series of novel reworkable high temperature (in excess of 350–400 ℃) adhesives have been developed, that can meet the requirements of adhesion, viscosity, thermal stability, and reworkability of the MCM-D production. Furthermore, scanning electron microscopy (SEM) microstructure images are presented for intuitive reworkability analysis.