Person:
Wong, C. P.

Permanent Link
https://hdl.handle.net/1853/71846
Associated Organization(s)
ORCID
ArchiveSpace Name Record

Filters

2001 - 2004 5
5
5
5
Reset filters

Settings
Author: Li, Haiying × Author: Wong, C. P. × End date: 2010 × search.filters.applied.f.isOrgUnitOfPublicationTitle: College of Engineering × search.filters.applied.f.resourcesubtype: Article ×

Publication Search Results

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    Novel Reworkable Fluxing Underfill for Board-Level Assembly
    (Georgia Institute of Technology, 2004-09) Wong, C. P. ; Zhang, Zhuqing ; Li, Haiying
    Underfills are traditionally applied for flip-chip applications. Recently, there has been increasing use of underfill for board-level assembly including ball grid arrays (BGAs) and chip scale packages (CSPs) to enhance reliability in harsh environments and impact resistance to mechanical shocks. The no-flow underfill process eliminates the need for capillary flow and combines fluxing and underfilling into one process step, which simplifies the assembly of underfilled BGAs and CSPs for SMT applications. However, the lack of reworkability decreases the final yield of assembled systems. In this paper, no-flow underfill formulations are developed to provide fluxing capability, reworkability, high impact resistance, and good reliability for the board-level components. The designed underfill materials are characterized with the differential scanning calorimeter (DSC), the thermal mechanical analyzer (TMA), and the dynamic mechanical analyzer (DMA). The potential reworkability of the underfills is evaluated using the die shear test at elevated temperatures. The 3-point bending test and the DMA frequency sweep indicate that the developed materials have high fracture toughness and good damping properties. CSP components are assembled on the board using developed underfill. High interconnect yield is achieved. Reworkability of the underfills is demonstrated. The reliability of the components is evaluated in air-to-air thermal shock (AATS). The developed formulations have potentially high reliability for board-level components.
  • Thumbnail Image
    Item
    A Reworkable Epoxy Resin for Isotropically Conductive Adhesive
    (Georgia Institute of Technology, 2004-02) Wong, C. P. ; Li, Haiying
    Electrically conductive adhesive (ECA) is a promising alternative to the toxic eutectic tin-lead solder as an interconnect material. Typical ECAs use epoxy resin as their matrix, which has superior properties over other polymers, such as high adhesion, and low dielectric constant. However, once cured, it is not reworkable. In this study, a liquid diepoxide was designed and synthesized, and used in isotropically conductive adhesive (ICA) formulations. This diepoxide has a molecular structure able to thermally decompose at mild temperature that allows selective individual removal of the bad component without damaging the board and its surroundings. The characterizations including proton and carbon 13 nuclear magnetic resonance, infrared spectroscopy indicated the success of the synthesis. A dual-epoxy system containing this secondary diepoxide and an equivalent bisphenol-A diepoxide were formulated and cured with an anhydride hardener and an imidazole catalyst. Thermal analyses, such as differential scanning calorimetry, thermo-gravimetry analysis (TGA), thermo-mechanical analysis (TMA) and dynamic mechanical analysis (DMA) were employed for the curing kinetics, thermal degradation behavior, glass transition temperature, coefficient of thermal expansion (CTE), and mechanical modulus, respectively. The dual-epoxy system showed two exothermal curing peaks at 140°C and 180°C, respectively. The thermoset of this dual-epoxy system has a decomposition temperature around 234°C, a glass transition temperature around 80 to 90°C, and CTEs of 74 ppm/°C and 225 ppm/°C below and above its Tg, respectively. The rework test on a surface mount component bonded to copper surface showed this ECA can be easily and quickly removed from the copper surface. The bulk resistance and contact resistance of ICAs were measured before and during an accelerated aging process in a temperature/humidity chamber (85°C/85% RH). The ECA showed good bulk resistivity and contact resistance comparable to its control and a commercial ECA on gold and copper surface finishes.
  • Thumbnail Image
    Item
    Development of New No-Flow Underfill Materials for Both Eutectic Sn-Pb Solder and a High Temperature Melting Lead-Free Solder
    (Georgia Institute of Technology, 2003-06) Wong, C. P. ; Li, Haiying ; Johnson, Ashanti
    In recent years, no-flow underfill technology has drawn more attention due to its potential cost-savings advantages over conventional underfill technology, and as a result several no-flow underfill materials have been developed and reported. However, most of these materials are not suitable for lead-free solder, such as Sn/Ag (m.p. 225°C), Sn/Ag/Cu (m.p. 217°C), applications that usually have higher melting temperatures than the eutectic Sn-Pb solder (m.p. 183°C). Due to the increasing environmental concern, the demand for friendly lead-free solders has become an apparent trend. This paper demonstrates a study on two new formulas of no-flow underfill developed for lead-free solders with a melting point around 220°C. As compared to the G25, a no-flow underfill material developed in our research group, which uses a solid metal chelate curing catalyst to match the reflow profile of eutectic Sn-Pb solder, these novel formulas employ a liquid curing catalyst thus provides ease in preparation of the no-flow underfill materials. In this study, curing kinetics, glass transition temperature (Tg), thermal expansion coefficient (TCE), storage modulus (E [superscript v]) and loss modulus (E″) of these materials were studied with a differential scanning calorimetry (DSC), a thermo-mechanical analysis (TMA), and a dynamic-mechanical analysis (DMA), respectively. The pot-life in terms of viscosity of these materials was characterized with a stress rheometer. The adhesive strength of the materials on the surface of silicon chips were studied with a die-shear instrument. The influences of fluxing agents on the materials curing kinetics were studied with a DSC. The materials compatibility to the solder penetration and wetting on copper clad during solder reflow was investigated with both eutectic Sn-Pb and 95.9Sn/3.4Ag/0.7Cu solders on copper laminated FR-4 organic boards.
  • Thumbnail Image
    Item
    An Improvement of Thermal Conductivity of Underfill Materials for Flip-Chip Packages
    (Georgia Institute of Technology, 2003-02) Wong, C. P. ; Li, Haiying ; Jacob, Karl I.
    Effective heat dissipation is crucial to enhance the performance and reliability of electronic devices. In this work, the performance of encapsulants filled with carbon fiber was studied and compared with silica filled encapsulants. Encapsulants filled with mixed combination of fillers for optimizing key properties were also investigated. The thermal and electrical conductivities were investigated and glass transition temperature (Tg), thermal expansion coefficient (TCE), and storage modulus ( ) of these materials were studied with thermal analysis methods. The composites filled with both carbon fiber and silica showed an increase of thermal conductivity three to five times of that of silica filled encapsulants of the same filler loading while maintaining/enhancing major mechanical and thermal properties.
  • Thumbnail Image
    Item
    Reworkable No-Flow Underfills for Flip Chip Applications
    (Georgia Institute of Technology, 2001-04) Wong, C. P. ; Wang, Lejun ; Li, Haiying
    Underfill is a polymeric material used in the flip-chip devices that fills the gap between the integrated circuit (IC) chip and the substrate (especially on the organic printed circuit board), and encapsulates the solder interconnects. This underfill can dramatically enhance the reliability of the flip-chip devices as compared to the nonunderfilled devices. No-flow (compress-flow) underfill is a new type of underfill that allows simultaneous solder bump reflow and underfill cure, which leads to a more efficient no-flow underfilling process as compared to the standard capillary-flow underfilling process. Reworkable underfill is another type of underfill that allows the faulty chips to be replaced individually. It is the key material to address the nonreworkability issue of the current flip-chip devices. Reworkability is especially important to the no-flow underfill because electrical test of the assembled chips can only be done at the end of the no-flow underfilling process. The goal of this study is to demonstrate the feasibility of a no-flow reworkable underfill. Two approaches are taken to develop this new type of underfill. The first one is to add a special additive into a standard no-flow underfill formulation (underfill 0) to make it reworkable, called underfill 1. The second approach is to develop a no-flow underfill based on a new thermally degradable epoxy resin that decomposes around 240℃, called underfill 2. Comparing to underfill 0, these two underfills have similar properties including glass transition temperature (T[subscript g]), coefficient of thermal expansion (CTE) and modulus. Underfill 1 has similar curing and fluxing capability as to underfill 0. Underfill 2 cures faster than underfill 0, and it has slightly weaker fluxing capability than underfill 0, but it still allows 100% of solder bumps wetting and collapsing on the copper board. Moreover, underfill 1 and underfill 2 allow the flip chips to be reworked using a developed rework process while underfill 0 does not.