By Dr. Roger E. Weiss and David M. Barnum, Paricon Technologies Corp., Fall River, Mass.
Each generation of computers, telecommunication equipment and other electronic devices is typically smaller, faster more complex and less expensive than its predecessors. Continuation of this remarkable trend, however, requires the constant introduction of new and cost-effective technologies, especially with interconnects between ICs and the next level. Unique Material This article describes a unique material that serves as a high-performance interconnection medium. This material is a thin, flexible fabric that is conductive through its thickness but not in plane. It also combines the unique properties of being a compressible, electrical interconnection and an environmental seal. This technology readily lends itself to being constructed in a format which can be integrated with other hardware, or custom configured to any 2D object. This interconnection technology* has already been employed in interconnection products.
It is comprised of highly organized conductive columns of spherical particles supported in an elastomeric matrix (See Figure 1). These columns provide a compliant interconnect between opposing pad layers.
Redundancy Multiple columns are provided for each interconnect, yielding a high level of redundancy (See Figure 2). Unlike wire-based elastomer interconnection systems, the columns do not set, due to the classic phenomena known as Euler column failure (See Figure 3). Instead, as the column's spherical particles move with the system, they maintain contact with each other. As a result, the columns display high cycle life and will not be damaged by short-term overloading. The columns are completely configurable to various applications. Products designed for contact spacings ranging from 2.0mm, 1.27mm, 1.0mm, 0.8mm, 0.65 and 0.5mm to chip scale have been provided. Custom designs, including shorting contacts, have also been developed. The height of the columns may also vary from 0.002" to 0.020."
Thermal Cycling An interconnection system using this material at 1.0mm contact spacing, was subjected to 700 thermal shock cycles between room temperature and 125°C. This was followed by continuous cycling to 80°C for a total of over 1100 hours of thermal cycling.
Figure 4 presents a plot of the room temperature resistance of the 230 contacts as the device is thermally cycled. Throughout the entire study, a stable, average resistance of ~6milliΩ was maintained. The standard deviation was approximately 1milliΩ. Products based on this interconnection technology are now being used in burn-in test systems at temperatures up to 150°C. Users have reported the ability to successfully cycle the interconnect system to above 1500 burn-in cycles at 150°C.
Stability Figure 5 presents a single time slice of the room temperature data from a thermal cycle study. This data is plotted in the normal distribution format which is designed to emphasize any deviation from normality. The plot shows that the data is well behaved, tending to follow a normal distribution with some tailing at the upper limit. This characteristic is expected in that it is the conductance not the resistance which should be normally distributed. Thermal Coefficient of Resistance All conductor materials of interest tend to demonstrate an increase in resistance with temperature. This increase applies to gold, silver, copper, etc. The TCR of this interconnection system was measured and is shown in Figure 6. The plot includes silver to provide a comparison with a well known metal.
Life Cycle Capability Life cycle testing has been conducted using gold blocks and test boards with different pad geometries. Figure 7 presents the results of a typical study. This data also confirms the reduced resistance with increased pad area. The actual end of life has not been determined but is expected to be several hundred thousand cycles-based on application.
Frequency Response The frequency response of the interconnect was measured by an independent test house as having a characteristic impedance of ~55 ohms and a loss of ~1 dB at 40GHz. The test equipment was being operated at its limit and the actual performance may be better. The table shows the material's high frequency characteristics.
Current Carrying Capability As with resistance, current carrying capability is a function of interconnect area and of system's heat sinking capability. Using the same setup as used to measure the resistance, it was demonstrated that the 1.0mm formulation is capable of conducting 3.0 amps continuously between 0.025" pads with filled vias. Summary This new interconnect materials technology is a new way of testing, burning-in and simply interconnecting high speed devices and systems. It is reliable, easy to use and provides excellent electrical and mechanical properties. It is one of the few interconnection technologies that can meet the future needs of interconnecting electronic packages and systems. * BallWire is a trademark of Paricon Technologies Corp., and has been incorporated in its PariPoser product lines.
|
Copyright © 2003