Herbert Stanley Cole

Optical absorption of some polymers in the region 240–170 nm

Absorption coefficients for some technologically important polymer materials are given in the wavelength range ∼240–170 nm. Absorption coefficients at 193 nm for these polymers show a wide range of values from ∼2×102 cm−1 for polytetrafluoroethylene (Teflon) to ∼4×105 cm−1 for polyimide. The general nature of the optical properties of polymers in the vacuum ultraviolet is also discussed.

Theory of polymer ablation

A new formula is presented for the etch depth l per pulse of an excimer laser of fluence F. Incremental ablation is defined as the etch depth per pulse after many pulses. We show that l is proportional to F, rather than ln(F).

Laser-induced selective copper deposition on polyimide

Laser irradiation of organometallic palladium compounds with an argon ion laser at 351 nm is used to selectively deposit catalytic amounts of palladium on polyimide. Subsequent immersion of the irradiated samples in an electroless copper solution results in copper deposition. Since a few monolayers of palladium are sufficient to catalyze the electroless copper process, fast writing speeds of several centimeters per second are obtained.

Use of BCB in high frequency MCM interconnects

Multichip modules (MCMs) are increasingly used for high frequency, microwave, and millimeter wave applications. This has prompted the need for low loss dielectrics to meet the performance requirements of multilayer interconnects used in MCMs. In the GE high density interconnect (HDI) process, adhesives are used to bond dielectric film layers over bare chips and components. After vias are formed in the dielectric and adhesive, patterned metal is fabricated, and additional layers of dielectric are bonded and additional patterned metal is fabricated to complete the interconnect structure. In this study, we evaluated the electrical performance of selected adhesives used to bond one dielectric film layer to another. The use of a low loss thermoset polymer such as benzocyclobutene (BCB) as the adhesive resulted in lower dielectric losses compared to an epoxy-based adhesive evaluated over the 10-20 GHz regime tested. Based on the experimental data derived in this study, the electrical performance improvement should be even more significant at higher frequencies.

Dependence of photoetching rates of polymers at 193 nm on optical absorption depth

Mixtures of poly(methyl methacrylate) and poly(α‐methyl styrene) were prepared and their optical absorption coefficients at 193 nm were measured. A study of photoetching rate of these polymeric materials using an ArF excimer laser at 193 nm shows two regions of distinctly different etching characteristics. At relatively high fluences (>300 mJ/cm2) the photoetch rate decreased with increasing absorption in the polymer films, while at lower fluences, an optimum range of absorption coefficients was found to give the maximum photoetching rate.

Development of a plastic encapsulated multichip technology for high volume, low cost commercial electronics

Non-military/non-computer electronics industry segments such as PCs, workstations, portable electronics, automotive, medical, automated test equipment and high end consumer, are evolving to higher complexity and higher performance circuits and components. At the same time, many of these industry segments are being driven to shrink size, weigh and power dissipation. Standard low cost packaging approaches such as thru-hole PCB and chip and wire hybrids, can no longer efficiently interconnect these more complex circuits. These industry segments are being forced to turn to new higher performance packaging approaches such as SMT, MCM and COB. This paper describes the development of an innovative embedded chip MCM technology that eliminates high cost structures, materials and processes in current thin film MCM technologies. A plastic encapsulated multichip technology has been developed in which an epoxy encapsulant is molded around bare die to form the MCM substrate. This new MCM process readily scales-up to high volume production and is inherently high yielding, while maintaining all of the performance advantages of the GE developed overlay HDI process. This paper describes the thermal, mechanical and chemical stability issues that drove this development, the process used to fabricate the modules and the cost and yield advantages associated with this structure.<<ETX>>

A new reflective dichroic liquid‐crystal display device

A new reflective dichroic display device is described. The only components include a quarter‐wave retarder positioned between an aligned dichroic nematic liquid‐crystal display cell and a diffuse metallic reflector. This configuration allows both polarizations of incident light to be absorbed without affecting the polarizer‐free high brightness voltage activated state.

Ultra low loss millimeter wave multichip module interconnects

We present the design and electrical characterization of a multilayer organic based multichip module (MCM) for use at W-band (75-110 GHz). The ultra-low loss microstrip transmission line on Kapton E(R) (a trademark of DuPont) thin films and benzocyclobutene (BCB) adhesives is reported at W-band. An electrical model for a vertically stacked via interconnect to an integrated circuit (IC) is experimentally developed. This interconnect exhibits very low parasitics and preserves excellent matched conditions for devices and circuits in a module. The electrical performance of the vertically stacked via offers superior performance relative to ribbon and wire bond results reported in the literature at millimeter wave frequencies. We conclude that this technology is capable of realizing compact modules at millimeter wave frequencies.

Dependence of absorption and optical contrast of a dichroic dye guest on the pitch of a chiral nematic host

Absorption of unpolarized light by a dichroic dye dissolved in a chiral nematic host increased with a decrease in pitch of the host, accompanied by a proportionate increase in contrast ratio, in qualitative agreement with a theoretical analysis by White and Taylor. Identical experimental values of order parameter of the guest‐host system were obtained by two independent methods.

Laser ablation of polymers for high-density interconnect

Abstract Fabrication of micro-vias with a diameter of less than 100 μm in polymeric materials is a key processing technology for high-density interconnect applications. This paper discusses material properties that are relevant to laser ablation and describes several laser techniques (e.g. excimer, UV YAG and CW argon ions lasers) for micro-via fabrication in a thin-film multilayer structure for high-density interconnect applications.