Michael T. Pottiger

New low coefficient of thermal expansion polyimide for inorganic substrates

Recent interest in using polyimides for high-density interconnect applications (HDI) in which multilayer structures are formed has created a need for polyimides that have a coefficient of thermal expansion (CTE) matched to that of the underlying substrate. A polyimide chemistry that allows for a significant lowering of the CTE and subsequent reduction of stress on silicon and ceramic substrates while giving improved dielectric constant

Internal Stress Development In Spin Coated Polyimide Films

The effect of processing on the development of internal stresses in spin coated polyimide films was investigated. The internal stresses are a result of the coefficient of thermal expansion (CTE) mismatch between the polymer and the substrate. Birefringence and CTE were used to characterize the in-plane molecular orientation. In-plane orientation was shown to be sensitive to processing conditions. Increasing the spin speed results in higher in-plane orientation as observed by an increase in birefringence and a corresponding decrease in CTE. Heating rate during cure was observed to have a significant effect on in-plane orientation. Faster heating rates during cure resulted in a lower birefringence. The lower birefringence is attributed to relaxation effects that can occur during a rapid cure. The decrease in orientation was accompanied by an increase in internal stress.

Effect Of Moisture On The Physical Properties Of Polyimide Films

Moisture absorption and its effect on electrical properties were measured for several polyimides. A Quartz Crystal Microbalance (QCM) was used to investigate the moisture absorption in BPDA/PPD, PMDA/ODA, and BTDA//ODA/MPD polyimides. The steady-state moisture uptake in polyimides as a function of relative humidity (RH) was determined by exposing film samples to successively higher RH values ranging from 10 to 85% at 25°C. The isothermal moisture absorption as a function of percent RH was found to be nearly linear for all of the polyimides studied. The effect of moisture on the electrical properties of a BPDA/PPD polyimide was also investigated. The relative dielectric constant at 25 °C was found to be a linear function of the moisture absorbed.

Advances in NanoScratch Testing of Automotive Clearcoats

The primary functions of automotive clearcoats are to protect the underlying layers and maintain a glossy showroom appearance for as long as possible. One of the most common sources of damage is from polymeric carwash brushes and small embedded dirt and grit particles that create small scratches in the clearcoat surface. Complex multiasperity contact, unknown geometries, and stress states make it difficult to quantify this damage. Since the mid-1990s, researchers have developed sophisticated single indenter nano- and microscratch techniques to quantify the surface mechanical properties and to understand the connection to scratch performance. Indenter size and shape were selected so that the scratches produced would be similar in size and appearance to the damage produced under real-world conditions. In this chapter, four automotive clearcoats with different crosslink densities, including a 2K urethane, a 1K melamine, and two experimental clearcoats, are evaluated and compared. New statistical methods for creating and analyzing scratch damage based on NanoScratch testing are discussed. Recovery of scratches in both short timescale (minutes) and long timescale (days) is analyzed by the NanoScratch testing and Atomic Force Microscope (AFM) analysis. The connection between the scratch morphology and the visual appearance is explored using dark field imaging as an objective surrogate for appearance. Two components to scratch resistance, damage resistance and scratch visibility, are analyzed. The damage resistance can be characterized by residual depth and fracture threshold, and the scratch visibility can be characterized by the contrast and size of a scratch image. Crosslink density appears to affect the residual depth and scratch visibility. A coating with good damage resistance does not automatically lead to low scratch visibility. The methods presented offer new ways to further understand scratch performance of coatings.