Polyimide dielectric dissipation factors

Dielectric dissipation factors for polyamides and polyimides increase rapidly on exposure to ultraviolet (290-400 nm) radiation in air [120] short-wave UV radiation (254 nm) has a similar effect on poly(vinylidene chloride) [1658]. Photodegradation of polyethylene rapidly increases both... 

Figure 6. Real part of the dielectric constant t, (1 MHz) and dissipation factor D (1 MHz) as a function of polyimide thickness.

Relative to microelectronic applications, the out-of-plane dielectric constant for BPDA-PFMB films measmed after aging at 50% relative humidity for 48 h at 23°C was between 2.8 and 2.9 (0.1 kHz to 1 MHz) (ASTM D-150-81These values are considerably lower than that of commercial polyimides such as PMDA-ODA (pyromellitic dianhydride, PMDA) (s = 3.5 at 1 kHz and 3.3 at 10 MHz). The dielectric constant and tan 8 (dissipation factor) were temperature- and frequency-dependent. The dielectric constant, which was independent of temperature until near 210°C increased above this point until a frequency-dependent maximum was reached at about 290°C. The dissipation factor, which was also independent of temperatme below 200°C, underwent a rapid increase with no maximum between 200 and 400°C owing to ion conductivity. The temperatme at which this increase occurred increased as the frequency increased. The films also... 

The optimum characteristic impedance is dictated by a combination of factors. Interconnections with low characteristic impedance (<40 fl) cause high power dissipation and delay in driver circuits, increased switching noise, and reduced receiver noise tolerance (35). High characteristic impedance causes increased coupling noise and usually has higher loss. Generally, a characteristic impedance of 50-100 fl is optimal for most systems (35), and a ZQ of 50 fl has become standard for a variety of cables, connectors, and PWBs. For a polyimide dielectric with er = 3.5, a 50-fl stripline can be obtained with b = 50 xm, tv = 25 xm, and t = 5 xm. 

Alternative polymers that have certain advantages over polyimides have also been introduced they include poly(phenylquinoxaline), poly(phenylquinoline), and poly(benzocyclobutenes) (PBCBs) (93,116). The PBCBs have a low curing temperature (250 °C), low dielectric constant (2.6), low dissipation factor (0.0045), and low moisture absorption (0.3%) The development of specialty polymers for packaging and high-density interconnections will continue to be an active area of research as polymer manufacturers focus on the needs of the microelectronic industry. 

A recently reported alternative to spin or spray coating is screen printing of polyimide solutions (82, 85, 90). Screen printing is a low-cost, high-throughput process capable of directly patterning the polyimide films as they are deposited. Another alternative is the vapor deposition of polyimides, which was reported by researchers who co-evaporated the diamine and dianhydride monomers at stoichiometric rates (140). The evaporated films had better adhesion, a lower dielectric constant, and a lower dissipation factor compared with spin-coated polyimides. With this process, uniform, defect-free, conformal films can be cured in situ during deposition. 

The dielectric properties of two different thermoset films derived from bis-benzocyclobutene monomers were described. The dielectric constant was 2.65 + 0.1. The dissipation factor was below 0.001 above 1.0 kHz. These values are significantly lower than those reported for polyimide thin films. Therefore, the BCB films described in this work are attractive candidates for interlevel dielectrics in dense multilevel interconnection structures. 

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