Flexible circuitry, application

Aromatic polyimides have found extensive use in electronic packaging due to their high thermal stability, low dielectric constant, and high electrical resistivity. Polyimides have been used as passivation coatings, (1) interlayer dielectrics, (2) die attach adhesives, (3) flexible circuitry substrates, (4) and more recently as the interlevel dielectric in high speed IC interconnections. (5) High speed applications require materials with a combination of low dielectric constant, flat dielectric response versus frequency and low water absorption. 

Figure 2). Orientation of the films is used to tailor and control the CTE, and the low dielectric thin film layers provide more controlled impedance and reduced crosstalk than other substrate materials. In addition to MLBs, ordered polymer films can be used to advantage in multichip molecules where silicon chips are directly bonded to the interconnect substrate. The very low permeability of PBO and PBZT films will protect the chips from moisture. Flexible circuitry is another promising application area for these films. 

In addition, there has been greater use of flexible circuitry and foldable flex circuits requiring a corresponding degree of flexibility in the adhesives used. For these applications, solders or other metallurgical attachment materials have often failed due to cracking, delamination, electrical opens, or changes in electrical parameters. Some... 

Silver particles can also be used to create conductive inks, which are then printed onto textile substrate. They were initially developed for smart cards and printed circuit boards but have found a lot of application in the flexible circuitry field. Some major challenges remain (Meoli and May-Plumlee, 2002) before conductive inks can be applied in a production environment since the ink viscosity (Perelaer et al., 2010)... 

In contrast, the consumption of polyimides has increased in the electronic industry, especially for the fabrication of flexible circuitry and its associated tape automated bonding process. High level of adhesion and thermoplasticity are the prominent parameters for these applications. Compared to aerospace applications, electronics imposes new requirements because of the exposition to high temperatures that is generally fimited to short-time exposures at 350 to 400°C. In the aerospace industry, Larc-TPI performs well to bond Kapton to itself as to... 

Flexible printed wiring is used primarily in electronic packaging applications where low weight or volume is a prerequisite, or excessive vibration is likely to be encountered. The main advantage of flexible circuitry is its ability to be shaped into more than one plane or conform to an irregular shaped package. 

In electronics, polyimides are now extensively used in the form of self-standing films for flexible circuitry, deposited films for interlayer dielectrics, passivation and buffer coatings, moulding thermoplastic powders for PCBs, and adhesive pastes or tapes. The basic polyimide chemistry has been adapted to fulfill the specific requirements of these applications. A series of books provides complete information not only on the chemistry of polyimides but also on their utilization in electronics [4,23,24]. The following figures summarize the chemical formulae of the most important categories of polyimide precursors or precyclized polymers that are commonly used in electronics. 

Figure 30 Main applications of adhesives in electronic and semiconductor industries (a) polyimide interlayer dielectric films in the fabrication of integrated circuits (b) die attachment in plastic packages (c) die attachment in ceramic packages (d) multichip module with flip chip and surface-mounted devices (e) flexible circuitry (f) tape automated bonding (g) liquid crystal display panels.

PPO/PPE blends are used in business and computer machine housing, structural and interior components in electrical equipment and telecommimications equipment. PPO/PPE blends are suitable for various telecommunications applications such as enclosures, switchgear, networking devices, flexible circuitry and cable and wire extensions. Key properties are their good chemical resistance to most solvents, fuels and other contaminants, excellent processability, impact performance at extreme temperatures, and thin wall performance that can reduce cycle times. 

In 2006 GE announced a new amorphous TPI, Extern , with Tg < 311°C, and high strength, stiffness, chemical and creep resistance at T < 230°C.The new TPI finds applications in auto, aerospace and military products, downhole oil and gas production, medical membranes, electrical connectors, electronics for lead-free soldering, semiconductor wafer handling, and specialty films for insulators and flexible circuitry. 

As discussed in the introduction requirements for the different applications envisaged for printable electronics are very different and will require substrates with different sets of properties. This is summarized in Fig. 7.13 and for this classification covers simple organic circuitry, e.g. RFID, organic based active matrix backplanes, OLED displays, but also includes the requirements of inorganic TFTs on flexible substrates. 

Because of their toughness, flexibility and remarkable thermal stability, linear all-aromatic polyimides are excellent candidate film and coating materials for advanced electronic circuitry and wire coating applications. In past years, however, the inherent insolubility (1-2) of these polymers has somewhat limited their usefulness for electronic applications. 

This elastomer finds many applications in the electrical industry as wire and cable insulation and jacketing plenum cable insulation, oil well wire and cable insulation logging wire jacketing and jacketing for cathodic protection aircraft, mass transit and automotive wire cormectors coil forms resistor sleeves wire tie wraps tapes, tubing and flexible printed circuitry and flat cable. 

Major Applications Optical materials, photoresists, . flexible electronic circuitry, adhesives,i° textiles,". method for counting leukocytes,i enzyme binding assays, 4 DNA chips Safety/Toxicity No data available... 

A process has been described for laminating polyimide films to each other and to conductive metal foils in the production of flexible electrical circuitry. This will find use in aircraft, spacecraft, and missiles as well as industrial applications. It is expected that the market for such constructions will grow as the market share of multilayered circuit boards increases. 

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