Conductive-paste adhesives

To assure optimum conductance, the adhesive must be applied as thinly and uniformly as possible. To control the thicknesses bond lines, thermally conductive paste adhesives have been formulated with collapsible spacers. The spacers are reported to control bond line thickness to 30 pm. Bond line thicknesses and uniformity may also be achieved by using film or preform tape adhesives and controlling the applied pressure and heat during cure. 

Both conductive paste adhesives and pressure-sensitive tapes are widely used for EMI protection. Two-part epoxies or one-part silicones filled with silver or silver-plated copper particles are widely used as paste adhesives while acrylic conductive and nonconductive adhesives on aluminum or copper foil are used as pressure-sensitive tapes. EMI shielding tapes are suitable fortemperatures ranging from -40°Cto 121°C and are available in thicknesses from 1.5 mil to 5 miLl" Shielding effectiveness is measured as attenuation in dB at several frequencies, for example, from 1 MHz to 20 GHz. Values for several ARclad shielding tapes are given in Table 5.13. 

Magneli phase TiO (x = 1.67 to 1.9) is conductive. A proprietary material of this composition in the form of solid sheets or a honeycomb has been patented for use as current-collectors in either monopolar or bipolar lead-acid batteries [15]. The honeycombed structure holds the paste and thereby improves paste adhesion and the mechanical stability of the plate, as well as the electrical conductivity. The material is stable at the potentials of the positive plate [16,17]. 

The result of these arrangements will be homogeneous metal particles/ nanocomposites distribution in acetylacetone ligand shell. In the capacity of conductive filler silver nanoclusters/nanocrystals and copper-nickel/ carbon nanocomposites can be used. It should be lead to decrease volume resistance from 10" to 10" Q-cm and increase of adhesive/paste adhesion. 

A third approach to underfilling involves applying an insulative thermoplastic preform (film) prior to attaching the device. Under pressure and heat, the preform softens and flows around the solder bumps, then solidifies quickly on cooUng. The devices may then be solder reflowed to make the connections or the preform may be formulated to flow and encapsulate the solder during solder reflow. Table 5.6 lists some commercially available preforms used as underfills. Anisotropic film adhesives have also been used as underfill preforms, in which case z-direction conductive paths are formed beneath the solder bumps at the same time that the rest of the insulating film flows and cures around the bumps. Anisotropic paste adhesives can be similarly used (Figure 5.11). 

Once the epoxy bumps have been formed, the wafer is thinned from the backside, the devices are singulated, and their edges beveled at 45° to expose gold pads at the periphery of die. The chips are then stacked and bonded with thermally conductive, electrically insulative epoxy (Figure 5.16). Paste adhesives are cost effective and can be dispensed with existing epoxy dispensing equipment. However, with... 

In the manufacture of smart cards, microprocessor chips, memory chips, EEPROMs or combinations in flip- chip configuration are electrically bonded onto the circuit card using anisotropic electrically conductive paste or film adhesive (see Chapter 1). Smart cards may be contact or contactless types. In contact cards, the electrical contacts of the card connect to a card reader when the card is inserted. Contactless cards transfer data in proximity to a reader (www.smartcard.gov) without physical contact. 

Uses Lubricant, filler for thermally conductive materials, adhesives, pastes, potting compds., polymer matrices, elec, (due to high elec, resist.), refractories, refractory coatings, mold/die release, metal/ceramic and ceramic/matrix composites, as ingred. in release agents and lubricants in high temp, processing Features Inert... 

Electrically conductive epoxy paste adhesive for low-stress and in-line die attach ME8418-DA AIT echnology 80 40 -... 

Fast curing, electrically conductive epoxy paste adhesive Epo-Tek H20E Epoxy Technology 100 31 120... 

Layer pairs are prepared using conventional processes of etching, plating, drilling, and so on, or by conductive paste processes. The layer pairs are laminated together using B-stage resin systems or some other form of dielectric adhesive into which conductive paste vias have been placed. 

In order to prevent the delamination explained above, it is effective to optimize the laminating conditions (temperature and pressure), improve the adhesive properties of the resinous constituent of the green sheets and conductive paste, and to check the parallelism of the press and so on. In addition, forming dummy conductors in the edge parts where conductors are not normally formed to adjust their thickness is an effective method of preventing delamination. 

Electrically conductive adhesives are used for such applications as bonding lead wire to electrodes, solder paste replacement in the assembly of SMD, die attachment, and repair of conducting paths. Adhesives such as epoxies or acrylics are highly filled (typically 80%) with conductive metal particles. Metals such as nickel and copper cannot be used because of their susceptibility to oxidation. Precious... 

Conductive adhesives are used for many other electronic assembly operations, in addition to die attach. Epoxy paste adhesives are used for capacitor and other component attach in hybrid components or on printed circuit boards. In general, these electronic assemblies require high purity adhesives which do not give off im-... 

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