Anisotropic conductive film adhesives

M Product Data Sheet 3M Anisotropic Conductive Film Adhesive 7393. May, 2009. The Light Bulb Goes Digital. Fortune. Febmary 8, 2010 33-8. 

Table 6.5 Properties of anisotropic conductive film adhesives" ...

Shiozawa, N., Isaka, K., Ohta, T. (1994). Electric properties of connections by anisotropic conductive films. Adhesives in Electronics 94, International Conference on Adhesives Joining Technology Electronics Manufacture, VDI/VDE-IT. 

Here the joining of an adhesive bonding a tape carrier package, in which a semiconductor chip has been incorporated, to a liquid crystal display panel through an anisotropic conductive film is shown. 

Adhesive/Supplier ThreeBond 3370C/ThreeBond Anisolm AC-2056/Hitachi Anisotropic conductive Film 7393/3 M... 

Nitto Denko Corporation developed an anisotropic conductive film for fine-pitch flip-chip applications [33]. This ACF (1) is connectable between bumpless chips and a fine-pitch printed circuit board (PCB) (2) has high electrical conductivity (3) is repairable (easy to peal off chips from a printed circuit board at elevated temperatures) (4) has high reliability and (5) can be stored at room temperature. The other notable features are it is usable at pitches down to 25 pm the conductive elements are micrometallic columns as opposed to random-shaped particles this adhesive matrix consists of a thermoplastic polymer resin and the conductive columns are coated with an insulator and a high- Tg polymer that completely separates the columns from the adhesive (Fig. 8). 

MD-200 Technical Data Sheet, Thermoset, Lord Chemical Products Dec. 18, 1997. Watanabe I, Takemura K. Anisotropic conductive adhesive films for flip-chip interconnection. In Liu J, ed. Conductive Adhesives for Electronic Packaging. Electrochemical Publications Ltd 1999 [chapter 10]. 

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). 

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. 

Electrically conductive adhesives are being used to interconnect flip-chip devices in smart cards resulting in thinner and smaller structures. Flip-chip silicon devices that have been thinned to several mils may be connected to a substrate with silver-filled paste epoxy or with anisotropic film adhesive instead of solder, then embedded and laminated to form a card that is less than 40-mils thick. Requirements for adhesives used in smart cards, in many respects, are more severe than those for other commercial applications. Besides having to withstand high humidity and temperature extremes, smart cards must take the continued abuse of human handling, repeated bending, exposure to human sweat and salt residues, and exposure to ultraviolet radiation from sunlight. 

Most commercially available anisotropically conductive adhesives are formulated on the bridging concept, as illustrated in Fig. 1. A concentration of conductive particles far below the percolation threshold is dispersed in an adhesive. The composite is applied to the surface either by screen printing a paste or laminating a film. When a device is attached to a PWB, the placement force displaces the adhesive composite such that a layer the thickness of a single particle remains. Individual particles span the gap between device and PWB and form an electrical interconnection. For successful implementation of anisotropically conductive adhesives, the concentration of metal particles must be carefully controlled such that a sufficient number of particles is present to assure reliable electrical conductivity between the PWB and the device (Z direction) while electrical isolation is maintained between adjacent pads (X,Y directions). 

Isotropic adhesives conduct current equally in all directions and are the most common and widely used in industry. The anisotropic types, also referred to as z-direction adhesives or anisotropic-conductive adhesives (ACA), although filled with metal particles, are filled at much lower levels (0.5%-5% by volume) than isotropic types (filled 25%-30% by volume). The volume Iraction of filler is well below the percolation threshold at which the adhesive becomes highly conductive in all directions. Because of the low volume Iraction of metal particles, there are no continuous electrically conductive paths in the x-y plane. During the connection process, the anisotropic adhesive, either as a film or paste, is positioned between a flip-chip bumped die or a tape-automated bonded (TAB) die and the corresponding pads of an interconnect substrate. Pressure and heat are... 

Watanabe, L, and Takemura, K., Anisotropic Conductive Adhesive Films For Flip-Chip Interconnection, Conductive Adhesives for Electronic Packaging, Ch. 10, (J. Liu, ed.), Electrochemical Publications Ltd. (1999)... 

Anisotropic Paste or Film Adhesive with Conductive Particles... 

IPC-3406 Guidelines for Electrically Conductive Surface Mount Adhesive IPC-3407 General Requirements for Isotropically Conductive Adhesives lPC-3408 General Requirements for Anisotropically Conductive Adhesive Films lPC-4101 Specification for Base Materials for Rigid and Multilayer Boards lPC-4103 Specification for Plastic Substrates, Clad or Unclad, for High Speed/High Frequency Interconnection... 

D.D. Chang et ah. An Overview and Eval-uahon of Anisotropically Conductive Adhesive Films for Fine-Pitch Electronic Assembly, IEEE Transactions on Components, Hybrids and Manufacturing Technology, Vol 16, 1993, p 828-835... 

A recent publication describes a pragmatic approach for developing a thermosetting anisotropic conductive adhesive film to electrically connect a flexible circuit to ITO terminal pads [121], The basic components are a solid high molecular weight bisphenol-A diglycidyl ether, a liquid bisphenol-F diglycidyl ether, a phenoxy resin M = Tg = 94°C), (2,3-epoxypropyl)... 

The long-term reliability of isotropic and anisotropic conductive adhesives for surface-mount applications has been extensively studied [144-148]. The data accumulated with die attached chips cannot be transposed to the hybrids or surface-mounted wiring boards because of the dissimilar requirements in mechanical and electrical properties [149]. As shown in Figure 41(a) and (b) of Section 6.5.7, the active and passive devices can be attached to thick film... 

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