Adhesives die-attach

The general area of adhesion and adhesion science has been one of the most important application areas identified thus far in a variety of applications for the subject imide-siloxane copolymers [74-82]. Many references in the patent literature [83-90] have been found that relate to the utilization of the copolymers in various important applications such as die attach adhesives, encapsulants, interphase agents, etc. It would appear that the combination of very good thermal stability, coupled with the adhesive bonding capabilities provided by the siloxane mobile segment, has attracted a great deal of attention and will be the... 

US 5,204,399 (American) 1991 Thermally conductive thermoplastic polyimide film die attach adhesives and their preparation National Starch and Chemical Investment Holding Corp. R Edelman Adhesive formulations having excellent die shear strength A polyimide-siloxane was prepared from aromatic amines, bis aminophe-noxybutylsiloxane and aromatic dianhydrides... 

Edelman R, Papanu VD (1989) Thermoplastic film die attach adhesives. US Patent 4994207 A 910219 5 pp... 

Avatrel Dielectric Polymers (low-k dielectric applications such as interlayer dielectrics, passivation layers, die attach adhesives, chip encapsulants (both molding and adhesive) and underfill materials). 

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. 

During die attach, an adhesive creates a mechanical interface between the die and substrate in a semiconductor assembly. A typical dispense pattern has intersecting lines with strategically placed dots so that after die placement, the fluid is evenly distributed (Figure 10-12). Most die attach adhesives also provide thermal and/or electrical conductivity between the die and substrate. 

First specification to qualify die-attach adhesives (NASA MSFC-SPEC-592)... 

MIL-STD-883 Method 5011 coordinated and released Thermoplastic film adhesives Silver-glass die-attach adhesives introduced First underfills for flip-chip devices... 

Galloway DP, et al. Reliability of novel die attach adhesive for snap curing, Proc. lEMT Symp. IEEE 1995. 

Hannafin JJ, Pemice RF, Estes RH. Die Attach Adhesives A Guide to Material Properties and Applications. Epoxy Technology, Technical Paper GB-48. 

McCabe JD. Selecting the right die-attach adhesive. High Density Interconnect. Jul. 2001 32-6. 

Ying L. A novel approach— thermoplastic die attach adhesive. Solid State Technol. Sep. 1987. 

High-Tg die-attach adhesive 15 0% proprietary cyanate ester admixture, 60-85% silver filler ME 8863 (AI Technology)... 

Chien lY, Nguyen MN. Pursuing the Perfect Paste A Novel Cyanate Ester Die Attach Adhesive for Plastic Packaging. Solid State Technol. Nov. 1994. 

Flip chip and CSP underfills, die-attach adhesives for advanced electronics and semiconductor packaging... 

Estes R. A practical approach to die attach adhesive selection. Hybrid Circuit Technol. Jun. 1991. 

Hunadi R, Bilow N, Noack L. Determining corrosion tendencies of die-attach adhesives using the sealed glass tube test. Hybrid Circuit Technol. Apr. 1988. 

Figure 5.5 Examples of multichip modules in which die-attachment adhesives were used. Top Aluminum/polyimide interconnect (MCM-D) on silicon substrate in Kovar package. Bottom Multilayer thick-film (MCM-C) digital filter.

In Case 7, a thermoplastic die-attach adhesive was used. The large amount of carbon dioxide indicates decomposition, but the small amount of moisture indicates that moisture may have been generated, but gettered by oxides or metals in the package. Often when moisture is expected to be high, but is low, and hydrogen is present, the moisture is believed to have reacted with oxides or metals to produce hydrogen. 

Yoo HY, et al. Novel die attach adhesive for thin quad flat package, wwwJienkelna.coni/ industrial/white-papers-8082.htm. Accessed August 2010. 

The method and type of equipment used also vary with the type of adhesive. As an example, the viscosity of electrically conductive adhesives is measured according to ASTM D1824, Apparent Viscosity of Plastisols and Organosols at Low-Shear Rates by Brookfield Viscosity The viscosity of typical electrically conductive die-attach adhesives is measured with a Brookfield HBT viscometer with Spindle TB and Speed 5. For higher-viscosity conductive adhesives and for underfill adhesives, a Brookfield RVT or RVF viscometer is used with Spindles 6 or 7 at speeds of 4—10.4 rpm. Another Brookfield viscometer, the Cone-and-plate viscometer with a CP-51 spindle is used for low-to-intermediate viscosity adhesives. Finally, the Brookfield HAT and HBT instruments are used for the high-viscosity (1-2 million cP at 1 rpm) adhesives typically used in SMT applications. ... 

Internal visual inspection for substrate attachment is also performed at magnifications of 10X to 60x. The 50% and 75% fillet mles also apply for element or die-attach adhesives. 

Electrical-stability testing is essential for conductive adhesives used for electrical connections. Electrical conductivity can degrade at elevated temperatures, on aging with or without power, and on exposiue to humidity and temperature. The specific test method used depends on the application. One test used for die-attach adhesives specified in NASA MSFC-SPEC-592 (now inactive) involves a series of gold-plated Kovar tabs attached with conductive epoxy to metal pads on an interconnect substrate. In the test vehicle, a bias of 5 V and cmrent density of 139 3.9 A7cm (900 A/in ) are applied to a series of wire-connected tabs, and the resistance change is measured after exposure to 150 °C periodically up to 1,000 horns. The maximum allowable resistance change is 5%. 

Moisture absorption in uncured and cured adhesives is important for reliable adhesive bonding. Absorbed moisture in adhesives, particularly those used in surface-mounted parts, may result in voids in the bond hne due to moisture desorption or entrapment. Absorption of moisture after cure also affects reliability. Popcoming, the cracking of plastic parts during solder reflow, is due to the rapid vaporization and expulsion of moisture retained by the die-attach adhesive or the plastic encapsulant. 

Another method for measuring either die- or substrate-attach adhesion strength involves attaching a contact tool to the top of the die or substrate with an adhesive that is stronger than that of the die-attachment adhesive. The tool applies a vertical force until the die detaches from the substrate or until a minimum specified strength is achieved. The test method and failure criteria are specified in Method 2027 of MIL-STD-883F. i... 

Hysol KOI 10 Die-Attach Adhesive, Technical Data Sheets, Henkel Oct. 2001. 

Bell GC, RoseU CM, Josline ST. Rheology of silver filled glass die attach adhesive for high speed automatic processing, Du Pont semiconductor materials. In Proc. 37th Electronic Components Conference May 11-13, 1987. 

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