Die attach materials

Nguyen MN, Wood JH (1990) Silver filled polyimidesiloxane die attach material. Int SAMPE Electron Conf 4 (Electron Mater - Our Future), pp 291-301... 

Automated Fluid Dispensing for Fuel Cell Manufacture Die Attach Materials... 

The ideal die attach material has a short cure time at a relatively low-cure temperature, exhibits low moisture absorption, provides good adhesion to multiple surfaces, contributes low stress to the die and can be processed within a very tight tolerance. Many epoxies are now available meet some of these demands to a high degree, yet each material has limitations. 

Dietz RL, Winder L. New die attach material for hermetic packaging, Proc. Mfg. Eng. EMTAS Conf. Phoenix, AZ EE83-145 1983. 

Nguyen MN. Low stress silver-glass die attach material. IEEE Trans Components Hybrids Mfg Technol. Sep. 1990 13(3). 

Trigwell S. Die attach materials and methods. Solid State Technol. Apr. 1995. 

Shah T, Danzinger S, Moores K, Joshi Y. Cyanate Ester Die Attach Material for Radiation Hardened Electronic Packages. Proc. 3rd Inti. Conf. Adhesive Joining and Coating Techniques in Electronic Mfg. Sep. 1998 49-54. 

Nguyen MN. Low Stress Silver-Glass Die Attach Material. IEEE Trans. Components,... 

Silver-Filled Cyanate Ester Die Attach Material, Product Data Sheet for JMI7000, Johnson-Matthey (undated). 

A new area of concern for electrical stability arises because of the increasing use of conductive adhesives as replacements for solder. Some conductive adhesives show unstable electrical-contact resistance when used on non-noble metal surfaces such as copper or tin-lead solder. Although stable on gold, palladium, platinum, and silver surfaces, the same adhesives were found to be unstable on tin, tin-lead, copper, and nickel surfaces.The unstable resistance and increase in resistance in temperature-humidity exposures have been attributed to the growth of an oxide layer separating the filler particles from the substrate at the interface, a mechanism similar to that for the loss of backside contact in die-attach materials. 

Analysis of RGA results provides a good indication of the sources and mechanisms for the generation of the outgassed materials. Table 6.4 shows RGA data of sealed packages containing various die-attachment materials and processing conditions. ... 

Flaking, lifting, peeling, or crazing of the die-attach material. 

Although there is no standard test method for acoustic microscopy. Method 2030, Ultrasonic Inspection of Die Attach of MIL-STD-883F is used to nondestructively detect unbonded regions and voids in IC die-attachment materials. Parts are rejected if a single void larger than 15% of the contact area is present (>10% at a comer) or more than 70% of any given quadrant is detached. 

Conductive adhesives also form sufficiently robust joints that withstand the temperatures and pressures experienced during wirebonding and over molding. The formulation of die attach materials is discussed in Section IV. 

A U.S. military hybrid specification (MIL-A-87172 of MIL-STD-883) established the selection and qualification requirements for polymeric adhesives used in military hybrid circuits and is used as a guide for die attach materials for nonmilitary applications as well. 

Nguyen, M. N., Low Stress Silver-Glass Die Attach Material,/ EE Trans. Components, Hybrids, andMfg. Tech., 13(3) (Sep. 1990)... 

X-ray imaging of electronic assemblies can check for voids in the die-attach material to the substrate or to substrate-attach material to the package. There is no need to apply power to the DUT nor measure any electrical parameter. Devices may be potted or hermetically sealed for this test. 

If the thermal test chip were the same size as the actual active device and mounted in the test assembly with the same die-attach material, then the thermal resistance of the test assembly would be the same as the actual assembly. However, the chances of the thermal test die being the same size as the actual die are remote. Therefore, to find the thermal resistance for the actual assembly, the thermal resistance of the die (0oie) arid the die attach ( Die Att) need to be scaled. The equation for the die thermal resistance is... 

For some special applications conductivity may be more important than resistivity, as is the case with conductive adhesives. The conductance of a polymer is the reciprocal of its resistance and likewise its conductivity is the reciprocal of its resistivity. The units of specific conductivity are mhos per centimetre or Siemens per metre. As polymers are normally good insulators, conductivity is imparted by the incorporation of finely divided metals such as silver, gold and copper. Conductive polymers find important uses as electromagnetic and radio frequency shielding, as well as die attach materials for semiconductors. 

Metallic fillers can impart special properties to an epoxide formulation, such as giving response to magnetic fields and providing a radiation shielding capability. They are also used to enhance properties such as thermal conductivity and electrical conductivity and it is this last feature that makes them so useful in the electronics industry, where they find wide use in die attach materials. The principal metals used for enhancing electrical conductivity are silver, copper and gold, although various metal alloys such as silver/palladium have also been utilised. 

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