Substrate-attach adhesives applications

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. 

Materials are qualihed by passing a series of tests as severe or more severe than those of the intended application. Generally, accelerated environmental and mechanical tests are specihed and performed on actual or simulated parts representative of the hnal product. Since the parts are subjected to accelerated tests, some of which are destructive, qualihcation parts are seldom deliverable items. Once an adhesive and process have been qualihed, no changes in composition or processes are allowed without requalihcation. Testing at levels above the acceptance tests for an extended duration or number of cycles is necessary. The qualihcation tests for some applications, for example, for die and substrate attachment, have been specihed in NASA and MIL specihcations while those for other applications are being developed by industry and industry associations. 

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%. 

Some adhesive materials and processes are used across many applications. For example, adhesives used to attach bare die and substrates in hybrid or multichip modules may be used for a wide variety of ground-based military... 

Flooring adhesives are used for attaching floor coverings to a variety of substrates. The adhesives must develop a strong and durable bond between the floor covering and the substrate. They should not adversely affect coverings, supports and substrates, and after application, should remain odorless and have low emissions. Usually flooring adhesives are applied to the substrate by hand with trowels or sometimes rollers. 

An example of a relatively new application for conductive polymers, which has evolved with the semiconductor industry, is in the so-called die-attach adhesives. These typically epoxide- or polyimide-based materials are used to attach silicon integrated circuits to their substrates and leadframe components, and are often required to be electrically conducting so that the back of the chip is effectively earthed. 

From the above discussion, it is clear that label adhesives have to perform well under a broad range of conditions both during the actual application and after attachment to the substrate. 

Fully Adhered. The substrate, ie, insulation, cover board, etc, that the single-ply membrane is to be attached to is either fully adhered or mechanically fastened to the deck. However, there are also applications where the membrane is adhered direcdy to the deck. The membrane is then adhered to the substrate. The typical method for adhering the membrane to the substrate is by applying a contact adhesive to the membrane and substrate, rolling the membrane into place, and brooming once the adhesive is ready. There are one-sided applications where the membrane is rolled direcdy into the adhesive that has been applied to the substrate only. The membrane used in this application method may be fleece-backed. Fully adhered systems can be installed on any slope. The fully adhered application offers a smooth surface that is easy to maintain and inspect, as well as excellent wind resistance on account of positive attachment. 

The kinetics of the hydrolysis and condensation of organic functional trialkoxy silanes has been reported by Pohl and Osterholtz [17-19]. The silane coupling agents used as adhesion promoters [1-3] usually have a trialkoxy silane as one of the functional groups, i.e. (MeO)3Si—(CH,),—0,CC(Me)=CH2. If this attaches to a glass substrate, it will form Si—O—Si bonds or if it attaches to metal substrates, it can form M—O—Si bonds. Thus, the work described here can be applicable to providing additional understanding for those processes. 

What is accomplished by adhesion promotion treatments in IC manufacturing should actually be referred to as wafer substrate preparation, and not adhesion. Adhesion in the structural sense, as experienced in airplane composite material parts attachment, is not accomplished by silane wafer processing treatments except for the PI applications discussed early in this paper. The term adhesion, as it is used here, refers to a more practical definition—that is, resist image adhesion. Nevertheless, this type of adhesion is essential to the huge international semiconductor business, and the early silane work of Plueddemann and others was essential to early wafer adhesion process development. 

The main use of adhesives in labelling applications is in the form of pressure-sensitives, i.e., sticky labels attached either directly or indirectly (behind a potential barrier layer) to a foodstuff. Pressure-sensitive adhesives are a distinct category of adhesives that in dry form are permanently tacky at room temperature. These adhesives will adhere to a variety of substrates when applied with pressure they do not require activation by water, heat or solvents and they have sufficient cohesive strength to be handled with the fingers or by mechanical means in labelling stations. 

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