Adhesive-attached components

For adhesive-attached components or chip devices that are electrically connected by wire, TAB, or ribbon, the leads must first be excised. In the case of solder-connected components, the solder is heated to its melt temperature and wicked off the part. 

Finally, once a failure site or failure mode had been found, a mechanism based on knowledge of electrical, chemical, and physical reactions can be postulated, simulated, and verified and corrective action taken. Figure 6.1 is a flow diagram of some tests used in a PoF study for electronic modules containing adhesive-attached components. 

Figure 6.1 Flow diagram for PoF of electronic modules containing adhesive-attached components.

Sterilization. All devices implanted in the body or that come into contact with body fluids or blood must be sterilized and be resistant to the sterilization conditions. Adhesive-bonded parts are not used in direct contact with the body fluids. They are generally part of an electronic module that is hermetically sealed or otherwise encapsulated or shielded. However, the sterilization conditions for the module must not degrade the internal adhesive-attached components. Some adhesives such as cyanoacrylates andUV-cured acrylics degrade at the elevated temperatures and high humidity... 

Table 2 Examples for microengineered surfaces for a spatially controlled cell attachment that use proteins as adhesion-mediating component...

Although the detailed nature of the surface of costal strips is not known, evidence from binding studies indicate that cations such as Co and Fe + are preferentially adsorbed onto these structures (9). Similar interactions have been shown with organic and colloidal materials (9). For example, phospholipid vesicles were shown to be closely attached to the surfaces of costal rods incubated in aqueous dispersions of phosphatidylcholine for 24 hr. Similar observations were made for costal rods incubated in solutions of colloidal silica. These results indicate that a range of interactions can take place on the surface of biogenic silica and such events may serve important functional roles, such as inhibition of dissolution and adhesion of components in the construction of microscopic structures. 

Difficulty in applying adhesive to attach components smaller than 120 x 60 mils (1206 part types)... 

It should be noted that in using MIL-HBK-217, the rehability predictions are based on empirical data for different component types and do not necessarily take into account the rehabihty of adhesive attached and interconnected components. The effect of the adhesive and its various possible failure modes and mechanisms on the reliability of devices under both operating conditions and long-term accelerated conditions should be considered a part of the equation. 

When exposed to the wave, the adhesive-attached surface-mount devices pick up solder on their metal contacts and the solder bridges from the contact to its corresponding bonding pad on the bottom side of the PWB. In the case of solder-tail components, the molten solder is drawn by capillary action between the lead and the FTH barrel. If the barrel and lead are hot enough and well fluxed, the solder fills up the barrel and wick to form aiets from pin to barrel. As the board continues past the wave, it cools, solder sohdifies, and joint formation is complete. 

FIGURE 32.2 Focal adhesion schematic. The diagram illustrates the components of the focal adhesion attaching an adherent cell to an ECM substratum. Note the continuum of functional connections between the ECM and the cytoskeleton, bridged by both integrin and nonintegrin transmembrane receptors. 

Conductive Adhesives. Isotropically electrically conductive adhesives (ICAs) are widely used in the electronics industry when high-temperature soldering processes are unsuitable. Typical applications include silicon die attachment, component attachment in multi-chip modules (MCMs), surface mounted printed circuit board repair, and elec-tromagnetic/radio frequency (EMI/RFI) shielding. 

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