Wire bonding melting

Temperature Compatibility. If pin-in-paste soldering is to be used, check that components are temperature-compatible with the oven reflow process. The high temperatures and long exposures associated with oven reflow soldering may cause unsuited molded component bodies to melt or warp. Connector contact normal force may be affected if the molded connector body softens or distorts. Solder joints or wire bonds internal to some devices may become disbanded, and some, such as electrolytic capacitors, may leak or even explode as a result of an oven reflow cycle. Check the component manufacturer s specification for thermal hmits and compatibihty with oven reflow soldering. 

Polyphenylene sulphide has been used commercially to encapsulate ceramic capacitors for several years and mica capacitors encapsulated in Phillips Ryton BR61B have recently received the British Standard 9000 approval (BS9070-N-002). More recently, attempts have been made to encapsulate wire-bonded integrated circuits, which is one of the most difficult applications to successfully mould with a thermoplastic material because of problems with wire-bond sweep. By paying particular attention to the melt viscosity of the PPS and having careful control of the moulding parameters it has been shown that it is possible to mould successfully both TTL and linear operational amplifier type devices. 

Metallic solids Recall from Chapter 8 that metallic solids consist of positive metal ions surrounded by a sea of mobile electrons. The strength of the metallic bonds between cations and electrons varies among metals and accounts for their wide range of physical properties. For example, tin melts at 232°C, but nickel melts at 1455°C. The mobile electrons make metals malleable—easily hammered into shapes—and ductile—easily drawn into wires. When force is applied to a metal, the electrons shift and thereby keep the metal ions bonded in their new positions. Read Everyday Chemistry at the end of the chapter to learn about shape-memory metals. Mobile electrons make metals good conductors of heat and electricity. Power lines carry electricity from power plants to homes and businesses and to the electric train shown in Figure 13-21a. 

Polymers with crosslinked structures. They cannot melt under heat supply, since their individual chain segments are strongly chemically bonded (as, e.g., a wire mesh welded at the crossings). In Figure 3.5 such crosslink points are indicated by black dots. They are called thermoset materials. In contrast to most thermoplastics, they are also insoluble in organic solvents. 

Metals represent another type of atomic solid. Metals have familiar physical properties they can be pulled into wires, they can be hammered into sheets, and they are efficient conductors of heat and electricity. However, although the shapes of most pure metals can be changed relatively easily, metals are also durable and have high melting points. These facts indicate that it is difficult to separate metal atoms but relatively easy to slide them past each other. In other words, the bonding in most metals is strong but nondirectional. 

Chem. Descrip. High m.w. polyamide/polyester copolymers Uses Hot-melt adhesive for extrusion of fusible film, monofilament, netting, web, and multifilament, for thin film fusible coatings, for applic. by disp. techniques used in textile industry, adhesive for fusion bonding of textiles, leather, wood, glass, and metals, and misc. applies, incl. automotive interiors, belts, color cones., hats, hose construction, rainwear, shoes, television tubes, wire coating, etc. 

---