Solder electronic applications

Recently commercially available X-ray systems for laminography have a spatial resolution limited to hundred microns, which is not enough for modem multilayer electronic devices and assembles. Modem PCBs, flip-chips, BGA-connections etc. can contain contacts and soldering points of 10 to 20 microns. The classical approach for industrial laminography in electronic applications is shown in Fig.2. 

Tin. Application of tin on strip steel for can stock has decreased. Nevertheless, tin plating is still done in large volume, and tin plate for can stock was estimated at 11,750 t in 1990 (11). Additionally, 603 t of tin anodes were used for electroplating in electronic applications in the United States in 1990. The use of tin in solder manufacture is reported to exceed that used in can stock (12). The cost of tin in early 1993 was 7.50/kg (see Tin and tin alloys). 

Traditionally, the soldering iron was used to connect electronic components to circuit boards. The most common iron used in electronic applications is one with a narrow tip rated at 15 to 20 watts. Generally, the component was heated with the iron, then rosin-core solder (not acid-core) was applied to the component. The solder melted and, flowing into the joint, joined the component to the circuit board. 

In electronic applications, wires are commonly stripped by heat and soldered for hookup of circuits. Fluoropolymer insulation is subjected to heat and decomposition occurs. It is important to remove the fumes by local ventilation to avoid exposure to gases. 

In contrast to soldering, conductive adhesives are used for special electronic applications. Conductive adhesives simultaneously establish mechanical and electrical joints between PCBs and components by means of a particle-filled resin matrix. Whereas the polymer matrix is responsible for the mechanical interconnection, the fiUing particles (silver, palladium, or gold particles) provide the electrical contact between PCB and component. Therefore, in contrast to solder joints, conductive adhesive joints have a heterogeneous structure. 

Adhesion to metal is sometimes difficult to achieve. However, due to the development of adhesion promoters industrial applications on metal exist. Electronics applications are important photoresists (both wet and dry film), solder masks, potting compounds, and conformal coatings are products based on UV-curable materials. 

So far the retention or stabilisation of polymer characteristics has been discussed. The last part is functional additives in polymer electronics. In electronics applications, polymer tends to have contact with metals because metals are used as conductors, solder, springs, screws and other small parts. If the polymer is in contact with metals, especially transition metals, the degradation of polymer is accelerated. In that case, metal deactivation provides the solution. 

These unique combinations of transparency, hydrolytic, and heat resistance of polysulfones would be lost if other polymers are blended. Hence, there has been very little commercial incentive for blends of polysulfone. Nevertheless, in the early days of polysulfone commercialization, some blends with ABS and PET were developed primarily to lower the cost but also to improve selected properties such as plateability or chemical resistance. A PSU/ABS blend (Mindel A) was commercially offered for some time but is now no longer available. Additives such as phenoxy resins, styrene-maleic anhydride copolymers have been claimed to improve the compatibility and weld-line strength of the PSU/ABS blends (Robeson 1985). The blend was evaluated for selected appliance, plumbing, and sterilizable equipment plated parts. This blend lacked the heat resistance needed for the vapor phase solderability in electronic applications. 

Lowest melting (Eutectic) solder fa- electronic applications... 

However, conductive adhesive technology is still in its infancy, and concerns and limitations do exist. The main limitations of commercial ICAs include lower conductivity than that of solder materials, an unstable contact resistance with nonnoble metal finished components, and poor impact performance. The electrical conductivity ( 10 S2 cm ) of an ICA is lower than Sn-Pb solders ( 10 cm ). Although generally adequate for most electronics applications,... 

Electroless nickel coatings can be easily soldered and are used in electronic applications to facilitate soldering of light metals such as aluminum. Electroless nickel is often used as a barrier coating to be effective, the deposit must be free of pores and defects. In the as-deposited amorphous state, the coating corrosion resistance is excellent (Table 12), and in many environments is superior to that of pure nickel or chromium alloys. However, after heat treatment the corrosion resistance can deteriorate. 

In addition to wire harness connectors, printed circuit board-attached connectors, for automotive or electronic applications, also benefit from many of SPS s performance characteristics, including low viscosity, which helps to fill thin walls and heat resistance to maintain dimensional stability through lead-free reflow soldering operations (see Table 15.2). The trend toward miniaturization in automotive electronic control modules has increased the need for compact surface mount connector technology, as opposed to bulkier through-hole and wave-soldered alternatives. 

The primary uses for nickel are as an additive to make stainless steel, cupronickel and nickel-iron alloys, for electroplating other metals, and in batteries. Electronic applications include alloys with iron (42% nickel) that are used as leadframe material in ceramic packages for semiconductors, and as plating on component leads (terminations). Nickel is often plated onto copper to prevent copper from leaching into gold plating or melted solder. 

The National Center for Manufacturing Sciences (NCMS) backed by a consortium of North American industrial corporations, national laboratories, and academic institutions conducted an evaluation of alternatives to eutectic Sn-Pb solder between 1992 and 1996. Corporate participants included ATT-Lucent, Ford Motor Company, GM-Delco Electronics, GM-Hughes Aircraft, Hamilton Standard, National Institute for Standards and Technology (NIST), Rensse-lear Polytechnic Institute, Rockwell International, Sandia National Laboratories, Texas Instruments, and the U.S. Navy s Electronics Manufacturing Productivity Facility. The goal of the project was to determine whether safe, cost-effective, nontoxic, reliable lead solder alternatives could be identified. With over 79 alloys examined, the study results indicated that while a number of possible lead-free solders were functionally possible, there was no universal drop-in replacement for lead-based solders in electronics applications. This study is discussed in detail in Chap. 17. 

There is a substantial history of eutectic Bi-Sn solder utilization for electronic applications where low-temperature soldering is required [25,30]. However, when decreasing the soldering temperature, there is often an adverse impact on flux activation, which results in changing the wetting... 

Several electronic applications of Sn-5Sb solder have been reported the creation of hermetic seals in multichip modules, bonding a semiconductor device onto a substrate [64], and attachment of I/O pins to multilayer ceramic substrates [65]. The braze alloy, Au-20Sn, used to attach I/O pins to ceramic chip carriers was replaced by Sn-5Sb solder. The replacement provided several... 

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