Solder paste

The solder and ahoy market, including low melting or fusible ahoys, is a principal user of indium (see SoLDERS AND BRAZING ALLOYS). The addition of indium results in unique properties of solders such as improved corrosion and fatigue resistance, increased hardness, and compatibhity with gold substrates. To fachitate use in various appHcations, indium and its ahoys can be easily fabricated into wine, ribbon, foil, spheres, preforms, solder paste, and powder. 

Various documents relate to the use of formulations containing trietban olamine as flux for a variety of metals (118,119), for solders (120), for soldering pastes (121,122), and for low corrosion solder pastes (123). 

Ldt-fett, n. soldering paste, -flamme, /. blowpipe flame. -fiussigkeit,/. soldering fluid. 

Use of water-soluble solder pastes and fluxes, in applications where soldering is involved... 

Penreco. [Penreco] Petrolatum, petroleum distillates, or hydrocarboi solvents emoUient, base, carrier, binder, processing aid for rubber, polishes, corrosion pieventatives, lubricants, inks, solder pastes, agric. sprays, fruit and veg. processing, cleaners. 

MAJOR USES Used in the production of paints, pastes, gum, perfume, cleaning compounds, liquid soaps, cosmetics and hydraulic fluids semiconductors removal of greases, inks, solder paste, flux and oils. 

Soft soldering with a lead-tin solder is common. This is usually done with a soldering fluid (a solution of ZnClg in HCl) or soldering paste to deoxidize the junctions. However, a thorough mechanical cleaning of these junctions is also essential. St>ecial solders for aluminum are also conunerdaily available. 

Most IC materials are either solder pastes or silver epoxies. Besides providing an electrical path for a circuit, they can also be used to attach radio frequency shields. 

Solder paste consists of solder powder suspended in a flux. The material is dispensed as a slurry, then heated to its reflow temperature, and finally cooled to create a soHd solder joint. The liquid flux serves multiple purposes ... 

These materials are predominantly used in printed circuit board assembly, and the equipment for their dispensing and reflow is well standardized. Solder paste joints provide excellent electrical and thermal conductivity, and create a strong mechanical bond. 

Silver epoxies consist of silver flakes suspended in an adhesive carrier. The materials are designed so that the silver flakes touch each other when cured and provide an electrically conductive path. Generally, silver epoxies have lower conductivity than solder paste, but usually have the advantage of a reflow temperature lower than the temperature required for solder paste. 

The main advantage of stencil printing over screen printing occurs in applications where very small areas of paste have to be deposited. For components with pitches equal to or smaller than 0.65 mm, the stencil printing process is the only viable way for printing solder paste. Therefore, stencil printing has replaced screen printing in most cases. 

Figure 30 Alternative Principles for Application of Solder Paste, (a) Stencil printing. (i>) Dispensing.

For standard components, an accuracy of 100 /xm is sufficient. Complex components must be placed with an accuracy better than 50 /xm. For special applications, high-precision machines are used with an accuracy of 10 /xm related to a normal distribution and at a standard deviation of 4o-. This means, for example, that only 60 of 1 million components will be outside a range of 10 /rm. Due to the necessity for using a small amount of solder paste with fine-pitch components (down to 200 fxm pitch), minimal vertical bending of the component leads (about 70 /am) causes faulty solder points and requires cost-intensive manual repairs. 

Fine-pitch components must be placed within a close interval to guenantee sufficient contact with the solder paste but avoid deformations of the leads. Adapted driving profiles are necessary to reach the optimal positioning speed with accelerations up to 4 g, but the last millimeters of the placing process must be done under sensor control to take the positioning power down to a few newtons. 

Several optical inspection systems are available that measure, for example, shape and height of the applied solder paste or placement positions of components. These systems, based on image... 

Conventional printing processes are less useful for applying conductive adhesives or solder paste. Dispensing of single dots in a complex geometric application is therefore necessary. Three-dimensional circuit carriers also decrease the freedom of component placement, which leads to restrictions for placement systems. 

Discrimination, price, 681-682 Diseases, occupational. See also Occupational safety and health definition of, 1168-1170 descriptions of, 1167, 1169-1170 statistics related to, 1157, 1173-1174 Dispatching, 1723-1725 basic rules, 1723-1724 composite rules, 1724-1725 first-come-first-served (FCFS), 1511-1513 major activities of, 1770 notation used in modeling of, 1719-1722 rules, dispatching, 1511, 1513 Dispensing (solder paste), 425, 426 Display systems, virtual environment, 2502 Distance, computer screen viewing, 1197 Distance learning, 940 Distributed commerce model, 271-272 Distributed component object model (DCOM), 721... 

Aqueous and semi-aqueous cleaners are used primarily to clean printed-circuit boards prior to assembly, during application of the solder paste and adhesive (if they have been misprinted or smudged), and after assembly and solder reflowing. Highly automated multi-stage cleaning consoles are used in production where the parts are cleaned in a series of baths ending up with one or more deionized water rinses. 

Ultrasonic, spray-under immersion, or centrifugal for solder paste and low... 

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