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Soldering Wetting

The BLM layer uses a glue layer of chromium or titanium. These metals stick well to other metals and most dielectrics, but they are not solderable. Copper, nickel, and silver have been used as the solder-wetting layer for BLM in appHcations involving 95% lead—5% tin solders. Gold is commonly used as the oxidation layer on account of its resistance to oxidation and its excellent solderabiUty. [Pg.530]

In the case of so-called active soldering an active solder is used a metallic solder containing interface active additives which make certain that the molten solder wets the ceramics. An example of such a solder is a silver / copper alloy with a titanium or titanium / indium additive which can be used when soldering zirconium (IV) oxide to certain steels, aluminium oxide to nickel / cobalt or iron / nickel alloys and aluminium oxide to a iron / nickel / cobalt alloy. [Pg.287]

The lack of a tme thickness measnrement control is a key issue to OEMs that require control metrics. If the OSP coating is too thin, the PCBs will have inadequate protection. If the coating is too thick, there is a possibility for poor solder wetting and poor PTH filling. The OSP coating is invisible to the eye, so there is no way to inspect for unprotected copper if the OSP coating was not applied correctly. [Pg.759]

Solder wetting to joining surfaces and intermetallic formation... [Pg.1032]

FIGURE 44.2 Solder fillet formation (a) Cross-section of an SMT solder joint (b) a PTH solder joint in cross-section. In the case of the SMT solder joint, solder has wet to the pad and lead. The low wetting angles and good fillet formations are indications of good solder wetting. The PTH solder joint shows good fillet formation on the secondary side of the PWB. At the top, the primary side, the fillets are not as well formed, probably due to lower temperature at the top side of the board. (Courtesy of Hewlett-Packard.)... [Pg.1034]

Tin deposited directly over copper, whether by electrolytic or electroless methods, should be avoided except for low-end/low-cost, short-field-life products. Sn alloys with copper, even at room tenqjerature, form a brittle intermetaUic compound, albeit slowly. It has limited solderable shelf-Ufe at room tenqjerature and the Sn-Cu intermetaUic can inhibit soldering and may result in incomplete solder wetting or solder joints of inferior strength. For tin to be used effectively, an appropriate non-porous barrier metal, such as Ni, should be deposited between the Cu and the Sn. Immersion Sn can be plated only as a very thin layer since its deposition is by a self-limiting replacement reaction. When there is no more exposed Cu on the surface of the PWB during the surface-plating operation, Sn deposition wUl cease.Therefore, it is impossible to plate enough Sn by tins method to extend the solderable sheU-hfe or reduce the brittleness of the solder joint. [Pg.1052]

Fluxes are typically composed of acids and high molecular weight materials that are slow to dry, slow to evaporate, and slow to decompose. They are often so acidic that they can etch, dissolve, or disrupt oxides and tarnishes on solder and surfaces to be joined. Both the absence and presence of liquid flux have an effect on the extent of solder wetting. Some fluxes can transition from a runny hquid during preheat to a viscous liquid or gel and ultimately to a gummy sohd as it dries out, polymerizes, and decomposes during the soldering cycle. [Pg.1057]

Area-array devices have one thing in common their solder joints are hidden by the package body and it is impossible to repair an isolated open solder joint beneath the package. Nitrogen provides added insurance that best solder wetting will result if soldering conditions and materials are process-appropriate. [Pg.1068]

Thermal Soak. During this step, the solder, board, and components are further heated. The flux from the solder paste flows onto all metal surfaces in which it is in contact, continnes to react away surface oxides, and also acts as a barrier to prevent oxidation. The soak is designed to provide the requisite time and thermal energy for the flux s prolonged chemical reaction with oxides and tarnishes on metal surfaces and the solder. Were the flux to activate fully too early in the process, it could dry out or be spent too soon. If its potency is lost, fluxed metal surfaces will reoxidize in the critical moments before the onset of solder hquidus, and solder wetting (alloying) would be inhibited. [Pg.1085]

Onset of Solder Liquidus. In this step, the solder undergoes a phase change from solid to hquid.The Uquid metal solder wets onto fluxed metallic surfaces and flows along the component lead-to-PWB pad interfaces drawn by surface tension, capillary forces, and convective flows within the Uquid metal. This is the essence of soldering and effective solder-joint formation. [Pg.1085]

Hot air solder leveling (HASL) or reflowed tin on copper bond pads possess a thin intermetallic layer between the applied surface finish and the pads. During surface-mount technology (SMT) reflow, the addition of molten solder on top of this preexisting intermetallic layer will further its growth. Therefore, the TAL should be limited to minimize IMC but sufficient for good solder wetting. [Pg.1085]

Many wave designs are available from the various wave-solder machine manufacturers.There are wave machines that provide multiple smaller, turbulent wave(s), which are best for leadless components such as surface-mount passive devices (resistors, capacitors, etc.). Smoother-flowing waves are recommended for components with leads and through holes as well as coarse-pitch surface-mount devices. Wave dynamics are dictated by process values as well as the materials in contact with the wave. As the solder wets to the circuit board materials, solder wetting contact angle and solder viscosity imposes wave peel-off characteristics (see Fig. 47.23). [Pg.1107]

Limit the number or plane attachments Where possible, limit the number of ground or power plane attachments to a PTH barrel. Each attachment point will result in thermal dissipation into the copper plane. This lost heat will detract from the soldering process making the job of pre-heating and solder wetting all the more difficult. [Pg.1111]

EG. Yost, R.R. Rye and J. A. Mann, Solder wetting kinetics in narrow V-grooves, Acta Materialia 45,5337-5345 (1997). [Pg.43]

Fig, 10 Optical photographs of J-lead packages assembled with Sn-Pb solder and four lead-free solders. Note differences in solder wetting angle and appearance. The lead-free eutectic solder (Sn96.2Ag3.5) has the closest appearance to tin-lead solder. [Pg.235]

In those cases in which it is impractical to sustain base metal solderability, a metalhc coating is applied to the base metal. The molten solder wets and spreads over the coating and, ultimately, makes a bond to it. This coating is referred to as the solderable layer. Typically, a protective finish... [Pg.189]

The low surface tension of the Pb-Sn solders provides excellent solderability (wetting, spreading, and capillary flow behaviors) by the molten Pb-Sn solders in surface mount and through-hole interconnections. [Pg.207]


See other pages where Soldering Wetting is mentioned: [Pg.530]    [Pg.270]    [Pg.270]    [Pg.187]    [Pg.254]    [Pg.211]    [Pg.34]    [Pg.757]    [Pg.758]    [Pg.1031]    [Pg.1034]    [Pg.1034]    [Pg.1048]    [Pg.1059]    [Pg.1063]    [Pg.1068]    [Pg.1069]    [Pg.1070]    [Pg.1085]    [Pg.1102]    [Pg.1114]    [Pg.1137]    [Pg.1379]    [Pg.580]    [Pg.9]    [Pg.15]    [Pg.83]    [Pg.84]    [Pg.30]    [Pg.30]    [Pg.32]    [Pg.98]    [Pg.151]   
See also in sourсe #XX -- [ Pg.6 , Pg.7 , Pg.42 , Pg.43 ]




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