Soldering coating

Tin—2inc coatings (75 wt % tin) have appHcation as a solderable coating for radio, television, and electronic components. They also provide galvanic protection for steel in contact with aluminum. 

Figure 4.18. Schematic sketching the experimental procedure used in 3D mesoscale self-assembly. Molding of a polyurethane prepolymer in a PDMS master generated polyhedra. Lubricant was added to the polyhedra in a water-filled Morton flask the use of liquid solder as a lubricant required the covering of selected faces with solder-coated copper tape. Axial rotation of the flask provided the agitation needed to cause collisions between liquid-coated pieces. The schematic depicts the formation and self-...

This paper studies the effects of the addition of ethylene diamine to the Au-Sn plating solution reported in ref.[7]. The changes in the composition and microstructure of the Au-Sn solder coating produced by pulsed current electrodeposition are noted. The electroplating solution developed for the co-deposition of Au and Sn is slightly acidic so that it can be used in conjunction with alkaline-developable photoresists. 

Lead is plated onto metals such as steel, aluminium and copper to improve their solderability, coating properties and performance [29]. The plating bath usually contains fluoroboric acid and boric acid, whilst materials such as glue, resorcinol, gelatin and sometimes hydroquinone are added to improve deposition. 

Metal ization 75 Electroless Ni/Au 69 Selective lead-free solder coat 46 Immersion silver 29 SMOBC/ organic coat... 

Laser soldering is not prone to solder bridges and if component leads are held down to solder-coated PWB lands, then soldering defects are rare. Perhaps the most common characteristic... 

The use of solder paste is discouraged because blade heatup is fast and may result in explosive solder ball formation from rapidly volatilized paste constituents. Also, the paste is likely to squeeze out from between the component lead and circuit board pad, which can cause the solder to bridge to adjacent conductors. In fact, even with solid solder coatings on the circuit board, bridging can be problematic in hot-bar bonding. This is usually a function of the volume of solder on the pad, the quantity of flux, its degree of activity, and lead-pad pitch. As the... 

Solid solder coatings such as hot air-leveled pads, solder-plated boards, or stenciled solder paste reflowed prior to hot-bar bonding are preferred for this bonding method. 

Generally, the board is preheated on a hot stage beneath the hot-bar, off to the side or even in a box oven prior to soldering. Sometimes hot air is used for preheating. This step is generally done after flux apphcation, so the thermal profile has to be adjusted to prevent flux dry-out. Once component leads are ahgned with solder-coated PWB pads, the hot-bar is pressed against... 

Hot-bar blade Component lead Thermocouple bead Solder-coated bonding pad... 

Solder can be applied to the board as a paste, solid pre-form, or solder-coated pad. In all cases, the component must be held down during the soldering process to ensure contact of component leads with bonding pads. Proper gas pressure, temperature, nozzle translation speed, and flux are required to effect joint formation. Otherwise, the same reflow considerations are required for this technique as for any other. Heating ramp rate, solder paste preheating, peak temperature, liquidus duration, etc., must be observed for successful joint formation and joint reliability considerations. 

The Pb of Sn-Pb solder-coated barrels is known to reduce the force required for press-fit connector insertion and seating. Although Sn-Pb coating is one of the best surface finishes for pressing, if it is thick, then the press-fit connector pin may skive a thin shver of solder and push it out the secondary side of the PWB (see Fig. 49.8). Very often these slivers... 

Dewetting is a condition that results when molten solder coats a surface and then recedes to leave irregularly shaped mounds of solder that are separated by areas that are covered with a... 

Several solderable and protective finishes along with their thickness as specified by MIL-STD 1276D are listed in Table 5 [5,40]. One of the most commonly used solderable-plus-protective layer combinations is Ni and Au. The likelihood of Au embrittling Pb n solder joints is reduced by a hot-solder dipping operation that replaces the Au with a Pb-Sn finish [41,42]. Copper is a frequently used solderable coating it is often coated with a Pb n or Sn protective finish (electroplated, plated and fused, or hot-solder dipped). Other protective layers include... 

Peripherally leaded, surface mount packages use lead materials of Cu or an Fe-Ni alloy with a Ni solderable finish and an electroplated Pb n or Sn protective layer. Leadless chip devices have terminations comprised of a fired-on Ag thick film conductor that is overplated with a Ni or Cu solderable coating, followed with an electroplated Pb-Sn protective finish. Leadless ceramic chip components (LCCC) use castellated terminations with a thick-fihn Au finish. 

As the migration toward lead-free microelectronic assembhes moves forward, there will be a hybrid transition period. Some surface-mount-component lead frame terminations will be plated with Sn Pb solder coatings. The nominal lead (Pb) content in a typical solder joint depending on the plating thickness for Sn Pb solder compositions is given in Fig. 2. The effect of intentionally adding 3% and 6% Pb on the melting characteristics of several Sn Ag Bi-based alloys, on Sn-... 

Rice, L. Roberti, A. Corrosion-protective solder coating. IBM Tech. Dis. Bull. April 1984, 26 (11), 6092. 

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