Solder plating

The Fe, Co, and Ni deposits are extremely fine grained at high current density and pH. Electroless nickel, cobalt, and nickel—cobalt alloy plating from fluoroborate-containing baths yields a deposit of superior corrosion resistance, low stress, and excellent hardenabiUty (114). Lead is plated alone or ia combination with tin, iadium, and antimony (115). Sound iasulators are made as lead—plastic laminates by electrolyticaHy coating Pb from a fluoroborate bath to 0.5 mm on a copper-coated nylon or polypropylene film (116) (see Insulation, acoustic). Steel plates can be simultaneously electrocoated with lead and poly(tetrafluoroethylene) (117). Solder is plated ia solutioas containing Pb(Bp4)2 and Sn(Bp4)2 thus the lustrous solder-plated object is coated with a Pb—Sn alloy (118). 

Often, a reed switch has to be soldered or welded. Reed switches are usually plated with suitable solderable plating. Welding is also quite easy on the nickel/iron leads of the reed switch. However, both, if not carried out properly, can cause stress, cracking, chipping or a rupture in the reed switch. When soldering or welding, it is best to keep as far away from the glass seal as possible. This may,... 

Tests were also made on copper which had been fusion solder plated, zinc plated, or nickel plated. None of these showed good initial adhesion. 

PGA packages contain vertical solder-plated or gold-plated Kovar (a registered trade name of Carpenter Technology Corp.) leads on the bottom of a ceramic or plastic package (Fig. 1.11). Several rows of pins may emanate from the bottom perimeter of the package or there may be a full array of pins throughout the area. 

Lead has been used as solder and for solder plating. In the past, the most frequently used solder was a tin-lead alloy. However, the movement for lead free solder has accelerated the development of substitutes. Concretely speaking, Sn-Ag-Bi-Cu, Sn-Ag-Cu, Sn-Ag, Sn-Bi, Sn-Ag-In, Sn-Ag-Bi, etc. can be mentioned. 

In fabrication of printed circuit boards (Goh 1994), a resin formula is prepared and impregnated with fibreglass and other particles. This is baked to form a panel or a board. Lamination involves metallic copper being bonded to the board in (sandwiched) layers. Each side of the laminate is cleaned, photoprinted and etched to form the electrical circuits. Solder plating is done, and the boards are drilled and cut to the required sizes. Finally, the boards are marked and tested. 

Flip-chip technology, as shown in Fig. 11.14, is similar to TAB technology in that successive metal layers are deposited on the wafer, ending up with solder-plated bumps over the device contacts. One possible configuration utilizes an alloy of nickel and aluminum as an interface to the aluminum bonding pads. A thin film of pure nickel is plated over the Ni/Al, followed by copper and solder. The copper is plated to a thickness of about 0.0005 in., and the solder is plated to about 0.003 in. The solder is then reflowed to form a hemispherical bump. The devices are then mounted to the substrate face down by reflow solder methods. During reflow, the face of the device is prevented from contacting the substrate metallization by the copper bump. This process is sometimes referred to as the controlled collapse process. 

Through hole Also a plate through hole (PTH). A hole in a substrate that extends completely through a substrate, is solder plated, and is intended for a component lead. 

When plated, solder has a uniform matte finish. The deposit should be smooth to the touch. A coarse, crystaUine deposit usually indicates the need for additives or peptone or a current density that is too high. Peeling from copper is generally related to the procedure. The fluoboric acid predip should not be used as a holding tank (for more than 5 min.) prior to solder plating. 

Rothschild, B.F., Solder Plating of Printed Wiring Systems, Proceedings of the Printed Circuit Plating Symposium, California Circuits Association, November 5-6,1969, pp. 10-21, and November 12-13, 1968, pp. 61-65. 

Residue on solder plate, holes, and traces. These may be caused by etchant solution imbalance or by spent finisher. 

Salt crystallization. Salts crystallize on the board and cause streaks, damage the solder plate, and plug the spray nozzles or filters. When copper content is high, blue salts may precipitate. 

White films on solder surface. This may oceur normally or when the lead content in the solder plate is too high. 

Black film on solder. This condition can result when the solder alloy is high in tin. If solder reflow or component soldering is to follow, activate by tin immersion or with solder brighteners. Adjust phosphoric acad content in etchant and solder-plating conditions. 

Solder attack. The protective value of solder depends on the formation of insoluble compounds on the surface. Solder is attacked if the sulfate content of the bath becomes very low or contains chloride or nitrates. The solder plate composition can also cause etchant attack. When the lead content becomes low, the sulfate film protection is lowered, and protection is lost. 

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. 

Electro- and electroless plating of tin, nickel, gold, and solder are common surface treatments for flexible circuits. Solder plating by a hot-air leveler could be a low-cost solution. However, it entails severe high-temperature process conditions, and the poor uniformity of the solder is not acceptable for several applications. 

Although solder fusing (Figs. 64.4 and 64.5) is not a new technology for making connections for flex circuits, it is still a low-cost and reliable solution for multi trace connections.There has also been remarkable progress in fine-pitch capability. The newest applicator, coupled with well-controlled solder plating on fine traces of flex circuits, can provide a 150 /mi pitch connection... 

Aluminum 11 00, 3003, and clad alloys Bare of chromate-type film treatment Low electrical resistance Tin lead (solder) plate or tinplate preferred... 

Copper, copper alloys Bare, tinplate or tin lead (solder) plate preferred Cadmium or gold plate... 

Displacement plating When an ion in a solution has a smaller negative electrochemical potential than the atom of the solid and spontaneously displaces the atom of the solid and deposits on the solid. Examples Au (+ 1.50volts) plating onto Cu (+0.52 volts) Pb (-0.126 volts) or Sn (—0.136 volts) (from solder) plating on A1 (—1.67 volts). Also called Immersion plating. See also Electrochemical series. 

Association of Connecting Electronics Industries, IPC-JOStd-006 ICP-J-Std-002, 003 MIL-M-38510 JEDEC J-Std-620A Detailed list of both tin lead and lead-free solders Board and component lead solderability Plating thickness for good component lead solderability Plastic package moisture sensitivity, heat tolerance... 

---