Dip Soldering

Dip soldering is a small-scale soldering process (service) by which electronic components are soldered to a printed circuit board (PCB) to form an electronic assembly. The solder wets to the exposed metallic areas of the board (those not protected with solder mask), creating a reliable mechanical and electrical connection.

Dip Soldering Process

Dip soldering is accomplished by submerging parts to be joined into a molten solder bath. Thus, all components surfaces are coated with filler metal. Solders have low surface tension and high wetting capability. There are many types of solders, each used for different applications:

• Lead–silver is used for strength at higher-than-room temperature.

• Tin–lead is used as a general-purpose solder.

• Tin–zinc is used for aluminium.

• Cadmium–silver is used for strength at high temperatures.

• Zinc–aluminium is used for aluminium and corrosion resistance.

• Tin–silver and tin–bismuth are used for electronics.

Because of the toxicity of lead, lead-free solders are being developed and more widely used. The molten bath can be any suitable filler metal, but the selection is usually confined to the lower melting point elements. The most common dip soldering operations use zinc-aluminum and tin-lead solders.

• Solder pot metal: cast iron or steel, electrically heated.

• Bath temperature: 220 to 260 °C (for binary tin-lead alloys) or 350 to 400 °C (for lead-free alloys).

• Solder composition: 60% Sn, 40% Pb or eutectic alloy.

Wave Soldering

Wave soldering is a bulk soldering process used in the manufacture of printed circuit boards. The circuit board is passed over a pan of molten solder in which a pump produces an upwelling of solder that looks like a standing wave. As the circuit board makes contact with this wave, the components become soldered to the board. Wave soldering is used for both through-hole printed circuit assemblies, and surface mount. In the latter case, the components are glued onto the surface of a printed circuit board (PCB) by placement equipment, before being run through the molten solder wave. Wave soldering is mainly used in soldering of through hole components.

Wave Soldering Process

A simple wave soldering machine.

There are many types of wave solder machines; however, the basic components and principles of these machines are the same. The basic equipment used during the process is a conveyor that moves the PCB through the different zones, a pan of solder used in the soldering process, a pump that produces the actual wave, the sprayer for the flux and the preheating pad. The solder is usually a mixture of metals. A typical leaded solder has the chemical makeup of 50% tin, 49.5% lead, and 0.5% antimony. The Restriction of Hazardous Substances Directive (RoHS) has led to the elimination of leaded solder in modern manufacturing however, and lead-free alternatives are used. Both tin-silver-copper and tin-copper-nickel alloys are commonly used, with one common alloy (SN100C) being 99.25% tin, 0.7% copper, 0.05% nickel and <0.01% germanium.