Soldering success in all these environments depends on three factors - the solder and flux used, the soldering techniques, and the soldering tools or equipment utilised for the operation. Removal and replacement of Ball Grid Array (BGA) and SMT components in a rework or service environment must be done manually; this is a demanding operation with scope for many types of error if not performed correctly. For example if an IC is heated excessively, the IC itself, the PCB or neighbouring components can be damaged. Alternatively, if an IC is not sufficiently heated, and the solder fully melted before removal, pulling the IC up may tear some of the pads from the PCB, causing possibly irreparable damage. For this reason, rework stations need accurate heating profiles to allow successful BGA/SMT removal and replacement. These profiles approximate to those used in reflow ovens.

Soldering irons are available as standalone tools like the example in Fig. 4 that can be plugged into a mains supply, or they may be part of a soldering workstation that feeds the iron at a low voltage and provides a means of setting and displaying the operating temperature. If the station is described as not requiring calibration, this means that the actual tip temperature can always be expected to correspond closely with the displayed temperature to within a tight tolerance. This is important if the soldering station is to be used within an organisation contracted to work to IPC standards. Below, we describe the soldering issues you should consider, whether you are a hobbyist or a technician working in a service or manufacturing environment. We discuss the constituents of solder and their impact on soldering; this includes lead-free solder, which must now be used on most applications. We then look at the techniques essential for successful soldering, and finish by discussing the soldering tools available – from simple soldering irons to small, manually-operated soldering ovens. Solders and fluxes Inevitably some boards going through a production process will need to be reworked, due to faulty components, wrong components used, or modifications for other reasons. This task will be handled by a technician at a rework station, which will include desoldering as well as soldering capability, and possibly also fume extraction. Rework stations are also used by technicians in service centres to handle equipment returned for repair or upgrade. Using rework stations has become more challenging with the advent of complex SMT devices and lead-free solder. HARIMA’s 90iSC alloy was designed for applications and markets where extreme temperature resistance and reliability are non-negotiable and lead-free compliance is required. When traditional SAC alloys can’t deliver safety-critical performance, HARIMA’s 90iSC alloy is the answer. Tough, durable, adaptable, and high-temperature capable, 90iSC alloy is the lead-free benchmark for high reliability applications. 90iSC alloy has the ability to provide high creep and strain resistance within operating temperatures up to 150°C.We have seen how the right solder alloys and fluxes, and the right soldering techniques contribute to the quality of soldered joints. However solder joint quality depends also on using the most suitable and best-available soldering equipment; accordingly, we finish our look at soldering with a review of the soldering equipment currently on offer. A far more serious problem with tin/lead soldering alloys is their use of lead; this has high toxicity, coupled with a tendency to leach into the environment from PCB assemblies. As a result, lead-based solders are among the hazardous materials identified for restriction or banning by the European Union’s Restriction of Hazardous Substances Directive ( RoHS) and Waste Electrical and Electronic Equipment Directive (WEEE), which took effect in July 2006. These are required to be enforced and become law in each member state. Harima is a market leader in solder materials innovation, with a complete portfolio of MULTiCORE brand solder solutions that lowers overall cost and increases reliability. Our solder product range includes room temperature stable solder pastes as well as 90ISC high reliability solder paste which adds value to electronics assemblies. Our product range also includes solder wires, liquid fluxes, and solder rework materials.

Never heat the solder wire directly. Instead, heat the wire or terminal to be soldered to the correct working temperature, then introduce the solder. This melts and flows into the joint. After finishing soldering, carefully remove the soldering iron to leave a clean, smooth soldered joint. This is particularly important when using soldering guns – keep the power triggered on until the soldering tip is well away from the joint, to avoid leaving solder residues on the tip. To extend a solder tip’s life for as long as possible, tin it before returning to storage. Acceptability requirements for soldering are covered in the IPC Association's IPC-A-610D Section 5. This covers connections of all types, including SMT, through-hole and terminals. It also refers to three classes of equipment and environment, and their demands for soldering quality; Class 1 refers to general electronic products, Class 2 to dedicated service electronic products and Class 3 to high performance electronic products, such as life-support systems or other equipment where performance on demand is critical. Overall, fluxes are subject to the IPC Joint Industry Standard J-STD-004 or equivalent. Soldering techniques For small-scale soldering jobs, an iron of 40 W or less, with a tip of 6.3 mm or 5.0 mm is recommended. For larger-scale electrical soldering tasks and sheet metal working, 120 to 200 W irons with tips up to 20 mm wide are recommended. For service applications, cordless irons that are either battery- or gas-operated have proven to be very effective. For many years the most commonly available solder comprised a tin/lead alloy, with tin concentrations ranging from 5% to 70% by weight. These alloys are still in use today, although as we will see, their use is restricted because of health and safety risks and legislation. The greater the tin concentration, the greater the solder’s tensile and shear strengths. All alloys are solid at 183°C, but their melting points vary with their tin/lead ratio. 60/40 tin/lead alloys, for example, become liquid at 188°C, and are accordingly said to have a plastic range of 5°C. Their consistency is pasty within this plastic range.To ensure a perfect soldered connection, all grease, corrosion, oxidation or other contaminants must be removed from the joints with isopropyl alcohol before soldering as shown in Fig.3. A sound mechanical connection is also required. Accordingly, twist the stranded wire and wrap it around a terminal. Otherwise, thread the wire first through a hole in the soldering lug or board. Bend wire in soldering lugs by approximately 90° and in boards by approximately 45°. The soldering joint should be a minimum of 1.6 mm from the components so that the latter are not damaged by the effects of the heat. The weak point of a copper wire is the point where the wire emerges from the soldered joint. Therefore, after soldering is completed, the wire must not be bent upwards. Soldering using lead-free soldering wire presents some special challenges, as previously mentioned, because of the higher melting temperature of lead-free soldering alloys such as Sn/Cu/Ag and Sn/Cu, which are 30 to 40°C higher than leaded solder. As a result, lead free hand soldering requires stable dynamic temperatures. To achieve this, soldering irons must have more power and an efficient method of transferring thermal energy to the soldering iron tip. Attempting to overcome the heating problems by running lower-power soldering irons at higher temperatures to increase the heat energy in the tip are unsatisfactory.