Soldering is one of the most crucial parts of the production process for a lot of electronic devices. In this article, Sourabh Tiwari, sales manager, Weller, shows us how soldering has evolved over the years in tandem with a world full of ever-changing technologies
There are very few things in life that remain constant across generations. Technology, in spite of its constant development, stays on as a companion for the betterment of mankind. Soldering is the oldest joining technology known to man. The first interconnection based on metal diffusion can be traced back to prehistoric times, as per several archaeological excavations. Soldering technology is hinted at in literature dating back to 2350 BC. Even though the materials used for soldering have changed over time, the technology of joining two metal items has remained the same for centuries.
In the PCB manufacturing industry, this technology plays a vital role. This is because a quality solder joint enables a strong electrical bond and long life of the mechanical connection. Besides, being non-corrosive under normal environmental conditions as well as having shock-proof properties makes soldering the only joining technology that meets diverse requirements.
Venturing into the vast field of R&D and PCB repair, hand soldering is one of the most sought after activities. As the name suggests, it is nothing but manual soldering, which is different from wave soldering or the soldering done by reflow machines. The primary importance of hand soldering is that it can be used for areas and applications for which automatic machines are of no use. Besides, there are several IC packages which need different temperatures and varied fluxes for them to be soldered properly.
As far as desoldering is concerned, it is done by either using hot air or through the use of preheated plates. Both the procedures need a very precise temperature and timing for the clean removal of the IC without disturbing the PCB tracks. The world has moved on from conventional desoldering systems to rework stations, which have proved to be a very optimised solution for the PCB industry. These rework stations come in the form of complete benchtop solutions for R&D units, which can also be used for repairs.
With the world adopting more of surface-mount components rather than through-hole components, a precise rework station is the need of the hour for taking care of all types of SMT repairs. For instance, a huge multi-leg IC requires not only the right parameters but also the right tools for an optimum result after the repair is done. These tools have actually revolutionised hand soldering.
There are five main parameters on which the hand soldering process is based:
1) Process temperature
2) Process time
3) Kinds of flux
4) Solderability
5) Solder alloy
The process temperature should be sufficient for the soldering tip to heat up the solder joint quickly and wet the surface. It is important to know that the soldering temperature is the temperature of the tin while soldering. For every type of IC package, care must be taken not to let the soldering time and the soldering temperature go beyond the permissible limits.
Flux is used to obtain two major soldering conditions on the PCB board—to remove the oxidation residues and to maintain a good wettable surface. Solderability refers to the suitability of a substrate to be wetted with tin. In other words, it helps in judging whether it is a solderable substance or not. Last but not the least, is the solder alloy, which is being melted to form a solder joint. It may be leaded or lead-free, based on the RoHS compliance requirements.
One needs to have the right technology, in line with the application and usage. We live in a world in which there is a wide range of technologies available in this field. For instance, Weller offers three different technologies. The silver line technology is used for standard SMT and THT packages. It uses a silver core to heat up the tip, and provides high thermal conductivity and heat capacity, which in turn heats up the tip. Power response technology is for heavy mass soldering applications and high quality requirements. It uses the closed loop heating system, where the sensor is placed very near to the tip and offers fast heating and a quick recovery time. Active tip technology offers ultra-precise heating and temperature control, specifically designed for micro soldering applications. Various technologies like these are available in the market these days, thus making soldering jobs easier to handle compared to those done with the use of conventional technologies.
In hand soldering, the basic thumb rule to keep in mind while using a soldering iron is that the temperature should be maintained at the minimum level possible and precise amount of thermal energy should be used while soldering. This allows reflow within a reasonable time, resulting in minimal damage to the component and PCB.
The field of hand soldering is vast and has myriad applications—covering home appliances, industrial and medical electronics and solar. Most of the latest electronic products including smartphones, PDAs, audio and video devices, switches and routers are all made using some form of hand soldering. However, with the advances in technology, the aerospace, defence, security electronics and automotive electronics sectors are evolving as the major users for a wide variety of precise soldering applications. So hand soldering is sure to continue being a part of the ever changing world of technology, ready to evolve as per the changing needs of time.
