Molten Metal
Soldering can be described as gluing with molten metal. Two or more metal objects are joined together by heating them and then applying solder. The solder melts onto the joint (wetting) then, cools and bonds them together.
Flux Can
As technicians know, “flux is your friend” and removes oxides and prevents new build-up. Oxidation occurs when oxygen in the air reacts with the hot metal and forms a covering layer over the metal that keeps solder from sticking.
Flux can -
- Remove greasy dirt, dust and oxidized film
- Prevent re-oxidization
- Help to cause solder wetting
- Decrease solder tension to help solder “wet” to metal
What’s in Flux
When choosing a flux, how and what it will be used on must be considered. Choosing between a low-corrosive or high-corrosive flux is imperative when working with certain applications and metals to be joined. Certain fluxes can be harmful to components and others work best with, for example, chrome-plated or stainless steel components.
Some metals are easier to solder than others and range from excellent to poor, with tin being the easiest to solder and stainless steel the most difficult. Silver, gold, copper, lead and zinc can also be soldered. Depending on the type of flux, joints can be created between metals that would not normally be possible.
As with many areas of manufacturing, fluxes have advanced to meet regulatory requirements. Today you’ll find halogen-free flux, halogen-free solder and solder paste, as well as, some of the support equipment like the Lead Free Compatible Digital Solder Pot with Auto Shutoff Timer by Hakko.
Note: The mixture of heat, solder and flux causes toxic fumes that should be dissipated in some manner. Depending on the job, fume extractors like the Volume Fume Extraction Unit with Pre-HEPA by Hakko, may be a good solution.
Selecting Your Solde
Melting temperatures and solder strength differ as do diameters. Selections should be made depending on the application to avoid over- or under soldering joints.
With the introduction of lead-free solder, manufacturers have created new products to combat some of the problems, i.e., decreased flow ability, higher melting temperatures and shorter tip life. Accurate temperature control and thermal recovery rates on soldering irons, as well as, feed systems that reduce solder and flux splash can help.
Bigger is Not Always Better
Many factors can affect the flow of solder including the diameter of the wire. Larger diameter wire, improperly used, can cause uneven flow of flux. Thinner wire is easier to control, however, the time it takes to solder increases. Solder selection should be based on what might be suitable for the number of sections needing to be soldered, the application and the component.
Soldering Iron Selection
Depending on the job, you’ll need to decide on what type of tip, heater and wattage you will need.
Tips
Tips come in all shapes and sizes and should fit the size of what will be soldered. Two choices of tips are available, copper, which can be filed and causes corrosion during soldering, and copper tips plated with iron, which prevent corrosion and increase the life of the tip.
Heater
Generally, there are two types of heaters, Nichrome heaters (20 to 500W) and ceramic heaters. Nichrome heaters have a coil of nichrome wire running through them and tips heat from the outside and have a high melting point (about 1400°C or 2550°F). They don’t oxidize at high temperatures, expand too much while heating and have reasonable resistance.
Ceramic heaters (15 to 60W) contain a tungsten heating element sealed inside and therefore have excellent electrical insulation suitable, for instance, to solder integrated circuits (ICs) and other electronic components. Ceramic heaters cope well with high temperatures and can stand repeated heating and cooling.
Hakko’s ceramic heater soldering iron the Hakko Dash delivers a light weight and compact design, slender handle and reduces the handle-to-tip distance providing less motion for faster soldering.
What Wattage?
Higher wattage can transfer much more heat than a low wattage soldering iron to a metal surface. Depending on what you’re soldering will determine wattage. Keep in mind, soldering irons with higher wattage don’t provide more heat; they just have more power that allows them to heat for a longer time.
When soldering, consider the relative thermal mass of the joint to be soldered. The mass may vary greatly and each joint to be soldered has its own thermal mass. How the combined mass equates with the mass of the iron tip determines the time and temperature rise of the work.
Proper Soldering Can Be Critical
The December 2014 crash of the Indonesia AirAsia plane demonstrates the critical nature soldering can play. Investigators attribute cracked solder joints on a circuit board as the main reason for the crash.
Proper hand soldering can be determined by many aspects, such as, operator training, experience, skill and technique. Additionally, the type of solder used, diameter of solder, wattage, heater, soldering iron, type of flux, as well as, the quality of your equipment. Knowing how each factor works to create well-executed solder joints will help you choose the right products for your applications.