Have you ever wondered why your department gets through so many soldering tips? Our friends from Rapid have provided this useful guide on how to prolong the life of your soldering tips.
For more information on soldering techniques and general information, please visit the Soldering Guide in the Info Library section.
TOP TIPS for Extending tip life
Solder tip life has long been a contentious subject and it is now exacerbated by the higher temperatures of lead-free soldering. Cooper Tools has prepared a practical guide to help users extend solder tip life, which is summarised in this article.
There are five basic modes of failure for a standard soldering iron tip - Cracking of the tip plating caused by excess pressure; Extreme temperature shock; Wear and abrasion; De-wetting, and Corrosion. This article will look at each of these causes of tip failure and give some guidelines on how you can increase your tip life.
Cracking of the tip plating caused by excess pressure
This is a particular problem with very fine Surface Mount tips. In order to transfer the heat to the joint an inexperienced operator may press too hard onto the joint surface. Alternatively dropping the iron onto a hard surface can cause cracking of the tip plating, even with large tips. This will inevitably mean the tip will deform and bend which in turn will cause the plating layers to exfoliate. Once a fissure is created in the tip surface the copper core is exposed to moisture, oxygen and tin. This mechanical damage will inevitably accelerate the copper erosion failure mode.
- Always choose the correct tip geometry for the job in hand. Only use very fine tips when they are actually required due to the physical constraints of the joint or the access to it. Always use the largest tip that can be used for any given job. Use "Chisel" rather than "Conical" shapes wherever possible. When soldering the leads on a J leg or Gull wing component use a "GW" of tip with a liquid flux.
- Make sure the tip is tinned; use the solder to bridge the gap between the tip and the joint. This greatly increases the surface area over which the heat is transferred and reduces the compulsion to press hard.
- Make sure that the soldering iron support is the correct one for the iron and does not have a damaged or worn funnel. Failure to do this can result in the iron banging against the funnel spring on the support or even being dropped if the iron does not locate correctly into the funnel.
Cracking of the tip plating caused by Extreme Temperature Shock
Lead free applications require higher processing temperatures which means tip plating is exposed to higher surface temperatures. Bringing the hot tip into contact with a cleaning sponge that is too wet can result in an extreme temperature shock which may produce micro cracks in the iron plating layer.
- Do not over wet the cleaning sponge - the sponge should moist not wet. Alternatively a dry tip cleaner could be used.
Wear and Abrasion
Premature tip wear has many causes, most of them preventable by good training. However even under normal use with a well trained operator, all tips will abrade eventually. As the plating layers abrade they expose the copper core and in turn this leads to the corrosion failure mode.
- Excessive wear and abrasion can be caused by untrained operators rubbing the tip on the joint in an attempt to improve heat transfer to the joint. This does not work and the rubbing action can damage the PCB or component and it will abrade the iron layer on the tip. Heat transfer can only be improved by increased contact surface area. Always tin your tip prior to soldering the joint, this will increase the soldering contact area and of course use the correct size tip.
- Incorrect tip cleaning can also increase wear. Always use a genuine, cellulose sponge. Use the sponge the correct way up, i.e. with the orange fibre layer on top. The fibre is less abrasive than the sponge and also acts as a semi-permeable membrane that keeps excess moisture away from the tip. Never use domestic sponges as they are mostly plastic based. When the hot iron heats the plastic it can release chemicals that can corrode the tip. In addition it may release fumes that may be harmful to health.
- Always ensure that the sponges are moist not wet, excess water aids the de-wetting failure mode. Always use De-ionised water, rinse the sponge then squeeze the excess water out. The use of tap water will cause limescale, just like on the element in a kettle. This will in turn cause a non-wetting barrier to be formed on the tip. A recent trend has been for operators to use the water from a "Mineral Water Cooler" because it is close by. This is clearly a bad idea as the Minerals will cause even more excessive limescale build-up.
The de-wetting effect is found when the solder no longer adheres to the working surface of the tip. De-wetting is the most common tip failure mode and can occur because of over intensive tip cleaning, cleaning the tip at the wrong time or on a sponge that is too wet in a lead free application, particularly when using fine solder wire. De-wetting is caused by the outer atoms of the iron layer oxidising. This failure mode has an additional problem in that a de-wetted tip transfers heat less effectively. The good news is that with good practice de-wetting failure can be reduced to reasonable levels.
- The iron layer on the tip cannot oxidise if it is not exposed to oxygen so when the iron is not in use, keep the tip tinned. The solder tinning acts as a sacrificial barrier, only the solder oxidises. Never return an iron you have just cleaned to the iron support. This immediately exposes an unprotected, hot, wet tip to the oxygen, the worst possible scenario. Following this advice alone can have a dramatic effect on tip life.
- A tip will oxidise much more slowly at room temperature, if the iron is not in use, switch it off. If your power supply has a timer set back facility, use it to automatically switch your iron off when it has not been in use for a pre set time. Remember just switching the iron off every break and lunch could account for 5 hours use a week, per iron. Think of all the money you will save on your electricity bill and it will increase tip life.
- The higher the soldering temperature the faster tip oxidation will take place. Reduce soldering temperatures to the minimum required to do the job. If you find that you are soldering at over 375°C (700F) to keep throughput up, then you may be using the wrong iron.
- Check that the springs on your soldering iron supports are not worn. As the springs wear they will droop, this may cause the tip of the iron to come in contact with the spring. With the spring acting as a massive heat-sink, the iron will try to bring the spring up to the nominal temperature of the iron. This will cause the iron to be "On" (i.e. the elements heating) all the time, thus accelerating the ageing of the tips, heating elements and switches (where present).
- The use of Tip Activator or a large gauge RMA solder wire to tin tips for storage will maintain good wettability. The Tip Activator will also help to prevent tips from oxidising when small diameter lead free solder wire is used. Although Tip Activator might reactivate lightly oxidised tip surfaces the motto should always be Prevention is better than cure .
Corrosion is a function of the heat, oxygen, flux residues and other external influences on the soldering iron tip. The more active the flux used, the faster the tip will corrode.
- Use pure Rosin or RMA fluxes where your process allows it. Water-soluble fluxes are particularly aggressive because they are normally based on organic solvents, such as Citric acid. Unfortunately the choice of flux is not solely based on soldering iron tip life, so a balance will have to be made with all of the other factors, when making your process decisions.
- Make sure that your cleaning sponges are clean and free of dross. Dirty sponges collect contaminants that can form corrosive agents. Rinse your sponges daily with De-ionised water.