Invariably the possibility of implementing or switching to lead-free selective soldering is going to be or should be considered for many operations. There are a number of considerations as to why lead-free solder would be considered, given the potential impacts of lead as a material.
In much of the world, lead-free soldering of any kind, much less selective soldering, has become the rule rather than the exception though in some countries and indeed, down to some companies, there are still manufacturers that still use leaden or lead-alloy solders. Others may be considering a lead alloy solder such as the lead-tin alloy.
Why switch to or implement lead-free selective soldering? Here are a few reasons to consider doing so.
One of the first reasons to consider switching to lead-free solder or implementing lead-free solder is that lead solder is a major contributor both to the extent lead contained in landfills - which can contaminate groundwater - and can also be a major health risk when workers are exposed to lead in the form of lead fumes and overall lead exposure.
Whilst Japan and almost all European countries switched to lead-free solders years ago, the United States and other countries have not yet made the switch. While this doesn't necessarily mean that American manufacturers or other those located in other nations care nothing for the environment or their workers, it is still the case that the global standard is to avoid the use of lead in solder when possible.
The most common sources of lead in American municipal waste centers are lead batteries, cathode ray tubes and solder contained in discarded electronics. The latter two sources make up the majority of the lead in landfills by wide margins. Ergo, solder is a major contributor of lead waste. Other products containing lead have been mandated to go lead-free in past decades, such as in the case of gasoline and the prohibition of lead shotgun pellets being used in the hunting of waterfowl.
Additionally, the health risks of lead exposure and lead poisoning - one of the most common forms of metal poisoning - are too well-known to be described as anything other than incontrovertible. Lead, therefore, poses a risk to employees. Minimizing the risk of exposure, no matter how minimal, is good practices. Not only is it a moral hazard to disregard worker safety but it also can safeguard against liabilities.
However, not all lead-free alloys are necessarily the most environmentally friendly, so care must still be taken.
Lead-free solder has been know to be a viable alternative for SMT components, but adoption for selective soldering has been slower. Just as when lead-free gasoline, lead-free paint and other lead-free alternatives to formerly leaden products, early concerns and complaints were that the lead-free versions of these items did not or would not perform as well as the previous iterations containing lead.
However, lead-free solder has shown itself to be equal to the task in terms of establishing connections and also withstanding aging. Modern lead-free solder alloys form similar intermetallic compound layers during the soldering process just as lead alloys do, and therefore are able to withstand high heat levels, stress and aging just as well as lead alloys do.
While this would appear to mean that lead-free selective soldering means fewer environmental and safety risks with no loss in performance, it is more accurate to say that these attributes are present in lead-free solder but come at a price.
In order to ensure quality production in lead-free selective soldering, the lead-free alloy imposes certain requirements in order to function properly.
First, lead-free alloys require a higher thermal load in order to flow and achieve sufficient wetting. Typically, an additional 30 degrees to 40 degrees Centigrade is required for use of lead-free alloys. Some soldering techniques, specifically reflow or wave soldering, are made more complicated in this manner due to the risk the added heat poses to the PCB and other components, but with selective soldering the risk is mitigated by the far more limited contact time as specific joints are soldered, reducing the overall heat applied to the board.
It is also a requirement to prevent oxidation of the alloy and dross. There are two typical avenues to accomplishing this in selective soldering or any use of lead-free solder. First is nitrogen inerting, which is recommended for any lead-free soldering system. Second is to use electromagnetic solder pumps in lieu of impeller driven pumps, as the latter is able to push the solder through the pump without the agitation of a moving impeller, which oxidizes the solder.
That said, the benefits of lead-free solder far outweigh any costs in adoption, which has been a benefit to those operations that have switched to or implemented lead-free compatible selective soldering from the start. Contact Us if you have any questions about switching to lead-free selective soldering compatible machines.