Environmental and convenience concerns have led to a decrease in the size of electronic devices while consumers have expected increased speed, power, and efficiency. The materials that make up these devices have sparked conversation, consumer awareness, and government involvement regarding environmental issues, causing major changes to occur in the EMS industry. The desire for nontoxic materials as well as directives and mandates in Europe, Japan, and other countries regarding Restriction on Hazardous Materials (RoHS), has led many companies to move towards offering or switching entirely to solders, pastes, and components free of lead and other substances such as mercury and cadmium.
Various types of alloys have been made available as alternatives to leaded solders and solder pastes, many times made out of combinations of tin, silver, bismuth and/or copper. SAC305 is a combination of 96.5% tin, 3% silver, and 0.5% copper commonly used because of its strong joint strength, wetting capabilities, and lack of drossing which assists in prevention of solder bridges. Bismuth is added to some alloys, but it is not as readily available as other metals. If the ratio of bismuth to other metals is too high, wire applications used in hand soldering would not possible due to bismuth’s brittle nature. One of the major benefits of the lead-tin combination is that both metals are readily available and fairly inexpensive. Silver or nickel are alternative options containing low melting points and high wetting abilities, but are much more expensive than the lead-tin varieties.
The combination of tin and lead has a low melting point allowing for tin to be a top lead-free alternative choice for the coating of components. The issue with using tin only in place of a tin-lead mixture is that tin whiskers tend to develop which can cause shorts because of tin’s electrically conductive qualities. The reason for the formation of whiskers has not entirely been determined, but temperature, moisture levels, and density are a few of the possible causes of intermetallic growth leading to tin whiskers. Mixtures of other metals with tin reduce the likelihood of tin whickers from developing. OEMs can help mitigate the risk of tin whiskers and shorts through adding conformal coating to the PCBs. A study designed and performed by Thomas A. Woodrow, Ph.D. and Eugene A. Ledbury, both from The Boeing Company, studied the ability of conformal coating in preventing the formation of tin whiskers and “odd shaped eruptions”. The study found that a coating of Parylene C worked best for providing a consistent coating and suppression of these formations, allowing for the use of higher ratios of tin in EMS applications.
More research is needed to determine the standards and processes to be applied to the manufacture of lead-free products to ensure that the quality and reliability of the products will yield the same if not better results than leaded materials. Companies like Boeing are leading the way in research of how to counteract issues that may rise out of the use of lead-free solders and pastes. The greatest concern, currently, is related to the aerospace and defense industries due to the critical nature of products manufactured for this industry. Issues with satellite shorts as well as other military equipment failures raise concern for whether lead-free materials are a safe and viable substitute for the traditional lead-tin solders. Held to a different standard, it is likely that the aerospace and defense industries will prove to be the last to fully jump on board with the lead-free initiatives. Though not all countries have implemented the same policies, it is very likely that research will need to continue regarding alternatives, as the push for greener manufacturing and recycling processes does not appear to easing up, but rather gaining traction. Since the introduction of lead-free solders, a technology road map has been in the design stages, but is still not fully complete at the present time, and therefore international standards for electronic equipment manufacture are still not established.
There have been major changes to the electronics manufacturing industry over the last decade which has been driven by a combination of consumer needs and government regulations. Two that have been gaining interest and attention of late include the explosive rise in semiconductor sales and its impact on supply chain implications related to RoHS and other restrictions such as Conflict Minerals..
The various applications in which semiconductors are used have encouraged R&D efforts in determining alternatives to leaded materials. Concerns over cross contamination as well as the risks of component exposure to the higher heat required by lead-free processes affecting overall product reliability have led to increasing studies surrounding alternative materials. Lead-free solders have melting points that tend to reach over 200ºC, whereas the traditional tin-lead solders melt around 180 ºC generating the need for alternative materials to be used not only in solders and semiconductors, but in all parts that make up a PCB assembly.
The shift towards lead-free solders and semiconductors will not only affect these products and their processes, but the entire supply chain and manufacturing process will have to shift as well. There are implications of using lead-free solders and pastes that will affect the EMS industry immensely over the next many years. Changes in the metals and materials used raises concern for the boards and the components that will be exposed to these high temperatures during the reflow and solder wave processes. In certain industries, the higher level of temperature exposure can provide beneficial results such as the automotive industry, where electronic components would be regularly exposed to high temperatures in their working environment. Semiconductors have decreased in size, but increased in power and will continue to do so with the micro technologies used in current electronic devices. Changes to the packages of the semiconductor could greatly affect their ability to cool, especially due to their increased power required and smaller size. Europe began researching ways to better control semiconductor temperatures, and countries around the world have continued researching the best materials to meet functionality and customer demand.
In order to remain competitive in the industry, companies will have to work towards staying ahead of the policies, and invest in research to determine the most efficient and reliable ways to manufacture for industries ranging from commercial products, to those that are integral to safety of our men and women in the line of duty.