Consumer needs and government regulations have driven major changes to the EMS industry over the last decade. 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.
Smaller Devices Drive Manufacturing Challenges
As environmental and convenience concerns have led to smaller electronics devices, consumers have expected increased speed, power and efficiency. So, while semiconductors have decreased in size they have also increased in power, and will continue to do so with the micro technologies used in current electronic devices. This combination has added an extra challenge to both OEMs and contract manufacturers who must manage heat implications as a matter of both product function and manufacturing processes. 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 higher profile temperatures and smaller component packages are definitely critical factors in the surface mount assembly process. We are seeing more and more ‘lead-free’ labeled parts that are actually a bit unforgiving. Their peak temperature exposure rating is a firm value and exceeding this temperature a few degrees can cause failures,” states, Kenny Houck, ACDi SMT Engineer. Proper profiling is definitely something that contract manufacturers must be experts in to produce a quality product.
Tin Whiskers Debate Continues
Many military and commercial organizations still refuse to participate in lead-free manufacturing due to the risk of tin whiskers, a phenomena that can cause latent solder shorts and, ultimately, electronic product failures. 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. While its root cause is not entirely agreed upon, temperature, moisture levels, and density are a few of the possible causes of the intermetallic growth leading to tin whiskers. Recent studies suggest OEMs can help mitigate the risk of tin whiskers and shorts by applying conformal coating to the circuit card assemblies. 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 electronic manufacturing applications.
With the global shift to RoHS, many component manufacturers have stopped making leaded components which has left a gap in the supply chain for many. “Several of our prime defense OEMs and aerospace clients actually have ‘pure tin mitigation’ requirements,” said Gabe Kenny, COO for ACDi. Translation: Parts that are not available in leaded form must be converted by either tinning their leads with lead or re-balling RoHS BGAs with leaded balls. Mr. Kenny added, “It’s a doable but costly process, and ultimately drives up costs to the end-user.”
The Next Ten Years
The various applications in which semiconductors are used have encouraged R&D efforts in determining alternatives to leaded materials. 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. 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 has begun researching ways to better control semiconductor temperatures, and countries around the world have continued researching the best materials to meet functionality and customer demand.
Though not all countries have implemented the same policies, it is very likely that research will need to continue regarding lead 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 roamap has been in the design stages, but is still not fully complete at the present time, and therefore international standards for electronic equipment manufacturing are still not established.
In order to remain competitive in the industry, OEMs and contract manufacturers 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.