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There is no one sweeping technology trend for the EMS sector. EMS companies can leverage several technologies and trends to deal with present challenges while preparing for the future. Current trends include high-complexity lead-free, miniaturization, and new markets such as alternative energy.
By Irene Sterian, Celestica
The existing downturn in the economy will likely present challenges for all players in the electronics industry. What technologies and trends can EMS companies leverage to deal with present challenges while preparing for the future?
Continue with RoHS development work, and implementation of high-complexity lead-free solutions. The computing and telecommunication markets are in need of a lead-free solution. There is a lot of work ahead of us, especially in wave solder, rework, and large-thermal-mass assembly.
Large thermal mass boards may need vapor-phase rather than convection reflow to achieve the heat required by all components. Vapor phase rework tools have already appeared on the market to address the warpage and delamination issues that occur with large temperature variations.
Telecommunications and computing products – not be required to convert until 2014 – still need to fully transition to lead-free assembly. This looming deadline challenges the EMS companies that support OEMs in these market segments, especially in the areas of wave solder and rework.
For example, there is a tradeoff between minimizing copper dissolution and providing adequate barrel fill. There is great deal of work underway to develop the best alloy and flux chemistry, wave solder machine configuration, and lead-free board finish to create the best plated thru-hole (PTH) lead-free solder joint possible.
Another hurdle to overcome when processing thermally massive PCBs relates to temperature-sensitive components. At SMT reflow, the larger thermal mass, in addition to the higher peak temperatures and longer soak times driven by the lead-free metallurgy, may pose a risk to temperature-sensitive parts such as SMT electrolytic capacitors and plastic molded capacitors with temperature limitations.
The thermal mass of high-I/O BGAs complicates rework. Rework with a low-melting-point solder can solve this. Work is underway to improve the rework tools as well as the chemistry of the lead-free solder, targeting reliablity comprable to primary-attach joints.
ICT probing has not been fully addressed in the migration to lead-free. There are new test probes and solder pastes to improve probeability and reduce ICT false fail rates. Different board finishes, solder pastes, flux residues, and probe types factor into an optimal combination.
The consumer and mobile market segments likely face further pressure for cost reduction, despite the need to remain competitive and innovative. Reduce cost in the consumer and mobile market products through further miniaturization, and streamline assembly processes such as EMI shielding. Further miniaturization can be achieved by new, finer-pitch packaging such as 0.3-mm-pitch CSPs and the use of smaller passives such as 01005s.
Package miniaturization drives component stacking such as package on package (PoP) and internal die stacking (3D ICs), as well as smaller-pitch components. SMT equipment requirements have changed, incorporating dip flux and paste units, as screen printing fine pitch is no longer viable. In this case, we need a paste that is “dippable” instead of “screenable,” especially for PoP assembly. As components shrink, we may also need wafer feeders to accommodate them. Many components also require underfill – the quantity and accuracy of which may require newer, higher-accuracy dispense technologies. Reworkable underfill is another material under evaluation. It could reduce scrap costs, given many current assemblies cannot be reworked once underfilled.
Figure 1. A high-complexity lead-free PCB.
Smaller passives disrupt norms in placement and reflow. In late 2008, 0201s replaced 0402s as the dominant discrete component size in many smartphones. The industry had good yields for 0402 components and is now working to achieve comparable 0201 component yields. The next step – 01005s – will again pose yield challenges.
Upcoming legislation will dictate halogen-free PWBs versus lead-free PWBs. Preliminary experience with these materials has shown large variations in quality, resulting in PWB internal delamination and cut traces. The industry must develop materials that can withstand high-temperature lead-free soldering without delamination. Solder pastes that do not require nitrogen reflow will also reduce cost. Today, some of the better-performing materials still require nitrogen reflow, whether at primary SMT attach or rework.
Mobile products have distinct RF sections that must be isolated and protected with shields. EMI shields can be combined with a component package, added on top of the package, or added as part of the product’s cover. Costs must come down for shield assembly and associated rework. The popular method of placing a shield on top of a component set renders underfill and rework more difficult.
Miniaturization in mobile devices drives increased use of flex circuit subassemblies. Thin, flexible, durable flex circuits weave through moving parts and sneak around obstacles to connect boards and other components in different areas. At the same time, they help offload a few more components from main PWBs by using any tiny free space, including curved spaces.
Anisotropic conductive films (ACF) have proven successful in LCD attach and repair. They allow fine-pitch assembly up to 10× denser than SMT can achieve, down to about 0.03-mm pitch. They proffer fine-pitch assembly without alignment requirements. The capability and reliability of this technology is being examined for other applications, such as chip on board (COB) and flex on board (FOB). No connectors are needed to attach flex to rigid PWBs.
Expand into new markets, such as alternate energy, specifically solar module manufacturing. While this type of manufacturing requires investments in new equipment and an understanding of new technologies, it has not traditionally outsourced to EMS companies. Partnering with EMS providers may help streamline manufacturing and reduce assembly cost through lean deployment, economies of scale, line balancing through multiple customers, as well as smart trade-offs between manual assembly and automation.
Tabbing and stringing, for instance, is a process of soldering individual solar cells together. It is manually or automatically performed, depending on silicon’s fragility, throughput, and yield required. Hot bar, magnetic induction, laser, flame, hot air, and IR soldering are all available production techniques. EMS companies can help select the best method that suits a variety of cell assemblies and optimize them for both better throughput and higher yields.
The solar market also must comply with RoHS legislation and, as such, use lead-free interconnect materials and fluxes. EMS providers can draw on their previous experience with these lead-free materials, selecting the best option for solar interconnect materials, ensuring the best tab and string connection quality. Other materials used in solar module manufacturing can also be improved, reducing cycle time and overall cost of the assembly.
Each EMS provider must assess their geographic location and technical capability to determine whether they’re a match to new markets.
There is no one sweeping technology trend for the EMS sector this year, but rather a combination of these key trends. SMT
Irene Sterian, process engineering manager, Advanced Process Development, Celestica Corporate Engineering, may be contacted at (416) 448-5188; firstname.lastname@example.org.