Project MEMS - January 2009 - (Page 18) w feature hile semiconductors tend to capture people’s attention far more than their packaging, a die and its packaging are inseparable. The success of a device — especially an RF or microwave device — often depends on both. The choice of packaging material for interconnects involving printed circuit boards and devices, often referred to as Level 2 and 3 packaging, depends on many factors: in addition to assuring a viable interconnect, it may also need to provide for downstream testing and processing, compatibility with other components, in-use thermal management, and environmental-stress protection, among other functions. Level 2 and 3 packaging is usually made from epoxy-molding compound (EMC), ceramic, metal, or engineering thermoplastic. EMC is used to provide complete chip encapsulation, while the other materials create open-cavity packages when dies cannot be encapsulated. The choice of material is most often driven by economics and the need for optimum yield and performance. EMC transfer-molded packaging, which accounts for nearly all Level 2 and 3 packaging, is often the least expensive option. But in increasingly more instances, air-cavity packaging is the best option. Though a relatively small portion of today’s market, air-cavity packaging’s share is forecast to grow by more than 30% annually over the next five years. Driving this growth is the trend to higherpower devices and those that work at frequencies above 1 GHz, as well as the need to decrease attenuation and frequency shift and limit thermal loss. Several environmental factors have also been affecting material choice. The rise of Pb-free soldering has elevated processing temperatures by about 40°C, to between 240° and 260°C or more, Project Contents MeMS The desire for more intricate RF packages to optimize board area and meet dimensional constraints is changing packaging material choices. pushing the practical limits of EMC and most plastics and opening the door for highertemperature engineering plastics. In addition, relatively recent environmental regulations have worked against the use of EMC, as has the growth of devices that cannot be encapsulated, such as sensors based on MEMS for automotive, aerospace, military, medical and consumer products. Also, the trend toward thinnerwalled, more intricate packaging is creating demands that exceed the inherent design limitations of metal, ceramic, and EMC, and favor the use of injection-molded polymers. ePoxy-baSed Packaging Transfer molding using thermoset epoxy accounts for more than 90% of all semiconductor packaging. This is due to its economy, the large installed base of equipment for this process, and the industry’s comfort with it. EMC packaging begins by wire bonding a die to a metal leadframe and placing it in a mold. The compound, which contains epoxy, filler, flame retardants and other additives, is heated to 150°C so it can flow through runners and gates into the cavity and around the array. The EMC then polymerizes to a solid. The Viewpoint Solutions for Testing MEMS Devices on the Wafer Level Wireless Sensor Networks Have Arrived Choosing the Right Material for RF Packaging Home Page Product Training Module Online Ordering Suppliers Catalog 1 8 | P r o j E C T M E M S | vo L . 1 / N o . 1 http://ad.doubleclick.net/clk;210306059;32013581;o?http://www.digikey.com/ http://ad.doubleclick.net/clk;210306059;32013581;o?http://www.digikey.com/ http://ad.doubleclick.net/clk;210306136;32013581;k?http://digikey.com/PTM/PTMMaster.page?site=us&lang=en http://ad.doubleclick.net/clk;210306155;32013581;l?http://ordering.digikey.com/ordering/addpart.aspx?site=US&source=search http://ad.doubleclick.net/clk;210306414;32013581;j?http://digikey.com/Suppliers/SupplierIndex.page?site=us&lang=en http://ad.doubleclick.net/clk;210306629;32013581;r?http://dkc1.digikey.com/us/en/pdf/Current.html
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