Project MEMS - January 2009 - (Page 19) feature molding process generally takes 30s to 20 min, depending upon cure requirements Encapsulation with EMC typically costs just one-third of a U.S. cent per lead. It works well with most silicon dies in end uses like phone amplifiers, automotive switches, motherboard and peripherals elements for personal computers, and most other common consumer devices. Its use has been growing at a rate of 7% to 10% per year. Transfer molding has its limitations, however. It can cause attenuation, does not accommodate devices that need high heat dissipation and, because EMC is a poor moisture barrier material, does not protect microchips from water vapor. Waste is also an issue with EMC. As a thermoset, its polymerization cannot be reversed, so all runners, out-of-spec product and other items must be discarded. This can raise material loss to 50% or more and make higher-cost thermoplastics cost competitive with it. In addition, EMC may use substances, such as bromine flame retardants and mold release agents deemed hazardous, that make disposal difficult. Metal and ceraMic Metal and ceramic are traditional open-cavity package materials. Metal packaging accounts for less than 1% of the market and is most often found in military, aircraft and space applications. It can offer a total barrier to gases and moisture and estimated lifetimes to 20 years or more. Although metal is relatively inexpensive, fabrication which involves machining, electroplating and other steps pushes costs for metal package well above those for others. Ceramic has been the dominant open-cavity material for much of the past four decades. It was developed for hermetic, highend packaging where EMC cannot work. Today it is used to package MEMS, radio frequency and microwave devices, and many other components. Ceramic, primarily alumina, is fired at 1,600°C. It may be cofired with tungsten so leadframes can be attached, since this metal survives the firing temperature. Low-temperature co-fired ceramic, which is half glass and half alumina, processes at 700° to 800°C and allows the use of copper, silver or gold for printed metallization. Ceramic shrinks significantly during firing and often must be lapped to form flat mating surfaces. This raises ceramic packaging’s cost significantly and, tied with other cost factors such as secondary plating and brazing the leadframe during assembly and one-unit-at-a-time fabrication, has resulted in flat growth. PreMolded air-cavity With the move to Pb-free soldering, LCP (liquid crystal polymer) became the primary material for premolded air-cavity packaging. This thermoplastic can withstand assembly temperatures well beyond the abilities of polyester, polyethersulfone, and other engineering polymers. Only LCP and PEEK (polyetheretherketone) can Project Contents Viewpoint MeMS Solutions for Testing MEMS Devices on the Wafer Level Wireless Sensor Networks Have Arrived Choosing the Right Material for RF Packaging METAL PACKAGING ACCOUNTS FOR LESS THAN 1% OF THE MARKET AND IS MOST OFTEN FOUND IN MILITARY, AIRCRAFT AND SPACE APPLICATIONS. 1 9 | P r o j E C T M E M S | vo L . 1 / N o . 1 Home Page Product Training Module Online Ordering Suppliers Catalog 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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