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www.us-tech.com Nitrogen Helps Boost SMT Quality Continued from previous page
reduce nitrogen flow rates, increase solder joint quality, and ease the transition to lead-free solder technol- ogy.
gas, it prevents or slows oxidation in circuits and packages, although dif- ferent reactions may occur with a forming gas, depending upon its per- centages of hydrogen and nitrogen. Numerous studies have examined the effects of solder cooling speeds, the types of solder pastes, and the types of solder fluxes on the reliabili- ty of lead-free solder joints, while
Because N2 is not an oxidizing
But adjusting and monitoring the flow of nitrogen for an in-line reflow solder process can be accomplished without unusual modifications to a manufacturing process.
also considering the impact of the reflow atmosphere on the quality of the solder joints. While the studies indicate that performing reflow sol- der in a highly nitrogen atmosphere typically provided better quality lead-free solder joints, the cooling rate of the solder during the reflow process also affected the quality of the solder joints. Of course, controlling every sol-
der variable in an SMT manufactur- ing process can be near to impossible. In a white paper, “Developing a
Pillarhouse’s Pillargen 40 Nitrogen Generation system’s design technology (
www.pillarhouseusa.com) offers compact size coupled with ultra quiet operation.
is detailed, including the melting temperature of the solder alloy, the flux chemistry, the impact of solder voids on the SMT products, and the impact of nitrogen versus air reflow processes. An application note from device supplier Altera Corp. (
www.altera.com), “SMT Board
finish and PCB materials on the type and temperatures of the soldering process used and the expected relia- bility of the final products, since material factors can greatly impact an assembly process. But adjusting and monitoring
the flow of nitrogen for an in-line reflow solder process can be accom- plished without unusual modifica-
Reliable Lead-Free SMT Assembly Process,” from Kester (
www.kes -
ter.com), a list of 15 process variables
Assembly Process Recommen da - tions,” points out the importance of printed-circuit-board (PCB) surface
tions to a manufacturing process. In fact, some manufacturers of reflow solder systems, such as Manncorp. (
www.manncorp.com), offer their equipment with options for nitrogen compatible configurations. The firm’s CR-6000 can be equipped with a nitrogen-compatible heating cham- ber designed for efficient transfer of heat, so that nitrogen consumption is minimized while maintaining low levels of oxygen (O2) gas in the form- ing gas. To assist manufacturers seek-
ing to shift their SMT processes to nitrogen environments, companies such as Atlas-Copco (
www.atlascop-
co.com) offer industrial gas genera-
tors for N2 and O2. These systems are capable of on-site production of required gases at any time and for 24 hours per day, 7 days per week. The company points to the improved safe- ty of using its gas generators versus storing and handling high-pressure cylinders of gas, with significant economies of scale when investing in the gas generators. Its gas genera- tors are available in a variety of dif- ferent sizes and flow rates, for appli- cations in SMT manufacturing through food and beverage storage and even in fire prevention. Gas-gen- erating systems such as the NGM2 are constructed with all necessary filters, pressure gauges, and flow meters for accurate system monitor- ing at all times. Also, nitrogen gas generators
from South-Tek Systems (
www.south -
teksystems.com) include tank-mount- ed and cabinet-based systems for flex- ibility. The systems apply pressure swing adsorption (PSA) technology to
Continued on page 61
September, 2013
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