Assembly - February 2009 - (Page 50) Electronics Assembly up initially, but you often have better control over the temperature gradients across the board. “Of course, it depends on the components. Large boards are usually infrastructure products, and they tend to have components that require a large amount of very localized heat. Smaller boards are more densely populated, so the heat mass is more evenly distributed.” On the down side, optimal utilization of the oven is a concern, since large boards are typically produced in small lots. “The issue is how long the oven takes to go from one profile to another,” says Baggio. “The way to mitigate that is to keep the temperature recipe as close to constant as possible, but change the oven speed.” A Because big boards can absorb large amounts of heat, they need a powerful oven that can respond quickly to temperature changes. Photo courtesy Manncorp oven that can respond quickly to temperature changes. For even heating, forced convection ovens are better for large boards than infrared models. The cooling system must also be efficient, because big boards take longer to cool than small ones. In most cases, however, oven capacity is less of an issue with reflow than the ability to develop an adequate profile. “These boards are thick, with a lot of ground planes, so profiling is more difficult,” says Larry Moon, applications engineer with Juki Automation Systems Inc. (Morrisville, NC). “One good thing about a large board is that you have the ability to distribute heat more uniformly, because it’s such a big heat sink,” adds Baggio. “The panel may be more difficult to heat ASSEMBLY ONLINE For more information on electronics assembly, visit www.assemblymag.com to read these articles: Design for Medical Electronics Assembly. Getting the Vapors. Cool It! PRODUCT LINE EXPANDED OVER 1,859 Some of these offerings include: Ball Bearings Axial Needle Roller Thrust Bearings Resin Retainer Linear Ball Bushing Sleeve Bearings Solid Aluminum Shafting 303 Stainless Steel, Precision Shafting Linear Guide Blocks Linear Guide Rails “V” Groove Guide Wheels Needle Bearing Cam Followers Needle Bearing Yoke Roller Standard-Duty Bearing Units Rod Ends and Much Much More.. FREE CATALOG B620 NEW PRODUCTS SALES: 1.888.276.4787 PHONE: 1.516.616.0436 FAX: 1.516.616.0443 Shop On-line Anytime at our New eStore www.qbcbearings.com 50 ASSEMBLY / February 2009 www.assemblymag.com http://www.assemblymag.com http://www.qbcbearings.com http://www.konnexio.com http://www.qbcbearings.com http://www.konnexio.com http://www.assemblymag.com
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