Circuits Assembly - November 2007 - (Page 53)

importance, not only for the soldering process, but also for the reliable application of the circuit. For this reason, no real general recommendation can be given. There are so many different fluxes with different activators, rosin or resin-based, alcohol-based solvents or VOC-free, that one should contact the flux supplier and discuss the demands for the use of the board (circuit/equipment). But also the type of solderable finish and solder resist used are parameters to consider. These facts need to be known to receive good advice about the best flux and process settings. For consumer electronics, these demands may be quite different than those for medical equipment, for example. Preheating. Preheating the board is necessary to evaporate solvent from the flux and to prepare the board and flux for soldering. Different systems can be used for preheating. As long as the flux layer is wet, a medium wave quartz rod IR preheating is recommended. If the flux becomes sticky, forced air cooling can be used. A quartz heater can be used to boost the preheat temperature, in case different recipes need different preheater settings. The preheater setting must be optimized with relation to conveyor speed. Soldering temperature. The solder pot temperature setting depends on the solder type used, but may also be related to the product to be soldered. In general, low temperature settings are recommended. Low temperatures will create less dross, but will in most cases also extend the lifetime of the flux, so that it has a better tail activity. For SnPb solders, 245-250°C is a common setting; for SAC-alloys, 260-265°C is the recommended setting. Nitrogen application. Nitrogen may be helpful to support flux activity during the separation of the board from the wave. During this separation process, solder should stay on, but not in between, the joints. Solder oxide formation at this stage increases the risk of solder bridging considerably (Figure 1); this is why the flux must have sufficient activity left to reduce these solder oxides. Nitrogen used in that area can displace the air (oxygen) at that region and thus assist in better drainage conditions. Exhaust. Machine exhaust affects most other process settings as well, which is why the exhaust conditions, once set at the demanded values, should be kept constant. ■ Wave Soldering Expand your global reach with electronic reprints! Electronic reprints show your clients, partners and employees that you have been recognized in a well-respected industry magazine. They also serve as an attractive endorsement, adding credibility to your company and its products and services. For only $995 US per article, you’ll receive an Acrobat .PDF electronic reprint that has the following features: • A cover page, if you desire, with your company’s marketing copy, the UP Media Group and Circuits Assembly logos, and “as seen in the pages of Circuits Assembly” text. Your article in full color, formatted as it appeared in the print issue. A back cover containing marketing copy that you select or provide. The rights to post and distribute the article—for life! Looking for suppliers? Look here! The 2007 CIRCUITS ASSEMBLY Directory of EMS Companies • More than 1,250 EMS facility listings • Detailed info on sales, size, contacts, and more! • Price: Only $999 • • • To purchase or inquire about electronic reprints today, send an e-mail to: ca_reprints@upmediagroup.com circuitsassembly.com Order online at circuitsassembly.com/dems Circuits Assembly NOVEMBER 2007 53 http://circuitsassembly.com/dems http://circuitsassembly.com

Table of Contents Feed for the Digital Edition of Circuits Assembly - November 2007

Circuits Assembly - November 2007 Contents Caveat Lector Industry News Market Watch Talking Heads Focus on Business Global Sourcing On the Forefront Screen Printing Better Manufacturing Pb-Free Manufacturing from a Tier III EMS Perspective ‘Living Documents, Subject to Change’ Creating Ideal Solder Joints An Alternative Drying Process for MSDs ‘Customer Satisfaction is More than a Score’ Optoelectronic Substrates: Will They Happen? Tech Tips Wave Soldering Process Doctor Test and Inspection Getting Lean Materials World Equipment Advances Product Spotlight Assembly Insider Technical Abstracts Ad Index

Circuits Assembly - November 2007

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