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Getting the Most out of Selective Soldering Continued from previous page
tive soldering. Look for features including a nitrogen flow monitor that uses nitrogen pressure levels to indicate the level of solder in the sol- der pot, and a super-heated nitrogen path. A nitrogen flow monitoring sys- tem provides accurate solder pot capacity information, which is then used to initiate and control solder replenishment to keep the pot level exact for high repeatability and process stability. This is a better method than the traditional mechan- ical probe system that is still used by some suppliers. It is also important for any lead-free system to be able to “super-heat” the nitrogen supply within the solder pot. This enhances
the performance of the flowing solder by introducing preheated nitrogen to the entire travel path of the solder from the pot to the wave, and thus to the final solder joint. Prior to the development of the
super-heated nitrogen path, selective soldering performance had been some what vulnerable to the effects of the nitrogen temperature on the sol- der nozzle wave, especially the small- er nozzles. This development removes that variable, and together, these new developments enhance the overall sta- bility and robustness of the selective soldering process. A nitrogen peel-off jet improves
fine pitch selective soldering results. Even though significant advances
have been made in the metallurgy of lead-free solders, they still have wet- tability and bridging issues that make them more difficult to work with than traditional tin/lead solders in wave and selective soldering sys- tems, and fine-pitch spacing only exacerbates them. Tight spaces, small gaps between adjacent compo- nents and very fine pine pitch devices drive the need for a nitrogen peel-off jet, a directional jet of pre-
heated nitrogen (N2) to assist in min- imizing the accumulation of solder on specific solder joints that, due to design or configuration, might be more susceptible to accumulation. By
applying a jetted pulse of N2 at a crit- ical moment in the soldering process,
March, 2012
the resulting surface will be wetted with the minimal amount of solder required for a quality solder joint.
Dual Head Fluxers A Dual head fluxer option facil-
itates quick changeover of flux types. Dual flux heads usually involve one spray head and one drop-jet fluxer. A dual head fluxer is especially designed to meet the needs of selec- tive soldering applications that demand quick changeover from lead- ed to no-lead solders. The addition of a dual head fluxing system makes it possible to change flux types quickly. The spray head should offer control- lable spray point size, pattern and deposition volume and be control- lable down to a spot size of 2mm. Drop-jet spray head technology
allows the generation of a large num- ber of drops with a well-defined size; these types of fluxers are especially useful for applying precise amounts of flux to very small areas. Use of the drop-jet is mandatory for top side fil- lets (Class III) on thicker boards with high copper content. Since the flux is forced to the top side of the board, preparing the surfaces for solder to follow.
Swappable Solder Pots When looking at smaller selec-
tive soldering units with smaller sol- der pots or those of a manageable size, quickly swappable solder pots can be a major time-saving advan- tage for assemblers (such as EMS) who alternately may be manufactur- ing both lead-bearing and lead-free assemblies, but who do not choose to invest in separate, dedicated selec- tive soldering machines for both due to volume or price considerations. For machines capable of the
swappable pot option, customers gen- erally order two solder pots, one for lead-based, one for no-lead, to pre- vent cross-contamination. The pots should be clearly marked and color- coded to prevent mix-ups that can result in cross-contamination. Each pot should be equipped with its own solder pump and solder delivery sys- tems, with extra nozzles.
Larger Nozzles Larger — typically 3-in. (76mm)
—nozzles can increase throughput as well as close the gap between selec- tive, or secondary soldering, and full wave soldering. The 3-in. wave enables the quick conversion from a leaded soldering process to a no-lead solder process. By “painting” the sol- der side of a circuit with the 3-in. wide wave, for example, a selective soldering machine can deliver pro- ductivity that approaches that of the standard wave soldering tools com- monly available. Certainly there are many other
options and features available on various machines for the prospective user to choose from, but these are a few of the more significant ones that can enhance productivity and extend the range of applications to which the selective soldering system may be applied. Contact: ACE Production
Technologies, 3010 N. First Street, Spokane Valley, WA 99216 % 509-924-4898 fax: 509-533-1299 E-mail:
acable@ace-protech.com or
sales@ace-protech.com Web:
www.ace-protech.com r
See us at APEX, Booth 3009 See at IPC/APEX Booth #1636.
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