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With the increasing popularity of selective soldering in manufacturing processes, and the global migration toward the use of lead-free alloys, there are several considerations when choosing the appropriate technology to selectively solder products. This article focuses on non-contact laser soldering technologies for lead-free alloys.
Traditional selective soldering equipment is available with single and multiple pumps, and some newer OEMs now are offering more flexibility in their products than in the past. Non-contact laser technologies also are emerging as a viable means to selectively solder PCBs and other types of components for both tin/lead and lead-free applications.
Introduced in the 1980s, laser soldering provided a rough method for selective soldering joints onto PCBs and other electronic devices. Current technologies have redefined this, incorporating useful features for soldering tin/lead and lead-free alloys. Recently introduced systems include features such as variable beam size; fiducial recognition with dynamic compensation; X, Y, Z and theta motion control; independent control over the automatic solder feeder and soldering head; CAD/CAM import; and selectable soldering parameters for preheat, soldering and cool down.
Unlike traditional pump technologies, laser-soldering systems do not require that the bath be filled prior to soldering. With costs of lead-free alloys rising, start-up costs can range from $20,000 to $30,000 in lead-free baths, compared to the cost for a precision-wound lead-free spool of wire, which costs about $30.
Laser systems can be extremely flexible, allowing engineers to target the exact pad size, amount of preheat energy, soldering energy and cool-down time. Additionally, the angle and approach of the automatic solder feeder is dynamic, offering precision control over timing for wire release to the pad and amount of solder desired to obtain proper fill.
Variable beam technology allows the engineer to adjust the laser beam to meet most pad sizes (ranging from 0.7 to 2.5 mm within the same system). Because this adjustment is available on a pin-to-pin basis (no fixed-nozzle size), this feature is beneficial when products contain a varying range of pad sizes, component profiles and hard-to-reach areas.
A laser can be controlled precisely; therefore, each pin/pad can have its own thermal profile. Enhanced CAD/CAM import software can filter soldering areas only, and copy/paste features ease setup once the desired profile has been established. Most motion-control systems offer a high rate of repeatability (0.0004″) and move quickly (averaging at 1.2 M/sec). However, even at these pin-to-pin motion speeds, cycle time can be a gating factor compared to traditional pump-style systems. Laser systems generally shine in their ability to retrieve and setup a program quickly (for product changeover), and switch from tin/lead to lead-free alloy soldering. Both of these objectives generally can be accomplished within minutes.
A vision system is suggested for most applications. Vision offers the system fiducial recognition, dynamic compensation and a precise manner in which to selectively target each pin/pad. Some vision systems also offer the ability to read and compensate for each product contained within a carrier. This helps reduce costs often associated with precise fixturing. Other considerations should include maintenance and facility costs.
Unlike traditional selective soldering, non-contact laser systems do not require nitrogen. Most systems can use both flux-core and no-clean soldering wires for the process. Precision-wound wire is recommended, and most major solder-wire manufacturers offer a range of products for the laser-soldering process.
Many laser systems require only minimal maintenance. Because there are no dross issues, preheat or other related care requirements, personnel allocation is minimal. Most laser-based systems only require that the vision lens cover is cleaned, and that the laser runs through a calibration process about once every four hours in a continuous-run environment. This can be accomplished within minutes.
There have been many articles written about the corrosive nature of lead-free alloys, how increased weight will wear internal parts in both existing and newer machine technologies, as well as the effectiveness of higher temperatures on PCBs and certain components. While many strides have been made to address each of these issues, non-contact laser-soldering systems do not deal with any of these matters. Instead, this technology works successfully around them, making non-contact laser soldering a viable option in today’s manufacturing environment.
Gary Goldberg, president, PRO-MATION, Inc., may be contacted at (262) 942-4177; e-mail: gary_goldberg@pro-mation-inc.com.
SMT June, 2005
Author(s) :
Gary Goldberg
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