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Implementation of lead free soldering technology has created new interest in high performance cleaning of printed circuit assemblies (PCAs). Many studies have been commissioned regarding removal of flux residues from tight spaces; the effect of impact force on penetration; capillary action versus surface tension; and optimization of the pressure/flow balance in the wash module. Little attention, however, has been paid to the prewash section of an inline cleaner. The prewash is a key functional process in successful cleaning during which chemical reactions are initiated, PCA temperature israised, and gross contaminants are flushed from the board. 
Traditionally, fan-type nozzles have been used in the prewash. The small droplets produced by fan nozzles are indeed effective at wetting open surface areas. However, since mass is a critical component of both force (mass x acceleration) and kinetic energy (1/2mass x velocity2), they produce inherently low impact force due to their small size. This limits the ability of fan nozzles to break apart residue and to distribute wash chemistry beneath components on the board surface after initial impact. To address these issues, oscillating nozzle technology has been developed. These nozzles move the fluid stream back and forth providing a more effective spray pattern in terms of both coverage and impingement. The larger droplet size has more mass and increased impact force, enabling the nozzle to achievebetter results at lower pressure with reduced water usage. V-Jet history
The V-Jet nozzle has been used in the prewash since inline cleaning machines have been in service (figure 1).These nozzles commonly create a flow that tends to be heavier on the outside edges and more atomized (withsmaller droplets) in the center. This provides a non-uniformimpact profile on the product. 
Most prewash V-Jet nozzles are 65 degree fan and 0.041in orifice on top, and 105 degree fan and 0.041in orifice on the bottom. Both nozzles spray 0.30 gallons per minute (gpm) at 40 pounds per square inch (psi) and 0.42 gpm at 80 psi. There are typically 12 nozzles in the prewash. The combined consumption at 40 psi is 3.6 gpm. Figure 2 shows a complete range of consumption rates. 
S-Jet oscillating nozzles
The oscillating nozzle utilizes low and high pressures with a unique inner chamber that causes the water stream to oscillate back and forth in an S-pattern as it escapes thenozzle. The nozzle has no moving parts so there is nothing to wear out. Thekey to this systemis that largerdrops are createdwhich drasticallyimproves heattransfer. The resultis a more uniformcoverage and a moreforceful stream ofwater moving in arapid back and forth motion at 30 times per second. The oscillating nozzles work on a constant pressure. The nozzles are optimized at 15 to 20 psi. The normal configuration is six nozzles per spray bar (24-inch process) and five nozzles per spray bar (20-inch process). The spray bars are designed with a 5 degree angle so the spray pattern of the nozzles will not interfere with each other (see figure 4). There are four spray bars in a typical prewash. The prewash is powered by the wash pump, so a regulator is placed between the high pressure pump and the spray nozzles. This regulator is set to 22 psi. This protects the nozzles and limits fluid consumption. 
Typically the top bars are set at 20 psi and the bottom spray bars are set at 15 psi. This keeps the product from shifting while moving through the module. Typical consumption for the entire prewash module is 4 to 4.5 gpm. The new nozzles provide a much higher volume than the V-Jet nozzles. The result is larger droplet size and increased heat reaching the product. Applications
The application setup for the prewash is simple to define: the best cleaning performance possible with the least amount of cost and consumption. All applicationshave a cost associated with them. 
In a cleaning system the cost is in the consumption rate. If a deionized water bed is used, then great care needs to be taken in setting up the process. The incoming clean water enters the final rinse. The final rinse empties into the rinse tank. There is a cascade from the rinse into the wash tank (in aqueous applications only). The wash tank feeds the prewash which goes to drain. A balance between the incoming final rinse and the outgoing prewash must be established. With this, there are several factors to define. Is this an aqueous application or is it a chemical application? Is the incoming water deionized of just filtered? What kind of pressure does the incoming water have? Application 1 – Aqueous application with deionized water at 30 psi. This setup will have a small incoming volume and a lower pressure in the final rinse. With this, the new nozzles in the prewash will optimize the system more efficiently because of impact force and volume. Application 2 – Aqueous application with deionized or filtered water at 65 psi. This application has more volume in the final rinse, which allows more volume in the prewash. This will allow either of the nozzles to work efficiently. The V-Jet nozzles are effective above 65 psi as long as the final rinse can keep up with the demand and the facility can handle the load and the added cost of operation. Application 3 – Chemical application with any incoming water and any pressure. Since the prewash is drained back into the wash, the balance of the machine is not dependent on the prewash setup. The prewash can be run at full pressure with V-Jet nozzles or 20 psi with our new nozzles. This application is product dependent. Some products clean better with the new nozzles and some clean better with V-Jets. Conclusion
In any inline cleaning application, the prewash is the first module to start the cleaning process. This should be the most important starting point for the application setup. The prewash is defined by the type of process and the facilities feeding the machine. The type of nozzle used in the prewash should be determined by testing and application development. To achieve great cleaning results, the process needs a great start. Do not overlook the prewash module when setting up and running a cleaning application. Utilizing the new nozzle technology can significantly improveproduction rates and reduce operating costs. Reference
[1] Hobart Corporation (Troy, OH, US) – Opti-rinse nozzle, patent-pending.
[2] Spraying Systems (Wheaton IL, US) Publication – Engineering discussions.
[3] Bex Nozzles (Livonia, MI, US) Catalog 45 - Flat nozzle specifications. Special thanks to
Speedline Electrovert Applications Engineer John Neiderman. About the author
Eric Becker is a Mechanical Engineer with Speedline Technologies and is responsible for the development of cleaning products and technologies. He has been with the company for eight years and holds a BS in Mechanical Engineering from the University of Texas, SanAntonio, USA. | 
