Tuesday, June 28, 2016
VOLUME -25 NUMBER 3
Publication Date: 03/1/2010
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ARCHIVE >  March 2010 Issue >  Special Features: SMT and Production > 

Cleaning Challenges and the Environment
Flux residues around and under 0603 components.

The removal of contamination encompasses the entire electronics manufacturing floor. Over a decade ago, the emergence of no-clean flux technologies seemingly spelled the end of "precision cleaning." Ironically, exactly the opposite became true. The cleaning market has converted to cleaning at a pace not seen in prior years.

DI-water versus chemistry. Several studies have been conducted to address the advantages and disadvantages of using DI-water versus chemistry in high precision cleaning processes. The electronics manufacturing industry is being challenged to achieve the same cleanliness levels as component standoff heights are shrinking and boards are becoming more densely populated.

Cleaning Under Components
Cleaning under low-standoff components can be problematical. Initial results indicate that the cleanability of residues under low-standoff components has become an important issue.

During a recent study, a standard cleaning manifold was tested first to establish a base line. The results showed that even at belt speeds of 0.4 fpm (7.5 minutes exposure time) and less left minor residues underneath the components for leaded as well as lead-free formulations. These results correspond to values ascertained in other inline machines when cleaning no-clean and lead-free fluxes. During subsequent tests the cleaning equipment was modified to find that expedited cleaning under low standoff components is feasible with an appropriate spray configuration.

With this technique, marginal improvements in cleanliness were achieved at belt speeds not commensurate with the demands of the current production environment. Today's mechanical designs, when used in conjunction with the latest cleaning agent innovations, clearly improve the overall cleaning performance. In fact, it is the best achieved to-date in similar types of tests conducted over a period of years.

Cleaning in Tight Spaces
Improvements aimed at cleaning the latest lead-free, no-clean flux formulations did not include the challenges posed to current users employing only DI-water for the removal of OA (organic acid) flux types. The increased use of water-soluble, lead-free solder requires more activators and higher soldering temperatures, which result in more burnt-in fluxes which produce water-insoluble contamination. These findings coincide with the use of smaller, more densely-packed components which further limit the effectiveness of pure DI-water. Due to a surface tension of 70+ dynes/cm, water cannot effectively penetrate underneath low standoff components. Chemistry-assisted cleaning processes, however, can reduce the surface tension to 30 dynes/cm and below, thereby eliminating penetration problems. With the introduction of lead-free solder pastes, however, the solubility of residues in DI-water has become limited. If non-ionic contamination is produced, water alone cannot chemically dissolve it. A recent technical customer case study compared actual production assemblies and conditions. The findings revealed significant experimental data, which shed much needed light on this emerging industry challenge. The main objective was to determine the differences of cleaning water-soluble flux residues with DI-water versus chemistry-assisted processes. A standard IPC B-36 circuit board was used as a test vehicle. Each sample was populated with four 68-LCC components.

Three cleaning media were tested for cleaning leadless components with low standoffs of less than 1 mil. Cleaning agent 1 showed full removability at a belt speed of 1 fpm across all surfaces and under all quad areas. Given the findings, we encourage current DI-water users to take the time and closely investigate current cleanliness levels, especially under low-standoff components.

One previously highlighted advantage of using a chemistry-assisted process is that manufacturers can operate at lower temperatures and with a wider process window and clean not only OA but also RMA (rosin mildly activated) and no-clean fluxes. Despite all the valid arguments encouraging the use of chemistry-assisted processes, there is a note of caution here: most machines currently dedicated strictly to DI-water are not properly equipped to use a closed-loop chemistry because they do not have the necessary chemical isolation section. This is an essential qualification, not only to conserve chemistry, but also to minimize cross-contamination in the rinse tank. Employing a chemical product in the wash tank would lead to a continuous dilution of the recommended chemistry application concentration by DI-water. Companies that are strategically planning their capital purchases are therefore well advised to incorporate a mechanical option to run aqueous chemistries for long-term savings.

Going Greener
The Stockholm accord has recently begun to lay the foundation for industrial nations to adopt greener technologies. In the early 1990s, alternative cleaning products became obsolete. During the past decade, the transition to greener (lead-free) solder pastes has been completed for the majority of electronics manufacturing. In many cases, contract manufacturers use different fluxes for different projects.
Typical setup of a DI-water only inline cleaner. Fresh DI-water enters through the final rinse and cascades down to the rinse, wash and pre-wash sections. The overflow from the pre-wash returns back to the DI-water treatment system and thereby completely closes the system loop.


Sometimes it becomes necessary to clean no-clean fluxes. Having the right equipment to handle all types of cleaning agents becomes crucial. The introduction of a CI (chemical isolation) section allows the use of a "chemistry assisted" process, but it also presents a new challenge. With the inclusion of a CI section, manufacturers have now created a waste water source. Reducing drag-out losses now becomes a very important task. Fortunately, equipment manufacturers have shown a tremendous amount of innovation to limit, and in some cases even eliminate effluent rinses.

DI-Water Only. In a typical setup of a DI-water only inline cleaner, fresh DI-water from the DI-water treatment system enters through the final rinse and cascades down to the rinse, wash and pre-wash sections. The overflow from the pre-wash returns back to the DI-water treatment system and thereby completely closes the system loop.

Chemistry Capable Machines. A chemistry-capable inline differs from a DI-water inline in one major respect — the presence of a CI section. The CI section is located between the wash section and the rinse section of the inline machine. It is also sometimes referred to as the pre-rinse section.

Furthermore, there is no cascading in a chemistry-capable inline system, since it would constantly dilute the chemistry. Therefore, the wash section is close-looped by itself. A separate treatment system to recover and regenerate the wash solution is a commonly available option. This is typically a filtration system that will remove any contaminants from the wash chemistry.
A typical chemistry capable inline machine setup.


The rinse section in a chemistry-capable inline is also close-looped; however, it does include a DI-water treatment system within its loop.

Keeping it Isolated
Based on board geometry and complexity, chemistry will remain on the board after it passes through the wash section. Chemistry is also dragged out by the conveyor belt and any baskets that are used. The function of a chemical isolation section is to minimize this chemistry drag-out. The advantages of minimizing drag-out include but are not limited to chemistry conservation and carbon bed preservation in the DI-water treatment system.

Chemistry Conservation. The CI section strips away the chemistry remaining on the board as well as on the conveyor belt and moves it back into the wash section. This process recovers the bulk of the chemistry which would otherwise be lost.

Carbon bed preservation in the DI-water treatment system. The carbon beds in the DI-water treatment system are rapidly consumed by increasing the organic content in the effluent stream. Thus, a chemical isolation module helps to preserve the DI-beds by reducing the amount of chemistry being dragged out to the rinse section.

Treating CI Effluent
When the chemical isolation effluent cannot be sent to drain, there are three treatment and disposal methods that may be used:

Evaporation. The effluent can be sent to an evaporator which provides zero discharge. The evaporator should be able to handle the flow rate of the chemical isolation section.

Treatment. The treatment beds can include carbon beds, chelating resin beds and mixed resin beds. With this option, carbon beds present the greatest cost since they will have to be replaced frequently.

Treatment using an RO membrane. A reverse osmosis membrane can also be used to treat the effluent.

Implementing a new process through the integration of state-of-the-art chemical isolation sections goes hand in hand with other process improvements. While the chemical isolation section will help reduce the effluent, the evaporative losses also play a vital role, especially with conveyorized inline cleaning equipment.

Reducing VOCs
Recently, the demand to recover and reuse waste vapor by utilizing highly efficient systems has increased dramatically across every manufacturing sector. This is not surprising, given the economics involved. Vapor recovery is a relatively simple and effective way to reduce unnecessary operational costs and eliminate emission violations. As a result, there are many different methods for reducing the VOC (Volatile Organic Compound) concentration in a vapor stream.
Table 1: Recent cleaning performance of DI-water when compared to chemistry assisted processes for solder paste 5.


Pressure drops, flux leaks, low recovery efficiency, fan blower strain, and unnecessary machine modifications can all be traced back to poor demister design and cheap device construction. The two primary issues that require immediate attention are related to pressure drops and efficiency.

Efficiency is much more than a measure of how well the unit is working. In vapor recovery, efficiency means fewer VOCs and lower costs. While demisters passively return vapor containing cleaning chemistry back to the wash tank for reuse, they are no match for condensers. Engineers have now designed condenser technologies which eliminate all concerns over pressure drops and machine issues, while delivering unparalleled efficiency.

State-of-the-art demisters and condensers are specifically designed for the recovery of exhaust vapors originating from automated cleaning processes without negatively affecting the operation of any associated equipment. VOC emissions are reduced by up to 85 percent, which can help customers meet and exceed stringent local environmental regulations.

Water as a Cleaning Agent
Cleaning agent technologies exist that are effective at cleaning OA and no-clean fluxes at concentrations as low as 5 percent. With an effective chemical isolation section, the effective organic content in the rinse water can be reduced to less than 0.1 percent. This, in turn, opens the opportunity to use mixed beds to fully close loop cleaning processes, even in inline equipment with higher effluent flow rates. The latest products are fully biodegradable and allow for easy, yet compliant disposal into the municipal water treatment system. To further the effort, previously unimaginable pH-neutral defluxing technologies emerged in the market in early 2009. They offer additional benefits by eliminating alkalinity and allowing manufacturers to meet pH limits set forth by most waste water permits and avoiding any adverse effect on the environment.
Table 2: Variable and fixed process parameters, DI-water vs. chemistry assisted processes.


An emerging focus on environmental conservation combined with an increase in cleaning complexity requires new levels of innovations for cleaning products. As a result, more effective cleaning technologies have emerged. They are able to reduce the effective concentration while offering unprecedented benefits over previously known cleaning agents. Products designed on a pH-neutral basis are at the forefront of the green technology trend and are supplemented by other process improvements that reduce evaporative losses as well. We all understand that while chemistry will never be just DI-water, significant advances have been made and should become the basis for each and every new product evaluation.

Contact: Zestron America, 11285 Assett Loop, Manassas, VA 20109 703-393-9880 fax: 703-393-8618 Web:
http://www.zestron.com

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