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Cleaning Without Damage to Materials
Before cleaning. Note the flux residue.
By Umut Tosun, Application Technology Manager, and Jigar Patel, Senior Process Engineer, Zestron, Manassas, VA
In close collaboration with a leading military and government contractor and provider of homeland defense products and services, Zestron performed extensive cleaning trials and material compatibility testing to help the customer find the most suitable cleaning process solution that would ensure that these mission-critical assemblies would not fail in the field.
In recent years, several factors have converged to create the perfect storm in the cleaning world, significantly affecting the long-term reliability of assemblies. First, there has been a consistent drive toward miniaturization. The resulting complex geometries, densely packed boards and low standoff spacing negatively impact the cleaning chemistries' ability to reach and soften residues.
Next, this challenge is increasing at a time when processes have been rapidly converted from eutectic to lead-free pastes. The associated higher reflow temperatures of lead-free processes have resulted in higher amounts of burned-in residues that are polymerized and hardened more than their eutectic counterparts.
After cleaning — no more residue.
Therefore, these challenges demand more of cleaning agents as the difficulty to penetrate tight spaces equates to less exposure time of the cleaning agent to the trapped residues. All too often, industry failures are traced back to residues under low standoff components even after boards have passed ionic testing. This requires cleaning agents that can rapidly soften and dissolve the harder lead-free residues in a fraction of the time that was needed to clean the less complicated boards of the past.
High Reliability Products
Finally, the demand for high reliability products in the automotive, military, medical, and semiconductor industries is at an all time high, while the automotive industry also continues to demand long term reliable products to satisfy ever lengthening warranty periods. The difficult cleaning challenges and the need to ensure long term reliability requires cleaning agents that will clean a wide range of fluxes with short exposure times, while exhibiting the highest levels of material compatibility with sensitive parts.
In this particular case study, numerous prior evaluations with several cleaning agents provided perfectly clean single-sided and double-sided boards. However, two of the substrates — olive-drab coated parts and electro-less nickel plated connectors — showed material compatibility issues. In order to meet the customer's requirements, Zestron's R&D department set out to develop a new, broad spectrum chemistry that would eliminate any material compatibility issues while providing exceptional cleanliness levels. As a result, the FAST
Technology-based cleaning agent ATRON
AC 207 was formulated.
Critical Parts Compatibility
To ensure that this new chemistry would be compatible with the customer's critical parts, Zestron performed internal short-term (15-minute exposure) and long-term (24-hour exposure) beaker tests. Olive-drab coated metal and electro-less nickel plated coupons as well as anodized coated metal connectors were exposed to the cleaning agent while being continuously agitated. All tested substrates were deemed compatible with ATRON AC 207.
The cleaning trials ensued. The company's standard FR4 test boards, single-sided and populated with various SMT components (1812, 1206 and 0603), were used as test vehicles. After applying a commonly used leaded solder paste, all boards were reflowed twice, omitting intermediate cleaning. Subsequently, the boards were washed in a Speedline AS 200 inline cleaner using ATRON AC 207 in 15 percent concentration at 60°C. Wash pressure was 90 PSI top and 60 PSI bottom.A visual surface cleanliness inspection showed excellent results, as all flux residues were removed.
For the compatibility trials, each board was passed through the inline cleaner 5 times (worst-case scenario) applying the above process parameters. After each pass, the critical parts were visually inspected for possible degradation or discoloration. ATRON AC 207 proved to be compatible with all substrates, as no material changes were observed.
Based on these findings, it became obvious that not all precision cleaners are created equal. Cleaning has become an integral part of the SMT production process, especially when manufacturing for high reliability applications where in-field failures are simply not an option. Because of this, both cleanability and material compatibility of the substrate must be considered. Furthermore, to ensure a successful process implementation, customers should not only evaluate the cleaning agent itself, but also the supplier, to confirm that they are well-equipped to assist them in finding the best possible solution.
Formulated to Be Gentle
ATRON AC 207 is formulated to have a particularly gentle impact on sensitive metals, while continuing to offer the proven cleaning performance of Zestron's FAST Technology based cleaning agents. Specifically designed to be used in spray-in-air batch and inline processes, the cleaning performance of this cleaner was assessed during extensive cleaning trials performed at the company's Global Technical Centers as well as during extensive MOC and cleaning evaluations in military manufacturer cleaning processes.
As a result, it was confirmed that ATRON AC 207 offers an exceptional level of material compatibility with sensitive materials such as aluminum, brass, and nickel, while maintaining the high level of cleaning performance expected from a FAST Technology product at concentrations as low as 5 percent.
Contact: Zestron America, 11285 Assett Loop, Manassas, VA 20109
703-393-9880 fax: 703-393-8618 E-mail: infoUSA@zestron.com Web:
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