The cleanliness of circuit boards is critical to the performance and reliability of the assembly. One of the trusted methods to measure circuit board cleanliness is a test called ROSE, which stands for Resistivity Of Solvent Extract. ROSE is an ionic cleanliness test used to determine the amount of ions present on a circuit assembly. It should be noted that the ROSE test only detects ions and is not a measure of other contaminants such as dirt, dust, or surfactants that have no ionic reactivity.
The ionic contaminants being measured are generally sodium, chlorine, bromine, and fluorine. These ions are a result of various steps in the circuit board assembly process such as soldering, etching, or plating, and are often referred to as flux residues.
Ions cause chemical reactions to occur on the circuit board that form a material called dendrite, and result in circuit board performance issues, and in some cases, failures. ROSE testing is the recognized industry standard for measuring and tracking ionic cleanliness in circuit boards and assemblies in order to prevent these performance issues, especially within sensitive industries such as the military and medical fields.
History of ROSE
The ROSE test was created in response to space and military systems failures in the 1960’s. ROSE testing was developed to detect residual ionic residue from rosin-based fluxes. In the 1990’s, electronics manufacturers started using a new type of flux called “no-clean fluxes” and also introduced higher temperature “lead free” solders which expose flux residues to hotter conditions for a longer duration during assembly; these changes made circuit board cleaning more difficult and presented challenges to the ROSE test. Additionally, as electronics technologies continue to advance over time, assemblies are getting smaller with tighter clearances – resulting boards and assemblies that are harder to clean and inspect.
How is ROSE Testing Performed?
To start the test, a bare circuit board or full assembly is selected as the sample for a given batch. The resistivity of a known volume of 75% isopropyl alcohol (IPA) and 25% purified water solution is measured and the solution is sprayed on the board, or alternatively the board can be immersed in the solution. The solution dissolves the salts and other ionic substances present on the board. The resistivity of the solution after it has been in contact with the board is measured. The results are reported in sodium chloride (NaCl) equivalent. The amount of ionic contaminants removed from the board is then determined based on the drop in the resistance between the initial and final solutions. It should be noted that the result represents the total ions detected whether the ions are NaCl or not.
The duration of the test may impact the results; therefore, the appropriate time should be used for each application. For example, a shorter ROSE test may accurately reflect the level of sodium chloride ions present since these ions usually dissolve quickly in a IPA/water solvent solution; however, if certain flux residues are present, a longer test may be needed to ensure the contaminants have sufficient time to dissolve in the solvent and be detected by the ROSE test.
The extent of contamination is an excellent indication of whether a bare board will be soldered successfully, or if the circuit board will perform reliably when in service. For these reasons, ROSE test results are used to establish process control limits to ensure electronics can be assembled successfully and perform reliably once in the field. Additionally, ROSE data are often tracked over time to identify ways to optimize the cleaning process.
ROSE tester technologies continue to advance and current machines are designed so that the only manual aspect of the test is the insertion and removal of the circuit board before and after the ROSE test – all other steps are automated!
Benefits and Challenges of the ROSE Test
There are a few key limitations to the ROSE test. First, the contaminants must be soluble in the water/IPA solution; furthermore, the introduction of “no-clean fluxes” and “lead free” solders resulted in new flux residues that were not as soluble in the IPA/water solvent. To address this challenge, extraction solvents other than the traditional IPA/water solution are starting to be used more frequently. In many cases, deionized water is the best solvent due to its high polarity and can be easily used to provide ROSE results in both batch and inline cleaning.
Second, since the ROSE test is often only performed on a sample of circuit boards at a given frequency, 100% of the products being produced are not tested, giving rise to concerns that some contaminated boards are escaping. To address this issue, manufacturers are working towards testing 100% of products by inserting the ROSE test into the cleaning process between the final rinse and drying steps. In fact, some new ROSE testers, such as the Aqua Rose Batch, are imbedded in batch cleaning machines to allow PC Board assemblers to perform the ROSE test automatically with every batch! This saves time, allowing for higher production rates, and provides Operators with real-time feedback on process parameters so action can be taken immediately if the process is trending out of control.
Although there are some challenges, there are also many benefits of the ROSE test. For starters, the test is easy to perform and can be completed quickly, in a matter of minutes. Additionally, the ROSE test is the most reliable and accurate method available for measuring ionic contaminants, and continues to adapt to industry technology changes in order to remain the industry standard. An important factor to keep in mind is that current ROSE testing standards are being reviewed by the IPC and are changing, but it still remains the only cost-effective process control available.
Austin American Technologies’ ROSE Testing
AAT is an innovative, market-leading company, engineering and manufacturing production and assembly systems for the electronics manufacturing industry. From general purpose to high reliability requirements, AAT systems are design-driven by the science of cleaning. Applications include solar panel cleaning, medical, military, aerospace, cleaning printed circuit board cleaning (aqueous and semi-aqueous), SMT, flip chip, BGA, etc. Our systems include batch and in-line, aqueous and solvent, spray-in-air, and spray under immersion with ultrasonics.
One of our newer products is Aqua Rose Batch – the world’s first aqueous batch cleaner and ROSE tester in one!
- This system contains an automatic ROSE cleanliness tester as well as programmable ROSE control limits
- Fast Cycle Time for Wash, Rinse, ROSE Test, and Dry
- Every batch cleaned can be programmed with an automatic ROSE test of 1 to 10 minutes which occurs prior to the final DI rinse and before the drying operation eliminating the possibility of a batch escape and cuts the need for extra board handling and test equipment.
- Selectable cycles for cleaning with either commercial aqueous based de-fluxing agents or water only.
- Offers open loop as well as closed loop configurations with zero discharge to drain, saving thousands of gallons of water annually.
Contact us today to learn more about our batch cleaner & ROSE tester or any of our other electronics cleaning solutions.