Cleanliness directly affects the electrical stability and long-term performance of printed circuit boards. IPC-TM-650 Method 2.3.25 defines a standardized way to measure ionizable surface contamination using ROSE testing, translating invisible residues into quantifiable data.
IPC-TM-650 Method 2.3.25: ROSE Testing Overview
IPC-TM-650 Method 2.3.25 is a standardized IPC test method for determining the level of ionizable surface contamination on printed circuit boards using ROSE (Resistivity of Solvent Extract) testing. ROSE testing is defined as a process where ionic residues are extracted from the board into a specified solvent, and contamination is quantified by measuring the resulting change in the solution’s electrical resistivity (or conductivity).
Why ROSE Testing Matters
A PCB can look clean but still contain invisible ionic residues. In humid conditions, these residues dissolve into thin moisture films and become electrically active. This increases leakage risk and supports corrosion-related failure mechanisms.
ROSE testing provides a numeric cleanliness baseline that helps you:
• verify soldering and cleaning performance
• confirm process changes
• qualify suppliers or contract manufacturers
• reduce early-life failures and hidden reliability risks
ROSE data also supports compliance programs linked to standards such as J-STD-001, IPC-A-610, and IPC-6012. It does not replace these standards. It supports them with measurable cleanliness data.
What ROSE Actually Measures
ROSE measures the total ionizable contamination that dissolves into the solvent under controlled extraction conditions.
Measurement sequence:
• Extract ionic residues into the solvent
• Measure conductivity or resistivity change
• Convert the electrical change into a contamination value
• Report results as micrograms of sodium chloride (NaCl) equivalent per square centimeter (µg/cm²)
ROSE detects:
• water-soluble flux residues
• ionic salts from handling
• plating or etching chemistry carryover
• ionically active cleaning residues
ROSE does not identify:
• the exact chemical species present
• whether contamination is localized or uniform
• actual field reliability under humidity and voltage bias
How Ionic Residues Trigger Leakage, Corrosion, and Field Failures
Ionic contamination becomes electrically harmful mainly when moisture is present. In humid conditions, a thin film of water can form on the PCB surface. When ionic residues dissolve into that film, they create a weak electrolyte that lowers insulation resistance across solder mask and laminate surfaces, especially between closely spaced conductors. Even if a board passes initial electrical tests, this reduced resistance can allow small leakage paths to form and grow over time.
Once voltage bias is applied, the situation can escalate. The electric field drives ions across the surface, increasing surface leakage current and enabling electrochemical migration. As metal ions move and redeposit, they can form dendritic growths that bridge adjacent traces or pads. These conductive filaments can eventually trigger insulation breakdown, causing intermittent faults that appear only under certain humidity or temperature conditions, or delayed failures that show up after weeks or months in the field.
The risk is highest in environments and designs that encourage moisture films and narrow spacing. High-humidity service conditions, automotive under-hood electronics, and outdoor systems all expose assemblies to moisture, contaminants, and temperature cycling that accelerate these mechanisms. Higher-voltage assemblies raise the driving force for migration, while fine-pitch, high-density layouts reduce the distance needed for dendrites or leakage paths to create functional shorts. In this context, ROSE testing does not replicate the combined stresses of humidity, bias, and long-term exposure that cause these failure modes; instead, it helps reduce risk by enforcing a measurable cleanliness limit before shipment.
How to Interpret ROSE Results and Set Action Limits
Results are reported in µg/cm² NaCl equivalent. Many production lines reference 1.56 µg/cm² as a general benchmark. This value originated from legacy military specifications such as MIL-P-28809, where it was used as a practical screening threshold for assemblies cleaned with rosin-based flux systems. It later became widely adopted across commercial manufacturing as a default reference point.
It is not a universal reliability guarantee. IPC-TM-650 Method 2.3.25 defines the test procedure, not a mandatory pass/fail limit. Cleanliness limits are typically set by: customer specifications, internal quality programs, industry standards such as J-STD-001 (when invoked).
High-reliability sectors (automotive, aerospace, medical) often apply tighter limits than 1.56 µg/cm². Some programs establish product-specific baselines derived from SIR correlation data.
Practical interpretation:
• Below 1.56 µg/cm²: low ionic load for many commercial applications
• 1.56–3.06 µg/cm²: elevated residue; review cleaning and handling
• Above 3.06 µg/cm²: high residue; corrective action and validation required
When results exceed defined thresholds, follow-up testing commonly includes ion chromatography to identify specific ionic species and determine root cause. ROSE values should be interpreted as process indicators, not separate reliability predictions.
IPC-TM-650 2.3.25 ROSE Test Procedure
Step 1 — Select and Handle the Sample
Begin by selecting a representative bare board or assembled PCB that reflects normal production conditions. The sample must not be specially cleaned or handled differently from routine manufacturing flow. Use gloves and controlled handling practices to prevent adding external contamination during preparation. Record the part number, lot information, and calculate the total tested surface area, since the final cleanliness value is normalized to area.
Step 2 — Prepare the Solvent
Prepare the extraction solvent according to standard practice, typically a mixture of 75% isopropyl alcohol (IPA) and 25% deionized (DI) water. The solvent must be fresh and verified to ensure it meets baseline resistivity or conductivity requirements before testing begins. Confirm the system’s initial conductivity reading to establish a stable reference point prior to introducing the sample.
Step 3 — Extract Ionic Residues
Place the sample into the ROSE test system, either in an immersion bath or a spray-in-chamber configuration. Ensure complete wetting of all board surfaces so ionic residues can dissolve effectively into the solvent. Maintain the defined extraction duration, commonly 5 to 10 minutes for routine production monitoring without interruption, as time consistency directly affects the measured contamination level.
Step 4 — Measure Electrical Change
After extraction begins, the system measures the change in the solvent’s electrical properties using a calibrated conductivity or resistivity cell. Verify that temperature is properly monitored or automatically compensated, since conductivity varies with temperature. Accurate calibration and stable measurement conditions are critical for producing repeatable data.
Step 5 — Convert to Sodium Chloride (NaCl) Equivalent
The measured conductivity change is mathematically converted into micrograms per square centimeter (µg/cm²) of sodium chloride (NaCl) equivalent contamination. Ensure the instrument calibration constants are correct and that the board surface area calculation is accurate. Errors in surface area input directly affect the reported cleanliness value.
Step 6 — Record and Report Results
Document the final value along with the test date, lot number, operator identification, and equipment used. Compare the measured result to internal process limits or customer-defined acceptance criteria. Consistent documentation enables trend tracking, lot comparison, and long-term process control.
Accurate surface area calculation and strict timing control significantly influence ROSE results. Maintaining procedural consistency ensures that cleanliness data remains comparable across different lots, operators, and production periods.
Common Sources of Ionic Contamination Across the Process
Ionic contamination originates from multiple stages of PCB manufacturing and handling.
• Soldering Process: In soldering, flux activators and weak organic acids can remain on the assembly when flux does not fully volatilize during reflow. Excessive flux application increases residue volume, and solder paste residues can become trapped under low-standoff components, making them harder to remove and more likely to persist.
• Cleaning Process: Cleaning is another frequent origin of ionic residues when the wash process does not fully remove chemistry from the board. Incomplete rinsing after an aqueous wash can leave dissolved ions behind, and high-conductivity rinse water can reintroduce contaminants. Cleaner chemistry can also carry over if concentration control is poor, and insufficient drying can cause residues to redeposit as moisture evaporates and concentrates remaining ionic material.
• Fabrication & Surface Treatment: Fabrication and surface treatment steps can contribute contamination before assembly even begins. Plating and etching chemistries may leave residual ionic species if process baths or rinses are not well controlled. Inadequate post-fabrication rinsing can allow these residues to remain on the surface, while certain surface-finish processes can introduce additional ionic byproducts that persist unless properly removed.
• Environment & Storage: The surrounding environment and storage conditions can add contamination even after a board is manufactured. Coastal airborne salts can settle on exposed surfaces, and high-humidity storage can promote adsorption and activation of ionic films. Corrosive industrial atmospheres may introduce reactive contaminants, and packaging materials themselves can be a source if they contain ionic additives or become contaminated during storage and transport.
• Handling & Human Contact: Handling and human contact are common, preventable sources of ionic residue. Fingerprints can deposit sodium and chloride salts, and bare-hand contact during inspection can transfer additional ionic contaminants. Even gloves and work surfaces can introduce residues if they are contaminated or not maintained, and weak packaging controls can allow boards to pick up salts or other ionic materials before shipment or assembly.
ROSE vs. Ion Chromatography vs. SIR vs. Visual Inspection
| Aspect | ROSE (IPC-TM-650 2.3.25) | Ion Chromatography (IPC-TM-650 2.3.28) | Surface Insulation Resistance (SIR) |
|---|---|---|---|
| What It Measures | Total extractable ionic contamination (bulk ionic load) | Individual ionic species (chloride, bromide, sulfate, organic acids, etc.) | Electrical insulation performance under humidity, temperature, and voltage bias |
| Data Output Type | µg/cm² NaCl equivalent (numeric value) | ppm or µg/cm² by ion species | Resistance over time (log-scale trend data) |
| Detects Specific Ions? | No – combined contamination value only | Yes – detailed chemical breakdown | No – evaluates electrical behavior, not chemistry |
| Evaluates Reliability Under Stress? | No – does not simulate humidity or bias | No – chemical identification only | Yes – simulates environmental and electrical stress |
| Production Speed | Fast (minutes) | Slow (lab-based) | Very slow (days to weeks) |
| Best Used For | Routine process control and cleanliness screening | Root-cause analysis, supplier qualification, contamination source tracing | High-reliability validation (automotive, aerospace, medical) |
| Production Suitability | Excellent for inline or near-line monitoring | Limited to lab or engineering investigation | Not suitable for routine production screening |
| Destructive? | Non-destructive | Sample preparation required; often destructive to test coupon | Typically non-destructive but long stress exposure |
ROSE Testing Pros and Cons
Pros
• Fast production feedback: Delivers quick pass/fail-style insight that helps catch cleanliness drift before lots ship.
• Cost-effective routine monitoring: Low per-test cost makes it practical for frequent checks across lines, shifts, or suppliers.
• Standardized and widely recognized: Built on an IPC method, which supports consistent reporting, audits, and cross-site benchmarking.
• Strong for trending process stability: Best value comes from tracking results over time spotting gradual drift after chemistry changes, maintenance, or operator shifts.
Cons
• Does not identify specific contaminant species: It reports total ionic load, so it can’t tell whether residues are chlorides, weak organic acids, activators, etc.
• Does not detect non-ionic residues (e.g., oils, silicones, rosin films): These can still cause assembly or coating issues even when ROSE results look acceptable.
• Sensitive to process-control discipline: Results can swing with test parameters (sample handling, extraction conditions, solution control), so consistency matters.
• Cannot reveal localized contamination without targeted sampling: It averages what is extracted, so small hot spots (under components, tight gaps, edges) may be masked unless you isolate or focus the sample area.
Implementing ROSE in Production
• Use ROSE for Process Control: To make ROSE data meaningful, it must be integrated into the formal quality management system rather than treated as a standalone test. ROSE should be positioned as a process control tool, with testing performed at defined checkpoints, commonly after soldering and again after cleaning. Results should be trended by production line, shift, and product family to identify variation patterns. This structured tracking transforms single test values into actionable manufacturing intelligence.
• Standardize Sampling: Sampling must be standardized to ensure trend reliability. Define a consistent sample size and testing frequency based on product risk level and production volume. Surface area calculations should follow a uniform method so results remain comparable over time. Boards selected for testing should represent actual production conditions, including complexity, copper density, and assembly configuration. Consistency in sampling prevents distorted data and false process signals.
• Control Test Variables: Test variables must remain tightly controlled. Solvent preparation should follow disciplined procedures, including concentration verification and contamination checks. Extraction time must be consistent across all tests to maintain repeatability. Temperature stability during testing is also critical, as conductivity and resistivity measurements are temperature-sensitive. Tight control of these variables ensures that changes in ROSE values reflect process shifts, not test instability.
• Pair with Follow-up Methods: ROSE should be paired with deeper analytical methods when needed. If a result exceeds internal limits, follow-up testing such as ion chromatography can identify specific ionic species and support root-cause analysis. In high-reliability programs, Surface Insulation Resistance (SIR) testing may be added to validate long-term electrical performance under humidity and bias conditions. ROSE functions as an early screening indicator, while advanced methods provide diagnostic depth.
• Document Everything: Comprehensive documentation is needed for maintaining data integrity and audit readiness. Calibration records, solvent quality checks, and equipment maintenance logs should be retained and reviewed regularly. Corrective actions must be documented whenever limits are exceeded. ROSE trend data should also be linked to documented process changes such as flux formulation, cleaner chemistry, rinse water quality, or conveyor speed adjustments. When implemented with discipline and consistency, ROSE delivers stable trend data that strengthens PCB cleanliness control across the manufacturing line.
Conclusion
IPC-TM-650 Method 2.3.25 frames ROSE testing as a repeatable process-control check within a broader contamination management program. It does not forecast long-term field reliability or identify specific residue types, but it delivers consistent and measurable cleanliness data. When supported by controlled execution, defined and documented limits, and confirmatory methods such as ion chromatography or SIR, ROSE improves manufacturing confidence and helps reduce latent electrical risk.
Frequently Asked Questions [FAQ]
What is the difference between static and dynamic ROSE testing systems?
Static ROSE systems immerse the PCB in a fixed solvent volume with minimal circulation, while dynamic systems continuously spray or circulate solvent over the surface. Dynamic systems extract residues more efficiently and provide faster stabilization of conductivity readings, making them more suitable for high-throughput production environments.
Can no-clean flux assemblies skip ROSE testing?
No-clean flux does not mean no ionic residue. Even low-residue fluxes can leave activators or byproducts that become conductive under humidity. ROSE testing verifies whether contamination levels remain within defined limits after reflow, helping confirm that cleaning can truly be omitted without increasing leakage or corrosion risk.
How often should ROSE testing be performed in PCB manufacturing?
Test frequency depends on product class, customer requirements, and process stability. Many production lines perform ROSE checks per shift, per lot, or after process changes such as new flux, cleaner adjustments, or rinse-water modifications. High-reliability sectors often apply tighter monitoring intervals to maintain stable cleanliness trends.
Does ROSE testing damage the PCB or assembly?
ROSE testing is non-destructive when performed correctly. The solvent mixture (commonly IPA and DI water) extracts ionic residues without harming solder joints, laminate, or components. After testing, assemblies must be properly dried to prevent moisture retention before further processing or packaging.
What factors can cause false high ROSE readings?
False elevations can result from contaminated solvent, inaccurate surface area calculation, poor temperature control, dirty extraction chambers, or improper handling (such as bare-hand contact). Consistent solvent baseline checks, calibrated equipment, and controlled sample handling reduce the risk of misleading results.
