resistivity of solvent extract
**Resistivity of Solvent Extract (ROSE)** is a **bulk ionic cleanliness test that measures the total ionic contamination on an electronic assembly by dissolving surface contaminants in an alcohol-water solvent and measuring the resulting change in solution resistivity** — providing a quick, inexpensive pass/fail determination of whether an assembly meets ionic cleanliness specifications, widely used in PCB and SMT manufacturing as the primary quality control method for verifying cleaning process effectiveness.
**What Is ROSE?**
- **Definition**: A test method (IPC-TM-650 2.3.25) where an electronic assembly is immersed in or flushed with a 75% isopropanol / 25% deionized water solution — ionic contaminants dissolve from the assembly surface into the solvent, reducing the solution's resistivity. The resistivity change is converted to an equivalent NaCl concentration (μg NaCl eq/cm²) and compared against the cleanliness specification.
- **Resistivity Measurement**: Pure IPA/DI water has very high resistivity (>6 MΩ·cm) — dissolved ions reduce resistivity proportionally to their concentration. The ROSE instrument continuously monitors resistivity as the solvent circulates over the assembly, calculating total ionic contamination from the resistivity decrease.
- **NaCl Equivalent**: Results are expressed as micrograms of NaCl equivalent per square centimeter — this normalizes all ionic species to a common reference, allowing comparison against a single specification limit regardless of the actual ionic species present.
- **Dynamic vs. Static**: Dynamic ROSE circulates solvent over the assembly and monitors resistivity in real-time — static ROSE immerses the assembly for a fixed time and measures the final solution. Dynamic ROSE is more common and provides extraction kinetics information.
**Why ROSE Matters**
- **Manufacturing Standard**: ROSE is the most widely used ionic cleanliness test in electronics manufacturing — virtually every SMT assembly line has a ROSE tester for routine quality control of cleaning processes.
- **Quick and Cheap**: A ROSE test takes 5-15 minutes and costs < $5 per test — enabling 100% lot testing or high-frequency sampling that would be impractical with more expensive methods like ion chromatography.
- **Pass/Fail Simplicity**: ROSE provides a single number (μg NaCl eq/cm²) compared against a single limit — no interpretation required, making it suitable for production operators without analytical chemistry expertise.
- **Process Control**: ROSE trending reveals cleaning process drift — gradually increasing contamination levels indicate aging wash chemistry, clogged nozzles, or changing flux formulations before the specification limit is exceeded.
**ROSE Limitations**
- **No Species ID**: ROSE cannot distinguish between harmful ions (chloride) and benign ions (weak organic acids) — a ROSE failure could be caused by aggressive chloride contamination or harmless flux residue, requiring IC follow-up for root cause.
- **Extraction Efficiency**: ROSE may not extract all contamination — ions trapped under components, in crevices, or absorbed into the laminate may not dissolve during the short test duration.
- **No-Clean Flux Challenge**: No-clean flux residues are designed to be benign but can contribute to ROSE readings — some manufacturers exempt no-clean assemblies from ROSE testing, relying instead on process qualification.
| ROSE Parameter | Typical Value |
|---------------|-------------|
| Solvent | 75% IPA / 25% DI water |
| Temperature | 40°C (heated for better extraction) |
| Test Duration | 5-15 minutes |
| Pass Limit (Class 3) | < 1.56 μg NaCl eq/cm² |
| Pass Limit (Class 2) | < 1.56 μg NaCl eq/cm² |
| Instrument Cost | $500-2,000 |
| Cost per Test | < $5 |
**ROSE is the workhorse ionic cleanliness test of electronics manufacturing** — providing quick, inexpensive bulk contamination measurements that verify cleaning process effectiveness and ensure assemblies meet ionic cleanliness specifications, serving as the first-line quality gate that catches contamination issues before they become field reliability failures.