Contents
Complements workflow

IPC-TM-650: board cleanliness, SIR and coating test methods, and the contact angle check beside them

IPC-TM-650 is the IPC manual of test methods for printed boards and assemblies. Its cleanliness and coating methods measure ionic residue by ROSE (2.3.25) or ion chromatography (2.3.28), surface insulation resistance on comb patterns in humid heat (2.6.3.7), and solder mask and conformal coating adhesion and insulation (2.4.28.1, 2.6.3.4). The Dropometer measures none of these quantities, and no current TM-650 method measures contact angle or surface tension. It complements the workflow with a room temperature water contact angle on the board, which flags non ionic films such as silicone, rosin residue or handling oils. ROSE does not detect those films, and they are a common reason conformal coating dewets.

What brings you here?

Who this is for
Printed board fabricators, electronics assemblers, cleanliness test labs and suppliers of cleaning chemistry, solder mask and conformal coating.
Compliance tier
Complements workflow: the Dropometer does not measure ionic residue, insulation resistance or tape adhesion. It adds a water contact angle check for non ionic films before coating.
Measurement
Sessile drop water contact angle, 10° to 175° range, ±0.35° accuracy (Dropometer datasheet).
Setup
About 2 minutes. Battery powered, 1 kg, runs at the coating line or in the lab.
Last updated
October 18, 2026
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Free one page checklist for a water contact angle check next to IPC-TM-650 cleanliness and coating tests: what to prepare, which boards to keep water off, the settings to lock and what to record. Made for assembly cleaning and coating lines.

Talk to an expert

Book a 15 minute demo on your boards

Tell us your solder mask, cleaning process, conformal coating and the TM-650 tests you run today. We will measure a reference board and a problem board live and tell you plainly where the Dropometer fits next to ROSE and SIR, and where it does not.

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View the official standard
Gurdeep-Saini-Photo
Written by
Gurdeep Singh Saini
Holds a BASc in Mechanical Engineering from Ryerson University (now Toronto Metropolitan University) and an MASc from York University. He develops the automatic edge and baseline detection behind the Dropometer's analysis.
COO at Droplet Lab
Read More
Droplet-Lab logo
Technical Review by
Droplet Lab Team
Droplet Lab builds precision instruments and software for surface science measurement, specialising in contact angle analysis and surface tension characterisation. Used by researchers across materials science, pharmaceuticals, coatings, and advanced manufacturing, Droplet Lab's Dropometer has contributed to studies published in peer-reviewed journals including Advanced Functional Materials (Impact Factor 19). The team combines instrument engineering with deep domain knowledge in wettability science with a focus on practical accuracy.
Read More
Verified against IPC-TM-650
Gurdeep-Saini-Photo
Written By

Gurdeep Singh Saini

COO at Droplet Lab

Holds a BASc in Mechanical Engineering from Ryerson University (now Toronto Metropolitan University) and an MASc from York University. He develops the automatic edge and baseline detection behind the Dropometer's analysis.

Droplet-Lab logo
Reviewed By

Droplet Lab Team

Droplet Lab builds precision instruments and software for surface science measurement, specialising in contact angle analysis and surface tension characterisation. Used by researchers across materials science, pharmaceuticals, coatings, and advanced manufacturing, Droplet Lab's Dropometer has contributed to studies published in peer-reviewed journals including Advanced Functional Materials (Impact Factor 19). The team combines instrument engineering with deep domain knowledge in wettability science with a focus on practical accuracy.

Featured Studies & Publications

Research Paper Contact angle measurement with a smartphone
Research Paper Surface tension measurement with a smartphone using a pendant drop

Evidence box

Standard

IPC-TM-650 Test Methods Manual, published by IPC as separate methods, each with its own revision. Methods on this page: 2.3.25D ROSE (November 2012), 2.3.28B ion chromatography (November 2012), 2.3.28.2 bare board cleanliness by ion chromatography (December 2009), 2.6.3.7 surface insulation resistance (March 2007), 2.6.3.5 bare board cleanliness by SIR (January 2004), 2.6.3.4A conformal coating moisture and insulation resistance (July 2003) and 2.4.28.1F solder mask tape adhesion (March 2007). See the IPC test methods listing.

Compliance tier

Complements workflow. The Dropometer measures none of the quantities these TM-650 methods report: extract resistivity, ion content, insulation resistance or mask removed by tape. No current TM-650 method measures contact angle or surface tension. The Dropometer adds a water contact angle check for non ionic films before coating.

Instrument performance

Contact angle range 10° to 175°, accuracy ±0.35°, display resolution 0.01°, from the Dropometer product specification.

Peer reviewed method

The drop shape method is validated against a KRUSS DSA100E in two peer reviewed papers. See our validation publications.

Customer evidence

A plating chemistry maker uses the Dropometer for contact angle and surface tension work. Read the case study. We have no published client study run alongside IPC-TM-650.

What it does not tell you

A water contact angle does not measure ionic cleanliness, insulation resistance or coating adhesion. Only the TM-650 tests do. Any link between an angle and those results comes from your own correlation study.

Executive summary

What this standard measures, who uses it and how the Dropometer fits

IPC-TM-650 is the IPC test methods manual for printed boards and assemblies; for cleanliness and coatings, its methods measure ionic residue, surface insulation resistance and coating adhesion, not wetting. Board fabricators, assemblers, cleaning chemistry and conformal coating suppliers, and test labs use these methods to qualify materials and control processes. The Dropometer complements this workflow. It measures none of the TM-650 quantities. It adds a water contact angle on the board surface before coating, which shows non ionic films that the ionic tests do not see.

IPC publishes each method as its own document with its own revision. The methods closest to cleanliness and coating are 2.3.25D (ROSE: the resistivity of an isopropanol and water extract, reported as µg NaCl equivalent per cm²), 2.3.28B and 2.3.28.2 (ion chromatography), 2.6.3.7 and 2.6.3.5 (surface insulation resistance on comb patterns), 2.6.3.4A (moisture and insulation resistance of conformal coating), 2.4.28.1F (solder mask tape adhesion) and 2.3.42 (solder mask resistance to solvents and cleaning agents). The surface organic contaminant detection test, 2.3.38C, is listed as cancelled. The TM-650 wetting methods, such as edge dip (2.4.12A) and the flux wetting balance (2.4.14.2A), use molten solder, which the Dropometer cannot test.

The gap the Dropometer fills is non ionic residue. TM-650 2.3.25D states that ROSE reads only ionic material dissolved in the extract. Silicone, rosin residue and handling oils lower the wettability of the board, so a conformal coating can bead up, dewet or show fisheyes. The Dropometer contact angle and surface energy kit reads the water contact angle on solder mask areas from 10° to 175° with ±0.35° accuracy, so you can compare each board with a reference board that coated well. The PCB surface prep use case covers this check for solder mask, conformal coating and cleanliness. A plating chemistry maker uses the Dropometer for contact angle and surface tension work. For background, read the telecommunications guide and the contact angle measurement guide.

Further reading: reproducible contact angle measurement, water contact angle reference values for common surfaces and choosing a contact angle goniometer for industrial QA.

How the Dropometer fits the workflow

A water contact angle check next to IPC-TM-650 cleanliness and coating tests, step by step

From a cleaned board to a coat or hold decision

These steps describe a check on the Dropometer that sits before conformal coating and next to IPC-TM-650 tests. It is not part of any TM-650 method and does not replace ROSE, ion chromatography, SIR or a tape test. Download the current revision of each method from IPC and follow it for every result you report.

±0.35°

Contact angle accuracy

From the Dropometer product specification. Display resolution is 0.01°.

About 2 min

Setup

Base plate, phone holder, LED and syringe. No PC needed.

10 to 45 °C

Operating range

Room temperature checks only. No humidity chamber, no electrical test and no molten solder.

1

Pick the boards and the reference

Choose a reference board that coated well and passed your TM-650 cleanliness tests, with the same solder mask and cleaning process. Keep water off any board or area that goes to ROSE, ion chromatography or SIR, because a drop dissolves ionic residue. Handle boards by the edges with clean gloves.

2

Set up the Dropometer

Place the base plate on a level bench, mount the phone and LED, and fill a clean syringe with deionised water. Check the setup on a reference surface you keep for this purpose before the first board.

3

Map the test areas

Mark flat solder mask areas larger than the drop footprint, away from components, text and vias. Use the same positions on every board, because residue collects in some areas more than others, such as near through hole joints.

4

Place the drops and read the angle

Dispense a fixed drop volume on each area without touching the board. Capture at the same time after placement for every drop. Automatic edge and baseline detection reads the left and right angles, so two operators get the same reading from the same image.

5

Compare with your gate

Compare each board mean with the reference and your gate. A rise above the gate points to silicone, rosin residue, oils or an incomplete rinse. Hold the board, check the cleaning step, then decide whether to coat. The PCB surface prep use case lists common causes.

6

Run the TM-650 tests and log both

Run the ROSE, ion chromatography, SIR or tape tests your specification names, each as the IPC-TM-650 method specifies. Log the contact angles next to each result and each coating outcome. Over time, that log is the correlation study that sets your gate.

7

Watch the full measurement

This video shows a complete Dropometer contact angle measurement, from setup to result. It covers the steps above in one run.

Dropometer contact angle measurement, start to finish.

Validated measurement approach

Independent benchmarking and publication-based validation references.

Peer reviewed method

The Dropometer drop shape method is validated against a KRUSS DSA100E in two peer reviewed papers, one in Review of Scientific Instruments and one in Colloids and Surfaces A. Published contact angle accuracy is ±0.35° (Dropometer product specification).

Read the validation papers

Customer evidence

A plating chemistry maker uses the Dropometer for contact angle and surface tension work. We have no published client study run alongside IPC-TM-650, and no published data linking contact angle to TM-650 results.

Read the case study

Set your gate from your own boards

IPC-TM-650 · cleanliness · conformal coating

No IPC-TM-650 method sets a water contact angle or surface energy limit for board cleanliness or coating readiness. The TM-650 methods report ionic residue, insulation resistance or tape adhesion, and the documents that call them up, such as your customer specification or IPC-CC-830 for conformal coating, set the pass criteria (source: IPC-TM-650 2.6.3.4A). So any contact angle gate comes from your own data.

Measure boards that coated well and passed your ROSE, ion chromatography or SIR checks, and boards that dewetted or failed. Use the same solder mask, cleaning process and drop positions for both groups. Set the gate from the gap between them, for example a maximum rise above the reference board. Repeat the study when you change solder mask, flux, cleaning chemistry, packaging or coating.

Some coating suppliers give a minimum dyne level before coating (source: HumiSeal on PCB surface energy). A contact angle relates to a dyne level only through your own correlation. For what a dyne level does and does not tell you about adhesion, read Beyond 38 Dynes.

Example output

Example data for illustration only. These are not measured results. Your own solder mask, cleaning process and correlation data decide the numbers.

Example: water contact angle on solder mask areas of four cleaned assemblies, before conformal coating

Board Drops (n) Mean angle (°) Std dev (°) Change vs reference (°) Next step
Reference board (coated well)564.01.30.0Reference
Board B565.81.5+1.8Inside example gate: coat
Board C570.91.9+6.9Near gate: coat, note the reading, check the rinse
Board D581.62.4+17.6Above example gate: hold, check for silicone or oils

How to read this table

Each row is the mean of five drops of deionised water on flat solder mask areas, read at the same time after placement, on boards kept out of ROSE and SIR testing. The example gate is the reference reading plus 8°, set from a correlation study against boards that coated well and boards that dewetted. In this example all four boards met the site's ROSE limit: the angle flags a non ionic film that ROSE does not see.

Example output chart

The same example data as the table, with the reference reading and the example gate marked.

Bar chart of example water contact angles on four cleaned assemblies, with three boards near the 64.0 degree reference and one board at 81.6 degrees above an example gate of 72.0 degrees

Example data, not measured results.

Business impact

What changes when a contact angle check sits next to your TM-650 tests

Metric Before Dropometer With Dropometer Results
Non ionic residue such as silicone or oils Not read by ROSE; found as dewetting after coating Flagged by a water contact angle before coating IPC-TM-650 2.3.25D scope; no published benchmark
Ionic cleanliness and SIR ROSE, ion chromatography or SIR to TM-650 Unchanged: still the TM-650 tests IPC-TM-650 method scopes
Result format Visual inspection of the cured coating An angle per drop, ±0.35° accuracy, 0.01° display resolution Dropometer product specification
Where it runs Cleanliness lab, after the batch is coated At the coating line, on battery for up to 8 h Dropometer product specification

See the check on your own boards

Bring a board that coated well and one that dewetted. We will measure both live at room temperature.

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ROI estimate

Estimate the cost of the coating failures found too late

Enter your own numbers. The defaults are examples, not Droplet Lab results.

Quality cost snapshot

Estimate what wetting related failures cost you.

Example only. Use what you see in a trial on your own samples.
Your own figure.
Your own estimate.

Result

~0
Estimated annual cost today
~0
Estimated annual cost avoided
~0
Payback period

Annual exposure combines audit/CAPA cost, customer rejections, and recall probability; avoided exposure applies the risk reduction percentage.

Method settings

Lock these before you compare readings between boards, shifts or sites

Parameter Recommended Setting Technical Rationale
Role of the check Before coating and next to TM-650 tests, never in place of them The Dropometer measures none of the TM-650 quantities.
Specimen Sibling board, or areas excluded from ROSE, ion chromatography and SIR A water drop dissolves ionic residue and could change those results.
Test liquid Deionised water Water is most sensitive to hydrophobic films such as silicone and oils.
Drop volume Fixed for every drop A changing volume adds spread that is not about the surface.
Positions The same mapped flat solder mask areas on every board Residue varies across a board; the drop needs a flat area larger than itself.
Reading time Fixed for every drop Drops can spread or evaporate, so the time must not vary.
Fit model Young-Laplace or polynomial, the same for every run Both models are in the Dropometer software. Do not mix them within one study.
Environment Record room temperature and humidity The Dropometer runs at 10 to 45 °C and has no temperature or humidity control.

Which IPC-TM-650 test, or a contact angle check?

Pick the method by the question you need answered

Start: What do you need to know about the board surface?

Ionic residue after cleaning

Signals:

You need a number for ionic cleanliness for process control, or to know which ions are present.

Rule-out:

Use ROSE to IPC-TM-650 2.3.25, or ion chromatography to 2.3.28 to identify the ions. The Dropometer does not run these tests.

Insulation loss in humid heat

Signals:

You need reliability evidence for a flux, cleaning process or conformal coating.

Rule-out:

Use surface insulation resistance to IPC-TM-650 2.6.3.7, or 2.6.3.4 for conformal coating. The Dropometer does not run these tests.

Non ionic film before coating

Signals:

Coating beads, dewets or shows fisheyes, and ROSE still passes.

Rule-out:

Use a water contact angle against a reference board on the Dropometer. See the PCB surface prep use case.

Will the coating liquid wet the mask?

Signals:

You are choosing a solder mask and coating pair, or a new cleaning chemistry.

Rule-out:

Compare the solder mask surface free energy from two or three test liquids with the coating liquid's surface tension by pendant drop, both on the Dropometer. See ASTM D7490.

Decision tree at a glance

Start from the question you need answered. Blue boxes are measurements the Dropometer runs. The TM-650 tests themselves are not.

Decision tree showing that ionic residue and insulation resistance need IPC-TM-650 ROSE, ion chromatography or SIR tests, while non ionic films and coating wetting can be checked on the Dropometer at room temperature

Which IPC-TM-650 test, or a contact angle check?

Interpreting results

What the angle tells you, and what it does not

A higher angle flags a non ionic film: Silicone, oils and rosin residue raise the water angle on solder mask. Compare with your reference board on the same mask.
A normal angle is not ionic cleanliness: Ionic residue does not reliably raise the angle. Keep ROSE or ion chromatography for ions.
Angle is not adhesion or SIR: A good angle shows the coating can wet the surface. It does not prove adhesion or insulation resistance.
Compare like with like: A gate holds for one solder mask, one cleaning process and one board design. Set a new one when they change.
Expert perspective

Why a board can pass ROSE and still dewet a coating

On a real surface, the receding angle from a sessile drop and from a tilted plate can disagree wildly: one method is not a substitute for the other. The application decides.

Dr. Alidad Amirfazli

Department of Mechanical Engineering, York University, Co-founder and Scientific Advisor, Droplet Lab

Common pitfalls and limits

Honest limits of the check and of the Dropometer

The Dropometer measures none of the IPC-TM-650 quantities on this page: extract resistivity, ion content, insulation resistance or tape adhesion. It complements those tests and never replaces them.
A water drop dissolves ionic residue. Do not place drops on boards or areas that go to ROSE, ion chromatography or SIR.
Small or crowded areas may be smaller than a drop. Use flat solder mask areas larger than the drop footprint.
Matte or textured solder mask gives an apparent angle that reflects texture as well as chemistry. Compare only the same mask.
The Dropometer has no temperature or humidity control and runs at 10 to 45 °C. It cannot run the SIR humidity exposure or test molten solder.
No IPC-TM-650 method publishes a contact angle limit for coating readiness. Set your gate from your own correlation study.
FAQ

Frequently asked questions

What is IPC-TM-650?

It is the IPC test methods manual for printed boards, assemblies and their materials. IPC publishes each method as a separate document with its own number and revision, on its test methods page. Specifications such as IPC-CC-830 for conformal coating call up these methods and set the pass criteria.

Which IPC-TM-650 methods cover board cleanliness?

ROSE (2.3.25 and 2.3.25.1) reads the resistivity of an isopropanol and water extract as µg NaCl equivalent per cm². Ion chromatography (2.3.28 and 2.3.28.2) identifies the ions. Surface insulation resistance (2.6.3.5 and 2.6.3.7) tests comb patterns under bias in humid heat. The surface organic contaminant detection test, 2.3.38, is listed as cancelled.

Can the Dropometer run IPC-TM-650 tests?

No. The Dropometer does not measure extract resistivity, ion content, insulation resistance or tape adhesion, and it cannot test molten solder. It complements the workflow with a water contact angle on the board before coating. That check flags non ionic films, such as silicone or oils, that ROSE does not read and that can make a conformal coating dewet.

Does any IPC-TM-650 method measure contact angle or surface tension?

Not in the current IPC listing. The TM-650 wetting methods, such as edge dip (2.4.12A), the flux wetting balance (2.4.14.2A), the solder paste wetting test (2.4.45) and the spread test (2.4.46A), all use molten solder. For room temperature checks before solderability testing, see our IPC J-STD-003 page.

Why does conformal coating dewet when ROSE passes?

ROSE reads only ionic material that dissolves into the extract, so non ionic films go unseen. Silicone, oils and some flux residues lower the surface energy of the board. A coating wets well only when the board's surface energy is higher than the coating's surface tension (source: HumiSeal on PCB surface energy). A higher water angle than your reference board is an early sign.

What water contact angle should a board have before conformal coating?

No IPC-TM-650 method sets one. Angles differ between solder mask products and cures, so compare each board with a reference board on the same mask that coated well. Set your gate from boards that coated well and boards that dewetted. If your line uses dyne pens, relate them to the angle only through your own data; see Beyond 38 Dynes.

Legal note

This page summarises selected IPC-TM-650 methods in our own words and does not reproduce them. Download the current revision of each method from IPC before you write a procedure. The Dropometer complements the workflow: it measures water contact angle at room temperature and does not measure ionic residue, insulation resistance, tape adhesion or solder wetting. Droplet Lab does not certify compliance. Your own method validation does.

View the official standard Book a 15 minute demo

How this page was created

Sources, review and tools

Transparency 4 checklist items
01

Sources

IPC TM-650 Test Methods Manual listing (method numbers, titles, revision dates and status); IPC-TM-650 2.3.25D: Ionizable Surface Contaminants by ROSE; IPC-TM-650 2.6.3.7: Surface Insulation Resistance; IPC-TM-650 2.6.3.4A: Moisture and Insulation Resistance, Conformal Coating, the Dropometer product specification and Droplet Lab validation papers.

02

Drafting assistance

Drafted with Claude (Anthropic) from the sources listed, then reviewed by Droplet Lab.

03

What we did not do

We did not copy text from the standard. Buy the current edition for the full procedure.

04

Last checked

October 2026

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References

1. IPC-TM-650 Test Methods Manual. electronics.org/test-methods
2. IPC-TM-650 2.3.25D: Ionizable Surface Contaminants by ROSE. electronics.org/sites/default/files/test_methods_docs/2-3_2-3-25d.pdf
3. IPC-TM-650 2.6.3.7: Surface Insulation Resistance. electronics.org/sites/default/files/test_methods_docs/2-6-3-7.pdf
4. IPC-TM-650 2.6.3.4A: Moisture and Insulation Resistance, Conformal Coating. electronics.org/sites/default/files/test_methods_docs/2-6_2-6-3-4a.pdf
5. Droplet Lab. Peer reviewed validation papers in Review of Scientific Instruments and Colloids and Surfaces A. dropletlab.com/validation/publications/
6. Droplet Lab. Dropometer product specification, 2026. dropletlab.com/products/dropometer/