IPC-A-610 thickness ranges by coating type, why thickness matters, and the limits of each way of measuring it.
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Conformal coating thickness requirements depend on the coating type. The IPC-A-610 ranges, as published by Specialty Coating Systems, are 30 to 130 microns for acrylic, epoxy and urethane, 50 to 210 microns for silicone and 10 to 50 microns for parylene. Measuring against those ranges is harder than it looks: the common mechanical gauge reads in steps of 25 microns, which an IPC conference paper notes is roughly equal to the lower specification limit itself. This page sets out the ranges, why thickness matters, and the strengths and limits of each measurement method.
| Coating type (IPC code) | Thickness range (microns) | Thickness range (mm) |
|---|---|---|
| Acrylic (AR), epoxy (ER), urethane (UR) | 30 to 130 | 0.03 to 0.13 |
| Silicone (SR) | 50 to 210 | 0.05 to 0.21 |
| Parylene (XY) | 10 to 50 | 0.01 to 0.05 |
These are the IPC-A-610 ranges as summarised by Specialty Coating Systems, a coating supplier. Your drawing, the coating datasheet and the current revision of the standard take precedence. The same supplier says parylene is usually applied between about 13 and 51 microns, and acrylic at a dry film thickness of about 51 to 127 microns.
Thin coating leaves gaps in protection, but thick coating causes problems of its own. A paper presented at IPC APEX 2009 by Fritz Byle of Astronautics Corporation of America lists the reasons manufacturers control thickness:
Each method has a catch. The table below summarises the options, drawing on the IPC APEX paper and Techspray's overview of measurement methods.
| Method | How it works | Limits to know about |
|---|---|---|
| Wet film gauge | A notched comb pressed into the wet coating | Gives an approximate reading of the wet film, not the final dry thickness |
| Mechanical gauge (micrometer) | Board measured before and after coating | Coarse steps of 12.5 or 25 microns, operator-dependent, hard to hit the same spot twice, and double-sided boards must be halved |
| Eddy current gauge | Probe senses distance to the metal beneath the coating | Needs roughly a 12 mm diameter area of continuous coating over a ground plane, with no solder mask in between |
| Ultrasonic gauge | Times a sound pulse reflected from the substrate | Depends on a clear reflection from the coating-substrate interface |
| Optical (focal) microscopy | Microscope focuses on the coating surface, then on the substrate beneath | Only works on clear or translucent coatings and needs the coating's refractive index |
| Cross-section | A sample is cut and the coating measured under a microscope | Destructive |
| Weight difference | Weigh before and after coating | Gives an average only, with confounding factors |
The IPC APEX paper describes a low-cost optical method built on a used metallurgical microscope, which measured coatings from under 25 to over 750 microns with repeatability close to 2.5 microns. It needed a correction for the coating's refractive index: the paper measured 1.54 for an acrylic and 1.60 for a urethane, and found a generic value of 1.55 kept the error within about 3.5%.
Our suggestion is to agree measurement points in advance rather than leave them to the inspector. Flat areas over copper suit eddy current gauges; the IPC APEX paper found that legend ink, lands and component tops made good focusing points for optical measurement, while plain solder mask did not. A flat coupon coated alongside the boards is another option: it gives a measurable sample without touching the product.
IPC-CC-830 specifies thickness for the samples used to qualify a coating material, not for every production board. In production, the limits come from IPC-A-610 according to coating type, from the coating supplier's datasheet, and from your customer's drawing, which overrides both. Our conformal coating standards page explains how these documents fit together, and our conformal coating types page compares the coatings themselves.
Systemation Euro offers liquid conformal coating and parylene coating to the specification on your drawing, with inspection after coating and a certificate of conformity if required. Tell us the coating type, the thickness requirement and any measurement points when you request a quote.
It depends on the type. IPC-A-610 ranges, as published by Specialty Coating Systems, are 30 to 130 microns for acrylic, epoxy and urethane, 50 to 210 microns for silicone and 10 to 50 microns for parylene.
The IPC-A-610 range for parylene is 10 to 50 microns. Specialty Coating Systems says it is usually applied between about 13 and 51 microns and can be applied thinner.
Yes. Excess thickness adds thermo-mechanical stress on components and solder joints, raises thermal impedance, and causes curing and rework problems.
There is no single best method. Eddy current gauges suit flat areas over copper, optical methods suit clear coatings, and cross-sections give a direct reading at the cost of a sample. Agree the method and measurement points with your customer before production.
Sources: F. Byle, Low Cost Optical Thickness Measurement of Conformal Coatings, IPC APEX 2009 (gauge limits, eddy current requirement, refractive indices, reasons to control thickness); Specialty Coating Systems, Conformal Coating Specifications (IPC-A-610 ranges); Techspray, How do you measure the thickness of conformal coating (method overview). Check the current revision of each standard for exact requirements.
Tell us the assembly, the operating environment and any specification you work to, and we will advise on the coating. Add a phone number if you would like a call back, or call us on 01604 491107.
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