Choosing the Right IPC-A-610 Class for a Box Build Program

When a box-build RFQ lands at an EMS factory, one of the first questions the quoting engineer asks is which IPC class the product must meet. The answer changes the inspection plan, the AOI settings, the bare board specification, the operator skill level and the price. Many RFQs leave it blank, and the factory then quotes its own default, which is almost always Class 2.

This article explains what the three classes of IPC-A-610 mean, where the criteria differ, how the standard relates to IPC J-STD-001 and IPC/WHMA-A-620 and how to write the class into your drawings and RFQ so every factory quotes the same thing. It is written for engineers and buyers sourcing box build assembly in Vietnam or elsewhere.

The criteria below are summarised from public descriptions of IPC-A-610, a licensed document sold by IPC. Check the exact tables in the revision you contract to before signing a quality agreement.

What IPC-A-610 is, and what it is not

IPC-A-610, ‘Acceptability of Electronic Assemblies’, is the most widely used workmanship standard for printed circuit board assemblies. Revision J was released in 2024. It is a visual acceptance standard: it tells an inspector what a finished solder joint, component placement, conformal coating or hardware mounting must look like to be accepted. It uses four conditions for each criterion:

• Target: close to perfect, desirable but not always achievable.
• Acceptable: not perfect, but maintains integrity and reliability in service.
• Process indicator: not a defect, but a sign that the process needs attention. No rework is required.
• Defect: unacceptable; the unit must be reworked, repaired, scrapped or used as is by agreement.

What it is not:

• Not a process specification: soldering methods, materials and process verification are in IPC J-STD-001.
• Not a bare board standard: PCB fabrication is covered by IPC-6012.
• Not a cable standard: crimps, splices and harnesses are covered by IPC/WHMA-A-620.
• Not a sampling plan: how many units get inspected is a contract term.

The three classes

IPC-A-610 groups products into three classes by the consequence of failure and the service environment. The standard makes the user, meaning the buyer, responsible for choosing.

• Class 1, general electronic products. The main requirement is that the product works. Cosmetic imperfections are tolerated. Explicit Class 1 call-outs are uncommon in professional box-build work.
• Class 2, dedicated service electronic products. Continued performance and extended life are required, and uninterrupted service is desired but not critical. The typical end-use environment would not cause failures. Most commercial, communications and industrial products sit here.
• Class 3, high performance or harsh environment electronic products. Continued high performance or performance on demand is critical, downtime cannot be tolerated and the equipment must function when required, often in a harsh environment. Life-support systems are the classic example.

A higher class is not simply ‘better quality’; it is a set of tighter limits that pays back only when a marginal joint has serious field consequences.

Where the criteria differ in practice

The table below shows representative criteria that change between classes, plus contract practices that usually travel with the class. The first four rows are drawn from the standard’s criteria as commonly summarised; the last rows are typical contract practice, not requirements of IPC-A-610 itself.

Item	Class 1	Class 2	Class 3
Chip component end joint width (minimum)	50% of termination or land width	50%	75%
Chip component side overhang (maximum)	50% of component or land width	50%	25%
Through-hole barrel vertical fill	Least stringent	75% typical minimum, limited exceptions for heavy thermal planes	75% minimum
Through-hole circumferential wetting, solder destination side	Not specified	180 degrees	270 degrees
Cleanliness evidence	Per process	Objective evidence per J-STD-001	Objective evidence, often backed by SIR or ion chromatography qualification
Inspection coverage (contract practice)	Sample based	AOI plus sample visual	100% visual plus AOI, X-ray on BGA and bottom-terminated parts commonly specified
Rework and repair (contract practice)	Liberal	Normal limits	Tighter limits on number of rework cycles, repairs often need buyer approval

Lead protrusion, wire wrap on terminals, conformal coating coverage and laminate damage also tighten at Class 3. The pattern is consistent: Class 3 accepts less deviation from target and turns more Class 2 ‘acceptable’ conditions into defects.

Cleanliness is a moving target

Earlier practice relied on a single ROSE (resistivity of solvent extract) pass/fail number. Recent revisions of J-STD-001 moved away from that figure and require objective evidence that the assembly is clean enough for its application. For a Class 3 product with high-impedance circuits, conformal coating or condensation exposure, buyers commonly ask for SIR (surface insulation resistance) or ion chromatography data on the actual process. Put that request in writing.

How IPC-A-610, J-STD-001 and IPC/WHMA-A-620 fit together

Think of the documents as a set, each with its own class selection:

• IPC J-STD-001 sets the requirements for soldered electrical and electronic assemblies: materials, methods and verification. It is the process side.
• IPC-A-610 is the acceptance side for the same assemblies. A factory can build to J-STD-001 and inspect to IPC-A-610.
• IPC/WHMA-A-620 covers cable and wire harness assemblies: crimp terminations, insulation displacement, splices, connectors, overmolding, marking and electrical test. It uses the same three class definitions.
• IPC-6012 covers the bare rigid board, again with Class 1, 2 and 3.

A box build usually involves all four. If the PCBA is Class 3, the bare board should normally be Class 3 as well, and any cable that carries the same critical function should be built to IPC/WHMA-A-620 Class 3. Mismatched classes are one of the most common gaps found when an RFQ package is reviewed. There are also addenda for space and military hardware that add requirements on top of Class 3; if your program needs them, name them explicitly.

Which products typically need which class

The class follows the consequence of failure, not the price of the product. Typical assignments:

Product type	Typical class	Notes
IoT gateways, smart-home hubs, Wi-Fi mesh nodes	Class 2	Standard commercial expectation
Consumer audio: speakers, soundbars, headphones	Class 2	Class 1 occasionally for very low-cost items
Industrial controllers, PLC enclosures, edge gateways	Class 2, sometimes Class 3 on selected boards	Class 3 where downtime is expensive or vibration and temperature cycling are severe
Display modules: digital signage, kiosks, POS terminals	Class 2	Cosmetic spec matters more than solder class
Battery-powered trackers, wearables, scanners	Class 2	Watch fine-pitch and bottom-terminated parts
Wellness and fitness devices (non-FDA)	Class 2	Class 3 not normally required
Life-support or diagnostic medical equipment	Class 3	Usually combined with ISO 13485 quality system requirements
Aerospace, defence, safety-critical transport	Class 3 plus addenda	Often with customer-specific requirements

Mixed classes are allowed and often sensible. A smart meter might be Class 2 overall with the power supply board called out as Class 3. An industrial gateway might be Class 2 except for the connector board that sits next to a motor drive.

Cost and yield impact of Class 3

Moving from Class 2 to Class 3 affects cost in several places at once:

• Inspection time. 100% visual inspection under magnification, plus AOI tuned to tighter limits, plus X-ray on area-array packages.
• First-pass yield. Joints that pass as Class 2 acceptable become Class 3 defects, so more units go to rework. Rework cycles themselves are often limited, which increases scrap.
• Bare boards. IPC-6012 Class 3 fabrication requires tighter annular ring, plating and via reliability controls and costs more per panel.
• People and documentation. Certified IPC specialists on the line, fuller traceability records and more formal handling of process indicators.
• Process qualification. Cleanliness evidence, reflow profile qualification and sometimes cross-sections on first articles.

Commonly quoted uplifts for Class 3 assembly and inspection labor are in the range of roughly 10 to 30 percent over Class 2 for the same board, with bare board premiums on top. These are indicative figures only; the real number depends on the design, the package mix and the factory, and it must be confirmed by factory quotes. The cost article in this series, box build cost in Vietnam, shows where inspection and test sit in a full cost breakdown.

The practical rule: do not specify Class 3 on a consumer product because it sounds safer, and do not leave a genuinely critical assembly at Class 2 to save cost.

How to specify the class on drawings and in the RFQ

Put the class on each assembly drawing as a note, not only in an email. A typical note block:

1. Solder per IPC J-STD-001, Class 2.
2. Workmanship and acceptance per IPC-A-610, revision J, Class 2.
3. Cable and harness assemblies per IPC/WHMA-A-620, Class 2.
4. Bare PCB per IPC-6012, Class 2.
5. Where this drawing conflicts with the documents above, this drawing governs.

In the RFQ itself, add the items the standard leaves to the contract:

• Class per assembly, with any Class 3 exceptions listed by part number.
• Revision of each standard you contract to.
• Inspection coverage: AOI, 100% or sample visual, X-ray on which packages.
• Cleanliness requirement and the evidence you expect.
• Conformal coating material and coverage areas, if used.
• Rework limits and whether repairs need your approval.
• Outgoing sampling plan, for example an AQL per ISO 2859-1.
• How process indicators are reported and trended.

The box build RFQ checklist covers the rest of the package: BOM, drawings, test specification and volumes. If you are unsure of the class, say so in the RFQ and describe the environment and consequence of failure; a good factory engineer will ask the right follow-up questions.

What to ask a Vietnamese factory about IPC class capability

Many EMS lines in the northern clusters (Bac Ninh, Bac Giang, Hai Phong) and southern clusters (Binh Duong, Dong Nai) build to IPC-A-610 Class 2 by default for export customers. Class 3 capability is less common and should be verified, not assumed. Useful questions:

• Which revision of IPC-A-610 and J-STD-001 are your inspectors trained and certified on?
• How many certified IPC specialists (CIS) work on the line, and is there a certified trainer (CIT) in house?
• Can you show a redacted inspection report or AOI program from a Class 3 build?
• Do you have X-ray inspection on site, and what is the process for BGA voiding assessment?
• How do you provide objective evidence of cleanliness?
• Which IPC/WHMA-A-620 class do your cable operators work to?

The wider vetting process is covered in how to vet an EMS provider in Vietnam, and the box build assembly guide explains where inspection sits in the overall project flow.

Getting quotes on a like-for-like basis

Two quotes for the same product, one at Class 2 with sample inspection and one at Class 3 with 100% inspection and X-ray, cannot be compared. Fixing the class, revision and inspection coverage in the RFQ makes the numbers line up.

boxbuildvn.com is a matching service, not a factory. The class and inspection requirements you state are used to shortlist factories whose stated capability fits, and you then verify and work with them directly. Send your BOM, drawings and class requirements through the box-build RFQ form and get matched with up to 3 Vietnamese EMS factories within 24 business hours. Free for buyers, NDA on request. For PCBA-only or cable work, see EMS contract manufacturing in Vietnam, or go straight to the RFQ form.