The Global Electronics Association, formally known as IPC, publishes the industry standard for PCB manufacturing, IPC-A-610. IPC-A-610 outlines IPC class 2 requirements and criteria for the acceptability of electronic assemblies, guiding manufacturers on quality assurance and inspection processes. The standard lists three classifications of PCB manufacturing requirements: Class 1, 2, and 3.
Frequently, designers may be concerned about whether or not their boards adhere to the highest manufacturing standards. However, it’s essential to recognize that aiming for Class 2 standards may often be sufficient. IPC Class 2 PCBs balance cost-effectiveness and reliability, making them a practical choice for many electronic products.
How IPC-A-610 Class 2 Requirements Compare to Other Classes
The first step in identifying which classification your PCB needs is to understand the differences between the classes and their requirements:
| Class | Description | Manufacturing Requirements | Intended Applications | Notes |
| 1 | General electronic products | Least stringent | Toys, lower-level consumer products | Intended for inexpensive applications, does not expect product longevity, requires low assembly costs |
| 2 | Dedicated service electronic products | More rigorous | Most industrial products, consumer appliances | Intended for assemblies where extended reliability is the goal, it allows for some imperfections that are fully functional electrically and mechanically |
| 3 | High-performance electronic products | Most stringent | Military, aerospace, automotive applications, and environments where the PCB experiences harsh conditions | Demands for perfection in assembly, including aesthetic appearance, come at a higher cost to meet all requirements. |
Although Class 3 requirements are necessary for aerospace applications, these boards are not exclusive to that industry. Class 3 requirements for circuit board manufacturing apply to any board used in a harsh environment where its long-term ability to function reliably is mission-critical, i.e., anywhere the PCB experiences a harsh operating environment, such as in a car’s engine compartment. Most PCBs do not require this amount of exacting specifications.
The Advantages of IPC Class 2 PCB Manufacturing
Since more PCBs fit into Class 2 manufacturing requirements, trying to build to Class 3 requirements is an unnecessary expense. Due to the relaxation of specifications, Class 2 PCBs have numerous advantages over Class 3:
| Class 3 Requirements | Class 2 Advantages | |
| Design | Boards must conform to tighter tolerances and specifications, including annular ring sizes. A minimum of 1 mil annular ring width without any breakout is required; increasing pad diameters reduces routing channels and could affect placement. | Allows for some breakout of the hole from the pad provided that the minimum lateral spacing is maintained, offering flexibility with smaller pad diameters that increase space for placement and routing. |
| Manufacturing | Processes are often slowed down, causing more time and expense. Standards call for a 75% solder fill in the barrel for thru-hole leads and perfectly aligned surface mount parts. | Only a 50% solder fill in the barrel for thru-hole leads is necessary. Surface mount parts can be slightly off-center if it doesn’t impact electrical or mechanical function. |
| Inspection | Must pass more rigid requirements, increasing inspection times, and additional costs. Tight tolerances on annular rings, perfectly aligned surface mount parts, and thru-hole leads filled to 75% must be inspected and verified. | Less stringent than Class 3, with allowances for slight imperfections that do not affect electrical or mechanical functionality |
Most PCBs do need to conform to the highest standard, Class 3. Designers may get better overall results by building for the requirements of an IPC-A-610 Class 2 PCB instead. Consider a closer look at the differences between these three classifications and how they can affect PCB manufacturing. Class 2 requirements are the standard for most products that demand high reliability, such as network equipment, industrial electronics, and many electronic medical devices. Not only is the production line much quicker for a Class 2 board, but the requirements are well-known and easier to work with for manufacturers, which also increases the throughput of the manufacturing process.
IPC Class 2 Requirements for Inspection Standards
IPC-A-610 establishes a framework, emphasizing criteria that inspectors must check to meet IPC class 2 requirements. The standard outlines detailed acceptability requirements for the following:
- Component placement
- Solder joints
- Cleanliness
- Marking
Tools such as magnifiers (typically 5–10× for small components), microscopes, and calibrated measurement aids are specified to verify features like lead-to-pad alignment, fillet dimensions, and solder coverage. In certain cases, such as hidden solder joints under BGAs, X-ray inspection or other non-destructive techniques can be used, guided by related IPC documents (e.g., IPC-7095 for BGAs) (ipc.org).
Inspection criteria are organized by subject area (e.g., soldered connections, component placement, cleanliness) and by classification. For each inspected feature, IPC-A-610 provides visual examples of acceptable, marginal, and unacceptable conditions. This includes images and descriptions showing the correct:
- Solder fillet shape
- Acceptable fillet size
- Wetting
- Absence of solder bridges
- Permissible minor voids
The standard also references related workmanship standards, such as J-STD-001 for soldering processes, to ensure inspectors understand the root of defects and the processes that produce them.
Routine inspection workflows often include first-article inspections, in-process sampling, and final inspections:
- First-article inspections verify that the initial boards meet specified criteria.
- In-process sampling checks ongoing production consistency.
- Final inspections ensure completed assemblies conform before shipment.
IPC Class 2 Inspection Reports Requirements
Inspection reports record findings, non-conformities, and corrective actions. Many manufacturers implement SPC (Statistical Process Control) or other quality systems aligned with ISO 9001 or IATF 16949.
Operator and inspector calibration is another cornerstone: regular review sessions, “golden boards” samples, and cross-audits ensure consistent interpretation of marginal conditions. This reduces false failures or escapes, optimizing yield without compromising reliability.
Additional documentation and traceability requirements may apply to boards in regulated industries (e.g., medical devices), but the fundamental IPC-A-610 visual criteria remain the baseline for acceptability.
IPC-A-610 Class 2 Requirements
IPC-A-610 Class 2 targets “dedicated service electronic products” where extended reliability is important, but no mission-critical uninterrupted service is required. This includes industrial equipment, network devices, many medical instruments (non-life-support), and consumer appliances demanding longer lifecycles.
Solder Joint Criteria
For Class 2:
- Solder joints must exhibit good wetting, smooth fillet geometry, and sufficient coverage.
- Surface mount joints require a proper fillet shape, and side fillets should meet minimum fillet height (e.g., for chip components, a minimum side fillet of approximately 75% of the lead thickness per IPC-A-610 guidance).
- Thru-hole joints must achieve at least 50% barrel fill with solder to provide reliable mechanical retention and electrical contact.
- Minor imperfections (e.g., slight curvature in the fillet or small voids within limits) are acceptable, provided they do not impair function or lead to early failures under expected stresses.
Component Placement and Alignment
- Placement variation of up to ±0.5 mm for most parts is acceptable if solder joint integrity and inspection access are not compromised.
- Component rotation, coplanarity, and lead-to-pad alignment must ensure reliable solder fillet formation. Slight misalignments that do not lead to insufficient wetting or solder bridges are permitted.
- Critical polarized components (e.g., diodes, electrolytic capacitors) must still be oriented correctly, with clear polarity marking visible for inspection and maintenance.
Cleanliness and Residue Control
Class 2 boards require appropriate cleaning to remove flux residues that could lead to corrosion or electrical leakage over time. Class 2 cleaning standards aim for levels that ensure long-term reliability under normal environments. Inspection criteria include:
- Verifying that residues are within acceptable limits (e.g., no visible flux residues in critical areas).
- Conformal coating (if applied) must be uniform and free of voids that could trap contaminants.
Marking and Documentation
Legible silkscreen markings for component designators, polarity indicators, and revision information are required. Class 2 mandates that markings remain readable after assembly and cleaning processes. Documentation accompanying assemblies (e.g., inspection reports, assembly drawings) must reflect the product’s classification and any deviations approved under change control processes.
Acceptable Imperfections and Repair
IPC-A-610 for Class 2 explicitly shows examples of acceptable vs. unacceptable defects. For instance, slight solder fillet irregularities are acceptable, but insufficient wetting or cold joints are not.
Repairs (rework) must follow approved procedures (e.g., per J-STD-001 for soldering practices), ensuring reworked joints meet the same Class 2 criteria as nominal joints. Inspection after repair should confirm that no new defects, such as lifted pads or solder bridges, have been introduced.
Inspection Sampling and Qualification
For Class 2 production, manufacturers often adopt sampling plans consistent with IPC guidelines or customer-specific requirements. First-article inspections verify that processes yield assemblies meeting Class 2 criteria.
Periodic process audits and in-line inspections ensure consistency; many CMs can document process capability metrics (e.g., yield rates, defect densities) to demonstrate sustained performance aligned with Class 2 expectations.
Related Process Standards
While IPC-A-610 provides acceptance criteria, complementary standards govern process control:
- J-STD-001 covers soldering materials and workmanship
- IPC-2221 covers generic PCB design rules that influence manufacturability
- IPC-A-600 covers bare-board fabrication acceptability
- IPC-7711/7721 covers rework and repair
Adhering to these ensures that the assembly process supports achieving Class 2 acceptance consistently.
Finding an Assembly Partner for Your IPC Class 2 PCB
Some PCB designers may confuse Class 3 requirements as necessary for a high-quality, reliable product regardless of application. The truth is that IPC Class 2 PCB requirements often meet quality and reliability needs at a significantly lower price point. Class 2 is the appropriate choice in most applications and will meet the performance expectations designers seek. Minor issues, such as slightly misaligned surface mount parts, are entirely acceptable for Class 2 boards. Often, attempting to “fix” them is unnecessary and poses too much of a risk to the integrity of the finished product.
Another important point regarding Class 2 manufacturing is that contract manufacturers with well-controlled assembly processes will produce Class 2 circuit boards built to the higher-quality levels that approach Class 3 boards, especially in their surface mount technology processes. This nuance doesn’t mean that they are building Class 3 boards; their processes are such that they exceed the standards of the IPC Class 2 requirements.
Designers who demand a high level of quality require a CM who is skilled and experienced in their manufacturing processes. At VSE, we’re a team of engineers committed to building electronics for our customers and guiding them through the DFM process. We’ve produced life-changing and life-saving designs with our manufacturing partners for over forty years.
If you are looking for a CM that prides itself on its care and attention to detail to ensure that each PCB assembly is built to the highest standards, look no further than VSE. Contact us today to learn more about partnering with us for your next project.
