A PCB assembly can look complete and still have a misplaced component, an inaccessible solder joint or a function that does not respond as expected. Finding these issues before shipment requires a test plan suited to the board—not simply a list of equipment.

GreatPCB supports PCB assembly projects from prototype to production. We can discuss the inspection and testing requirements for your design alongside the assembly scope, component packages, production quantity and acceptance criteria. Confirm the selected methods, coverage and reporting requirements for your order before production.

Discuss Your Testing Requirements

PCB assembly testing and inspection examine a populated circuit board after components are placed and soldered. Some methods look for visible assembly defects; others use electrical measurements or operate selected functions of the board. Each answers a different question.

For example, AOI might flag a visibly displaced resistor, while a functional test checks whether a defined output behaves correctly. A board can pass one check and still need another: a good-looking board may fail to communicate, and a board that communicates during one test may still have a defect outside that test’s scope.

Bare-board and assembled-board testing serve different stages. A bare PCB has no components installed. Its electrical test checks specified connections and isolation before assembly; component placement and operating functions need their own checks afterward. See our bare-board PCB testing page for fabrication inspection and electrical testing.

An inspector examines accessible parts of the assembly for issues such as damaged components, obvious placement errors, solder bridges or contamination. Magnification can help with small features, and a defined acceptance standard gives the inspector a consistent basis for deciding what to review.

Manual inspection is also useful when an automated system flags a potential defect. The operator can examine the flagged area, compare it with the drawing or acceptance criteria and decide whether further investigation is needed.

Its effectiveness depends on access, visibility, the inspection criteria and the features being examined. A joint underneath a package may not be visible even under magnification.

AOI uses cameras and programmed inspection criteria to examine visible features of the assembly. Depending on the equipment and program, it can flag missing or misaligned components, orientation issues and selected solder-joint defects.

AOI can be used at different points in the assembly process. The inspection program should match the production stage: a placement check before reflow and a solder-joint check after reflow do not answer the same question.

A flagged image is a prompt for review, not automatically a confirmed defect. Equally, an AOI pass covers the programmed and visible features; it does not prove that a hidden BGA joint is sound or that the board’s firmware operates correctly.

Some components have connections underneath the package. BGA and QFN solder joints, for example, may not be accessible to a camera or microscope from the top of the assembly.

X-ray imaging helps an inspector examine selected hidden joints. Depending on the equipment and inspection setup, images may reveal features such as solder bridges, voids or joint placement. GÖPEL electronic explains the complementary roles of optical and X-ray inspection.

An image must still be interpreted against the agreed criteria. What can be resolved depends on the package, board construction, equipment and inspection method. X-ray inspection does not replace a specified electrical or functional test.

If your design contains hidden joints, identify the packages and inspection requirements when requesting a quote. Confirm whether the plan covers selected locations or a defined sample or production quantity.

In-circuit testing (ICT) uses electrical contact with accessible points to check selected features of an assembled board. Depending on the tester and test program, measurements can help identify certain opens, shorts or component-value issues.

A bed-of-nails fixture uses spring-loaded probes positioned for a particular board. Once the fixture and program are prepared, multiple test points can be contacted during a test cycle. This can make a dedicated fixture attractive for a stable design with repeat production, although the upfront development and fixture cost must be considered.

The fixture cannot measure every feature automatically. Coverage depends on which nets and components are accessible, the test equipment, the program and the agreed fault model. An unprobed net or a function that requires a separate operating sequence may need another test method.

Manufacturing defect analysis (MDA) is a related approach that focuses on selected assembly defects and electrical measurements. The checks available under an MDA or ICT plan depend on the equipment and program; ask for the expected scope rather than relying on the name alone.

A flying probe tester moves probes to programmed contact locations on the assembly. It avoids the need for a dedicated bed-of-nails fixture, although the board still needs suitable support, accessible contact points and a test program.

Because probe positions are controlled by the program, this approach can be useful for prototypes, smaller batches or designs that may change. The probes must travel between measurements, so test time can become a consideration as the number of checks and boards increases.

Flying probes can also perform in-circuit measurements. The practical comparison is therefore between different ways to access and test the circuit, not a rule that flying probe and ICT are unrelated. Keysight describes both approaches.

These are planning considerations, not universal quantity thresholds. Board density, access, required coverage and the test program can change the result for either approach.

A fixture has an upfront cost; both approaches also require engineering and a per-board test cycle. For an initial comparison, include program development, fixture or setup work, the estimated cycle time, and any expected revisions or retests. Ask the test provider what each quotation includes.

For illustration only, suppose a fixture and its setup cost $1,000, with a test cost of $1 per board. If an alternative has no dedicated fixture charge and costs $3 per board, the direct comparison is $1,000 + $1 × quantity versus $3 × quantity. The two totals are equal at 500 boards. Below or above that quantity, the cheaper option changes under those assumptions.

This example is not a GreatPCB price or a recommendation to select a method on cost alone. Coverage, contact access, changes to the design and the consequences of a missed defect can change the decision. A fixture may also be modified for some revisions; it does not necessarily need to be discarded after every design change.

Functional testing checks whether specified parts of the assembled board operate under defined conditions. A test might apply power, verify a voltage, send a command through an interface or check that an output responds within an agreed range.

Unlike a general visual inspection, a useful functional test needs a procedure. That procedure should identify the board revision, firmware, power supply, connections, inputs, expected responses and pass/fail limits. Some products also need a fixture, a programmed test application, a load or a simulated connection to another system.

Consider a controller board with a communication port. A defined functional test could verify that the board starts, draws current within an agreed range and responds to a specified command. Passing those steps confirms those conditions; it does not automatically validate every software feature, temperature range or lifetime requirement.

For a simple hypothetical procedure, the product owner specifies a 12 V input, a permitted idle current of 80–120 mA, and a required response to a communication command. The operator connects the approved supply and interface, applies power under the specified setup, measures idle current and sends the command. A result of 105 mA meets the illustrative current limit; a missing response still fails the communication step. The values are examples, not limits for your design or GreatPCB service specifications.

The test setup matters as much as the list of functions. A motor controller checked with a resistive load, for example, has not necessarily been evaluated against the transient behavior of the intended motor. Where that behavior matters, agree whether the test needs a representative load or a separate validation step.

Record the firmware version and the expected response for each step. An onboard self-test can provide useful information, but it may not exercise every external interface or operating mode. Decide which results need an independent measurement and which conditions belong to product qualification rather than routine production testing.

Agree who supplies the test procedure, equipment, fixtures and firmware, and how failures and retests will be handled. Altium’s testing overview explains why functional requirements should be communicated to the manufacturer early.

Start with the failures that matter to the product, then work backward to the inspection or test that can find them. Volume, package type, access, available documentation and the consequences of a missed defect all influence the plan.

Testability is easier to address before the layout is released. Once components and enclosures limit access, adding a reliable probe contact can require a board revision or a different test approach.

Identify the nets, power rails, grounds and interfaces needed for the intended checks. A test point can provide a known location for a probe, but its usefulness depends on the surrounding components, solder mask, board geometry and the type of test.

For example, a pad may exist in the CAD data but be blocked by a connector or too close to a tall component for the intended probe. Review physical access on the assembled board, not only the unpopulated layout.

Avoid adding arbitrary test points to sensitive signals without engineering review. High-speed or RF structures may require a measurement approach that considers signal integrity, connectors and the test setup.

A fixture needs a repeatable way to locate and support the assembly. Probe contact, component clearance and support positions all matter. Excessive or uneven force can bend a board or stress solder joints; the fixture design should suit the board thickness, size and component layout.

Agree the required test-point dimensions, spacing, edge clearance and board support with the fixture or test equipment provider for the specific design. There is no single dimension that can be assumed to fit every tester and assembly. Altium’s ICT design checklist provides further context for early testability planning.

Provide the board revision, netlist and proposed test points for review. Ask which required nets are accessible, which checks cannot be performed and whether any additional access or alternative method is needed.

Record design changes that affect test points or component placement. A new board revision may also require changes to the fixture, program, functional procedure or acceptance limits.

Test access is not the same as fault coverage. A reachable pad gives a probe a contact location; it does not by itself show that a particular open, component fault or functional failure will be detected. When a coverage percentage is requested, define the denominator, fault types, test conditions and any exclusions with the test provider before comparing figures.

Place test points on a common side where practical, but verify this against the actual assembly and fixture. A via can sometimes provide access, depending on its finish, construction and probe design; do not assume every via must be filled or that every via is suitable. Probe type, pad size and spacing need project-specific review.

When a board fails, record the board identifier and revision, test step, measured result, limits and disposition. Separate a confirmed defect from a probe-contact problem or an unverified test setup; repeat the agreed check after authorized repair or correction.

For repeat builds, grouping confirmed failures by component, location or process stage can reveal a recurring issue. Discuss findings with the engineering and production teams so that an assembly process or test program can be reviewed. The format and availability of records should be agreed for the order.

The right documents depend on the project and test method. The following information helps establish the scope before a quotation or production release:

If the test procedure is not yet complete, identify the functions and risks that matter most. GreatPCB can review the available project information with you and clarify the proposed inspection and test scope. Confirm the actual services, fixture arrangements and deliverables in the quotation.