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3D Automated Optical Inspection (AOI)
The results of post-reflow image inspection can affect whether the output is used as part of the acceptance reference. The inspection setup determines whether there is enough evidence for an acceptance or rejection decision. It also helps identify when additional verification is needed for visible solder indicators, component position, height-related indicators, and the review status of a printed circuit board assembly (PCBA). The use of 3D AOI can assist with aligning the inspection program setup, image evidence, and the files returned after PCBA sign-off. More commonly, 3D AOI allows clarification of package orientation, marking visibility, and reporting expectations before status decisions are made.
Use Upload BOM & Gerber to submit your project files. If you are still deciding on the inspection scope, use Request a Quote and provide information about your inspection project.
AOI Program Inputs: Program setup / Image evidence / Acceptance status / Traceable inspection files
Missing Board Data Can Change the AOI Setup
Once the project documentation for the physical PCB and the components being placed is received by SUGA, the first step in setting up the 3D AOI program is to validate the PCB physical dimensions against the provided placement reference and acceptance criteria. If there is a discrepancy in the Gerber data, PCB drawings, and the component placement list (CPL), it may cause the program to reference a missed pad location, incorrect XY position, or incorrect rotation. Consequently, this could cause an incorrect acceptance or rejection result due to building the initial setup on an incomplete or incorrect basis.
These inputs assist in identifying initial setup issues before 3D AOI programming begins.
Project Inputs for AOI Planning
| Input | AOI Use | Required Input | If Missing | When It Matters | Review Focus |
|---|---|---|---|---|---|
| Gerber or PCB file | Pad location; board reference | Released PCB data | AOI pre-programming delay | Quote and NPI | Pad and location review |
| Bill of materials (BOM) | Component identity; package; polarity | Approved BOM | Package library not confirmed | Quote and NPI | Part and marking review |
| CPL or centroid file | XY position; rotation; placement basis | Released CPL or centroid file | Offset basis incomplete | Before AOI setup | Position review |
| Approved assembly drawing | IPC class; polarity; acceptance basis | Drawing or order record | Acceptance criteria not confirmed | Quote and order confirmation | Acceptance review |
| Special report need | Image record; report field; traceability scope | Quality plan or purchase order note | Report requirements need review | Quote planning | Report and lot record |
| Hidden-joint package list | Ball grid array (BGA), quad flat no-lead (QFN), land grid array (LGA), shielded or limited-access areas | Identified package types and locations | X-Ray coverage may need review | Quote and inspection planning | Hidden-joint review |
Board and Placement Data
The programming coordinates for AOI setup at SUGA are defined by board and placement data. A rotation mismatch or incomplete centroid placement reference will affect the interpretation during first setup of visible offset, polarity cues, and same-location flags.
BOM and Drawing Basis
The BOM and assembly drawing provide the connection between each component, package, polarity mark, and acceptance criteria. This does not create a default inspection class; instead, it provides a basis for aligning inspection decision criteria with the agreed order criteria.
Record and Hidden-Joint Notes
Image files, lot traceability, and early identification of hidden-joint packages are common requirements for some projects. If these locations are only identified after setup has started, the inspection plan may need to separate visible image review from supporting checks, resulting in additional questions before quotation.
From Board Data to AOI Program Setup
Once the board data has been prepared for use, it is converted into an initial AOI program used in establishing the new product introduction (NPI) or first-off review. The program first registers the physical board and verifies each component orientation. This step is directly related to the package outline, the polarity mark used to identify the package, and the reference image used to create the AOI program.
Confirmed Equipment and AOI Setup Record
Equipment characteristics, including speed, field of view, resolution, and board size, can only be used when the actual asset and program setup have been confirmed for AOI. SUGA uses currently verified equipment and program setup for model-specific values. These values do not come from generalized specification claims; they are confirmed through hardware and setup records.
AOI Program Setup Basis
| Setup Item | Setup Basis | Reviewed Against | Limit or Note |
|---|---|---|---|
| AOI model basis | Confirmed equipment asset | Confirmed equipment; setup record | Model values only when verified |
| Fiducial and board support | Fiducial alignment; board support setup | Program setup record | Board support affects height signal |
| Golden board baseline | Baseline images; first-off images | Baseline image; revision record | Establishes reference only; does not predict yield |
| CAD-to-AOI file conversion | BOM; CPL; centroid file; drawing | Physical location; polarity; package mapping | Not placement-machine validation |
| Package library | Package outline; body height; polarity marker; lead geometry | Library record; approved package data | Land-pattern reference only when documented |
| Threshold change | Algorithm threshold; image comparison | Program revision record; engineering or quality review | Requires baseline verification before adjustment |
Fiducial, Board Support, and Baseline Images
The ability of a 3D AOI program to read height, tilt, and seating references consistently relies on correct fiducial alignment and correct board support. A baseline image or reference image set serves as the first-off or confirmed state of a board condition and is the first reference point for comparing board inspection output. While a baseline image establishes a reference point for developing a final inspection decision, it does not by itself close that decision.
Golden Board Baseline and First-Off Image Check
When available, a first-off or golden board baseline image may be used to compare the package outline, position of the polarity marker, height of the package body, and image threshold response. If no golden board is available, first-off images may be the first point of reference for comparison to the initial configuration of the AOI program. This step is only used to establish setup confidence but does not necessarily mean every threshold is correlated with confirmed defect references.
Package Library and Threshold Setup
A package library entry establishes what the program anticipates, such as body outline, lead configuration, expected marking location, and package height range. The program may flag a good component or miss a marginal condition if the component surface or marking type does not match. The original threshold settings are determined during first setup; subsequent false-call trends and program changes will be addressed when production feedback is reviewed. 3D AOI inspects the board using actual image data and height-related information, including lead height, body location, surface profile, and tilt of an actual component.
Visible Post-Reflow Defect Identification
After reflow, AOI inspection is used to understand visible defect signals. Based on the program setup, AOI will evaluate visible defects according to its ability to match signals, evidence, and coverage limits.
Post-Reflow 3D AOI Signals
| Signal | 3D AOI Evidence | Risk | Limit |
|---|---|---|---|
| Coplanarity and tilt | Body height; lead height; tilt signal | Lifted lead; poor seating | Visible area only |
| Visible solder joint profile | Fillet shape; wetting pattern; excess or insufficient solder | Solder joint dispute | Hidden joint not covered |
| Bridge and solder short | Adjacent-pad solder connection | Short risk | Electrical test not replaced |
| Lifted lead or lifted body | Lead height; body height; seating signal | Open risk | Final status follows approved criteria |
| Component presence and position | Missing part; offset; rotation; polarity; marking | Wrong part; wrong orientation | Marking depends on package surface |
| Tombstone and non-wet | End lift; wetting imbalance; pad wetting pattern | Wetting risk | Root cause not assigned by AOI alone |
| Visible foreign material and solder ball | Visible particle; solder ball location | Visible contamination risk | Ionic cleanliness not covered |
Height, Tilt, and Seating Signals
Height signals may be used to assess lifted leads, body seating, coplanarity, or tilt issues. These measurements and assessments are most valuable when the package outline, board support, and reference images correlate to the actual board.
Visible Solder and Bridge Signals
Using a 3D AOI inspection system can assist in flagging solder profile issues and identifying visible solder bridges on pads that should not be connected. The bridge should be visible in the image; however, this image alone will not determine that there is an electrical connection, since that is determined based on the circuit design and the nets involved.
Presence, Position, and Marking Signals
The presence of a component, correct orientation, and detection of a marking on the component can all be supported by imaging. The recognition of markings can vary based on package surface, imprint contrast, package condition, and the imaging system used to obtain the image.
Visible Contamination Signals
Visible contamination may result in flagging particles and solder balls within the inspection view; however, ionic cleanliness requires chemical evidence for classification that cannot be provided by the imaging inspection system.
After an AOI Signal Is Flagged
After an AOI signal has been flagged, the flag starts a review to verify the condition of the flagged item and identify any corrective actions.
AOI Review and Disposition
| Scenario | First Check | Escalation Trigger | Final Status | Supporting Verification |
|---|---|---|---|---|
| Repeated offset signal | XY position; rotation; fiducial match | Same-location repeat | AOI code; engineering or quality review | Solder paste inspection (SPI) offset data when available |
| Bridge signal after reflow | Adjacent-pad solder connection | Short-risk signal | Rework, hold, or accept status | Electrical test when included |
| Lifted lead or coplanarity signal | Lead height; body height; seating signal | Height-sensitive package | AOI image; lot action | Approved acceptance basis |
| Disputed solder joint image | Fillet image; wetting pattern; IPC class basis | Engineering or quality review needed | Quality disposition; lot sign-off record | X-Ray when hidden-joint coverage is included |
| Tombstone or non-wet signal | End lift; wetting imbalance; pad wetting | Repeated wetting signal | Process feedback record | AOI does not assign root cause alone |
| Visible contamination signal | Visible particle or solder ball location | Removal or review need | Removal, review, or accept status | Chemistry and ionic cleanliness not covered |
Initial AOI Image Check
The initial image evaluation consists of comparing the flagged image to the setup record, checking the package library match, assessing fiducial alignment, and checking whether the finding matches the acceptance criteria during inspection. This evaluation separates apparent flagged images that can be immediately identified through image review from images that require a second opinion.
Marginal Calls for Engineering or Quality Review
Repeated, marginal, or disputed signals will continue to engineering or quality input. The operator will see the flagged image, engineering will determine if it matches a process condition, and quality will verify that the output meets agreed criteria. This separation of responsibilities helps avoid making a final decision based on the machine flag alone.
Cases That Need Another Check
Some findings may require additional support from electrical tests, X-Ray, SPI data, or chemistry records if those checks are part of the project or available for additional evidence. At this point, the next step is to identify which additional evidence can be used to close the finding: image result, test result, X-Ray result, or separate cleanliness record.
Final Status Follows Approved Criteria
The final disposition will either be to accept, hold, rework, or require a further check based on the agreed acceptance criteria and project files. The record should include the flagged image, rationale for disposition, and evidence used to close or request customer confirmation for any finding marked for hold or disputed disposition.
Where AOI Ends and Other Checks Begin
Some findings can only close using image evidence. Others require another type of verification beyond optical evidence. 3D AOI will address both visible image and height-related findings but may require SPI, X-Ray, or electrical testing to resolve the finding.
AOI and SPI
SPI is performed prior to component placement and verifies the deposited solder paste. AOI is performed after reflow and verifies the visible assembly condition, including component placement, solder appearance, and other height-related indicators.
AOI and X-Ray
When solder joints are under the component body, optical inspection has no physical way to view the connection. This is a limitation based on physical inspection access, not equipment capability alone. However, inspection of visible component location, body seating indicators, surrounding components, and nearby solder appearance allows AOI to evaluate visible conditions around a BGA or another under-body package. X-Ray is used to verify solder joint integrity below the package body. AOI and X-Ray can provide different but related data regarding the same areas of the assembly, so the two paths should be separated before finalizing the inspection plan.
AOI and ICT
AOI may flag conditions with visible short risk, missing parts, offset, or polarity concerns. ICT is used when circuit-level testing with test access is necessary.
2D AOI and 3D AOI
3D AOI adds height, surface profile, and tilt data to image comparison, which can help evaluate body seating, coplanarity, and lifted-lead concerns beyond what 2D AOI can show from images alone.
PCBA Conditions That Need Closer AOI Setup
Once the setup process is clear, specific conditions should be identified before the quote is prepared or AOI setup begins, as they can affect how much can be judged from visible image evidence compared with what requires supporting data from another source.
Dense Placement or Limited Visual Access
In PCBAs that have fine-pitch leads or dense passives mounted close to other component bodies, as well as polarity markings on adjacent components, CPL and centroid rotation should be confirmed before the AOI setup. SUGA should also work with the customer to define a convention for referencing rotation so that the respective orientation reference can be verified before making image-based decisions.
Height-Sensitive Package Seating
Requirements for height-sensitive acceptance limits based on lead coplanarity, body seating, or tilt limits usually require stable board support and confirmed fiducial alignment on the PCBA before the AOI setup. These requirements should be flagged for the AOI setup review, and therefore, the height information on the board should not simply be evaluated as normal visual reference checks.
Hidden or Shielded Areas
Protected areas of the PCBA with BGA, QFN, LGA, or shielded packages where no visibility exists should be marked and called out on either the package list or assembly drawings before requesting a quote. Bodies that are taller than nearby components may also reduce marking visibility, edge visibility, or lighting access for checks adjacent to other components. As such, visible image checks and supporting checks may need to be separated at the time of setup.
Record-Sensitive Projects
Projects that require image files on each board as well as lot records, reporting fields, or MES traceability should have that reporting expectation supplied to SUGA before requesting a quote. Setting expectations at the time of quote can enhance the ability of SUGA to provide the correct documentation early rather than after the fact when clarification is needed.
AOI Records for Repeated Signal Review
The usefulness of inspection data increases substantially when the same signal appears at the same position on multiple assemblies of the same family or on the same production run. SUGA uses defect codes, board ID, and position information to allow for comparison of patterns or make program adjustments as needed.
AOI SPC and Program Change
| Review Item | Signal Used | When Reviewed | Related Process | Record or Result |
|---|---|---|---|---|
| Defect coding | Defect code; image; board ID; location | Lot review; first article; repeated signal | Placement; stencil; reflow review | Inspection report; lot record or traceability file |
| Pareto trend | Same-family defect; same-location defect | Defined review trigger | Placement, stencil, reflow feedback | Trend chart; corrective and preventive action (CAPA) record when opened |
| False call review | False call category; image mismatch | Repeated false calls after program setup | Package library; threshold review | Program revision record |
| SPI-AOI comparison | Paste signal; offset signal; post-reflow result | SPI and AOI records both available | Print, placement, reflow review | Linked inspection record |
| Threshold change | Threshold revision; image baseline | False call trend or missed-signal review | Engineering or quality program review | Program revision record |
| Final lot status | AOI result; review status; shipment status | After inspection completion | Quality review | Lot-level quality record |
Repeated Signals at the Same Location
When a repeated signal appears at the same reference designator across boards, it may indicate a pattern rather than an isolated defect. The review process should be different from that of a single random flag. Possible causes could include placement drift, package library mismatch, marking contrast, solder condition, or an image reference that no longer correlates with the current build. By reviewing the same-location pattern, SUGA can help determine if the defect belongs to the process, program setting, or component condition.
False Calls After Program Setup
If the program continuously flags defects in joints that have passed inspection, then it likely has a false-call category issue rather than an actual solder problem. If this is true, the image threshold response, package surface, or baseline image match may need to be reviewed for those defects. If false calls continue to cluster around the same package family, the image reference may be out of date for the current component surface or marking condition.
SPI and AOI Record Comparison
When both SPI and AOI records are available, they can be compared and may help identify differences in print, placement, and post-reflow contributions without presuming that every project has linked MES data.
Program Revision Records
Any updates to programs should maintain the threshold revision history, image reference, engineering or quality input if applicable, and final lot status. Process engineering checks whether the signal pattern is consistent with the process variable. Quality assurance will then assess whether the revised thresholds continue to meet the previously established acceptance criteria. CAPA records only pertain to projects if opened for that project. Any expectation of special report fields or traceability review should be included in the submitted project brief.
AOI Setup and Review Effort by Project
Setup and review efforts vary per PCBA project and are driven less by the scan itself and more by what needs to be prepared and organized before and after the scan. The major variables are package variety, number of board sides, access density, and required documentation scope.
Package Data and Setup Work
More than total component count, package variety drives how much library setup is necessary. For example, a board with many repeated passive components may require less library setup than a board containing fewer components but varying package sizes, custom connectors, low-contrast markings, or differing component body heights. All of these variables require first-off image comparison before trusting any entries.
Board Side and Coverage Setup
Single-side assemblies may need a different setup than double-sided assemblies. In a double-sided PCBA assembly, when each side has its own program setup, reference image set, and side-specific comparison, the visible state of the second side assembly may differ due to the second side having already experienced thermal exposure, handling, or support changes. This could affect height reference, surface condition, and baseline confidence; therefore, side-specific comparison is more than simply running the same setup twice.
Access, Density, and Image Evaluation Time
Due to dense assembly, limited viewing angles, tight spacing between components, and weak marking contrast, image evaluation can take longer. If small passive components are placed adjacent to large component edges or in an area obscured from light, each signal must be individually evaluated to check whether it is an actual offset, shadow from an adjacent body, lighting incidence, or mismatch between package surface and body. Many instances of this type of placement will also add review time even when the total component count appears moderate.
Records and Supporting Checks in the Quotation Scope
Standard inspection results will indicate a pass, fail, or review status. When the order requires image files for each board, lot-level summaries, SPI-AOI comparison, X-Ray support, or electrical test correlation, the scope of work will require more than simply reviewing images. In addition to record handling, formatting requirements and coordination between the inspection steps will be greater; therefore, these requirements should be identified with the submitted board files, not after setup has begun.
Project Files for an AOI Quotation
To provide an AOI quotation, SUGA requires project data related to board layout, component location, visible inspection requirements, and report delivery requirements. The aim is to minimize setup clarifications after the quote has been reviewed.
Start with Core Board Data
Send the BOM and the Gerber files first, followed by the CPL or centroid data, and the assembly drawing for areas that need confirmation of rotation, polarity, package outline, or placement reference.
Add Inspection Notes When Available
For locations that require verification for under-body solder joints, shielded zones, or special reporting requirements, mark the corresponding locations on the project files or the assembly drawing. A brief note may also suffice to assist SUGA in distinguishing visual inspection reviews from auxiliary checks for the quote.
Request a Quote
Use the upload option to submit any available files and related inspection notes. Once you have submitted the files, SUGA can verify the clarity of the AOI scope and can clarify placement or polarity data, or whether hidden-solder-joint or report requirements will require separation before providing a quotation.
Submit available files using Upload BOM & Gerber, or use Request a Quote to discuss your inspection scope.
Upload BOM & Gerber
FAQ
3D AOI is used to inspect a PCBA after reflow. It includes inspection of visible solder, component placement, body height, tilt, and seating indicators. It serves as an additional structured check after an assembly has been reflowed: it compares the images as well as corresponding heights against the approved program setup and produces a traceable image record for visible assembly conditions.
3D AOI can identify visible conditions such as missing components, rotated components, lifted leads, tilted component bodies, excessive solder bridging pads, and visible solder balls. If a solder joint is not visible, a supporting verification method such as X-Ray may be required to confirm the joint condition.
2D AOI relies primarily on image comparison to evaluate whether certain visible features are present or absent. 3D AOI uses not only the image but also the height, profile, and tilt of the components to assist in determining whether the component is seated properly, coplanar, has lifted leads, or has a body-height concern. The added depth provided by 3D AOI is useful when there are differences in seating heights or packages whose seating affects a decision to accept or review.
3D AOI inspects assembled boards against prepared inspection programs, alignments, package library information, baseline images of the assemblies, and height and image reference points after the assembly is reflowed. 3D AOI uses height-related information, including body height, lead height, body profile, and body tilt, along with the images so that visible defects can be identified. Once a flag has been identified, the follow-on step is to determine whether additional evidence of the defect can help close the item or if a different verification method is necessary.
An AOI inspection program will be based on board data, placement data, component package details, polarity orientation, fiducial alignment, and first-off or baseline image evidence when available. This includes library matching and threshold creation; model-specific machine values will only be used after the actual machine and setup records have been verified.
AOI inspections are limited to the capabilities of the camera and to the approved process used for evaluation. If hidden solder joints, circuit function, firmware or functional verification, ionic cleanliness, or root cause analysis are required, then a different verification method will need to be used to support the project. The key consideration is which verification method can close the specific finding.
The primary difference is that AOI is used to check for visible defects such as placement, solder, polarity, height, and image-related issues, while ICT is used to verify circuit-level conditions using electrical test access. A visible short-risk signal may guide electrical confirmation, but ICT or another electrical test is needed when circuit performance must be verified.
Setup quality determines the effectiveness of using AOI: board support structure, placement data, fiducials, matching package libraries, baseline image quality, threshold settings, lighting conditions, and package surface characteristics are all important factors. These factors are as important as the equipment’s rated resolution. The focus on an actual project should be to achieve repeatable evaluation of the visible physical conditions being assessed.
3D AOI inspection cost is heavily based on the amount of time necessary to set up the inspection process, review and confirmation time, the amount of work required for the package-level library, documentation coverage, and supporting checks as specified in the quotation. The actual scanning process may be a smaller portion of the overall cost of inspection when there are large board-side setup efforts or additional reviews required because of low-contrast marks or result reformatting. Clear project files and report expectations will assist in reducing the amount of clarification needed on quotations.
In circuit board assembly, 3D AOI inspection is typically used after the solder reflow process. Inspections based on visible solder condition, proper polarity, component height, tilt, or whether the component was properly seated on the PCB after soldering are good candidates for using 3D AOI inspection. The same type of inspection applies when an electronic component’s body height affects visible bridging risk or whether the inspection will provide traceable documentation of inspection results.
Related Services
PCB & PCBA Inspection
PCB and PCBA Inspection includes inspection methods such as optical inspection, hidden-joint checks, first-article validation, and cosmetic inspection on a PCB or PCBA before the final assembly review method is selected.
3D Solder Paste Inspection
3D Solder Paste Inspection provides evidence for reviewing solder paste volume, height, area, or offset before components are placed on the PCB. It supports the pre-reflow phase before using AOI for inspection of conditions during the post-reflow phase.
X-Ray Inspection
X-Ray Inspection provides evidence for non-visible solder joint integrity in locations on circuit boards that cannot be inspected through optical inspection.
ICT
ICT provides verification of circuit-level electrical integrity through adequate test access.
Electrical Testing
Electrical Testing provides evidence to confirm that the PCB or PCBA complies with the functional or electrical response requirements established for the project.
Visual Inspection
Visual Inspection can provide evidence to support AOI results through physical evaluation of defined criteria, including cosmetic specifications, component markings, or defined visual specifications.