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What does a dark region in an X-ray image actually mean?

An X-ray image is a projection affected by the materials and geometry in the beam path. A feature may need additional angles or a different imaging method before it can be interpreted. An image alone does not establish electrical function or a universal pass/fail limit.

Review the evidence fields and engineering example

What does PCB X-ray inspection show?

PCB X-ray inspection uses differences in X-ray transmission to reveal features that ordinary cameras cannot see through. In an assembled board, the most common questions involve solder beneath BGA packages, bottom-terminated components, stacked structures or joints obstructed by surrounding parts. Image contrast can reveal geometry, missing material, bridges and void-like regions when the selected method provides sufficient resolution and separation.

An image is a measurement view, not a complete electrical or reliability verdict. Dense overlapping structures can conceal or imitate a feature in a two-dimensional projection. Interpretation depends on geometry, magnification, viewing angle, image processing and the expected joint construction. A normal-looking projection does not by itself prove wetting at every interface.

The practical first question is therefore 鈥渨hat defect or feature are we trying to evaluate?鈥� An investigation of a suspected BGA bridge needs a different scope from a report on exposed-pad void distribution, a through-hole barrel-fill question or a sample comparison following a reflow change. Define those questions before choosing inspection locations and acceptance limits.

2D projection, angled views and CT

A CT-capable equipment family does not establish that CT is included in a quotation. Specify the inspection method, number of locations, sample scope and report format with the supplier. illustrates how projection and sectional methods address different inspection tasks; its product capabilities should not be read as a 吃瓜tv equipment specification.

Automated X-ray inspection, often called AXI, describes automation of acquisition and analysis. It does not remove the need to validate the recipe against the product or to review ambiguous findings. Offline investigation and inline screening serve different cycle-time and evidence needs.

BGA, QFN and through-hole questions

For a BGA, identify package locations, ball-map orientation and the particular arrays or joints that matter. Missing or unusually shaped projected solder features can guide an investigation. A suspected bridge may need another angle, electrical correlation or a section to resolve overlap. Head-in-pillow and interfacial separation can be difficult to establish from a simple top-down projection alone.

For a QFN or other bottom-terminated component, the exposed pad and perimeter terminations have different geometries. Define whether you want an overall projected void-area ratio, a largest-void measure, a location-sensitive assessment or another agreed metric. The thermal design and exact package recommendations may matter as much as an overall percentage.

Through-hole and press-fit features require their own inspection criteria. Barrel fill, internal damage and pin geometry are not interchangeable questions. Review the suitable method and access with the engineer instead of assuming that a standard BGA program will answer them. BGA assembly process planning and through-hole assembly planning help connect the inspection request to the manufacturing route.

Why one void percentage cannot accept every joint

A two-dimensional void-area ratio is the segmented projected void area divided by the defined projected joint region, multiplied by 100. It is not automatically a three-dimensional void-volume fraction. Changing the region of interest, threshold, overlap handling or imaging angle can change the reported number even when the physical joint is unchanged.

Record the definition before comparing results. Are separate pale regions combined? Are overlapping projected voids counted once? Is the denominator the full pad projection, the soldered region or another agreed boundary? Does the specification also constrain the largest void, distribution or a critical heat-flow location? Without these definitions, two reports with the same percentage may describe different conditions.

Do not apply a single web-sourced limit to every BGA, QFN or power package. The applicable product class, package construction, customer specification, device guidance and agreed IPC criteria must be considered together. Where a requirement is unclear, keep the finding open and request a disposition rather than letting an online calculator invent a pass threshold.

Build a useful X-ray inspection request

The inspection brief builder helps you describe what should be imaged and what evidence should return with the result. Select the feature, question and proposed method, then identify the scope and acceptance reference. Unknown requirements remain visible in the brief so that they can be resolved during engineering review.

This tool does not upload or classify images, segment voids or diagnose hidden defects. That is deliberate: an engineering request with a defined region, method and criterion is more useful than a simulated 鈥淎I pass鈥� based on an illustration. You can download the brief or open an email draft containing the entered requirements.

For a prototype investigation, describe the observed symptom, affected locations and whether comparable known-good units are available. For recurring production, specify whether the request concerns every unit, selected components on each unit, or a documented sample. These are different coverage statements and should appear clearly in the quotation.

Apply the right acceptance basis

IPC-A-610 is relevant to assembly acceptability; IPC-7095 addresses BGA design and process implementation, and IPC-7093 addresses bottom-terminated component implementation. Check the and use the agreed editions and applicable customer criteria. A document title alone does not assign a universal void limit or a mandatory X-ray sampling rate.

Keep the test method separate from the acceptance authority. An analyst may measure and flag a feature, while engineering or the customer decides disposition under the contract. If destructive analysis or additional electrical testing is needed to answer the question, identify the affected samples and obtain the appropriate project authorization.

Also identify components with X-ray exposure restrictions. Some devices or stored data may require manufacturer guidance on exposure and handling. The responsible inspection team should define a suitable acquisition plan; the page does not prescribe exposure settings or certify radiation safety.

From an image to a traceable decision

A useful report identifies the unit or lot, assembly revision, reference designator, inspected region, imaging method, acquisition view and criterion. Where a numeric value is reported, retain its units, region definition and analysis method. Include the finding, reviewer and disposition so the next engineer can understand what was accepted, reworked or escalated.

Repeat inspection after rework should be linked to the original finding and the approved rework record. Avoid replacing the original image without preserving the history. Comparison images are most useful when their acquisition conditions are sufficiently consistent to support the intended comparison.

Inspection cost is driven by programming, handling, imaging method, locations, sample quantity, analysis and reporting. CT investigation and a recurring screening recipe do not have identical economics. Ask for those scope elements to be stated in the quotation; a flat price per board without coverage details is difficult to compare.

Use AOI for visible assembly features alongside hidden-joint inspection. Add in-circuit test or functional testing when electrical behavior must be verified. The test-method comparison helps coordinate these routes without assuming that every method is automatically included.

For PCB Assembly enquiries, send the released files and the inspection brief together. Quality assurance and supplier review explains the wider discussion about records, acceptance and evidence.

Make the X-ray result reproducible

Use these fields to scope the report with your quotation. The table is a planning example, not a 吃瓜tv test result or a promise that every record is included by default.

Continue to combine imaging with appropriate electrical and functional tests.

The email link opens a draft for you to complete. Contact is a separate form; these pages do not send messages automatically.

Questions engineers and buyers ask