In most plants, cross-sections are not part of the routine inspection plan. It appears when something goes wrong: the product is returned, the customer complains, the shipment fails the reliability test. Calling a cross-section at that stage is both expensive and late.
This article lists seven situations that almost certainly require a cross-section, the early warning signs of each situation, and how to move from firefighting to control.
1. Why does the section often appear late?
Three common reasons:
- As a destruction method: model must be sacrificed, so it should only be used when there is a good reason.
- Not seeing immediate benefits: The results of a passing sample do not produce the same clear value as a blocked lot.
- Missing specific question: If you send a sample without clearly stating what needs to be answered, the testing laboratory can only return photos, not conclusions.
The result: when things go wrong, time and costs increase, and pressure from customers reduces the ability to analyze calmly.
2. Seven situations that require a cross-section
Situation 1: The customer complains about cracked solder joints after assembly
Questions to answer: Is the crack located in the intermetallic compound (IMC) layer, in the solder joint body, or at the interface between the component base and the tin?
Where to cut: cut longitudinally through the complained solder joint itself, with an intact adjacent solder joint for comparison.
Conclusions can be obtained: Distinguish errors due to the solder jointing process (temperature, holding time) from errors due to mechanical stress after solder jointing.
Scenario 2: First batch of boards from new supplier
Questions to answer: Is the plating thickness in the hole, hole concentricity and surface coating quality in accordance with the order requirements?
Where to cut: Choose multiple holes in different locations on the panel (near the edge, middle of the panel, smallest hole) instead of multiple holes next to each other.
Conclusions can be obtained: Detect discrepancies between supplier documents and actual products before mass assembly.
Situation 3: Cracked solder joint after thermal shock or thermal cycle test
Questions to answer: Where and by what mechanism does the crack form — intermetallic embrittlement, expansion coefficient differences, or a pre-existing initial defect?
Where to cut: Cut the exact tested sample, and cut a sample from the same lot that has not been tested for comparison.
Conclusions can be obtained: Determine whether the error is due to design, materials or solder jointing process.
Situation 4: The multi-layer circuit board is suspected of having misaligned layers or layer errors
Questions to answer: Is the actual number of layers, offset between layers, and dielectric layer thickness within design tolerances?
Where to cut: Cut at the edge of the panel and the middle of the panel to compare the deviation level.
Conclusions can be obtained: Prove that the circuit board is different from the design, as a basis for comparison with the supplier.
Situation 5: Borehole resistance increases abnormally
Questions to answer: The plating hole wall is thin, is there a crack or separation between the plating and the hole wall?
Where to cut: Cut the correct hole with increased resistance, and cut the control hole at the same time.
Conclusions can be obtained: Identify plating errors, drilling errors or errors caused by the assembly process.
Situation 6: The wire connector or wire connection is stripped, the contact resistance increases
Questions to answer: Is the conductor compressed tightly enough in the head body, are there broken strands, are there unusual gaps?
Where to cut: Cut along the body of the crimp terminal, keeping the pressed wire intact.
Conclusions can be obtained: Distinguish injection mold errors, crimp terminal size errors from worker operation errors.
Situation 7: Product fails after corrosion or humidity test
Questions to answer: Where does the corrosion start and in which direction does it spread within the structure?
Where to cut: cut along the direction of suspected corrosion, usually near the edge or near the hole.
Conclusions can be obtained: Determine whether the cause is the material, protective coating or test conditions.
3. Summary table: signs and cutting positions
| Situation | Early signs | Main cutting location | Key criteria |
|---|---|---|---|
| Complaints about cracked solder joints | The error rate increased in one product code | Correct defective solder joint + control solder joint | Crack location and mechanism |
| New board supplier | Documents are complete but details are scarce | Multiple positions on the panel | Plating thickness, concentricity |
| Cracking after thermal shock | The test sample failed at high loop | Tested sample + control sample | Crack initiation location |
| Misaligned circuit board layers | Impedance or mechanical tolerance deviation | Panel edge and middle of panel | Number of layers, layer deviation |
| Hole resistance increases | The hole has an unusually high resistance | Defective hole + control hole | Thickness and continuity of plating |
| The wire connection slips | Contact resistance gradually increases | Cosse head body | Compression, space |
| Damage after corrosion | Corrosion products appear at the edge area | Along the direction of suspected corrosion | Corrosion initiation location |
4. Four signs to cut before problems occur
- Change supply: new board, solder, coating, or fabricator suppliers.
- Change process: Change heat profile, change solder jointing equipment, change line speed.
- Design changes: Change hole diameter, number of layers, board thickness, pad size.
- Drift process index: The error rate increased slightly but steadily over many batches, although it did not exceed the warning threshold.
5. From troubleshooting to routine control
| Time | Scope | Purpose |
|---|---|---|
| First batch from new supplier | Multiple positions on the panel | Confirm the actual capacity of the supplier |
| When changing materials, processes, and designs | According to the change category | Confirm changes do not cause structural errors |
| Regularly according to plan | At least one representative panel | Watch for stable or drifting trends |
| When something goes wrong | Right location and right related object | Root cause analysis |
The cost of a recurring program is usually much lower than the cost of a one-time recall, because its nature is to detect drift trends early.
6. Frequently asked questions
Does a small factory need a cross-section program?
No need to invest in equipment. Can be outsourced in batches and on a regular schedule of 3–6 months, with clearly defined acceptance criteria.
If you only have the budget for one cut, which time should you choose?
Choose a new board supplier’s first batch or when there are major changes in materials and processes, as these are the times when risk is highest.
Does cross-section help reduce customer complaints?
Yes, in two ways: detecting problems early before shipping, and having quantitative evidence when it comes to technical discussions with customers.
Should cross-sections be included in periodic quality reports?
Should. Putting cross-sectional results into the same report set as other indicators helps see the correlation between structure and performance.
What do I need to prepare before sending samples?
Identify the question to be answered, localize the cutting location, mark the cutting direction on the sample, and include information about the batch, process, and observed anomalies.
7. Conclusion
The seven situations above all have one thing in common: they relate to internal dimensions or the quality of bonds between material layers — a group of questions that only a cross-section can answer.
Three things to do: make a list of times when samples are required to be cut (first batch, change of supply, change of process); Watch for early signs to cut off before the problem flares up; and always send samples with specific questions instead of just asking to “check for help”.
References
- IPC-TM-650 Method 2.1.1 — Microsectioning.
- IPC-A-600 — Printed circuit board acceptance criteria.
- IPC-6012 — Technical and performance requirements for rigid printed circuit boards.
- IPC-A-610 and J-STD-001 — Welding material requirements and acceptance criteria.
- IPC-7095 — BGA design and assembly.
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- Cross Section in Automotive and Medical Devices: How the Requirements Differ
- From cross-sectional image to root cause: 5 investigation steps
- Cross-section small chip components 0201/0402: tombstone, insufficient solder and solder bridge
- What is Cross Section? Why do we have to cut samples to evaluate solder joints and circuit boards?
- 10 circuit board defects can only be detected by cross-section
- Why do solder joints crack after thermal shock test? Read the marks on the cross-section
- Choose the cutting position and send the cross-section sample: one wrong step and you will lose the entire data set
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Disclaimer
This article is an interpretive content compiled by us; not legal advice. Enterprises need to compare relevant documents/standards verbatim before applying them to specific products.
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