Barrel crack is a type of damage in which the coating in the hole is broken longitudinally or circularly. What makes it difficult to handle is the timing of its appearance: the product passes the output test, passes the function test, but it is not until the final assembly stage or even after delivery that a connection loss error occurs.

This article guides you on how to read cracks and holes on cross-sections, distinguish the origin and how to prove where the error arose.

1. Why do cracks appear after assembly?

The in-hole plating is a thin metal tube that penetrates the substrate material. When the board is bent or subjected to mechanical force, this plated tube is the place where the greatest stress is concentrated because it is harder than the surrounding material but the cross-section is small.

Important point: mechanical stress does not cause immediate cracking. It creates cumulative microcracks, and each time the board is bent, the crack spreads a little further. This is the reason the error appears late.

2. Marks to be read on the cross-section

Practical note: if the crack is located in the transition area between the plating layer and the pad on the surface, it is a corner crack. If the crack is in the middle of the hole body depth and runs around, it is usually the result of board flexing stress.

3. Distinguishing origins

4. How to prove at which stage the error occurs

Principle: must capture the state of the sample after each step, instead of just comparing input with output.

1. Sampling at multiple points along the line: after solder jointing, after dividing the panels, after installing into the shell, before packaging.
2. Cut the sample at each point: at least three samples per point to eliminate random variation.
3. Compare the same hole position: Must cut at exactly the same hole in samples with different points, otherwise comparison will not be possible.
4. Record process parameters: clamping force, board placement, plate dividing tool, screw tightening torque.
5. Conclusion according to the data: If the sample after stage A does not have cracks, but after stage B it already exists, then stage B is the main candidate.

It’s a time-consuming process, but it’s the only way to move from speculation to evidence — and evidence is essential when talking to customers or suppliers.

5. Additional testing should be combined

• Measure hole resistance using the four-wire method: Detect cracks that have not yet become completely open circuits, thereby detecting errors earlier.
• Try three-point bending: reproduce mechanical stress in a controlled environment.
• Vibration test: Assess cumulative effects over operating time.
• Check the bare circuit board before soldering: eliminate the possibility of a plating error available from the board supplier.

6. Frequently asked questions

Is the crack in the hole the fault of the board supplier?

Only when the thickness or plating quality is below standard. If the plating meets standards but still cracks, the cause often lies in mechanical stress during assembly or use.

How to detect early without having to cut many samples?

Use the four-wire hole resistance measurement in the first batch to find holes that tend to increase resistance, then cut only those holes. This method reduces the number of samples that have to be cut while still having the focus.

Should I test the circuit board before shipping?

For products with high-risk of stress, there should be a bending test according to applicable standards. This test helps detect cracking trends before the product leaves the factory.

If just a few holes are cracked, is it serious?

Have. A crack can cause a complete loss of connection and lead to product failure. For products with high safety requirements, the acceptance threshold is often very strict.

Does solder jointing temperature cause cracks in holes?

It is possible, if the heat is too high or the exposure time is too long, and can also cause cracking other than mechanical stress cracking. It is necessary to compare both thermal profiles and assembly conditions.

7. Conclusion

Hole cracking is a cumulative error, so the time of detection is often far from the time of formation. To determine the origin, samples must be taken at each stage and compared at the same hole location.

Four things to do: localize the steps that create bending or tensile forces; Cut the sample according to the stage mark in exactly one hole; measure four-wire hole resistance to get quantitative data; and only conclude the origin when there is two-way evidence.

References

• IPC-6012 — Technical requirements for rigid printed circuit boards, hole plating reliability section.
• IPC-TM-650 Method 2.1.1 — Microsectioning.
• IPC-TM-650 — Bending and thermal cycling test methods.
• IPC-A-610 — Electronic assembly acceptance criteria, through-hole solder joint section.

Related articles

• Cross-section through-hole solder joint: when does the pin solder joint crack?
• Why do solder joints crack after thermal shock test? Read the marks on the cross-section
• From cross-sectional image to root cause: 5 investigation steps
• 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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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.

See more: Copyright Policy & Disclaimer by ticforall.com.

Thermal shock testing is a common test to evaluate the reliability of solder joints. But when a sample cracks after testing, the important question is not “whether there is a crack” — but “was the crack created by the test, or was it pre-existing and only revealed when subjected to stress”.

This article provides instructions on reading crack marks on a cross-section after a thermal shock test, distinguishing cracks caused by testing from pre-existing cracks, and how to design a test to have a certain conclusion.

1. Why does thermal shock testing cause cracked solder joints?

In a solder joint, there are many materials with different levels of thermal expansion: circuit board base material, copper plating, solder, and component body. When the temperature changes rapidly, these materials do not expand at the same rate, creating concentrated stress at the transition points.

Point to remember: the first three mechanisms are design or process causes, while the fourth mechanism only exposes a pre-existing defect. Cross-section helps distinguish these two groups.

2. Five marks to read on the cross-section

The fourth trace is the most important fact to distinguish new cracks from old cracks. An oxidized crack edge indicates that the crack has existed long enough for the surface to be exposed to air — meaning it formed before the test.

3. Distinguish between test cracks and existing cracks

The final signal — comparison with the pre-test sample — is the strongest evidence. Without a background image, any conclusions about the cause are speculative.

4. Note: errors in sample preparation can easily be mistaken for real cracks

Cutting and grinding the sample can also create marks that look like cracks. Easily confused forms:

• Scratches due to abrasive particles: parallel, even lines, usually located on the surface.
• Cracking due to shear force: appears at the edge of the sample, in the direction of the cutting edge.
• Pulled metal burrs: long, thin metal strip that runs along the grinding surface.
• False gap due to sample pitting: voids form when the casting material is not completely absorbed.

How to distinguish: real cracks usually have a direction related to the solder joint structure and penetrate deeply into the material, while cracks caused by sample preparation are usually located in the surface layer and do not follow stress logic.

5. How to design a trial to get solid conclusions

1. Cut the sample before testing: This is a mandatory, irreplaceable comparison benchmark.
2. Record actual thermal profile: temperature, time, number of cycles, heat transfer rate.
3. Cut samples at many landmarks: after few cycles and after many cycles to see the rate of progress.
4. Select model by location: components at the edge of the board, in the middle, and near areas of high thermal mass.
5. Keep control samples: same batch, not tested, to eliminate existing errors.

6. Frequently asked questions

Is cracking after thermal shock test a fault of the solder jointing process?

Not necessarily. Can be a consequence of design (material selection, component placement), solder jointing profile, or pre-existing defects. It is necessary to read the trace and compare it with the background sample.

What does the crack pattern in the first cycle mean?

Usually suggests a pre-existing defect or serious material problem. It is necessary to check the sample before testing the same batch to confirm.

Should I cut the sample immediately after testing or let it cool and then cut?

The sample should be brought to room temperature before cutting, to avoid causing additional stress. Clearly state the cutting time compared to the end of the test.

How to distinguish test cracks from grinding scratches?

Scratches caused by grinding are usually parallel, even and only on the surface. Stress cracking is structurally oriented and penetrates deep into the material. If you are not sure, you should grind again and observe at a deeper layer.

How many cycles is enough?

Depending on applicable standards and assessment objectives. It is important to clearly state the actual number of cycles and always have a control sample for comparison.

7. Conclusion

After thermal shock testing, cracks are data, not conclusions. To know the cause of the crack, you must read its location, direction, edges and secondary traces — then compare it with the pre-test sample.

Four things to do: always cut samples before testing; record actual thermal profile; Observe the edge of the crack to evaluate whether it is new or old; and eliminate the possibility of fake stains due to sample preparation before conclusion.

References

• IPC-TM-650 — Test methods, thermal shock and thermal cycling test sections.
• J-STD-001 — Requirements for electrical soldering and electronic assembly.
• IPC-TM-650 Method 2.1.1 — Microsectioning.
• IPC-A-610 — Electronic Assembly Acceptance Criteria.

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• Barrel crack after assembly: causes and proof
• From cross-sectional image to root cause: 5 investigation steps
• Cross-section through-hole solder joint: when does the pin solder joint crack?
• Measuring dimensions on cross-sectional images: how to set the ruler to minimize the error?

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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.

See more: Copyright Policy & Disclaimer by ticforall.com.

There is a group of board defects that all non-destructive testing methods miss: structural defects. They are located inside the material, underneath the component base, or at the interface between layers — places where X-ray, AOI, and electrical measurements are unreadable.

This article summarizes 10 such errors, with identifying signs on cross-sectional images and reasons why other methods cannot detect them.

1. Ten errors can only be seen by cross-section

2. Error group belongs to the solder joint

This is the most common group and is also the main reason why factories make cross-sections periodically. Common point: all links are hidden.

1. No wetting: The tin is adjacent to the surface but not bonded. The cause is usually surface contamination or oxidation.
2. Head-in-pillow: The two tin parts come into mechanical contact without forming a bond. This is the most difficult error to diagnose in this group.
3. Thick or broken intermetallic compound (IMC) layer: The bond is formed but the quality is not met, leading to brittleness or a cracking initiation point.
4. Large void at the bearing position: void itself is not a defect, but large voids in the right position reduce durability and heat conductivity.

3. Error group belongs to the circuit board

1. Cracked into plated holes: The most severe structural error of a through-hole solder joint, causing loss of connection between layers.
2. Lack of copper in the hole: The plating thickness is below the required level, causing local overheating when large current flows through.
3. Separating the base material layer: Gaps between layers of material, often related to solder jointing temperature or residual moisture in the material.

4. Error groups belong to components and coatings

1. Cracking of multi-layer ceramic capacitors: Cracks form due to bending stress, which may not appear until moisture penetrates.
2. Peeling off protective coating: The coating does not adhere well enough, allowing moisture and impurities to penetrate over time.
3. Circuit breakage due to local heat: The cross-section shows that the cause of the break lies in the heat, not in the overload current.

5. Why can’t other methods detect it?

The role of cross-section is not to replace the other methods, but to supplement the layer of information that they do not have: internal structure and interface.

6. When should you proactively cut off inspection?

• The first batch of a new product or a new process.
• After changing the supplier of circuit boards, solder paste, components or thermal profiles.
• When there are complaints about operational errors but electrical measurements cannot find the cause.
• After a field problem there are signs that accumulate over time.
• Periodically follow the quality control plan, even when there are no problems.

7. Frequently asked questions

Is there any method to replace cross-section?

No method gives equivalent results regarding the internal structure. Optical tomography can be used for transparent samples, but is not suitable for circuit boards and metal components.

Does cross-section destroy the pattern?

Yes, the model is cut and molded so it cannot be returned to production. This is why it is important to choose a highly represented cutting location.

With a product running well, is it necessary to cut and check?

Should be done with the first batch and when there are process changes. Working well in the early stages does not eliminate errors that accumulate over time.

Which error should we focus on in the list above?

Depending on the product. Multi-layer circuit boards with through holes should focus on plated holes; Products with BGA components should focus on the head-in-pillow and void groups; Products with many ceramic capacitors should pay attention to cracks due to bending.

Are the sectional results conclusive for the whole batch?

Not directly. Sectional results only apply to cut samples. To draw conclusions for a batch, it is necessary to combine process data, other test data and the appropriate number of samples.

8. Conclusion

The ten defects in this article have one thing in common: they are located where light, X-rays, and electric current cannot reach. That’s why cross-sections still play an irreplaceable role in electronic quality control.

Four things to do: build a separate list of critical errors for each product; cut inspection at the first batch and after each process change; Always cut with a control sample; and combine cross-sectional results with process data instead of drawing conclusions from images alone.

References

• IPC-A-610 — Electronic Assembly Acceptance Criteria.
• IPC-6012 — Technical requirements for rigid printed circuit boards.
• IPC-TM-650 Method 2.1.1 — Microsectioning.
• J-STD-001 — Requirements for electrical soldering and electronic assembly.

Related articles

• What is Cross Section? Why do we have to cut samples to evaluate solder joints and circuit boards?
• How is Cross Section different from X-ray, AOI and ultrasound? When must the sample be destroyed?
• From cross-sectional image to root cause: 5 investigation steps
• 5 strange marks on the cross-section: distinguish real errors from phenomena due to sample preparation
• Set of standards governing cross-section: IPC-A-600, IPC-6012, IPC-TM-650 2.1.1, J-STD-001 and IPC-A-610

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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.

See more: Copyright Policy & Disclaimer by ticforall.com.

The wire connection to the connector is not soldered but mechanically compressed. That means everything that determines the quality of the joint is inside the tube body, and no external test can read it. The section is the only tool that sees the part.

This article teaches you how to read cross-sections of the crimp terminal, evaluate compression, broken strands, gaps and four common injection mold errors.

1. Why must pressure joints be evaluated by cross-section?

• The link is inside the squeeze tube: cannot be observed from the outside.
• Appearances can be deceiving: A strong-looking crimp may still hold fewer strands of wire than designed.
• Injection mold error only appears when dissecting the sample: Mold wear, wrong size or eccentricity cannot be detected by eye.
• Consequences appear late: Poorly pressed joints increase contact resistance, causing local heating and corrosion over time.

2. The structure needs to be read in section

3. Evaluate compression

Compression represents the degree of deformation of the wire when pressed by the mold. How to evaluate on cross-section:

1. Distortion level: Are the strings flattened and pressed together or still keeping their circular shape intact?
2. Uniformity: Does all the ropes deform, or only some of them bear the force?
3. Symmetry: The compression level is evenly distributed around the pipe circumference or concentrated on one side.
4. Fill level: How far is the volume inside the tube filled by the string?

4. Broken wire rays and gaps

These are the two most important criteria when evaluating pressure joints:

• Broken wire beam: The wire is cut off by the mold, reducing the actual conductive cross-section. The number of broken strands allowed depends on the applicable standard, quality class and number of strands of the wire.
• Space: the area not covered by the wire in the tube. The voids create a way for moisture and impurities to penetrate, leading to galvanic corrosion and increased contact resistance over time.

Correct way to record: count the number of broken fibers at each location, clearly state the total number of fibers in the wire, and describe the location of the gap (at the mouth of the tube, at the center, or on the opposite side of the compression point).

5. Four common injection mold errors

Point to remember: these four errors are all invisible to the eye and can only be determined by cross-section. Therefore, periodic cross-section inspection is a more effective means of mold control than relying on visual inspection.

6. Additional testing should be combined

1. Pull force test: Measure the force that breaks or loosens the joint and compare it to the standard.
2. Measuring contact resistance: detect joints with insufficient conductive cross-section.
3. Vibration test and thermal cycle test: Evaluate the stability of the joint under operating conditions.
4. Salt mist corrosion test: Evaluate the ability to resist penetration of moisture and impurities through gaps.

7. Frequently asked questions

Does a pressure joint that achieves traction mean it achieves all aspects?

Not really. Pressed joints can achieve tensile strength but still have voids inside, leading to corrosion in the long run. These two indicators complement each other and do not replace each other.

How many broken threads are considered defective?

Depending on applicable standards, quality level and number of strands of wire. What needs to be done is to clearly state the total number of threads and the number of broken threads, then compare them with the agreed criteria.

Do small multi-strand ropes and large few-strand ropes have the same evaluation?

No. Small multi-strand ropes need to evaluate the uniformity between the strands; In a wire with several large strands, each broken strand has a much larger effect on the conduction cross-section.

Is there a way to check pressure joints non-destructively?

X-ray can be used to see the shape of the tube body and the filling level, but it is not enough to conclude about fiber deformation and number of broken fibers. The cross-section is still needed for the final conclusion.

Where should the sample be cut on the pressure joint?

Cut along the axis of the cose head to see the entire length of the tube, the transition part and the insulating clamp part in the same section.

8. Conclusion

The wire connection is mechanically compressed so its quality is only apparent when dissecting the sample. The three things to read are compression, broken strands, and clearance — all three of which cannot be assessed by eye or by inspection of appearance.

Four things to do: cut along the axis to see the entire joint in one section; clearly state the total number of threads and the number of broken threads; Always include the results of the traction force test and contact resistance measurement; and periodically check injection molds because this is the most common source of errors but the hardest to detect.

References

• IPC/WHMA-A-620 — Requirements and acceptance criteria for cable and conductor assemblies.
• IPC-TM-650 Method 2.1.1 — Microsectioning.
• Technical standards for crimp terminals and injection molds of the manufacturer.
• UL 486A-486B — Standard for wire connectors, press splice requirements section.

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• QCVN 4:2009/BKHCN: safety requirements for electrical and electronic equipment and Amendment 1:2016
• Cross-section MLCC capacitors: cracks due to board flexing and delamination defects
• Cross-section solder joint: wetting angle, fillet penetration and intermetallic compound (IMC) layer
• What is Cross Section? Why do we have to cut samples to evaluate solder joints and circuit boards?
• Cross Section in Automotive and Medical Devices: How the Requirements Differ

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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.

See more: Copyright Policy & Disclaimer by ticforall.com.

High-power LEDs and power modules use solder joints not only to conduct electricity but also to conduct heat. This makes their solder joint evaluation standards more stringent than conventional components: a void in an unimportant location for a signal component can be a serious problem for a power component.

This article provides instructions on reading the solder layer cross-section of LEDs and power modules, evaluating the intermetallic compound (IMC) layer thickness, identifying cracks due to thermal cycling, and how to verify reliability.

1. Why are power components different from regular components?

2. Four characteristics to read on a cross-section

3. The intermetallic compound (IMC) layer thickens with working temperature

The intermetallic compound (IMC) layer forms immediately upon solder jointing and continues to grow over time, with the rate increasing sharply at high temperatures. With power components working continuously at high temperatures, this layer can thicken significantly over the product life cycle.

Since this process takes place throughout the product life cycle, evaluating the intermetallic compound (IMC) layer only in its initial state is not enough. Results need to be placed in the context of actual working conditions.

4. Void with power components

Void affects two ways, not just one:

1. Thermal line: void reduces the thermal conduction cross-section, causing heat to accumulate in the component and the junction temperature to be higher than designed.
2. Mechanical path: void is the stress concentration point, becoming the place where cracking begins when there is a thermal cycle.

Therefore, when evaluating voids in a power solder jointing layer, it is necessary to record all three parameters: area ratio, largest void size, and void position relative to the main heat path. Void located on the main heat path is much more serious than void at the edge.

5. Common errors and how to distinguish them

Important rule: to confirm cracking due to thermal cycling, there must be an untested control sample. Without a background image, the possibility of a pre-existing crack cannot be ruled out.

6. Verify reliability

1. Try thermal cycling or thermal shock: Create repetitive stress to reveal cracking tendency.
2. Try high power for a long time: Evaluate the evolution of the intermetallic compound (IMC) layer and the void.
3. Measure junction temperature or thermal resistance: evaluate the actual impact of void on heat dissipation ability.
4. Cut samples at multiple time points: before the test, between the test and after the test to see the progress.

7. Frequently asked questions

How much Void affects heat dissipation?

There is no general threshold, as it depends on heat sink design, power and junction temperature requirements. The threshold should be determined according to the thermal model of the specific product.

Is a dead LED light caused by solder joints?

Not necessarily. It could be due to the luminescent layer, the internal connection wire, or the solder joint. The cross-section helps determine exactly which floor is damaged.

Is it necessary to cut the sample after thermal cycling?

Highly recommended. This is the only way to confirm that the crack formed during the test instead of being pre-existing.

Is a thick intermetallic compound (IMC) layer always bad?

Not always, but when it exceeds a certain level, brittleness increases and reliability decreases. Need to evaluate according to the actual working conditions of the components.

Does the power module need to cut through multiple locations?

Yes. Cutting should be done in high current areas, areas near heat sinks, and edge areas — because thermal and mechanical conditions are markedly different.

8. Conclusion

With power components, the solder joint is both an electrical and thermal conductor, and that is why it ages over time. Two processes to monitor are intermetallic compound (IMC) layer thickening and void progression — both of which are difficult to detect if only examined in the initial state.

Four things to do: put the intermetallic compound (IMC) layer assessment in the context of actual working temperatures; write void according to position relative to heat path; Always have a pre-test sample as a control; and combine thermal cycling testing with thermal resistance measurements for evidence of actual effects.

References

• IPC-A-610 — Electronic Assembly Acceptance Criteria.
• J-STD-001 — Requirements for electrical soldering and electronic assembly.
• IPC-TM-650 Method 2.1.1 — Microsectioning.
• Technical documentation on thermal management and power component reliability from the manufacturer.

Related articles

• Cross-section QFN/DFN: void under the heat sink and solder pins
• Cross-section solder joint: wetting angle, fillet penetration and intermetallic compound (IMC) layer
• Why do solder joints crack after thermal shock test? Read the marks on the cross-section
• Measuring dimensions on cross-sectional images: how to set the ruler to minimize the error?

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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.

See more: Copyright Policy & Disclaimer by ticforall.com.

Multi-layer ceramic capacitors (MLCC) are components with a structure consisting of hundreds of ceramic layers and electrodes stacked, pressed and baked into a block. That structure allows for large capacitance in a small size, but also makes the capacitor brittle and very sensitive to board flexing forces.

The worry is that the crack inside the capacitor body may not be visible to the outside. This article guides you on reading MLCC capacitor cross-sections, identifying cracks caused by circuit board flexing and distinguishing them from delamination defects from the manufacturer.

1. Why do MLCC capacitors fail underground?

• Brittle ceramic: Good compression resistance but poor tensile and bending resistance.
• Cracks that are not visible: Cracks in the capacitor body still allow the capacitor to operate normally during the initial period.
• Progressive failure: After a while, moisture penetrates through the crack, causing electrical leakage and progressing to a short circuit.
• The location near the solder joint is the weak point: This is where the board flexing force transmitted to the capacitor body is most concentrated.

2. Four characteristics to read on a cross-section

3. Cracks due to circuit board flexing

Cracks caused by circuit board flexing have a quite characteristic morphology, and identifying this morphology is the key to determining the origin:

1. Starting point: usually at the condensation corner near the solder joint — where bending stress is most concentrated.
2. Orchid direction: Run into the condenser body in an oblique direction, creating an angle of about 45 degrees compared to the condenser axis.
3. Scope: Can cut through multiple electrode layers, creating bridges between layers.
4. Secondary signs: It is common to see a slightly curved circuit board, or deformed solder joints in the surrounding area.

Mechanism: when the circuit board is bent, the hard ceramic capacitor cannot deform accordingly, so all the stress is concentrated in the area near the solder joint. Cracks form from there.

4. Distinguish from manufacturer errors

Principle: if the error only appears in the capacitor mounted on the board, but the separate capacitor model of the same batch has no problem, then the cause is more likely to lie in the assembly process, not in the components.

5. Additional testing should be combined

• Try bending the circuit board: Evaluate the curvature threshold that the capacitor can still withstand, according to the instructions of the applicable standard.
• Heat shock test: Detect cracks that progress with thermal cycles.
• Measure insulation resistance and leakage current: detect cracks that have not yet become a complete short circuit.
• Check the procedure of dividing the board: This is the step that creates the largest bending stress in production.

6. How to prevent in production

1. Control bending force at every stage: from clamping, soldering, dividing the board to assembling.
2. Arrange capacitors to avoid large bending areas: Do not place near the edge of the board or near the dividers.
3. Suitable pad design: Avoid too much tin in the solder joint.
4. Choose the right type of capacitor for the stressed location: There are more flexible capacitors designed for these locations.
5. Check by lot and by location: Focus on high stress locations instead of random inspections.

7. Frequently asked questions

Cracked MLCC capacitors are always caused by circuit board flexing?

No. Also due to thermal shock, overheating when solder jointing, or delamination defects from the manufacturer. The morphology and location of cracks are the main basis for differentiation.

Can capacitor cracks be detected without cutting the sample?

Ultrasound scans or high-resolution X-rays can be used to suggest, but reliability is limited. Cross-section remains the confirmatory method.

Do cracked capacitors always fail immediately?

No. In many cases, capacitors still function normally and only fail after a period of time when moisture penetrates through the crack. This is why this error is difficult to diagnose late.

Can the cross-section determine when the crack formed?

Not directly. But combining cross-sectional images with process data and bending and thermal shock test results can determine which stage causes the crack.

How many capacitors should be cut per batch?

You should choose according to the location on the board: capacitors near the edge and near the dividing line, capacitors in the middle of the board, and capacitors in the vicinity of large connections. The amount depends on the risk level of the product.

8. Conclusion

MLCC capacitors fail cumulatively: cracks form in a moment but the consequences appear many months later. The cross-section is the primary tool for seeing cracks and distinguishing the source — board flexing, thermal shock, or delamination errors.

Four things to do: read the crack morphology before drawing conclusions; Compare with separate capacitor samples of the same batch; Check the stages of creating bending force; and combine bending testing with cross-sections for two-dimensional evidence.

References

• IPC-A-610 — Acceptance criteria of electronic assembly, chip components.
• IPC-TM-650 Method 2.1.1 — Microsectioning.
• J-STD-001 — Requirements for electrical soldering and electronic assembly.
• Technical documentation on bending stress and mechanical strength of multilayer ceramic capacitors from the manufacturer.

Related articles

• Cross-section small chip components 0201/0402: tombstone, insufficient solder and solder bridge
• Cross-section of crimp terminal and cable: compression, broken strands and gaps
• 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

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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.

See more: Copyright Policy & Disclaimer by ticforall.com.

Chip components 0201 and 0402 weigh only a few thousandths of a gram, and the amount of tin used to make the solder joints for them is also very small. At that scale, a difference of a few tens of micrometers in the amount of solder paste is enough to turn a successful solder joint into a defect — but it is very difficult to detect with the naked eye or with conventional optical inspection.

This article guides you on reading solder cross-sections of small chip components, identifying three main defects: tombstone, insufficient solder and solder bridge, as well as design factors that affect the results.

1. Why are small chip components difficult to test?

• Tin volume is too small: The absolute error is small but the error ratio over the total amount of tin is large.
• The solder joint is located under the two ends of the component: Most of the link area is hidden.
• Optical inspection is difficult to expand the viewing angle: The components are low, the bottom part of the foot cannot be seen.
• Easily affected by manipulation: The suction force of the pick-up head and slight collision will also cause movement.

2. Four characteristics to read on a cross-section

3. Three main defects and signs on the section

Point to emphasize: tombstone is not a component error but an imbalance error during the solder jointing process. The cross-section helps confirm the clearance under the component head, which is direct evidence of this type of defect.

4. Why does tombstone happen?

When the solder paste melts, surface tension forces pull the component toward the melting mass of tin. If the two ends do not melt at the same time, the pulling force is unbalanced and one end lifts up. Common causes:

1. Heat difference between two ends: due to uneven copper density around the pad or due to the direction of the heat exchanger.
2. Difference in solder paste amount: one end has more cream due to stencil or misprinting.
3. Asymmetrical pad: a larger pad or connected to a large copper area.
4. One end is oxidized: Tin is impervious to wetting on one side.
5. Vibration or impact when the tin is still molten.

5. Influence of design and stencil

6. Additional testing should be combined

• Measuring shear force (shear test) on the solder joint to evaluate the bond strength.
• Try heat shock to evaluate the ability of small solder joint joints to withstand thermal cycling.
• Try bending the circuit board because small chip components are sensitive to bending stress.
• Automated testing with expanded viewing angle to increase the ability to detect fillet errors.

7. Frequently asked questions

Does component 0201 need periodic cutting and inspection?

Recommended for products with a high density of small components, because this is the group that is most susceptible to process drift and is also difficult to detect errors with normal testing.

Can X-ray be used to check chip components?

X-ray shows the amount of tin and void, but it is difficult to evaluate fillet shape and wetting condition. The cross-section is still necessary for conclusions about the bond.

Can Tombstone be detected before solder jointing?

No direct detection, but risk can be reduced by thermally symmetrical pad design and uniform thermal profile control at both ends.

Do small component solder joints need to measure fillet height?

Yes, but it is necessary to clearly define the measurement point because the small size causes measurement errors to increase. High magnification and repeated measurements should be used.

How many components should be cut per evaluation?

Choose by region: one component in a low density region, one in a high density region, and one near the edge of the board — because thermal conditions are markedly different.

8. Conclusion

Small chip components are a group for which conventional testing is difficult, while cross-sections provide direct information about the connection. The three main defects — tombstone, tin deficiency, solder bridge — all have characteristic marks on the cross-section and are all tied to the pad design, stencil and thermal profile.

Four things to do: cross-section inspection of the first batch and when there are process changes; Always shoot at high enough magnification to see both ends of the component; Includes cutting force test to quantify durability; and compare the results with the stencil design and pad opening ratio.

References

• IPC-A-610 — Acceptance criteria of electronic assemblies, chip components and solder paste.
• J-STD-001 — Requirements for electrical soldering and electronic assembly.
• IPC-TM-650 Method 2.1.1 — Microsectioning.
• The document recommends the manufacturer’s pad and stencil designs for chip components.

Related articles

• Cross-section solder joint: wetting angle, fillet penetration and intermetallic compound (IMC) layer
• Cross-section MLCC capacitors: cracks due to board flexing and delamination defects
• 7 situations where factories are forced to do cross-sections
• Measuring dimensions on cross-sectional images: how to set the ruler to minimize the error?

Discuss further

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.

See more: Copyright Policy & Disclaimer by ticforall.com.

Through-hole solder joints are the type of solder joints that are subject to the greatest mechanical stress on the circuit board: the component pins transmit force from the component body to the board, while the plated hole wall must endure the expansion difference between the metal and the base material. Therefore, this is also the place where cracks appear earliest.

This article provides instructions on reading cross-hole solder joints, distinguishing crack types by location, and how to identify errors in the soldering, circuit board, or assembly process.

1. Why are through-hole solder joints easy to crack?

2. The structure needs to be read in section

3. Types of cracks and their locations

1. Barrel crack: Cracks run vertically or around the wall of the seedling hole. This is the most serious form because it causes the electrical connection between the two sides of the board to be lost.
2. Corner crack: appears at the transition zone between the plating layer into the hole and the pad on the surface.
3. Barrel-wall separation: The plating layer is intact but separated from the base material.
4. Cracks at the solder joint heel: Cracks originate from the outer edge of the fillet, usually due to mechanical stress.
5. Crack between tin and component pin: signs of problems in the soldering step or in the component pin coating.

4. Distinguish the source of errors

Principle: origin conclusions must be based on at least two data sources — cross-sectional images and process or test data. Cross-sectional images alone only show the shape of the defect.

5. Tin infiltration in hole body

Tin infiltration in the hole is evaluated according to the filling level of the hole body. Need to clearly state:

• Calculation benchmark: according to board thickness or actual hole length.
• Measurement location: at the center of the hole or near the mouth of the hole.
• Double-sided condition: is the tin applied evenly to both sides of the board or just one side.

With multi-layer circuit boards, tin can also fill the inner layers. In this case, it is necessary to observe the entire length of the hole instead of just looking at the two outer sides.

6. Additional testing should be combined

1. Measure hole resistance: Detection of cracks that have not yet become completely open circuit.
2. Thermal shock or thermal cycling test: Apply cyclic stress to detect cracking trends.
3. Vibration and bending test: Assess the effects of mechanical stress.
4. Cross check with the board supplier: Compare the announced and actual plating thickness.

7. Frequently asked questions

Can cracks be seen by X-ray?

Can be seen but difficult to quantify, especially when the crack is small or located out of direction. The cross-section gives clearer information about crack location and length.

Can hole cracks be caused by the wave soldering process?

Yes, when the temperature or exposure time is not suitable. However, it is necessary to distinguish it from cracking due to thermal stress during use, because these two causes lead to different corrective actions.

Should the sample be cut before or after the thermal shock test?

You should do both: crop first to get the background image, crop later for comparison. Without a background image, it is impossible to confirm whether the crack was caused by testing or was pre-existing.

How to handle burrs in drilled holes?

Record burrs as a separate defect, evaluate the impact on plating coverage and tin adhesion. Large burrs often result in discontinuous plating in the transition zone.

Is it difficult to cut through-hole patterns on thick circuit boards?

Yes, because large hole lengths require a more precise cutting plane. You should use a suitable clamp and cut from both sides if the hole is too long.

8. Conclusion

Through-hole solder joints are subjected to many types of stress at the same time, so the crack types are also diverse and located in very different locations. Sections are the primary tool for identifying crack location and morphology, but origin conclusions must be accompanied by process or test data.

Four things to do: capture the entire length of the hole, not just both sides of the board; clearly state the benchmark for calculating tin infiltration; always have a background image before testing; and separate conclusions according to each type of stress instead of grouping them into “solder joint errors”.

References

• IPC-A-610 — Electronic assembly acceptance criteria, through-hole solder joint section.
• J-STD-001 — Requirements for electrical soldering and electronic assembly.
• IPC-6012 — Technical requirements for rigid printed circuit boards, hole-plated quality parts.
• IPC-TM-650 Method 2.1.1 — Microsectioning.

Related articles

• Why do solder joints crack after thermal shock test? Read the marks on the cross-section
• Barrel crack after assembly: causes and proof
• Cross-section solder joint: wetting angle, fillet penetration and intermetallic compound (IMC) layer
• What is Cross Section? Why do we have to cut samples to evaluate solder joints and circuit boards?

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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.

See more: Copyright Policy & Disclaimer by ticforall.com.

QFN and DFN are groups of components with two types of solder joints with completely different roles: pins on the side to connect the signal, and a metal base below that is both grounded and conducts heat. A product may pass in one group of solder joints but fail in another group, and the naked eye cannot distinguish.

This article guides how to read cross-sections of two groups of QFN/DFN solder joints, how to evaluate voids under the substrate and four common errors.

1. Why is QFN/DFN difficult to evaluate?

• The side legs are very short: The amount of tin forming fillets is small, making it easy to wrongly conclude that there is a lack of tin.
• The heat sink is located completely below: cannot be seen, cannot be checked by eye.
• Void under the sole does not appear: The product still works during the initial period.
• Two groups of solder joints have different criteria: same cross-section, the conclusions for the two groups may be opposite.

2. Two groups of solder joints, two sets of criteria

Because the two groups have different criteria, the section report for QFN/DFN must separate conclusions for each group, not grouping them into “pass solder joint” or “fail solder joint”.

3. Read the side leg section

1. Wetness: Does the tin spread evenly onto the edge of the foot and onto the pad or does it clump up?
2. Fillet height: Measure from the pad surface up to the foot edge, clearly stating the landmark.
3. Contact Width: Is the tin part between the foot and pad continuous or has a gap?
4. Void in fillet: If so, write size and location.

A practical note: with QFN/DFN, the criteria often focus on having a metallic bond at the interface, not requiring a thick fillet. So don’t conclude an error just because the fillet is low.

4. Read the cross-section of the heat sink base

5. Why is the void under the base dangerous?

The heat sink is the main heat escape route of the component. When there is a large void, heat cannot escape to the circuit board but accumulates in the components, leading to:

• Junction temperature is higher than design, reducing component life.
• Ground impedance increases, affecting high frequency performance.
• Thermal cycling causes voids to spread over time, causing the solder joint to deteriorate faster.

This is the reason subbase voids are often evaluated more severely than voids in signal solder joints.

6. Four common mistakes

7. How to properly cut QFN/DFN samples

1. Cut perpendicular to the foot row let the cross-section cut through multiple legs at the same time.
2. Make sure the section passes through the center of the base to see both the center and the two edges of the base.
3. Choose at least two components: one at the edge of the board, one at the middle of the board, because of different thermal conditions.
4. Record the cutting direction to compare with the pinout when needed.

8. Frequently asked questions

X-ray shows void under the sole, is it necessary to cut?

Should be cut if the void is large or located in the central area. X-ray shows the scale over the entire sole; The cross-section shows which layer the void is in and the actual extent of coverage.

Is low fillet an error?

Not automatically. With QFN/DFN, the main criterion is the presence of metallic bonding at the interface. It is necessary to determine the link before concluding an error.

Are there general criteria for void under the base?

The threshold depends on the applicable standard and the heat dissipation requirements of the design. Internal thresholds should be agreed upon with the customer before assessment.

Can small DFN components be cut?

Yes, but you need to prepare the sample carefully because the area to be surveyed is small. It is recommended to use cold casting and reduce force in the polishing step.

What else should be checked besides the cross-section?

It is recommended to check the junction temperature during operation and measure the grounding impedance, because these are two indicators that reflect the actual influence of the void under the substrate.

9. Conclusion

QFN/DFN has two groups of solder joints with different roles, so they must be evaluated separately. Side pins need to confirm metal connection; The heat sink base needs to be evaluated for tin and void coverage — because this is the main heat escape route of the component.

Four things to do: cut perpendicular to the foot row and through the center of the sole; separate conclusions for two groups of solder joints; record void by scale, maximum size and position; and agree on assessment thresholds with customers before starting.

References

• IPC-A-610 — Acceptance criteria for electronic assemblies, pinless components and flat components.
• J-STD-001 — Requirements for electrical soldering and electronic assembly.
• IPC-TM-650 Method 2.1.1 — Microsectioning.
• Design and assembly instructions for components with heat sinks from the manufacturer.

Related articles

• Cross-section BGA: void measurement and head-in-pillow detection
• Cross-section solder joint: wetting angle, fillet penetration and intermetallic compound (IMC) layer
• LED cross-section and power module: intermetallic compound (IMC) layer and solder crack
• 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.

See more: Copyright Policy & Disclaimer by ticforall.com.

BGA is a type of component where the entire solder joint is located under the body, cannot be seen with the eye and cannot be inspected with a probe. Therefore, every evaluation of BGA must go through two doors: X-ray to localize, and cross-section to confirm the structure.

This article provides instructions on choosing a row of balls to cut, reading the BGA ball cross-section, measuring void properly, identifying head-in-pillow and the limitations that must be stated when concluding.

1. Why is BGA more difficult to evaluate than regular solder joints?

• Not visible: The solder joint is completely under the component body.
• Unable to check each connection: The number of balls is large, it is impossible to detect each point.
• Defects often lie at the interface: The hardest to observe is where errors often occur.
• Expensive repairs: Disassembling and re-soldering the BGA is a high-risk step, easily damaging the entire board.

2. Select the marble row to cut

Effective way: cut perpendicular to the row of balls so that the cutting plane passes through the center of the most balls. Oblique cutting distorts the image and any measured numbers no longer represent the true diameter of the ball.

3. Four reading characteristics on the BGA ball cross-section

4. Measure the void in the BGA ball

There are three parameters to record, instead of just one:

1. Void area ratio on the total cross-sectional area of the ball.
2. Largest void size — determines the stress concentration level.
3. Void location — located in the pad junction area, in the middle of the ball or on the package side.

Because the two methods provide two different types of information, the void ratio reported by X-ray and the void ratio reported by cross-section will not match — this does not mean that either is wrong.

5. Head-in-pillow: identification sign

Head-in-pillow is a situation where the solder ball has melted but the solder paste on the pad has not completely melted, causing the two parts to come into mechanical contact without forming a metal bond. On cross-section, recognizable features include:

• There is a clear boundary between the ball part and the solder paste part, almost two separate blocks.
• The contact surface curves evenly according to the original shape of the ball, not flattening along the pad.
• No intermetallic band is seen at the interface.
• There may be microscopic gaps between the two parts.

Factors commonly associated with head-in-pillow: thermal deformation of the package or circuit board causing the solder joint to separate during melting, oxidation of the solder paste, or insufficient thermal profile for both parts to reach the molten state at the same time.

6. Four other common errors on BGA cross-sections

1. The ball is flattened to one side: suggests uneven compression or a misaligned pad.
2. Tin bridge between two neighboring balls: confirms the solder bridge that X-ray only suggested.
3. Missing package side link: Signs of problems with the pad on the package or the package’s coating.
4. Cracks in ball neck: often related to post-solder joint mechanical stress.

7. Five-step process for BGA complaints

1. Collect X-ray data of the defective batch and sample to localize the suspect location.
2. Compare electrical data If yes: which pin, which board is the error?
3. Select cutting position according to the questionable position, accompanied by a row of reference balls.
4. Cut and read cross-sections according to the four characteristics in section 3.
5. Conclusion separated by each possibility: void, head-in-pillow, solder bridge, or mechanical defects — are not grouped together as “solder joint defects”.

8. Frequently asked questions

X-ray showed a large void, do I need to cut again?

Cutting should be done if the void is located in the bearing area or if the cause needs to be concluded. X-ray confirmed void; The cross-section shows where the void is located and whether the surrounding connections are good or not.

How many marbles are enough to reach a conclusion?

There is no fixed number. There should be at least one row of marbles at the edge and one row in the center, plus a row of control marbles.

Can head-in-pillow be diagnosed by X-ray?

Difficult, because the external shape of the solder joint can still be normal. Even on cross-sections, you need to carefully observe the interface to recognize it.

Should all marbles be cut in one row?

Depends on the goal. If evaluating row uniformity, you should cut along a row to see all the marbles in that row and compare them with each other.

Is a porous solder ball considered a defect?

Not automatically. Need to consider size, location and applicable standards. Small scattered voids are generally accepted; Large voids concentrated in the bearing area are the problem.

9. Conclusion

BGA evaluation requires both X-ray and cross-section: X-ray to know where to look, cross-section to know what is actually there. Sections provide depth information that X-rays do not provide, but only apply to the row of cut balls.

Four things to do: cut perpendicular to the marble row; Select both the edge row and the center row; write void in three parameters instead of one scale; and separate conclusions according to each specific type of disability.

References

• IPC-7095 — BGA design and assembly, content on voids and solder defects.
• IPC-A-610 — Electronic Assembly Acceptance Criteria.
• J-STD-001 — Requirements for electrical soldering and electronic assembly.
• IPC-TM-650 Method 2.1.1 — Microsectioning.

Related articles

• Barrel crack after assembly: causes and proof
• Cross-section solder joint: wetting angle, fillet penetration and intermetallic compound (IMC) layer
• Cross-section QFN/DFN: void under the heat sink and solder pins
• IPC-7095: void criteria for level-specific BGA
• How is Cross Section different from X-ray, AOI and ultrasound? When must the sample be destroyed?

Discuss further

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.

See more: Copyright Policy & Disclaimer by ticforall.com.