Why Do So Many Engineers Eventually Turn to FIB in Chip Failure Analysis? Because Root Causes Often Hide in Just a Few Microns
Anyone involved in electronics knows that when a chip fails, replacing it is often easier than understanding why it failed.
This becomes especially critical in cases involving batch failures, field returns, or reliability problems. If the chip is simply replaced without identifying the root cause, the same issue is likely to return.
That is exactly why FIB has become a key method in failure analysis for more and more projects.
Many critical defects are not visible on the package surface and cannot be identified with a simple microscope inspection. They are buried deep inside the die, between metal layers, near contact vias, or within microscopic localized defects only a few microns wide.
The Core Roles of FIB in Failure Analysis
FIB is important not because it sounds advanced, but because it can solve problems that conventional methods cannot.
1. Site-specific cross-sectioning
Instead of destructive bulk removal, FIB can cut precisely into a suspected location. This is crucial for confirming internal cracks, burn damage, voids, and delamination.
2. Layer-by-layer inspection
A chip is a multilayer structure. Looking only at the surface is often misleading. FIB makes it possible to expose and inspect deeper layers one by one until the actual defect is revealed.
3. Strong integration with SEM
FIB performs the processing, while SEM provides high-resolution imaging. One tool opens the structure, and the other helps engineers clearly examine what is inside.
4. Root cause confirmation
Electrical testing can often tell engineers that “something is wrong,” but not necessarily why. Cross-sectional evidence is usually needed for solid conclusions, and FIB is ideal for that role.
Common Failure Scenarios Where FIB Is Frequently Used
In practical projects, FIB is especially useful for:
- Internal chip short circuits or leakage
- Intermittent open circuits
- ESD or EOS damage
- Metal migration
- Contact via abnormalities
- Corrosion under passivation
- Early failures caused by process defects
- Internal cracking caused by package stress
It is particularly valuable when the chip looks normal externally but shows abnormal electrical behavior, especially in low-occurrence or difficult-to-reproduce failures. These are exactly the kinds of issues most likely to be misjudged if FIB is not used.
Case Study 1: RF Chip Output Degradation Caused by Internal Corrosion
In one project, a batch of RF chips showed degraded output performance, and some boards eventually lost output entirely.
At first, engineers suspected the external matching network. But after swapping boards, materials, and firmware, the issue still could not be completely resolved.
Electrical comparison testing then suggested that the chip itself was the problem. After decapsulation, there were no obvious signs of severe burn damage, although one local area appeared slightly darkened. FIB was then used to prepare a cross-section in the suspicious interconnect region.
The result showed mild corrosion beneath the passivation layer, with incomplete metal boundaries and degraded contact structures. This type of defect may not cause immediate total failure in the early stage, but it often first appears as performance drift or weakened output before eventually becoming a complete malfunction.
The root cause was traced to long-term exposure to a high-humidity environment, combined with weak local protection, which allowed internal corrosion to gradually develop.
This case highlights an important point:
Performance degradation does not always mean the design is flawed. It may indicate that the chip has already begun to deteriorate internally.
And without FIB, that type of deterioration can be very difficult to confirm.
Case Study 2: MCU Random Reset Failure Traced to Localized EOS Damage
Another difficult category involves MCUs that show random resets in the field.
In one case, a customer reported that a control board would occasionally restart during operation, and in severe cases the system would lock up completely. Firmware updates did not solve the issue, and replacing surrounding components only improved the situation slightly.
Because the symptoms resembled a software problem, that was initially the main suspicion. However, further electrical analysis showed that the standby current of the abnormal samples had already shifted away from normal, although the chips had not yet developed a full short circuit.
After hotspot localization, the suspicious region was narrowed down to the internal power-input-related structure. FIB cross-sectioning revealed clear localized melt damage in part of the metal and contact region, which is typical of electrical overstress. The damage had not yet progressed to catastrophic breakdown, but the internal structure had already been weakened.
This explains why the chips behaved so unpredictably. Under normal conditions they could still operate, but once temperature rose, load fluctuated, or external interference appeared, failures started to occur.
The conclusion was clear:
This was not a pure software issue, but localized EOS damage that caused progressive structural degradation inside the MCU.
For the customer, this kind of conclusion is extremely valuable, because it redirects corrective action toward the real risk points, such as:
- Is the surge protection on the power rail sufficient?
- Are there abnormal power-up or power-down sequences?
- Is there any risk of back-powering through external interfaces?
- Are there weak points in the system-level ESD/EOS protection design?
Why Many Reports Still Fall Short Without “The Final Cut”
In many projects, a lot of work has already been done before FIB is considered:
- Electrical testing has been completed
- Decapsulation has been performed
- Microscopy has been used
- X-ray imaging has been taken
- The suspicious region has been narrowed down
Yet the final report still feels inconclusive.
Why?
Because what is missing is direct structural evidence.
Without cross-sectional proof, the report often has to rely on words like “suspected,” “possible,” or “likely.” But what the customer really wants is a clear conclusion: where the defect is, what the mechanism is, and what needs to be improved next.
That is where FIB makes the difference. It does not make the report more complicated. It makes the report more conclusive.
When FIB Should Be Used—and When It Should Not Be Used Too Early
Some people assume that using FIB immediately is the most professional approach. In fact, that is not always true.
If the abnormal area has not yet been narrowed down, jumping directly into large-scale FIB work can waste both time and cost.
A more efficient path is:
- Start with basic electrical and visual confirmation
- Use non-destructive methods to reduce the search area
- Apply FIB only after the region of interest is reasonably localized
That approach usually produces faster, more accurate, and more cost-effective results.
At its core, chip failure analysis is not just about what can be seen. It is about whether the root cause can be explained clearly.
The value of FIB lies in turning microscopic internal abnormalities into evidence that can be confirmed, understood, and written into a meaningful technical report.
For companies, failure analysis is not just a cost. It is a way to avoid repeated loss. In projects involving batch failures, customer returns, or reliability issues, identifying the root cause early can save enormous time and expense later.
In many cases, the real problem is hidden within just a few microns.
And FIB is the tool that brings that hidden truth to light.
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