February 2026 Newsletter
Introduction
With the rapid advancement of artificial intelligence (AI) and high-performance computing (HPC), High Bandwidth Memory (HBM) has become a critical component in advanced computing systems. In advanced packaging and failure analysis (FA) workflows, engineers frequently use lasers for decapsulation (decap), material removal, or marking, and X-ray techniques (AXI / micro-CT) for non-destructive inspection of internal structures. In practice, many engineers share a common observation: when performing laser or X-ray inspections, fully packaged HBM devices tend to show fewer obvious electrical anomalies; in contrast, single-die or more directly exposed advanced DRAM devices require extremely strict control of energy and exposure conditions. Does this mean that the DRAM inside HBM is inherently “less sensitive” to lasers or X-rays? The answer is not that simple. In this issue, we explain—at a beginner-friendly level—three key perspectives:
• Why HBM often “appears more robust” in many scenarios
• Why advanced DRAM is particularly sensitive to energy exposure
• How engineers should correctly interpret and handle these two types of products in practice
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1. HBM Is Not Inherently Stronger—It Is Simply “Harder to Hit Directly”
One important concept to understand is this:
The internal structure of HBM is still DRAM. Its physical sensitivity to X-rays and high-energy exposure does not disappear just because it is called HBM.
So why does HBM often seem more robust in real-world practice?
The key lies in structure and inspection conditions.
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2. Why Is HBM “Relatively Safer” in Practical Analysis?
1️⃣ Shielding Effects from 3D Stacked Structures
HBM consists of multiple DRAM dies vertically stacked and interconnected through TSVs (Through-Silicon Vias) and micro-bumps, with additional packaging materials such as underfill and molding compound on the outside.
During X-ray or laser analysis:
• Energy must pass through multiple silicon dies, metal layers, and packaging materials
• Depending on the incident path and X-ray energy, a significant portion of the energy may be absorbed or scattered before reaching the core Active Area (transistor and capacitor regions)
As a result, in most packaging inspection scenarios:
• The packaging or interconnect structures receive the majority of the energy
• Rather than the DRAM cell array itself
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2️⃣ Inspection Targets Are Typically in the Back-End Package, Not the Transistors
The primary value of HBM lies in:
• TSV integrity
• Micro-bump bonding quality
• Interposer and overall package integrity
Therefore, when using X-ray or laser tools:
• Engineers are usually focused on detecting opens, shorts, or delamination in interconnects
• Tool settings are generally optimized for structural visibility, not high-dose exposure
This makes the electrical risk relatively manageable.
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3️⃣ The Key Factor Is Exposure Conditions, Not Process Node
It is sometimes said, “HBM uses more mature DRAM processes, so it is more robust.”
This statement is not entirely accurate.
In reality:
• The DRAM inside HBM continues to scale with each generation
• Gate oxides and cell capacitors remain extremely delicate
The real differentiators are:
• Whether energy directly reaches the Active Area
• Whether exposure time and dose are properly controlled
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3. Why Are Single-Die Advanced DRAM Devices Especially “Sensitive”?
1️⃣ DRAM Cells Are Extremely Sensitive to Charge
The fundamental structure of DRAM is 1T1C (one transistor plus one capacitor), and data is essentially stored as electrical charge in the capacitor.
When exposed to X-rays:
• Ionization effects occur
• Electron–hole pairs are generated in oxide layers
• Additional charge accumulation or charge trapping may result
Possible consequences include:
• Soft errors (transient errors) versus latent damage (long-term reliability degradation)
• Increased leakage current
• Reduced data retention time
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2️⃣ Advanced Nodes Leave Less Margin for Error
As DRAM continues to scale into the 10 nm-class generations, device dimensions and electrical tolerance margins shrink further:
• Thinner oxide layers
• Stronger electric fields
• Even minor electrical disturbances can have significant impact
Therefore:
• Even “inspection-level” X-ray exposure
• Can cause latent damage
• Failures often do not appear immediately but instead manifest as degraded reliability over time
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3️⃣ Laser-Induced Thermal Risks Are More Direct
When lasers are applied to single-die or thin-package DRAM:
• Thermal energy is more easily concentrated in the Active Area
• Improper parameter control may lead to:
o Oxide degradation
o Increased interface states
o Permanent electrical changes (hard failures)
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4. HBM vs. Single-Die DRAM Technical Comparison
📊 Overview of Key Differences
| Comparison Item | HBM (Packaged / Stacked State) | Single-Die Advanced DRAM |
|---|---|---|
| Typical Inspection Targets | TSVs, micro-bumps, package structures | DRAM cell array, electrical regions |
| Active Area Exposure | Low (shielded by multi-layer structures) | High (more direct exposure) |
| Primary X-ray Risk | In most package inspection scenarios, risks are limited to package/interconnect defects, with lower electrical risk | Charge trapping, retention degradation |
| Laser Impact | Attention required for HAZ and mechanical stress | High risk of thermal damage and electrical parameter shifts |
| Failure Modes | Mostly localized or package-related failures | Higher likelihood of permanent electrical failure |
| Engineering Focus | Dose, incident path, package thickness | Dose, exposure time, thermal management |
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5. Practical Advice for Junior Engineers
🔧 When Using X-ray
• Always start with the lowest dose and lowest magnification
• Increase settings only when structural details are not clearly visible
• Remember: HBM is not immune—it is simply harder to hit directly
🔧 When Using Lasers
• Pay close attention to the Heat Affected Zone (HAZ)
• Parameter control is more important than the tool itself
• For DRAM, always assume it is fragile
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Conclusion
The strength of HBM lies not only in bandwidth, but in its system-level design.
While its 3D structure delivers performance, it also makes it more difficult for analytical energy to directly impact core circuitry.
Advanced DRAM, by contrast, continuously operates at the edge of physical limits.
Understanding these differences helps ensure that during analysis, debugging, and reliability evaluation, diagnostic tools do not become the source of product damage.
