Selecting the wrong ESD packaging for shipping sensitive components introduces failure modes invisible until field returns arrive. This guide explains how to choose between metallic shielding bags and dissipative poly bags based on threat environment, device sensitivity class, and compliance requirements.
Key Takeaways
|
What Is an ESD Protective Bag?
An ESD protective bag is a packaging enclosure engineered to either block external electrostatic fields from reaching enclosed devices (shielding) or prevent charge accumulation on its surface through controlled charge dissipation (dissipative).
Internal Construction and Materials
Shielding bags use a multi-layer laminate: outer polyester film, an aluminium metalised layer with sheet resistance below 10³ Ω/sq, a middle insulating layer, and an inner polyethylene layer forming a Faraday cage analogue. Dissipative bags use carbon-loaded polyethylene or nylon with surface resistivity tuned to 10⁶–10¹² Ω/sq, slowing charge flow through distributed resistance rather than reflecting it.
Why ESD Bags Are Indispensable for Engineers
An unprotected CMOS device in a standard poly bag can sustain surface potentials above 5,000 V from triboelectric contact. A metallic shielding bag reduces electrostatic exposure to levels compliant with ESD Sensitivity Class 1 (ESDS ≤1,000 V HBM) throughout the full logistics chain.
What Are the Key Features and Advantages of ESD Bags?
| Feature | Description | Engineering Benefit |
| Field shielding (metallic) | Metalised layer achieves >35 dB attenuation at 1 MHz per ANSI/ESD S11.4; sheet resistance <10³ Ω/sq | Protects Class 0 and Class 1 ESDS devices in ungrounded transit without requiring a wrist strap or ESD mat at the receiving dock |
| Controlled dissipation | Surface resistivity 10⁶–10¹² Ω/sq per IEC 61340; decay from 1,000 V to <100 V in <1 s | Prevents sudden discharge through the device when opened at a grounded ESD workstation |
| Moisture barrier (MBB) | WVTR <0.001 g/m²/day at 38°C/90% RH in foil-reinforced variants per J-STD-033C | Enables combined MSL and ESD protection for ICs requiring dry-pack storage before reflow |
How Metallisation Thickness Drives Shielding Effectiveness
At 1 MHz, the aluminium skin depth is approximately 84 µm. A 10 µm metalised layer achieves roughly 1.5 skin depths, yielding ~13 dB per layer. A standard 4-ply laminate with two metalised plies exceeds 26 dB — above the 20 dB Class B floor in ANSI/ESD S11.4.
What Are the Critical Technical Specifications to Verify?
| Parameter | Shielding Bag | Dissipative Bag | Unit | Compliance |
| Surface resistivity (outer) | <10³ | 10⁶–10¹² | Ω/sq | IEC 61340-2-3; ASTM D257 |
| Electrostatic shielding | >35 | N/A | dB at 1 MHz | ANSI/ESD S11.4 |
| Charge decay to 10% of 1 kV | <0.5 | <2 | seconds | ANSI/ESD S11.31 |
| Triboelectric potential | <10 | <50 | V on surface | IEC 61340-5-1 |
| WVTR (MBB variant) | <0.001 | Not rated | g/m²/day | J-STD-033C, IPC-1601 |
| RoHS / REACH | RoHS 3 (EU 2015/863) | RoHS 3 (EU 2015/863) | — | EU Directive 2011/65 |
How Do These Specifications Affect Real-World Performance?
Resistivity floor: Surface resistivity below 10⁵ Ω/sq reclassifies a bag as conductive, creating a low-impedance path to ground. This risks a CDM event when device pins contact the interior at a grounded station.
Humidity derating: Carbon-loaded dissipative films rise approximately one resistance decade per 20% RH drop below 50% RH (IEC 61340-4-1). A bag at 10⁹ Ω/sq at 50% RH may reach 10¹¹ Ω/sq at 10% RH, approaching the insulative boundary.
What Customisation and Configuration Options Are Available?
Package Form Factors
Open-top heat-seal bags suit automated sealing lines with nitrogen purge for J-STD-033C dry-pack compliance. Ziplock reclosable bags serve service kits requiring repeated access. Gusseted stand-up bags accommodate populated PCBs with component height above 20 mm without stressing sealed seams.
Material Variants and Shielding Architecture
- Metallic 4-ply (PET / Al / PE / PE): Standard Class B shielding. A 6-ply variant adds a second metalised layer for >50 dB, specified for Class 0 ESDS or MIL-PRF-81705E Type I applications.
- Pink polyethylene dissipative: Resistivity 10⁹–10¹¹ Ω/sq; suited as innermost wrap inside a metallic outer. Not a standalone shipping solution for Class 1 devices.
- Black conductive foam-lined: Used inside shielding bags for IC tubes and trays; foam-to-lead contact equalises pin potentials and eliminates triboelectric differentials.
- Anti-static carrier tape (IEC 60286-3): Encloses SMD reels inside a shielding outer for kitting; specify both tape static decay and bag shielding rating.
How Are ESD Bags Used in Real-World Application Scenarios?
- Bare-die shipping: Class 1C CMOS dice (HBM 100–250 V) ship in 4-ply metallic bags with nitrogen purge. The metalised layer blocks induction from handling machinery while nitrogen suppresses bond-pad oxidation.
- PCB assembly kitting: Populated boards with BGA and fine-pitch QFN packages use ziplock metallic bags for inter-facility transfer, allowing part-number inspection without cutting the bag.
- Military avionics storage: GaAs MMIC radar front-ends rated below 50 V HBM require MIL-PRF-81705E Type I bags with >40 dB shielding and WVTR <0.002 g/m²/day for Class 3 long-term storage.
- E-commerce IC fulfilment: Distribution EPAs use reclosable dissipative bags (10⁹ Ω/sq) for bench kitting. The bag prevents charge buildup from pneumatic pick tubes and reseals rapidly between picks.
How Do Shielding Bags and Dissipative Bags Compare?
| Attribute | Metallic Shielding Bag | Dissipative Bag | Key Differentiator |
| Field attenuation | >35 dB at 1 MHz (ANSI/ESD S11.4) | None; no metalised layer | Only shielding bags protect against external induction in ungrounded environments |
| Surface resistivity | <10³ Ω/sq | 10⁶–10¹² Ω/sq | Resistivity decade determines whether bag contains or channels charge |
| Moisture barrier | Available (4- or 6-ply foil) | Not available | MBB required for MSL devices under J-STD-033C |
| Primary use | Shipping, transit, long-term storage | EPA bench handling, inner wrap | Dissipative bags need a shielding outer for any transit scenario |
Quick Selection Guide
- Device HBM ≤1,000 V (Class 1)? → Metallic shielding bag mandatory for all transit and storage.
- Handling within a grounded EPA only? → Dissipative bag sufficient; verify resistivity <10¹² Ω/sq at lowest expected humidity.
- MSL 2 or higher? → Metallic MBB bag per J-STD-033C with desiccant and humidity indicator card.
- Military or aerospace? → MIL-PRF-81705E Type I; commercial bags may not meet >40 dB or WVTR limits.
- SMD reel kitting in EPA? → IEC 60286-3 carrier tape inside a shielding bag outer; dissipative alone is insufficient for ungrounded transport.
Conclusion: Choosing the Right ESD Bag for Your Shipping Application
The core trade-off is precise: dissipative bags control charge on the bag surface; metallic shielding bags protect the device from charge on everything outside it. For any component leaving a controlled EPA, a metallic bag with verified ANSI/ESD S11.4 compliance is the correct specification.
When in doubt, the deciding factor is the threat environment. If the device contacts ungrounded handlers or surfaces at any point, dissipative alone fails. A bag providing >35 dB shielding at 1 MHz reduces induced voltage on the enclosed device by a factor of 56 relative to a standard poly bag: that ratio is the engineering argument in a single number.
Frequently Asked Questions
Q: Can a dissipative bag alone ship a Class 1B device (HBM 200–500 V)?
No. IEC 61340-5-1 and JEDEC JESD625B require both surface charge control and electrostatic field shielding for Class 1 ESDS devices outside an EPA. A dissipative bag provides zero field attenuation. A metallic shielding bag meeting ANSI/ESD S11.4 is required. The dissipative bag may serve as an inner wrap inside the metallic outer.
Q: How does low humidity affect dissipative bag performance?
Carbon-loaded films rise approximately one resistance decade per 20% RH drop below 50% RH per IEC 61340-4-1. A bag at 10⁹ Ω/sq at 50% RH may reach 10¹¹ Ω/sq at 10% RH. Specify bags with mid-range resistivity (10⁸–10¹° Ω/sq) for low-humidity facilities to maintain compliance under worst-case conditions.
Q: How do I verify incoming ESD bags without lab equipment?
Use a calibrated surface resistance meter per ANSI/ESD STM11.11 (two 2.5 kg cylindrical electrodes, 10 V applied) for surface resistivity. For shielding bags, the spark-gap tester in ANSI/ESD S11.4 Annex A confirms field attenuation: a compliant bag prevents a neon indicator from illuminating at 1,000 V. Condition samples at 23 ± 1°C and 12 ± 3% RH for 24 hours before measurement.
Q: How many reseals before a ziplock shielding bag loses effectiveness?
ANSI/ESD S11.4 sets no reseal cycle limit. However, supplier data from Desco and Protektive Pak shows shielding effectiveness drops 3–5 dB after 10 open-close cycles due to metalised layer delamination at the closure fold. Limit reuse to five cycles for Class 1 applications, or specify reinforced metalised fold zone bags and replace per your site ESD control plan.
Q: Is a pink anti-static bag compliant with IEC 61340-5-1 for shipping?
Only within a defined EPA. IEC 61340-5-1 Clause 5.3.4 requires electrostatic shielding capability for packaging used outside an EPA. Pink dissipative bags provide no field attenuation. Shipping Class 1 devices in them alone is a documented audit non-conformance and typically voids the component supplier’s warranty.
