Static control is a major issue in the electronics manufacturing industry today and can prove to be very costly if not addressed. Here at Production Automation we offer many solutions for static control problems. One very common static control problem is the Packaging and Transportation of static sensitive components. The following is an excerpt from a Static Control Components (SCC) technical bulletin regarding the different options for packaging and transporting static sensitive components.
Bags
One of the most common static preventative items is a bag. The use of protective bags began in the 1960’s with the introduction of “pink poly” bags. Static shielding bags were introduced in the late 1970’s. And while the military has long used moisture barrier bags, the proliferation of Surface Mount Technology has greatly increased usage.
Shielding Bags
Abilities: Static shielding bags provide the dissipative and antistatic attributes of other packaging and transportation options but they add a metal shield and polyester dielectric to stop static from entering the bag. The test for shielding demonstrates the difference between the various bags. Shielding bags will generally stop 97% of a 1000 volt static pulse applied to the outside of the bag from reaching the inside, whereas other packaging and transportation options only stop about 10% – 30%.
Construction: Static Shielding bags consist of several layers. From the interior to the exterior the layers are: dissipative poly laminated (glued) to metalized polyester. The outside polyester has an antistat coating. The metal is vapor deposited in a vacuum chamber. Aluminum is the metal most used in this process, with nickel and copper also being used. Shielding bags such as this, with the metal between two layers of plastic, are typically referred to as ‘Metal-In Static Shielding Bags.’
Bags where the poly is laminated to the polyester with metal on top are referred to as ‘Metal-Out Static Shielding Bags.’ The metal generally used is an abrasion coated nickel and it is sputtered instead of vapor deposited. Metal-In bags offer better protection of the transparent metal shield by placing it between two plastic layers, whereas Metal-Out bags have a conductive outer surface which provides fast charge dissipation. However, the conductive outer surface of Metal-Out bags can be sparked.
Applications: Static shielding bags should be used for all electronic components, boards and assemblies. Shielding bags are referred to as Type III under MIL-B-81705C.
We offer static shielding bags from the following four manufacturers:
3M, Desco, Miller Packaging, and SCC.
3M
Desco
| Miller Packaging
SCC |
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Moisture Barrier Bags
Abilities: Moisture barrier bags provide dissipation, antistatic properties, static shielding, and add a moisture vapor barrier. The moisture barrier protects moisture sensitive items and improves long term storage.
Construction: Moisture barrier bags are physically stronger than static shielding bags, but are similar in structure. The two types or moisture barrier bags are ‘Foil and Tyvek’ and ‘Heavy Metallization.’ The ‘Foil and Tyvek’ structure from the interior to the exterior is dissipative poly laminated to thin aluminum foil and tyvek. Tyvek is a DuPont spunbonded
polyethylene material.
The ‘heavy metallization’ structure is essentially that of a shielding bag but with opaque, thick aluminum metallization or multiple layers of metallization. Nylon may be used in place of Tyvek or polyester. It provides the needed strength at a lower cost than Tyvek. Both foil and metallized moisture barriers provide good service.
Applications: The moisture barrier bag is used when barrier protection is needed or when maximum shielding protection is desired but transparency is not an issue. Surface mount devices are placed in moisture barrier bags to avoid moisture absorption by the IC case material. During reflow soldering, absorbed moisture will expand and crack the case. The moisturebarrier bag is also referred to as MIL-B-81705 TYPE I.
Desco, Miller Packaging, and SCC offer the following moisture barrier bags:
Background Information
Almost everyone is aware of the effects of static electricity in general terms. For example, scuffing one’s shoes on carpet and touching a person or metal door handle produces a brief shock. The static electricity behind these common events can destroy modern electronic circuits and devices.
As electronic circuits and their connecting pathways have continued to shrink in size, their susceptibility to damage from static electricity has increased. A factor of 10 shrinkage in feature size can make gate oxides 10 times more sensitive. Protective handling and packaging techniques have been adopted by all segments of the electronics industry from the chip foundry to the production floor to the field service arena.
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Static Threats A device needs to be protected from three primary static threats: A discharge directly to a bag can subject the device inside to very high current, melting or fusing the circuit |
Testing of Static Shielding
The Static Shielding test, EIA 541 Appendix E, applies a direct discharge to a bag. An oscilloscope connected to a sensor inside the bag measures the amount of voltage that penetrates the bag. This test also addresses the Field threat. Fields are generated by the discharge to the outside of the bag.
Tribocharging tests are difficult to perform and are not very repeatable. Data from bag specs are only a benchmark, and do not describe how materials will perform in everyday use. Bag users are left to compare these benchmarks or perform their own tests.
Surface Resistivity is an indication of a material’s ability to allow static to dissipate (move around). It is does not necessarily suggest low tribocharging.
For more information and purchasing details on these and other static control products check out our Static Control section, or Browse by Manufacturer
