03 Mar

Selecting the Proper Shielding Bags

Choosing the Right Shielding Bag

In Michio Kaku’s book, Physics of the Future, he notes that today’s smart phones have more computing power than NASA had in the 60’s when they were plotting and launching the moon landings.

The latest SONY Playstation can outperform the supercomputers the US Government used in 1997 – 14 years after the movie WarGames.

In 1965, Gordon Moore, one of the founders of Intel, observed what became known as “Moore’s law.” He postulated that computers would progressively become more dense while at the same time increasing their processing speed.

This can be both good and bad news for computers. The bad news being that every time a component gets 10% smaller, it gets 10x more sensitive to electrical shocks, even those coming from simple static electricity. Static in your workplace can be dangerous and expensive if you’re not properly prepared.

One important weapon in your arsenal for defense against Electrostatic Discharge (ESD) is shielding bags.  Which bag is best? They all have their pros and cons to consider.

Pink Poly Bags

The earliest defense against ESD was created in the 1960’s.  Dissipative Poly Bags, usually referred to as Pink Poly bags because of their unique color – introduced as an easy way to differentiate their static control abilities from standard plastic bags – are coated with a chemical that resists static.

Unfortunately, Pink Poly bags have no shielding capability. An ESD of any significance will travel through the bag and potentially damage components inside. They are best utilized today to package support or processing materials that do not themselves need shielding.

The antistatic properties of the bags help to protect sensitive components near the bags. This makes them a helpful solution as opposed to normal plastic bags, but you should always have a grounding system in place – mats and personal wrist straps at a minimum.

Black Conductive Poly Bags

Black Poly Bags are obviously a step up from their Pink predecessors. But in this case, their advantages are also their biggest flaw. Like the Pink Poly’s, the Black bags are antistatic, with the added benefit of some conductivity, designed to help protect its contents from ESD’s.

The problem lies in how quickly the bags dissipate the electrical charge. The rapid discharge of the ESD can actually generate a spark between the person or object creating the charge, and because the bags lack an additional insulation layer inside the bag, that charge can easily penetrate it.

Plus, there’s the added complication of the bag’s color. The conductive carbon leaves the bag opaque, requiring the contents to be removed to be seen, leaving the potential for damage.

The biggest benefit of the Black Poly’s was some shielding at a lower price point.  But in recent years, shielding bags have become much more affordable, and reputable vendors have effectively eliminated them from their inventory.

Shielding Bags

Shielding bags combine the antistatic and dissipative qualities of the poly bags with metal shielding and a polyester insulator (or dielectric) layer. Where Pink Poly’s stop about 10% and Black Poly’s 30%, Shielding Bags stop 97% of electrostatic pulses.

Shielding bags are classified in two ways:

Buried Metal (Metal-In)

Buried Metal bags consist of a dissipative poly layer, glued or laminated on top of a metallized polyester – usually aluminum, but sometimes nickel or copper – laid over an additional dielectric polyester layer.

The metal between two layers of plastic offers better protection than the alternative.

Surface Metal (Metal Out)

In Surface Metal bags, the layers are ordered differently, with the poly and the dielectric polyester glued together, then coated with a nickel sprayed with an abrasion resistance coating.

Unfortunately, the outside metal coating causes a faster dissipation of electrical charges, resulting in sparking issues similar to that of the Black Poly Bags, although not as dangerous.

Moisture Barrier Bags

For long term storage or moisture sensitive items, Moisture Barrier bags provide the ultimate protection. These bags are similar to, but stronger than normal shielding bags and provide an additional protection with a moisture vapor barrier.

There are two types of Moisture Barrier bags: Foil and Tyvek (utilizing the DuPont material) or Heavy Metallization.  Both provide similar levels of protection, the difference primarily being the higher cost of the Tyvek structured bags.

Static protective bags should always be implemented as part of a more comprehensive static control environment, which should always include proper grounding tools.  And while expenditures are always a factor, consider the insignificant price of proper protective measures when compared to the cost of replacing the delicate components inside the package.

Contact us today for more information; we would love to be your full service, seamless ESD solution provider.

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  1. Pingback: Finding ESD Storage Solutions - Ground Zero Electrostatics Blog

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