How do anti static bags work?

1 Why can anti static bags protect electrostatic sensitive components?

2 Is there any other cheap ways to store electrostatic sensitive components if I do not have anti static bags in hand?

To tell you th truth I have never used anti static bags in my life and I have never blown a component. I am always careful not to touch any component legs and I also ground myself. I store my components in a plastic utility container. But thats my opinion only.

The level of static is highly dependent on the atmospheric humidity. Where I live on a west coast, static is never a problem but in some places I have worked, particularly in central land masses, the air can be very dry and it is a real issue.

1. The anti-static bags work by either being conductive or dissipative. Essentially, the bag itself can hold a static charge just like everything else but all points on it's surface charge to the same potential. As it isn't the static voltage that causes problems but the potential difference between two or more points discharging together, keeping the bag's contents at the same voltage potential removes any chance of a discharge occurring.

2. The classic way of storing components is to use a carbon impregnated mat or sponge. It is a dense foam which you buy in sheets or rolls and the idea is you sandwich the component between layers of it or if the component has pins, you push them into it. The carbon content makes it slightly conductive so potential differences across it are eliminated. There are other systems, including ion generators which are supposed to flood the area with static neutralizing air but my experience with these is not good!

Brian.

The bags are cheap, so if you are storing a lot of electronic chips, you should just get a bunch. Probably $10 on ebay for 50 bags.

The bags are electrically conductive, so charges outside the bag do not get inside of the bag.

If you do not want to spring for bags, just make a small envelope out of aluminum foil and put the parts in there.

Do NOT put things like scotch tape anywhere on the package near the chips, even if you are using approved antistatic bags! Scotch tape is a high voltage generator (see for youself, pull off to strips around 2" long, and try to get them to touch. Electrostatic repulsion will force them apart.)

Hello biff44:
Thank you for the answer.
I just used a multimeter to measure one anti static bag. I pressed the two legs of the meter on
two different points of the bag.
I selected the continuity function on the meter (marked with a diode symbol).
But the bag does not conduct. Thus I doubt the bags are electrically conductive?

biff44 said:

The bags are cheap, so if you are storing a lot of electronic chips, you should just get a bunch. Probably $10 on ebay for 50 bags.

The bags are electrically conductive, so charges outside the bag do not get inside of the bag.

If you do not want to spring for bags, just make a small envelope out of aluminum foil and put the parts in there.

Do NOT put things like scotch tape anywhere on the package near the chips, even if you are using approved antistatic bags! Scotch tape is a high voltage generator (see for youself, pull off to strips around 2" long, and try to get them to touch. Electrostatic repulsion will force them apart.)

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Check this Link. This may helpful to you
ESD Journal - ESD Bags

ESD damage may not be apparent at first. The damaged components may not fail completely. Instead, the damage may result in below-normal performance for an extended period of time before you experience a total failure.

How ESD Damage Occurs????

Whenever an object containing a static charge touches a circuit, current will rush into the circuit until the components reach the same voltage as the source of the static charge. If the voltage or current that passes through a component during that brief period exceeds its normal operating specifications, it may be damaged or destroyed.

Preventing ESD Damage???
ESD damage cannot occur if there is no voltage difference between the components and any object that touches them. That is how anti-static packaging works. Anti-static bags allow the static charge to flow over their surface, so that any part of the bag that touches the components inside are all at the same potential at all times. Anti-static foam keeps the leads of sensitive components at the same potential.

Most importantly, you must have a way of continuously draining off any static charges that occur on your body. Such charges are easy to create, even while sitting quietly at the work bench. Moving your feet on the floor, shifting position in your chair or even moving your arms so that clothing rubs against itself can produce destructive static charges.

A field expedient method of protecting PCB's from ESD and physical damage is to wrap them in aluminum foil and put them in a flat box, like a pizza box.

Before anti-static bags were common I seem to remember ICs being supplied with their legs pushed into polystyrene foam which had aluminium foil wrapped round it.

To answer the question about trying to measure the resistance - it is often too high a resistance to see on a multimeter.

Keith.

Antistatic Bags.
There is a lot of misconception with the term antistatic. It is not an electrical property of material, so measuing it with an ohm-meter or even a megohm-meter is just wrong. Antistatic is refered to as an ability to inhibit charge tribocharging by a material. In achieing this, most antistatic material is treated with some form of antistat and cause the material to absorb water from the environment. The water layer increase the conductivity of the material and would drain static charges away. If a device is rubbing again the antistatic bag, little tribocharing happens, thus ESD safe.
However, keeping the sensitive ICs in antistatic bags may not be safe enough to prevent ESD issues. The least expensive way of preventing ESD in IC is to shorts it pins together with say conductive polyurethane foams. You can also just use aluminum foils, but make sure that the ICs are charge neutral before touching the leads with aluminum foil.

Wayne Tan

most of anti-static bags are made of PE,NY,PET,CPE,PP and so on. These material have good function of electrical insulation