Product Information No: PIS 091 Page 1 of 2 Issue No 5 Date : 25 April 2002 Approved by: PINK ANTISTATIC BAGS Code BQ3.. Description These products are made of an antistatic polyethylene film that under normal working conditions doesn t generate triboelectric charges. The film is tough, amine free, does not affect polycarbonate housings and does not cause corrosion. The product is transparent and tinted pink. It is available in a range of bag sizes as well as roll widths. Typical film thickness is 70 micron. Bags are hot foil printed in yellow with a descriptive text and logo to comply with IEC 61340-1. The film is designed for use as packaging for non-ESD sensitive devices that are required in ESD protected areas e.g. passive components, screws. The antistatic properties are long lasting provided the film is stored in a cool dry place. Do not store outside and do not expose the film to heat or store in an overheated warehouse. Typical physical properties MD = Machine direction CD = Cross direction Tensile strength MD 30 kPa ASTM D882-A CD 29 kPa Elongation at break MD 1000 % ASTM D882-A CD 1100 % Elmendorf tear strength MD 8 N ASTM D882-A CD 10 N Dart drop impact strength 300 gr ASTM D1709-A 2 o Water vapour transmission rate <0.8 gr/m 24 hr at 50% rH & 20 C 2 Weight 0,07 kg/m Roll and bag width tolerance +15 mm (inside) -2 mm Bag length tolerance +30 mm (inside) -2 mm Typical electrical properties 11 Surface resistivity <10 ohm per square DIN54382 Charge decay time <2 sec EIA541 appendix F Availability and dimensions Bags are available in standard sizes. The first dimension is the width of the opening of the bag, the second is the length of the inside of the bag. The bottom skirt of the bag i.e., from weld to bottom of the bag is approximately 4mm. For further information, please contact Vermason Ltd, 1 Avenue One, Letchworth, Hertfordshire SG6 2HB Tel: +44(0)1462 672005 Fax: +44(0)1462 670440 e-mail : sales vermason.co.uk www.vermason.co.uk - An Elusive Term by Ben Baumgartner Faraday Cage Threshold, April 1996 Should the term Faraday Cage be used to describe the electric constructed. These enclosed spaces are still not totally free of field (E-field) shielding ability of an ESD protective package the E-field component of an electromagnetic wave. These For many people this term implies an electric field free area, enclosures, such as screen rooms and electronic packages that translates to absolute shielding. Protective bags and tote (black boxes), have their electromagnetic field attenuation boxes can only behave as a Faraday Cage for a static field (shielding) measured in decibels (dB or dBm). (stationary in time). Faraday showed by his ice pail The Faraday Cage shielding term is being used in the wrong experiment that electric charges placed on the inside surface sense by many in the ESD community. If the Faraday Cage of an ice pail move to, and eventually reside on, the outside of term is incorrectly used, we will have an ambiguous and a conductive container. The charges on the outside of the incorrect concept of what a metallized or even a foil bag is container have E-field lines that terminate on opposite polarity capable of shielding. Faraday Cage will replace E-field charges that are outside the pail or a conductive container. shielding in our jargon forever. The latest version of the Therefore, the area inside the pail is free of the electrostatic Military ESD Handbook (MIL-STD-263) does not use the fields associated with these charges. The Faraday Cage (area term Faraday Cage neither does the ESD Association s inside) is free of an electrostatic field only when the charges packaging Standard EOS/ESD S-11.31-1994. have moved to arrange themselves to suit the surrounding Faraday Cage implies total E-field protection to many people, surfaces and are static (stationary). while shielding to an electrical person indicates a degree of E- In the opposite case when the ice pail or container (ESD bag) field attenuation. Most electrical engineers recognise that the is placed in an electrostatic field, the free electrons in the degree of shielding varies and must be measured to determine metal arrange themselves to prevent field lines from passing the amount of attenuation (protection). Measuring how much through the conductive surface. This movement of charge shielding is provided by an ESD protective bag enclosure is takes a certain amount of time, depending mainly on the not an easy task. That is why ESD bag shielding has not been resistance of the material. This movement or charge does not satisfactorily addressed to determine if a given device is occur instantaneously. Therefore, the rate of change (or protected and to what level. It can be shown that a voltage movement) of the electrostatic field becomes a factor in sensitive (unprotected gate oxide) device can be damaged maintaining an electric field free area. As the frequency (shorted) in a metallized bag by ESD. When a 100 volt gate increases for AC electric fields, the inside of the ice pail or oxide transistor is put in place of the 500 ohm resistor in the ESD container becomes a less electric field free area. For the ESD Association s EOS/ESD S-11.31 Standard s fixture, the high frequencies of ESD, the maintaining of a electric field transistor can be damaged by a 2000 volt human body pulse. free area depends mainly on the resistivity of the container In fact, the 100 volt transistor can even be damaged in a 2 mil until very high frequencies are reached (Electromagnetic metal foil bag. No Faraday Cage here. waves in the form of light pass through metallized bags and Another question to be answered is: how much more X-rays also go through fairly easily). Therefore, does a protection does a metallized shielding bag provide in a real metallized bag maintain an electric field free area (shield) situation A discharge to the metallized bag is very evident effectively and will have a much higher current than a discharge to a A search of old school textbook indexes for Faraday s name surfactant type of bag. In an actual test using a handheld did not shown any reference to a Faraday Cage . The only HBM simulator, a discharge to a surfactant loaded shielding reference is in old transformer and radio books. The polyethylene bag is difficult to see. There is nothing more grounded copper shield (layered foil, not a closed cage) that is than a weak corona discharge as 12 kV. How does this type placed between the primary and secondary on a high voltage of ESD relate to the protection of energy sensitive devices transformer is called a Faraday shield . It is used to shield the Energy sensitive devices are certainly the most prevalent primary transformer and secondary winding from each other. devices around and may be better protected by a thicker bag Faraday Cage is not in the IEEE Standard Dictionary of or a bubble pack pouch (air space does not provide shielding, Electrical & Electronic Terms (1978 ed.) or other electronic it provides de-coupling, contrary to articles claiming air handbooks or references. The references that mention the attenuates). Faraday Cage Effect discuss it in terms of static charges. The high voltage punch thru of metallized bags versus 4 and The Faraday s ice pail principle does not apply to shielding for 6 mil polyethylene material has not been addressed either. high frequency electric fields (E-fields) such as those from The Electronic Industries Association EIA 541, Packaging electromagnetic waves or ESD. The space inside the cage is Task Force 1, discussed this problem many years ago, but an E-field free area only when an external static charge is never tackled it. It was and still is a difficult question to present on a surface and is stationary. A Faraday Cage for answer because a standard configuration that represents static charge is not necessarily effective in providing a devices would have to be agreed upon. complete electric field free shielding from radio frequency There is still a lot more work to be done. We can fool (RF) electromagnetic waves or an electrostatic discharge to ourselves by saying metallized bags protect devices because the Faraday Cage surface. A surfactant loaded polyethylene they are Faraday Cages , or we can analyse the situation to bag will provide a static free area inside the bag if you wait a find out what is really happening. Let us hope that a good few seconds for the charge to distribute itself around the analysis is not as elusive as the Faraday Cage . surface of the bag. Enclosures are effectively free of electromagnetic interference *Reference: Demonstration Experiments in Physics, Sutton, (EMI), only when enclosures are carefully designed and McGraw-Hill, 1938, p.263.