ESD container manufacturers are up against a double-edged sword–one side compels them to meet more restrictive environmental regulations while the other demands longer-lasting static-dissipative qualities. Unfortunately, the two are not always compatible.
Environmentally responsible users of ESD containers want the best of both sides of the issue. But how can you determine which container material meets the physical, chemical, safety and electrical requirements; is the right price; and fulfills the stringent environmental requirements?
Simply put, you must investigate your packaging needs, and determine what materials are available and if they meet environmental requirements of your area.
Environmental Influences
Packaging is estimated to make up 36% of material flowing in the waste stream today.1 Many of the most environmentally egregious packaging components have only superficial value.
For example, hexavalent chromium is carcinogenic and corrosive to living tissue, but it makes pleasing pigments. Cadmium, lead and mercury also are potentially deadly heavy metals used in paper and plastic packaging and are rapidly being ruled illegal in most states.
Fortunately, ESD package users are becoming more environmentally responsible. Companies are instituting mandates more stringent than current environmental regulations to implement aggressive recycling programs, to use more expensive plastic foams made without chlorofluorocarbons, and to ban the use of heavy metals in packaging.
Today the three Rs of the environmental packaging world are:
(o) Reduce material flow into the waste stream.
(o) Reuse to preserve resources.
(o) Recycle all materials for secondary benefits.
Biodegradability, the breakdown of materials by bacteria or enzymes, is another aspect of the packaging industry that is important but does not get much press. It is not popular because modern landfills are anaerobic, not aerobic in makeup, and composting sites are not available on a large scale.
Green Claims
A task force, comprised of the Environmental Protection Agency (EPA), the Federal Trade Commission and the United States Office of Consumer Affairs, investigated claims of environmental labeling. As a result, the task force issued guidelines for environmental labeling in July 1992.
The EPA developed definitions to guide the law on environmental policy. For example, recyclable packages are defined as packages that can be collected, separated and recovered from the waste stream and used in the manufacture of a new product or package.
Identifying ESD Plastics
Static-control plastic materials are similar to static- control paperboard materials because the basic raw materials are typically recyclable, but the addition of ESD characteristics usually makes them less easily recycled or not recyclable. The Society of Plastics Industry developed a coding system to help identify the resin types. The appropriate symbol can be found on the bottom of the container (Figure 1).
Currently, there are seven identified resin materials with a proposal to expand the list to nine. The first six are specific resins; the seventh is a catch-all category designated Other. It includes copolymers, specialty resins, coextrusions, multilayered laminates and any other plastic that does not fit in the first six categories. Often the Other category is marked with a 0 or 7, but they mean the same thing.
Almost all ESD-control plastics fall into the Other category. Unfortunately, this is the hardest category to recycle.
Foam Materials
Foam is created when a plastic resin is melted and expanded by the dispersion of a gas in the liquid resin. The foam may be recyclable, but it depends on what resin type is used and how it is processed. One process uses steam injection; another uses nuclear energy to create the gas bubbles. But the most common is via chemical reaction.
The ESD packaging industry usually uses a lightweight polyurethane foam. It is a thermoset foam and very difficult to recycle.
Thermoformed foams incorporate static-control qualities via a compounding operation that blends additives into the plastics. The additives are difficult to work with and can cause static hot spots if they are not dispersed evenly throughout the mixture. However, thermoformed foams have longer-lasting static-control properties and colorfastness. Depending on where they are disposed, they may be recycled into new materials.
Structural Plastics
ESD structural plastics are thermoformed into packaging via blow molding, reaction injection molding, vacuum forming and injection molding. Often these are initially more expensive than other ESD packaging types, but they are durable and can be reused, lowering their cost.
Since this packaging can be used many times, it ranks high for environmental benefits. But the material is difficult to work with and can develop hot spots during the manufacturing process.
Vacuum forming is one common method of making ESD structural plastic. Single sheets of roll-fed webs of plastic are heated until soft and pliable. The material then is draped over a wood or aluminum mold. As it cools the plastic regains its hardness and rigidity.
Glycol-modified polyethyleneterephthalate (PETG), styrene and polyvinyl chloride (PVC) are the most commonly vacuum-formed materials. The first two materials are easy to recycle but lack many of the performance and cost attributes of PVC.
PVC may be less expensive and have better static-prevention qualities than PETG and styrene, but it is at the center of environmental safety debates due to the toxicity of chlorine. Progress actually may be underway in this area, because according to the chlorine industry, recent technological advances have made possible the safe recycling and incinerating of PVC.
Paper and Paperboard
ESD paperboard typically is made by one of these methods:
(o) Treating the surface with a printed coating.
(o) Loading ingredients such as carbon into the pulp slurry to give it ESD-control qualities.
(o) Laminating a static-control film on the surface.
Printed coatings typically are made by using a carbon-black or graphite-based mixture to incorporate conductivity onto the surface. Often the product is treated on both sides and coated with a varnish to reduce sloughing of conductive particles.
Carbon-loaded materials are made by adding conductive powders into the oatmeal-like slurry. As a rule of thumb, the more carbon or other conductive element in the material, the less value it has on the recycled paperboard market.
Laminated paperboard materials are created by gluing static-control film to plain paperboard materials. The film adds strength to the paperboard substrate, which improves the reusability and reduces the quantity in the waste stream. The films are usually formulated from polyethyleneterephthalate (PET) made conductive by a vacuum-metallizing process on one side and covered with a static-dissipative coating.
The metallized layer provides ESD shielding superior to carbon technologies. But the metal-foil laminate version is impossible to recycle. Since the vacuum metallized layer is typically a couple hundred angstrom thick, it can be recycled fairly easily.
It is possible to filter the PET film from the pulp slurry. However, it is not worth the cost of the paperboard material gained by the effort.
Finding a film that will break down in a common process and still provide the ESD performance characteristics of a laminate is the aim of some manufacturers. Fortunately, a nonpetroleum- based family of plastics called biopolymers meets this requirement. These plastics have many of the needed characteristics for mechanical performance and chemical compatibility. They are inherently static-dissipative and accept metallization.
Cellulose acetate (cellophane) is an example of a biopolymer. Many other materials also can be modified and laminated to paperboard, resulting in a product with the required ESD characteristics and recycling capabilities.
Manufacturing environmentally superior ESD packaging is serious business today. You can do your part to save Mother Earth by using products that accommodate the three Rs of the packaging world in addition to your static-control needs.
Reference
1. Bradford, J., “ESD Packaging: An Environmental Perspective,” EOS/ESD Symposium, 1993.
Totes/Bins/Packaging Products
Packaging Materials
Are 100% Recyclable
Strata-Shield ENV(R) is a 100% recyclable ESD packaging material that can be formed into partitions, totes and cartons. The material has an amine-free film featuring a permanently dissipative surface with a buried shielding layer. It is available in solid fiber with film on two sides or corrugated with film on one or both sides. Bradford Co., (616) 399-3000.
Corrugated Containers Have
Buried Shielding Layer
The PROTEKTIVE PAK(R) line of corrugated static-dissipative containers is impregnated with a carbon layer to minimize sparking. The buried shielding layer has a surface resistivity of <104(ohm)/sq and the top layer ranges from 107(ohm)/sq to 1010(ohm)/sq. It is made from recycled linerboard and is recyclable after use. Brick Container Corp., (310) 903-9392.
Corrugated Material Provides
Buried Carbon Shielding
Cortronic is a recyclable, corrugated fiberboard which is either transparent or blue in color. A buried carbon shielding layer has a surface resistivity of <102(ohm)/sq. The fiberboard has a surface resistivity of 106(ohm)/sq to 108(ohm)/sq. Conductive Containers Inc., (800) FARADAY.
Static-Dissipative Folder
Is Reusable
Documents stored in the CRYSTAT(R) Static-Dissipative Shop Traveler do not generate ESD. The protective folders do not have the bulk associated with binders and can travel with parts and assemblies. The reusable folders have tang fasteners to accommodate documents punched with three holes. The front cover has a pocket to hold part numbers and product names. The folders are available in a variety of colors. Crystal-X Corp., (800) 255-1160.
Containers Developed
For Custom Applications
A line of containers includes a hopper front, a straight-walled version, nestable or stackable types, trays, collapsible containers and custom styles. Customers may choose from ESD-safe materials such as fiberboard, plastic-coated fiberboard, high-density polyethylene, rigid PVC and molded plastic. Conductive materials have a surface resistivity from 103(ohm)/sq to 105(ohm)/sq, and a volume resistivity of 103(ohm)·cm. Antistatic materials have a surface resistivity of 109(ohm)/sq to 1011(ohm)/sq and a volume resistivity of 1.8 x 102(ohm)ž cm. Flexcon Products Corp., (201) 467-3323.
Rigid Material Supplies
5 ft-lbf/in. Impact Strength
HMS-1000C is a rigid, bulk-conductive thermoforming styrenic material used for semiconductor and disk-drive packaging. The material provides 5 ft-lbf/in. notched izod impact strength. It is recyclable and offered in custom widths and gauges. Typical electrical properties include a surface resistivity of 500 k(ohm)/sq at a distance of 0.060(“) and a decay time from 5 kV to 0 in <0.01 s. HMS Compounds, Inc., (817) 468-3099.
Container Holds QFP Devices
Without Touching Leads
A single-unit container handles quad flat pack devices in a molded nest or with an assortment of foam inserts that support the body while the leads extend into the aircell of the container. A foam pad is used in the cover and a conductive rubber band holds the two pieces together. Industrial Custom Products, Ltd., (800) 654-0886.
Packaging Material
Is Transparent and Amine Free
Lemcen A.F.S.D. is a transparent, amine-free, permanently static-dissipative material which can be reused after washing. It is nonhumidity-dependent and appropriate for use in clean rooms. The noncorrosive material has a surface resistance of <1011(ohm) per ESD Association Standard 11.11-1993, and a static decay rate of <2 s per EIA 541. Stat-Tech, Division of Gary Plastic Packaging Corp., (714) 556-4121.Polycarbonate Compound Offered
For Antistatic Packaging
Stat-Loy D is an antistatic polycarbonate compound offering a 94 V-2 flammability rating at 0.125(“). It provides 6,500 psi tensile strength with a flexural strength at 9,500 psi and a flexural modulus at 250,000 psi. Notched izod impact strength is 2 ft-lbf/in. Surface resistivity is 1010(ohm)/sq to 1012(ohm)/sq. The product is nonsloughing, used for injection molding processes, and is not affected by humidity levels. LNP Engineering Plastics, (215) 363-4500.
Reinforced ESD Containers
Are Flame Retardant
The TOTELINE(R) System Series is a line of fiberglass reinforced composite containers available in heights from 3(“) to 15(“) and a footprint of 28(“) x 20(“). The series has extractor rails, a slide-resistant textured bottom and a bar code area. Flame-retardant or static-protective formulations, with a surface resistivity from 105(ohm)/sq to 108(ohm)/sq, are available. Molded Fiber Glass Tray Co., (800) 458-6050.
Corrugated Board Has
Buried Conductive Layer
CENTURIAN III is a recyclable, corrugated board constructed of a conductive layer between two dissipative outer layers. It prevents rapid discharge of devices coming in contact with the liner board. Surface resistivity is 107(ohm)/sq to 1010(ohm)/sq. The buried layer provides a resistivity of <104(ohm)/sq. Century Container Corp., (800) 346-8408.
Carrier System Provides
Faraday Shield For Boards
The Circuit Board Transport System is made of an aluminum carrier that provides physical protection for circuit boards as well as a Faraday shield during shipment. The system has foam strips, with a surface resistance of 104(ohm), to prevent scratching. Plastic inserts accommodate 10 circuit boards and provide a surface resistance from 105(ohm) to 109(ohm). The conductive chrome-plated transport system is equipped with clamping devices to secure the board carriers. Cymat Technologies Inc., (905) 602-1100.
Copyright 1995 Nelson Publishing Inc.
March 1995