Packaging Pointers for the Best ProtectionPackaging Pointers for the Best Protection

It may be the final step in the manufacturing cycle, but packaging electronic products is every bit as critical as the stage where ESD protection is designed into the device. Like a chain, packaging can protect your products from ESD only as well as the weakest link in the design and manufacturing loop.

To select the most effective totes/bins/packaging material for your static-sensitive products, first consider the technological issues such as the packaging materials and the forming techniques. For example, some materials may slough carbon, while others may be formed with too much or too little conductive properties, creating ineffective packaging protection.

Standards are available to help you choose the appropriate material and test procedure for your packaging product. Some of the current standards include EN 100015-1 Protection of ESD Sensitive Devices: Part 1; Minimum Requirements, and EOS/ESD Standard 11.11 Surface Resistance Measurement of Static Dissipative Planar Materials.

According to these standards, the packaging should not allow charge to accumulate but let it bleed off in a controlled manner. As a result, the conductivity of the material should fall within a surface resistivity range of 10⁶ W /sq to 10⁹ W /sq. Higher values are acceptable if the device itself dissipates charge before damage can occur.

But there are several other equally important issues to consider when qualifying ESD packaging materials, such as sloughing, contamination and reuse of materials, according to Dan Drzik of Mitech. And don’t forget the temperature and humidity range, the static decay time and how used trays are recycled.

Some device trays are treated with a topical antistatic. These trays usually cannot handle temperatures higher than 60° C. To accommodate higher temperatures, trays are made from a carbon-loaded plastic material which provides a resistivity ranging from 10⁵ W /sq to 10¹¹ W /sq.¹

Avoid homogenous conductive materials due to the high probability of sparking and the high potential of surface sloughing, said Jerry Joyce of Brick Container. Totes/bins/packaging products with a buried conductive layer and exterior static-dissipative surfaces are recommended. This combination provides a Faraday cage for protection as well as non-sparking and non-tribocharging surfaces, he said.

Also stay away from homogenous static-dissipative packaging, continued Mr. Joyce. Even though it may offer a non-tribocharging surface, it does not provide 100% protection from electrostatically induced fields. And some homogenous materials are a major source of chemical contamination.

Thermoformed products are also a problem for the packaging industry, said Brad Ahlm, President of Conductive Containers. Thermoformed products can have hot spots which drain charges too quickly.

Hot spots occur when carbon-loaded material congregates in one area during the manufacturing process. For example, manufacturers of plastic-type trays usually add conductive fillers such as carbon powder or carbon fibers to achieve the necessary resistivity. Carbon powder-filled plastic requires a substantial amount of powder to achieve an acceptable conductivity level because the particles of powder must be placed close to each other to form a conductive path. This highly packed powder also tends to slough and can contaminate device pins.

Carbon fibers used in trays are available in different sizes and shapes. Long fibers are used for molding smaller and less complicated packaging while short fibers are used in larger units. Short fibers give a more uniform surface resistivity and less chance of warpage. But more short fibers are required, which increases cost to achieve the desired conductivity.

To keep the cost of tray materials down, most manufacturers use recycled material called regrind. It is made when used trays are reclaimed and ground to the approximate size of the virgin material’s pellet.

The percentage of regrind, however, adversely affects the resistivity of the tray because the fiber length is reduced each time the material is processed. The more recycled material used in the mix, the less conductive and uniform the tray becomes.

If you consider a paperboard product, determine if the material can shield to the level needed by your components, added Mr. Joyce. Also ensure that the material is sealed properly and prevents a chemical response between the paperboard and the components inside.

Find the best packaging by focusing on what the container needs to do to protect your product, said Ken Beckman, Product Manager of Flexcon. For example, ask a manufacturer to build a prototype that meets your exact needs. Examine one or two samples so you can look for problem areas, because it is better to find trouble with one than with a shipment of 50,000.

Become familiar with the available materials and evaluate and test them prior to selecting one, advised Ed Weggeland, Vice President of Richmond Technology. Each vendor should provide test-lab reports, listing all tests done and the standards used.

Once the vendor’s material passes the in-house evaluation, establish a qualified product listing and an approved vendor list, added Mr. Weggeland. Then solicit quotations and issue orders only from those approved suppliers.

Reference

1. Tan, W., “Carbon Loaded Device Handling Trays: Analysis and Measurements,” EOS/ESD Symposium, 1995, pp. 236 – 244.

Totes/Bins/Packaging

Packaging Materials

Are 100% Recyclable

Strata-Shield ENV^® 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, (616) 399-3000.

Corrugated Containers Have

Buried Shielding Layer

The PROTEKTIVE PAK^® 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 W /sq and the top layer ranges from 10⁷ W /sq to 10¹⁰ W /sq. It is made from recycled linerboard and is recyclable. Brick Container, (310) 903-9392.

Corrugated Material Provides

Buried Carbon Shielding

Cortronic is a recyclable, corrugated fiberboard which is either transparent or blue. A buried carbon shielding layer has a surface resistivity of <10² W /sq. Surface resistivity is 10⁶ W /sq to 10⁸ W /sq. Conductive Containers, (800) FARADAY.

Corrugated Polymer Container

Is Clean-Room Compatible

Coroplast SI is a corrugated polymer material used for packaging or storage containers. It neutralizes corrosive gases, leaves no deposits and does not outgas. The material has a surface resistivity of 10⁶W /sq to 10⁹W /sq, contains triboelectric charging to <20 V and is humidity independent. It is a homogenous substance bonded into a polymer structure that is recyclable and breaks down into polymer dust in anaerobic environments. Coroplast, (800) 666-2241.

Conductive Polyolefin Tote

Offers Removable Dividers

The Heavy-Duty CONTRIM^® Tote Box is made from a vacuum-formable and permanently conductive polyethylene material. It has a telescoping lid that allows stacking. The tote walls are fitted with custom slotting arrays, allowing the box to be partitioned lengthwise with removable dividers. It has a tensile strength of 2,750 psi and an impact resistance of 8.8 ft-lb/in. Surface resistivity is 5 x 10⁴ W /sq. Crystal X, (800) 255-1160.

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 W , to prevent product scratches. Plastic inserts accommodate 10 circuit boards and provide a surface resistance from 10⁵ W to 10⁹ W . The conductive chrome-plated transport system is equipped with clamping devices to secure the board carriers. Cymat Technologies, (905) 602-1100.

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. Materials with conductive and antistatic properties are offered. Flexcon Containers, (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 kW /sq at a distance of 0.060″ and a decay time from 5 kV to 0 in <0.01 s. HMS Compounds, (817) 468-3099.

Corrugated-Layer Material

Is Conductive or Dissipative

Protech^® is a corrugated packaging material with a conductive carbon-polymer system incorporated into the fiber matrix of selected layers of the paper-sheet structure. The packaging material is available in conductive and static-dissipative types with a buried conductive layer. The fiber-polymer composite structure resists abrasion, punctures and score cracking. Jefferson Smurfit, (314) 746-1100.

Clear Acrylic Sheet Material

Is Clean-Room Safe

The clear static-dissipative ACRISTAT™ M-809 is a clean-room safe sheet material that thermoforms into trays. The nonblooming amine-free surface will not contaminate or corrode components or metal leads. The acrylic-based plastic and polymer additive has a surface resistivity range from 10⁹ W /sq to 10¹⁰ W /sq. Sheet thicknesses range from 0.012″ to 0.060″; the maximum width is 48″. Tensile strength is 3,850 psi. Mitech, (216) 425-1634.

Shipping Box Accommodates

Single/Double-Width Eurocards

The WEZ Shipping Box protects single- and double-width Eurocards from mechanical, environmental and ESD damage. Stackable vertically and horizontally and made of black conductive polypropylene, the box features vertically arranged slots to hold the boards in place. It provides a snap-on cover and internal foam cushioning and offers an adhesive tape to seal out dust and water. Teknis, (011) 441 1823-481248.

High-Impact Material Mixed

With Dissipative Material

Bins made with a mixture of Stat-Kon^® MI-HI, a statically dissipative, high-impact polypropylene, and the statically dissipative polystyrene, Stat-Kon C offer a surface resistivity of 10⁴ W /sq to 10⁶ W /sq. The bins are stackable and modular and provide the necessary static protection for CMOS chips, resistors, capacitors and other electronic components. The company also offers material that provides EMI shielding with ESD protection, and has a line of dissipative plastics in a variety of colors LNP Engineering Plastics, (610) 363-4500.

Acrylic Plastic Accommodates

Bending and Gluing

StatiCon^® AC-350™ is an acrylic plastic sheet used in semiconductor, electronic and micro-manufacturing operations. The material can be fabricated into a wide variety of configurations and accommodates bending and gluing. Typical applications include covers, windows, doors cabinets, boxes and static control shields. The surface resistivity is 10⁶ W /sq to 10⁸ W /sq. Static decay is <0.5 s per FTS 101C Method 4046.1. The material is humidity independent, and resists damage from chemicals and solvents. It is available in clear plastic and transparent colors including tints for filtering certain wavelengths. StatiCon, (800) 525-8183.

Multi-Device Trays Meet

JEDEC Handling Requirements

Medium-temperature, multi-device packaging trays are offered for handling and shipping IC devices including PQFP, CQFP, PLCC, MQFP and PGA package formats. The trays accommodate automatic handling and follow JEDEC dimension and tolerance outlines. Tray cells provide package containment to minimize device damage. The 140° C continuous-duty trays are made from a modified polysulfone with a conductive media of metalized glass or carbon fiber. Surface resistivity ranges from 10⁵ W /sq to 10¹² W /sq. 3M Electronic Products, (800) 328-0411.

Multi-Device Trays Are

Thermally Stable to 180° C

High-temperature multi-device packaging trays are offered for handling and shipping IC devices including PQFP, CQFP, PLCC, MQFP and PGA formats. The trays are compatible for automatic handling and follow JEDEC dimension and tolerance outlines. Tray cells are equipped with ribs and fences to minimize device damage. The 180° C continuous-duty trays are made from polyethersulfone and contain a nonsloughing carbon fiber. Surface resistivity ranges from 10⁵ W /sq to 10¹² W /sq. 3M Electronic Products, (800) 328-0411.

Polycarbonate Plastic Resists

Damage From Chemicals

PC-300™ is a polycarbonate plastic sheet made with the company’s proprietary permanently static-dissipative surfacing. The product exhibits chemical resistance, surface hardness, abrasion and impact resistance, and optical clarity. It can be used in semiconductor, electronic and micro-manufacturing operations. Typical applications include covers, windows, doors cabinets, boxes and static-control shields. Surface resistivity is 10⁶ W /sq to 10⁸ W /sq. Static decay is <0.05 s per FTS 101C Method 4046.1. The plastic is available in clear and transparent gray and bronze colors. StatiCon, (800) 525-8183.

Mobile Storage System

Directs Laminar Air Flow

The PureFlow™ Mobile Storage System directs a vertical laminar flow of HEPA- or ULPA-filtered air through the storage area. A rechargeable DC power cell maintains continuous filter/blower operation for 2 h. Electropolished stainless steel rod shelves optimize the laminar airflow inside the storage area, and static-dissipative PVC access doors provide full visibility while protecting against static charges and particulate. The system is available in several sizes and can be customized. Terra Universal, (714) 526-0100.

Opaque PETG Material

Is Clean-Room Safe

The opaque static-dissipative M-610 is a PETG-based clean-room safe material available in pellet form or sheet material for thermoforming into trays. The nonblooming amine-free surface will not contaminate or corrode components or metal leads. It has a surface resistivity of 2.5 ´ 10¹⁰ W /sq and a volume resistivity of 5.4 ´ 10¹⁰ W /sq. Sheet thicknesses range from 0.012″ to 0.060″; the maximum width is 48″. Tensile strength per ASTM D638 is 4,120 psi. Static decay @15% RH is 0.04 s. Mitech, (216) 425-1634.

Copyright 1996 Nelson Publishing Inc.

March 1996