Electrostatic Discharge

Maintenance & Service Guide

Presario 1600 Series Portable Computers

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This chapter provides general service information for the Compaq Presario Series of portable computers. Adherence to the procedures and precautions described in this chapter is essential for proper service. The topics covered include Electrostatic Discharge and its effects, a table of activities that

Generate Static and the potential voltages, ways of Preventing Electrostatic Damage to Equipment, and Preventing Damage to the Drive, Grounding Methods, Grounding Work Areas, and Recommended Materials and Equipment

to use in the service area. Return to Removal & Replacement Procedures.

Electrostatic Discharge

A sudden discharge of static electricity from a finger or other conductor can destroy static-sensitive devices or microcircuitry. Often the spark is neither felt nor heard, but damage occurs. An electronic device exposed to electrostatic discharge (ESD) may not be affected at all and will work perfectly throughout a normal cycle. Or it may function normally for a while, then degrade in the internal layers, reducing its life expectancy.

Networks built into many integrated circuits provide some protection, but in many cases, the discharge contains enough power to alter device parameters or melt silicon junctions.

Generating Static

The table below shows how different activities generate static electricity and at different electrostatic voltage levels.

Typical Electrostatic Voltages
	Relative Humidity
Event	10%	40%	55%
Walking across carpet	35,000 V	15,000 V	7,500 V
Walking across vinyl floor	12,000 V	5,000 V	3,000 V
Motions of bench worker	6,000 V	800 V	400 V
Removing DIPS from plastic tubes	2,000 V	700 V	400 V
Removing DIPS from vinyl trays	11,500 V	4,000 V	2,000 V
Removing DIPS from Styrofoam	14,500 V	5,000 V	3,500 V
Removing bubble pack from PCBs	26,000 V	20,000 V	7,000 V
Packing PCBs in foam-lined box	21,000 V	11,000 V	5,000 V
NOTE: 700 volts can degrade a
product.

Preventing Electrostatic Damage to Equipment

Many electronic components are sensitive to ESD. Circuitry design and structure determine the degree of sensitivity. The following proper packaging and grounding precautions are necessary to prevent damage:

■To avoid hand contact, transport products in the static-safe containers such as tubes, bags, or boxes.

■Protect all electrostatic parts and assemblies with conductive or approved containers or packaging.

■Keep electrostatic sensitive parts in their containers until they arrive at static-free stations.

■Place items on a grounded surface before removing them from their container.

■Always be properly grounded when touching a sensitive component or assembly.

■Place reusable electronic-sensitive parts from assemblies in protective packaging or conductive foam.

■Use transporters and conveyors made of anti-static belts and metal roller bushings. Mechanized equipment used for moving materials must be wired to ground and proper materials selected to avoid static charging. When grounding is not possible, use an ionizer to dissipate electric charges.

Preventing Damage to Drive

To prevent static damage to hard drive and diskette drive, use the following precautions:

■Handle drive gently, using static-guarding techniques.

■Store drive in the original shipping containers.

■Avoid dropping drive from any height onto any surface.

■Handle drive on surfaces that have at least one inch of shock-proof foam.

■Always place drive PCB assembly side down on the foam.

Grounding Methods

The method for grounding must include a wrist strap or a foot step at a grounded work area. When seated, wear a wrist-strap connected to a grounded system. When standing, use footstraps and a grounded floor mat.

Static-Shielding Protection Levels

Method	Voltages
Anti-static Plastic	1,500
Carbon-Loaded Plastic	7,500
Metallized Laminate	15,000

Grounding Work Areas

To prevent static damage at the work area, use the following precautions:

■Cover the work area with approved static-dissipative material. Provide a wrist strap connected to the work surface and properly grounded tools and equipment.

■Use static-dissipative mats, Heel straps, or air ionizers to give added protection.

■Handle electrostatic sensitive components, parts, and assemblies by the case or PCB laminate. Handle them only at static-free work areas.

■Avoid contact with pins, leads, or circuitry.

■Turn off power and input signals before inserting and removing connectors or test equipment.

■Use fixtures made of static-safe materials when fixtures must directly contact dissipative surfaces.

■Keep work area free of nonconductive materials such as ordinary plastic assembly aids and Styrofoam.

Use field service tools, such as cutters, screwdrivers, vacuums, that are conductive.

Use a portable field service kit with a static dissipative vinyl pouch that folds out of a work mat. Also use a wrist strap and a ground cord for the work surface. Ground the cord to the chassis of the equipment undergoing test or repair.

Grounding Equipment

Use the following equipment to prevent static electricity damage to the equipment:

Wrist-straps are flexible straps with a minimum of 1 megohm +/- 10% resistance to the ground cords. To provide proper ground, a strap must be worn snug against the skin. On grounded mats without banana-plug connectors, connect a wrist strap with alligator clips.

Heelstraps/Toestraps/Bootstraps can be used at standing work areas and are compatible with most types of boots and shoes. On conductive floors or dissipative floor mats, use them on both feet with a minimum of 1 megohm resistance between operator and ground. To be effective, the conductive strips must be worn in contact with the skin.

Recommended Materials and Equipment

Other materials and equipment that are recommended for use in preventing static electricity include:

■Anti-static tape

■Anti-static smocks, aprons, or sleeve protectors

■Conductive bins, and other assembly or soldering aids

■Conductive foam

■Conductive tabletop work areas with ground cord of 1 megohm of resistance

■Static dissipative table or floor mats with hard tie to ground

■Field service kits

■Static awareness labels

■Wrist-straps and footwear straps providing 1 megohm +/- 10% resistance

■Material handling packages

■Conductive plastic bags

■Conductive plastic tubes

■Conductive tote boxes

■Metal tote boxes

■Opaque shielding bags

■Transparent metallized shielding bags

■Transparent shielding tubes