ESD Precautions

Do NOT wear a grounded wrist strap when you: A. discharge a CRT or work on equipment that is plugged in B. handle a logic board C. open a computer case D. work at a customer site

A

ESD-preventive equipment reduces the risk of damage from ESD by: A. eliminating electrostatic charge B. storing electrostatic charge C. dispersing electrostatic charge D. increasing electrostatic charge

A

To reduce the risk of ESD damage, A. ground yourself B. make sure the equipment is on C. keep the equipment on a metal surface D. touch the equipment to plastic

A

necessary item 1

A conductive workbench mat and ground cord. When properly grounded, the workbench mat provides a safe place on which to set sensitive components and equipment. Such a mat consists of the following elements: - Layer of conductive mesh sandwiched between rubber layers. - 1 megohm resistor in grounding connector on mat. - "Soapy" film on surface of mat allows charge to drain away. NOTE: Cleaners for ESD mats restore the "soapy" film. Do not use solvent cleaners on ESD mats.

necessary item 4

A ground polarity tester. The ground polarity tester verifies proper grounding of power outlets.

necessary item 2

A wrist strap with a built-in 1-megohm resistor and ground cord. The wrist strap grounds you so that you can safely touch sensitive components without "zapping" them.

Which THREE of the following should you keep away from an ESD-safe workbench? A. plastics B. polyester clothing C. foam rubber D. Styrofoam E. ion generator F. alligator clips

ABD

necessary item 3

An equipment ground cord with alligator clips. This cord grounds the equipment so that static charges cannot build up; the ground cord is especially important when you are working on CRTs, which can build up static charges even when they are not plugged in.

ESD can damage a computer by: A. decalibrating the CRT B. damaging sensitive chips C. starting a fire in the enclosure D. damaging the laser in the optical drive

B

To reduce the risk of ESD damage, use static-shielding _____. A. mats B. bags C. clips D. straps

B

step 2

Before working on any circuit board or assembly containing ESD-sensitive circuits, ground yourself and the equipment you are working on to an earth or building ground. Use a grounded conductive workbench mat and a grounding wrist strap, and ground the equipment to the mat.

There are four basic pieces of equipment needed to reduce the risk of damage from ESD. Which one of the following is NOT one of the four? A. grounded mat B. wrist strap C. plastic storage bags D. ground cord with alligator clips E. ground polarity tester

C

To reduce the risk of ESD damage, handle all circuit boards by the _________________. A. pins B. body C. edges D. connectors E. exposed circuitry

C

What does ESD stand for? A. electronic surveillance device B. electric shock damage C. electrostatic discharge D. electronic software distribution

C

To reduce the risk of ESD damage, do not touch anyone who is working on: A. a CRT B. an expansion bay C. a photo conductor assembly D. a circuit board

D

step 5

Do not touch anyone who is working on ESD-sensitive circuits or circuit boards of any kind. If you touch someone who is properly grounded, your "zap" or body charge may cause damage to circuit boards and assemblies.

step 7

Do not wear polyester clothing or bring plastic, vinyl, or Styrofoam into the work environment. The electrostatic field that surrounds these nonconductors cannot be totally removed.

ESD Solutions

ESD guidelines are described in detail on the following pages, but the basic premise of these guidelines is to electrically connect the equipment being serviced, your body, and the workbench together to a good earth ground, in a particular way, so that it is virtually impossible for any one of these materials to build up a static electrical charge relative to the others. Please be aware of the dangers of ESD damage and follow these steps you every time you work with the ESD-sensitive components inside Mac computers. Handle all components by edges Ground yourself...except when the unit is plugged in Don't place components on metal surfaces Don't touch anyone while grounded Use static-shielded bags for storing components Keep nonconductors (polyester, vinyl, styrofoam) away from components 70-90% humidity is good Use ion generator if possible Clean ESD mats regularly

In conclusion

Ground yourself and the equipment you are working on. Do not touch anyone who is working on ESD-sensitive circuits or circuit boards of any kind. Use static-shielding storage bags for boards and ICs. Handle all ICs by the edges. Do not wear polyester clothing or bring plastic, vinyl, or Styrofoam into the work environment. Never place components on a metal surface. Do NOT wear a wrist strap when discharging a CRT. Keep the humidity between 70% and 90%. Remove all ESD hazards from your person and work area. Use the ground polarity tester to verify proper grounding of the power outlet. Lay out and ground the conductive workbench mat. Fasten the wrist strap to your wrist and connect it to the workbench.

step 1

Handle ALL circuit boards, such as logic boards, video cards, memory DIMMs, hard drive assemblies, optical drive assemblies, etc. by the board's or assembly's edges only. Treat any and all internal assemblies with circuit boards on them as ESD sensitive; this includes hard disk drive and optical drive assemblies. Avoid touching any edge connectors on any circuit boards and assemblies. Avoid touching or handling any components on the surfaces of these boards and assemblies. Never handle or pick up any circuit board by its components, such as a heat sink, because of the risk of damaging or destroying the board by accidentally pulling off components this way.

Misconception 2

I don't have time to be tied down with wrist straps and mats. Mishandling components creates damaged parts that slow down repairs and drive customer dissatisfaction. In addition, you can set up work areas using heel straps instead of wrist straps. This leaves your hands free.

Misconception 1

I don't use ESD precautions and have never had a problem. How would you know? You may be damaging parts in ways that do not show up immediately via system performance or diagnostic routines. Apple has tested for ESD damage and consistently found that mishandling components and computers creates IC damage.

IMPORTANT warnings about components

IMPORTANT: When you work at a customer site, you must take the same precautions to avoid ESD damage. Take time to make the work area ESD-safe. Use a workbench mat and a wrist strap. (For travel convenience, you may want to use mats that fold up.) Be sure everything is properly grounded. Never set parts on the floor.

Misconception 3

If Apple was really serious about ESD precautions, it would not tell customers to just touch metal before replacing DIY parts. Customers replace far fewer parts than service technicians. Since it is difficult to train customers in the best ESD techniques, Apple asks them to practice a less effective procedure that they can readily do.

step 8

If possible, keep the humidity in the service area between 70% and 90%, and use an ion generator. Charge levels are reduced (but not eliminated) in high-humidity environments.

step 10

If you have ESD mats in your service area, it is important to clean them at least once a week. To clean them you need to use a cleaner that is specifically designed for ESD mats. Otherwise the mats will not ground equipment placed on them.

step 3

Make sure you are NOT grounded when: • You work on plugged-in equipment • You discharge a cathode-ray tube (CRT) • You work on an unplugged CRT that has not been discharged • You are performing live adjustments

step 4

Never place components on any metal surface. Metal surfaces can hold a static charge that will damage sensitive electronic parts. Use antistatic, conductive, or foam rubber mats.

Misconception 4

Only RAM and logic boards require ESD precautions. Everything else is shielded. Not true. Most components have some circuitry. In addition, replacing a component such as a cable may require handling many other components that contain ICs. It is far wiser to take ESD precautions whenever you have to open up a computer.

What is ESD?

Static electricity, a normal and natural phenomenon, builds up on your body as you walk around. In fact, static electricity is created any time that two dissimilar materials rub against each other (such as shoes and carpet) and then pull apart. The word 'static' simply means that the electrical charge builds up on one of the two materials because it has nowhere to go. That is, until the charged material (this could even be your body) comes close to another material that has a different charge, or no charge at all. Then, like water trying to seek its own level, this accumulated electrical charge immediately discharges between the two materials in a tiny spark. This is what is known as Electro-Static Discharge (ESD). You experience an electrostatic discharge (ESD) when you touch an object and feel a spark.

ESD Risks

The discharge of static electricity near active electronic systems can cause memory corruption or temporary failures. It can cause irreparable damage to sensitive chips and printed circuitry of electronic components. Such damage is basically a hole blasted in the integrated circuit by the ESD. It can be a very small hole but can result in hard-to-trace computer behaviors. While only a few volts of static electricity can damage an integrated circuit, you can pick up a static charge of several hundred volts by simply walking across a room. The movement of you, your clothing, and the surrounding air combine to make this accumulation of charge possible. The nasty aspect of such damage is that it may not be readily detectable under conventional testing or use. Plastic utensils, polystyrene products, polyester clothing, and even the ungrounded touch of your hand can carry sufficient electrostatic charges to damage electronic components. The act of damaging electronic components with ESD (even if accidental) obviously works directly against your service goals, which are: To properly and quickly repair a customer's computer. To minimize repeat repairs (especially those due to latent component failures).

step 6

Use static-shielding storage bags for boards and assemblies with circuit boards on them. Before you leave your bench to take a board to a storage place, put the board in a static-shielding bag. Leave all Apple replacement modules in their ESD-safe packaging until you need them.

step 9

Using an ion generator helps neutralize the charge surrounding nonconductors. This device can't provide total protection because static charges often cause ESD damage before the neutralizing process fully eliminates the charge.

Misconception 5

You do not have to be hardwired to ground to practice correct ESD precautions. There are some products which claim to ground you without the use of direct connections to ground. Such "wireless" solutions have not been proven. Use a grounded wrist strap or heel strap. Those work.