SC07 1999 Handling 1 - Philips Semiconductors / NXP Semiconductors

1999 May 17 1

Philips Semiconductors

Handling MOS devices General

HANDLING MOS DEVICES(1)

Electrostatic charges

Electrostatic charges can exist in many things; for

example, man-made-fibre clothing, moving machinery,

objects with air blowing across them, plastic storage bins,

sheets of paper stored in plastic envelopes, paper from

electrostatic copying machines, and people. The charges

are caused by friction between two surfaces, at least one

of which is non-conductive. The magnitude and polarity of

the charges depend on the different affinities for electrons

of the two materials rubbing together, the friction force and

the humidity of the surrounding air.

Electrostatic discharge is the transfer of an electrostatic

charge between bodies at different potentials and occurs

with direct contact or when induced by an electrostatic

field. Our devices can be damaged if the following

precautions are not taken.

Work station

Figure 1 shows a working area suitable for safely handling

electrostatic sensitive devices. It has a work bench, the

surface of which is conductive or covered by an antistatic

sheet. Typical resistivity for the bench surface is between

1 and 500 kΩ per cm2. The floor should also be covered

with antistatic material.

The following precautions should be observed:

•Persons at a work bench should be earthed via a wrist

strap and a resistor.

•All mains-powered electrical equipment should be

connected via an earth leakage switch.

•Equipment cases should be earthed.

•Relative humidity should be maintained between 50 and

65%.

•An ionizer should be used to neutralize objects with

immobile static charges.

Receipt and storage

Our devices are packed for dispatch in

antistatic/conductive containers, usually boxes, tubes or

blister tape. The fact that the contents are sensitive to

electrostatic discharge is shown by warning labels on both

primary and secondary packing.

(1) These products are supplied in anti-static packing to

prevent damage caused by electrostatic discharge

during transport and handling. For further information,

refer to Philips specs.: SNW-EQ-608, SNW-FQ-302A

and SNW-FQ-302B.

The devices should be kept in their original packing whilst

in storage. If a bulk container is partially unpacked, the

unpacking should be performed at a protected work

station. Any devices that are stored temporarily should be

packed in conductive or antistatic packing or carriers.

Assembly

The devices must be removed from their protective

packing with earthed component pincers or short-circuit

clips. Short-circuit clips must remain in place during

mounting, soldering and cleansing/drying processes. Do

not remove more devices from the storage packing than

are needed at any one time. Production/assembly

documents should state that the product contains

electrostatic sensitive devices and that special precautions

need to be taken.

All tools used during assembly, including soldering tools

and solder baths, must be earthed. All hand tools should

be of conductive or antistatic material and, where possible,

should not be insulated.

Measuring and testing of completed circuit boards must be

done at a protected work station. Place the soldered side

of the circuit board on conductive or antistatic foam and

remove the short-circuit clips. Remove the circuit board

from the foam, holding the board only at the edges. Make

sure the circuit board does not touch the conductive

surface of the work bench. After testing, replace the circuit

board on the conductive foam to await packing.

Assembled circuit boards should be handled in the same

way as unmounted devices. They should also carry

warning labels and be packed in conductive or antistatic

packing.