Philips Semiconductors General Handling MOS devices ELECTROSTATIC CHARGES RECEIPT AND STORAGE 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. MOS 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. 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 MOS devices that are stored temporarily should be packed in conductive or antistatic packing or carriers. 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. All of our MOS devices are internally protected against electrostatic discharge but they can be damaged if the following precautions are not taken. ASSEMBLY MOS 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. WORK STATION Figure <.Normal_XRef>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 kW per cm2. The floor should also be covered with antistatic material. The following precautions should be observed: * * * * * During assembly, ensure that the MOS devices are the last of the components to be mounted and that this is done at a protected work station. 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. 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 containing MOS devices should be handled in the same way as unmounted MOS devices. They should also carry warning labels and be packed in conductive or antistatic packing. 1995 Mar 21 43 Philips Semiconductors General Handling MOS devices (1) handbook, full pagewidth (2) (2) (3) (5) (4) (1) (2) (3) (4) (5) (6) (7) (8) (9) Earthing rail. Resistor (500 kW 10%, 0.5 W). Ionizer. Work bench. Chair. Wrist strap. Electrical equipment. Conductive surface/antistatic sheet. Antistatic floor. Fig.1 1995 Mar 21 ,,,,,, Protected work station. 44