B. PROTECTION FROM ABUSE
The contact springs in standard card edge connectors are deflected by the p.c. board upon insertion. Chamfered boards are commonly used to lower insertion forces, protect the springs from buckling loads, and minimize wear. These chamfers are usually not controlled well, increasing the potential for damage. They also add additional costs to p.c. board manufacture.
Zero insertion force connectors are less prone to damage since the contact springs do not contact the p.c. board until after the board in inserted in the connector. However, another complication is present if a zero insertion force connector is used. This type of connector system is not as straight forward for a consumer to use because it must be actuated and deactuated. Extra care must, therefore, be taken in the design to prevent the cartridge from being inserted or removed without using the actuator. Protection against damage to the connector or actuating mechanism must be provided for since attempts will surely be made to insert or remove the cartridge when the actuator is in the wrong position. Common techniques prevent insertion of the cartridge when the contact springs are in the actuated position. They also lock the cartridge in place preventing its removal in the actuated state. This detail is easily overlooked by the user, and could lead to improper handling.
C. PROPER ALIGNMENT
This requirement is the easiest to satisfy in either type connector. When contact centerline spacings are .100 inch or greater, normal manufacturing tolerances provide proper alignment by controlling the clearance between the p.c. board and connector card slot, or between a key in the connector and a slot in the board. These methods are preferred for manufacturability rather than designing for cartridge alignment to the case, and ultimately the p.c. board to the connector.
D. ELECTRICAL STABILITY
Electrical stability is also a very simple requirement to fulfill with either type of connector. Based on current technology, either a low contact force system would be used with noble metal contact and p.c. board finishes, or a high contact force system with a non-noble metal finish. Gold is most commonly used with minimum normal forces of 50 or 100 grams, and nickel is currently under evaluation by. some manufacturers, for higher force systems. Higher forces are required in non-noble metal systems to break through insulating oxide films which form on the contact surfaces. Standard card edge connectors are preferred when nickel is considered as a contact metal since the relatively long wiping distance is useful in cleaning the contacts and p.c. board pads. When zero insertion force connectors are used, the wiping distance is considerably smaller, or nil, and gold or gold alloys are more commonly used. They are essentially immune to corrosion in a home environment if they are sufficiently thick and properly applied.
The choice of which system is appropriate is influenced most by the electrical characteristics required. In dry circuit applications where
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